The Effects of Modafinil on Convergent and Divergent Thinking of Creativity: A Randomized Controlled Trial
←
→
Page content transcription
If your browser does not render page correctly, please read the page content below
AHMED DAHIR MOHAMED
The Effects of Modafinil on Convergent
and Divergent Thinking of Creativity:
A Randomized Controlled Trial
ABSTRACT
Modafinil is a drug licensed for the treatment of narcolepsy and sleep apnea. Recently,
modafinil has been reported to be used as a pharmacological cognitive enhancer by
healthy individuals with no psychiatric disorders. This paper reports on a study that
investigated the effects of modafinil on divergent and convergent thinking tasks of crea-
tivity. Sixty-four healthy male (n = 31) and female (n = 33) volunteers participated in a
randomized double-blind placebo-controlled parallel group design study. For the conver-
gent thinking tasks, modafinil had no significant main effect on the Group Embedded
Figures Task and the Remote Associates Task (RAT). However, a median split analysis
showed that modafinil participants low in creativity personality trait had significantly
higher RAT scores (Mean [M] = 6.85, SD = 3.39; 95% confidence interval [95% CI]:
5.53–8.2) than those high in creativity personality trait (M = 4.27, SD = 3.0; 95% CI:
2.4–6.0). For the divergent thinking tasks, relative to placebo (M = 1.195, SD = 0.28;
95% CI: 1.0–1.3), modafinil (M = 0.77, SD = 0.37; 95% CI: 0.63–0.92) significantly
reduced the performance of flexibility scores and marginally reduced the elaboration
scores as measured by the Abbreviated Torrance Test for Adults (ATTA). Overall, partici-
pants on modafinil (M = 6.3, SD = 2.6; 95% CI: 5.3–7.4) had significantly lower ATTA
scores relative to participants on placebo (M = 9.5, SD = 2.3; 95% CI: 8.6–10.4). These
results indicate that modafinil might reduce divergent thinking of creativity in healthy
individuals. They suggest that, rather than being a more general cognitive enhancer,
modafinil might have negative and subtle effects on creativity. However, the results are
from a small-scale trial, which tested a small number of participants. Therefore, the
results need to be interpreted with caution. A replication with a large sample of partici-
pants is recommended.
Keywords: cognitive enhancement, convergent, creativity, divergent, double-blind,
healthy volunteers, healthy volunteers, modafinil, psychostimulants, random-
ized controlled trial, thinking.
Creativity is defined as an activity that involves thinking that is aimed at producing
ideas or products that are relatively novel and that are, in some respect, compelling
(Kaufman & Sternburg, 2006). It involves a novel product, idea, or solution to a problem
that is of value to the individual and/or to the larger social group (Hennessey & Amabile,
2010).
1 The Journal of Creative Behavior, Vol. 0, Iss. 0, pp. 1–21 © 2014 The Authors. The Journal of Creative Behavior published by Wiley Periodicals, Inc.
on behalf of Creative Education Foundation (CEF) Ó DOI: 10.1002/jocb.73.
This is an open access article under the terms of the Creative Commons Attribution License,
which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
Creativity researchers typically view creativity as involving two forms of thinking. One
form of creativity is called convergent thinking, which involves the ability to problem
solve in a highly domain specific manner. This form of creative performance expects par-
ticipants to have a set answer, or to arrive at a particular goal, and assesses the forming
of associations between two disparate concepts. Hennessey and Amabile (2010) argue
that convergent thinking is focused on narrowing possibilities to a workable solution.
The RAT, which gives participants three words and expects them to provide one correct
answer, can therefore be considered to be testing a form of convergent thought (Med-
nick, 1962).
On the other hand, divergent thinking assesses the ability to generate multiple abstract
ideas or solutions to a problem (Guilford, 1957), and has consistently remained as a con-
ceptually, internally, and externally valid element of the creative process (Gibson, Folley
& Park, 2009). Divergent thinking has been argued to consist of spontaneous, free-flow-
ing thinking with the goal of generating many different ideas (Hennessey & Amabile,
2010, p. 574).
THE EFFECTS OF PSYCHOSTIMULANTS ON CREATIVITY
The effects of psychostimulants on creativity in patients have been investigated. For
example, methylphenidate (Ritalin) has been shown to improve divergent thinking of
creativity in patients diagnosed with Attention Deficit Hyperactive Disorder (ADHD).
Solanto and Wender (1989) used the Wallach Kogan Tasks (Wallach & Kogan, 1965)
and tested nineteen ADHD children aged between 6 and 10 years, firstly at baseline, fol-
lowed by placebo, and then followed by three doses (3, 6, and 10 mg) of methylpheni-
date. The study reported enhanced divergent thinking under methylphenidate in ADHD
participants. In contrast, participants showed a significant decline in divergent thinking
across non-drug conditions. The study reported that healthy control participants on pla-
cebo were similarly impaired on the divergent thinking tasks. Although the authors did
not investigate whether drug and/or disorder related performance was a function of base-
line of creativity personality trait, they reported that, following methylphenidate adminis-
tration, there was a large increase in divergent thinking performance in some
participants. Solanto and Wender (1989) attributed these increased performances to be
representative of atypical subgroups of ADHD children who become enhanced after
methylphenidate.
However, a previous study using the same methodology with ADHD children reported
a dose dependent improvement by methylphenidate on divergent thinking and mental
flexibility tasks (Douglas, Barr, Desilets & Sherman, 1995). Hence, the effects of methyl-
phenidate, a conventional psychostimulant known to increase dopamine (DA) in the
brain (Wang et al., 1999), on divergent thinking, may not only depend on individual dif-
ferences in baseline of cognitive function, but might also depend on optimal dosing.
Indeed, a recent study investigating differences between patients diagnosed with ADHD
and healthy participants in creativity found that the ADHD patients were significantly
better on the divergent thinking task, while healthy controls were significantly better on
the convergent thinking task of creativity (White & Shah, 2006). However, in that study,
the ADHD participants were non-medicated.
With regard to healthy volunteers, there is a dearth of research investigating the effects
of psychostimulant drugs on creativity in healthy individuals. To our knowledge, only two
2
Journal of Creative Behavior
studies have been conducted thus far. A recent double-blind, placebo-controlled study
showed that Adderall, an amphetamine based psychostimulant licensed for the treatment
of ADHD, enhanced performance on convergent thinking tasks of creativity in healthy
participants with low baseline of creative performance, and impaired performance in those
with higher baseline of creative performance (Farah, Caroline, Sankoorikal, Smith & Chat-
terjee, 2009). In that study, adderall had no effect on divergent thinking tasks of creativity.
These results point to the view that psychostimulants might modulate creativity perfor-
mance according to one’s baseline, either improving or impairing one’s divergent and
convergent thinking of creativity.
However, a recent review by Rosenthal and Westreich (2010) indicated the lack of
well-controlled studies on the effects of psychostimulant drugs on creativity. This raises
the important question of whether popular drugs like modafinil, a putative cognitive
enhancer that has been recently reported to be used by healthy individuals for cognitive
enhancement (Franke et al., 2013; Mohamed & Sahakian, 2012), boosts brain systems
associated with creativity performance in the same way it has been reported to affect
executive functions and working memory in healthy individuals (Turner et al., 2003).
Modafinil is a drug licensed for the treatment of narcolepsy (Ballon & Feifel, 2006). It
has been consistently reported to be used by healthy people for cognitive enhancement
purposes (Franke et al., 2013; Mohamed, 2014; Mohamed & Sahakian, 2012). In 2004, it
was estimated that 90% of modafinil was being used off-label by healthy, non-sleep
deprived individuals (Baranski, Pigeau, Dinich & Jacobs, 2004). The global revenue of
modafinil is more than US$700 million per year (Norman & Berger, 2008). This off-label
and revenue figures are consistent with the claim that healthy physicians on call, students
and academics are increasingly using modafinil to enhance cognitive abilities (Franke
et al., 2013; Greely, 2006).
However, it is currently unclear as to whether modafinil affects creativity performance
in healthy individuals the same way as adderall. In one study, modafinil improved alert-
ness, vigilance, and verbal tasks of creative thinking, but only after sleep-deprivation
(Walsh, Randazzo, Stone & Schweitzer, 2004). No changes were reported in the non-ver-
bal creative thinking tasks. Hence, no previous study has directly investigated the effects
of modafinil on divergent and convergent thinking tasks of creativity in healthy non-
sleep deprived volunteers. The aim of this study was to shed light on this empirical
question.
THEORETICAL RATIONALE
The theoretical rational for investigating creativity with modafinil comes from the evi-
dence indicating that creativity output is modulated by mesolimbic dopaminergic
increase (Flaherty, 2005). It has recently been argued that there is a link between
increased DA in the above areas and creativity performance (Batir, 2009), and there is
evidence suggesting a unique role for a specific DA receptor gene (DRD2 TAQ IA) for
creativity (Reuter, Roth, Holve & Hennig, 2006). These researchers showed that subcom-
ponents of the gene was associated with higher verbal creativity (A1+ as compared with
A1 allele of DRD2) while carriers of the A allele of TPH1 showed significantly higher
scores in figural and in numeric creativity.
The nucleus accumbens (NAcc) DA release has been shown to increase novelty seek-
ing and creative drive in humans (Flaherty, 2005). For example, evidence suggests that
3The Effects of Modafinil on Convergent and Divergent Thinking of Creativity creative persons have a higher DA compared to Parkinson’s disease patients (Batir, 2009), a disorder associated with a significant loss of dopaminergic neurons (Beal, 2001). These patients are significantly impaired in the performance of creativity tasks when subjected to subthalamic deep brain stimulation, but performance is restored to normal levels when treated with DA replacement therapy (Batir, 2009). Currently, the mechanisms by which modafinil exerts its wakefulness effects and how it acts as a cognitive enhancing agent in healthy individuals are unclear. Several studies indicate that modafinil increases DA neurotransmitters (Mignot, Nishino, Guilleminault & Dement, 1994; Minzenberg & Carter, 2008; Volkow et al., 2009) in several regions of the brain, including the prefrontal cortex (PFC) and the striatum. Molecular studies show that modafinil binds to and requires intact DA transporters (DAT; Qu, Huang, Xu, Matsumoto & Urade, 2008). Furthermore, modafinil has been shown to increase DA in rats, mice, monkeys, and in healthy human brains (Minzenberg & Carter, 2008). Studies with healthy humans have shown that modafinil increases DA and activates the mesolim- bic areas of the brain (Volkow et al., 2009), which are known to be involved in novelty seeking and creative thinking (Flaherty, 2005; Reuter et al., 2006). For instance, a recent double-blind placebo-controlled cross-over design study with healthy males aimed to investigate the effects of modafinil on DA neurotransmitter and DA transporter (DAT; Volkow et al., 2009). The study employed a positron emission tomography technique with [11C] raclopride, D2/D3 radioligand which is sensitive to changes in endogenous DA and [11C] cocaine, a DAT radio ligand which is sensitive to changes on extracellular DA and on DAT. The study showed that after the administration of 200 mg and 400 mg of modafinil, the drug blocked both DAT and increased extracellular DA in the mesolimbic areas of the brain, more specifically in the caudate, putamen, and NAcc in healthy men. This was possible because mod- afinil decreased both the mean [11C] raclopride and [11C] cocaine binding potential in the caudate, putamen, and NAcc, reflecting both increases in extracellular DA and occupancy of DAT. This indirectly led to higher DA availability in above brain areas, which, among others, contain a cluster of distinct areas associated with creativity out- put (Flaherty, 2005). Given that DA increases in these areas have been shown to increase creativity and novelty seeking in humans (Bardo, Donohew & Harrington, 1996; Heilman, Nadeau & Beversdorf, 2003), it is likely that modafinil might influ- ence creative thinking through the modulation of DA in the caudate, putamen, and NAcc. However, one important empirical question that has yet to be addressed in the cognitive enhancing research is whether or not modafinil influences creativity perfor- mance in healthy young adults. To date, no previous research has investigated the effects of modafinil on divergent and convergent thinking tasks of creativity in healthy partici- pants. By using validated, reliable measures of divergent and convergent thinking of creativity (Kim, 2011), the aim of this study was to investigate the effects of modafinil on creative performance in healthy, non-sleep deprived volunteers. Given the above reviewed evi- dence, it was expected that modafinil will enhance both convergent and divergent think- ing of creativity. Furthermore, given the effects that were reported in the Farah et al. (2009) study, it was expected that modafinil will increase creativity performance as a function of creativity baseline trait. 4
Journal of Creative Behavior
METHODS
ETHICAL APPROVAL
The study was approved by the Cambridge Local Research and Ethics Committee
(LRECT No: 10/H0305/39) and the Medicines and Health Care Products Regulatory
Agency, the national drug licensing agency, London, United Kingdom.
DRUG FORMULATION
The drug and the placebo tablets, which were identical, were synthesized in the Royal
Free Hospital, London, United Kingdom.
SAMPLE SIZE ANALYSIS
A sample of 30 per group was estimated to provide sufficient statistical power based
on previous within-participant medication studies (Turner et al., 2003). For a large effect
size of modafinil study (d = 0.52), the statistical power software (G-Power) recom-
mended 30 participants to provide a power of 0.95 to detect a large effect size with 0.05
error (i.e., type I false positive error of 5%). A stronger interaction between creativity
performance and group (creativity scores 9 modafinil vs. placebo) with a large effect size
(d = 0.52), for false positives (a = 0.05) with 30 participants in each group will therefore
yield a power of 0.95.
PARTICIPANTS
Sixty-four healthy male (n = 31) and female (n = 33) volunteers (mean
age SD = 25.34 3.95, range 19–36 years) were identified via the City of Cambridge,
the Department of Psychiatry participant panel at the University of Cambridge, and via
local advertisements. Participants between the ages of 18–40 years were chosen to avoid
any effects of cognitive decline. The larger age range was chosen to be representative of a
wide range of ages and socio-economic statuses.
An experienced psychologist screened all volunteers for the presence of any of the
pre-specified exclusion criteria. Participants were excluded if they had any significant
psychiatric history, visual or motor impairment, or the concurrent use of any psycho-
tropic medications or any medication contra-indicated with modafinil. In addition,
participants with a history of hypertension, cardiac disorders, epilepsy, and drug or
alcohol abuse were also excluded. All participants were advised not to consume alcohol
or caffeine for 12 hours before the testing sessions. All participants were questioned
about compliance with alcohol and caffeine restrictions before inclusion into the study.
A light breakfast or snack and juice were allowed before, but not during the experi-
mental session. After participants were assessed by the experienced psychologist, a writ-
ten informed consent was obtained.
Evidence suggests that modafinil improves function in a dose dependent manner
(Chen et al., 2007), and the best therapeutic (Minzenberg & Carter, 2008) and experi-
mental dose is 200 mg (Turner et al., 2003; Wong, Gorman, MCCormick & Grebow,
1998). Hence, when participants completed baseline physiological measures (blood pres-
sure and pulse), they were given a single oral dose of 200 mg of modafinil or placebo
with a small glass of water.
They were then asked to rest in a quiet room. Peak plasma concentrations of modafi-
nil have been obtained within 2–3 hours after oral administration with an elimination
5The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
half-life of 12–15 hours (Wong et al., 1998). Therefore, 2 hours post-drug administra-
tion, participants completed a baseline measure of creativity personality trait and tasks
that measured divergent and convergent thinking of creativity (see below for detailed
descriptions of the tasks). After completing each creativity task, participants also com-
pleted a range of cognitive and motivational tasks for another experiment (the summary
of the results are reported in the Discussion). After the completion of the study, partici-
pants were debriefed by the psychologist. They received monetary compensation of £25,
plus local transport expenses. They were discharged by a clinical research nurse.
EXPERIMENTAL DESIGN
The study employed a randomized, double-blind placebo-controlled method with a
parallel group design, deliberately chosen to avoid problems with practice effects that are
common in cross-over design studies with participants performing creativity (Rose &
Lin, 1984) and working memory tasks (Lowe & Rabbitt, 1998). Participants in the study
were randomly allocated to receive either a single oral dose of 200 mg of modafinil or a
lactose placebo. In order to balance drug conditions for gender, males and females were
separately randomized for medications. Unblinding of the medication was undertaken
after the first data analysis.
All volunteers were asked to spend the waiting time with low arousing activities (read-
ing, watching TV, or napping) in a dayroom, and were monitored by research nurses.
The testing of the creativity tasks was performed exactly 2 hours after drug administra-
tion in a silent consultation room at the Wellcome Trust Clinical Research Facility at Ad-
denbrooke’s Centre for Clinical Investigation, Cambridge, United Kingdom.
CREATIVITY MEASURES
Creative Personality Scale (CPS)
The CPS is an adjective checklist questionnaire, which measures creativity personality
trait (Gough, 1979). The CPS was used to measure participants’ creativity baseline trait.
The CPS contains 18 creative adjective checklists and 12 conservative adjective checklists.
A positive point is awarded when a participant endorses a creative checklist (e.g., individu-
alistic), while a negative point is given when the participant chooses a conservative check-
list (e.g., conventional). The CPS is a reliable and valid measure for the identification of
creative personality (Carson, Peterson & Higgins, 2005; Kaduson & Schaefer, 1991), and
has been used consistently in recent research on creativity (Batey & Furnham, 2008; Dew-
ett & Gruys, 2007). Furthermore, the CPS was validated with ratings from over 1000 crea-
tivity participants (Gough, 1979).
CONVERGENT THINKING TASKS
Group Embedded Figures Task (GEFT)
The GEFT (Figure 1) is a non-verbal convergent thinking task that requires partici-
pants to regroup the elements of a geometric design in ways that reveal simple shapes
embedded in a complex figure (Witkin, Oltman, Raskin & Karp, 2002). During the
experiment, participants were provided with seven simple shapes on an A4 paper, fol-
lowed by nine complex test items.
Participants were instructed to identify and trace a simple geometric shape embedded
within a complex figure. They had 3 minutes to complete all of the nine complex items,
6Journal of Creative Behavior
FIGURE 1. The Group Embedded Figure Task (GEFT). This figure shows a simple shape,
a control item, and a complex figure. Participants had to find the simple
shape in complex figure and trace it.
in any order. A point was given for each correctly traced item, with a maximum score of
nine points.
Remote Associates Test (RAT)
Mednick (1962; Figure 2) theorized that creativity requires the capacity to generate
remote associations that can connect hitherto disparate ideas and devised the RAT. Since
then, the RAT has been shown to measure creativity trait (Eysenck, 1995, p. 80; Katz &
Pestell, 1989) and creative potential (Martindale & Dailey, 1996). Experimentally, it has
been used in variety of clinical studies, including manic depression (Fodor & Greenier,
1995) and schizotypy (Weinstein & Graves, 2001). Psychometrically, it has been tested
with Japanese (Baba, 1982), Jamaican (Hamilton, 1982) and Hebrew (Nevo, 1978) popu-
lations, and has been found to have excellent cross-cultural validity.
The RAT is the most reliable creativity test that provides a measure of convergent
thinking of creativity and insightful problem solving in the verbal domain (Mednick,
1962). During the experiment, participants were presented with fifteen triads, each con-
taining three words, and were asked to identify and supply a word that has an associative
linkage with three separate words. For example, if the given words were wheel, electric,
and high, participants had 30 seconds to supply the associated word (i.e., chair). Further
examples are presented above in Figure 2.
DIVERGENT THINKING TASKS
Drawing Task from the Abbreviated Torrance Test for Adults (ATTA)
The ATTA (Figure 3) is a standardized, abbreviated form of the Torrance Test of Cre-
ative Thinking (Goff, 2002). This task was used to assess divergent thinking of creativity.
It includes two picture-drawing items and a single verbal task. Only the picture items
were used in this experiment. Participants were given a piece of paper that had seven
incomplete figures (Fig 3).
Participants were instructed to use the incomplete figures to make an unusual picture,
by adding lines to the incomplete figures, and by sketching some interesting objects and
pictures. They were instructed to think of a picture or an object that no one else would
think of, and they had to make the picture tell as complete and interesting story as they
could, by adding lines to and building the first figure. They had to make up an interesting
7The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
FIGURE 2. Examples from the Remote Associates Test (RAT). Participants were shown
the triads on the left and were given 30 seconds to supply a word that has
an associative linkage with three separate words.
FIGURE 3. A completed example of the Abbreviated Torrance Test for Adults (ATTA).
On the task, participants were scored for flexibility and elaboration.
title for each of their drawings and write it at the bottom of each block, next to the num-
ber of the figure. They were given 7 minutes to complete the whole task. Two independent
judges, who were blind to the study objective and participant conditions, scored the task
according to the criteria set by Goff (2002).
ALTERNATIVE USES TASK (AUT)
The AUT measures divergent thinking of creativity (Guilford, 1957), and has been
used in recent cognitive and human psychopharmacological studies that attempted to
investigate the effects of stimulants on creativity (Farah et al., 2009). Participants were
given the name of an object, and were asked to come up with as many alternative uses
as they could think of for the named object within 1 minute and 20 seconds.
Participants were given an example during the instruction. For example, if the word
“tissue” was given as the object, an example of an appropriate alternative use would
be a “blanket for a doll”. They were told that the alternative use must make sense, so
a response such as “eat as food” would not count. The objects used in this experimen-
tal work were shoe, button, key, barrel, car tire, and pencil. The responses of the
8Journal of Creative Behavior
participants were recorded and scored by two individuals who were double-blind to
the study objective and participant condition. The responses were scored for original-
ity, fluency, flexibility, and detail, according to the criteria of Guilford (1957). Scoring
was comprised of the below four components.
Originality: Each response is compared to the total amount of responses from all of the
participants. Responses that were given by only 5% of the group count as
unusual (one point) and responses given by only 1% of them count as unique
(two points).
Fluency: The total of all responses.
Flexibility: The number of different categories used.
Elaboration: The amount of detail (e.g., “a doorstop” counts zero, whereas “a door-stop to
prevent a door slamming shut in a strong wind” counts two (one point for
explanation of door slamming and another for further detail about the wind).
WALLACH AND KOGAN PATTERN MEANING (PM) AND LINE DRAWING (LD)
TASKS
Wallach and Kogan (1965) tests of divergent thinking assess the generation of associa-
tions through pattern meaning (Figure 4) and line drawings. These tasks were chosen
because they reliably measure originality and fluency and they have been used to assess
divergent thinking of creativity in high functioning adults (Claridge & McDonald, 2009),
and in ADHD patients (Solanto & Wender, 1989). These tasks have demonstrated high
reliability and high internal consistency (Cropley & Mansley, 1969).
Furthermore, the tasks are poorly correlated with intelligence tests (Cropley &
Mansley, 1969) and can be scored objectively and reliably without the need for an
external evaluator (Claridge & McDonald, 2009; Cropley & Mansley, 1969; Plucker &
Renzulli, 1999). Participants were instructed to look at six patterns and six line draw-
ings. At each one, they were asked to list all the things they could think each of the
FIGURE 4. An example of the Pattern Meaning (PM) section in the Wallach and Kogan
task.
9The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
complete patterns and drawings might be. For instance, participants were shown Fig-
ure 4 and were awarded one point if they came up with a speedometer or a hedge-
hog as an answer. They were allowed to turn or move the drawings in any way to
help their efforts. Dependent variables were the total number of generated responses
and unique responses that no other participant had given.
RESULTS
CONVERGENT THINKING TASKS OF CREATIVITY
GEFT
To test the hypothesis of whether there was a significant difference between the mod-
afinil and the placebo group on the performance of the GEFT, a one-way ANOVA was
conducted and found a marginal effect of drug on the GEFT,
F(1,63) = 3.047, p = .09, d = 0.43. Participants on modafinil performed marginally better
(Mean [M] = 6.5, SD = 3.7; 95% CI: 5.05–7.85), relative to participants on placebo
(M = 5.09, SD = 3.39; 95% CI: 3.89–6.29).
To test the hypothesis of whether creativity personality baseline and drug condition
(modafinil or placebo) were predictors of the mean GEFT performance, a multiple linear
regression analysis was conducted and found the overall regression non-significant, F
(2,61) = 1.159, p = .28, R2 = 0.37, Cohen’s f2(f2) = 0.58.1
RAT
To test the hypothesis of whether there was a significant difference between the mod-
afinil and placebo group on the RAT, a one-way ANOVA was conducted and was found
to be non-significant, F(1,62) = 0.13, p = .72, d = 0.03.
To test the hypothesis of whether creativity personality trait and drug condition
(modafinil or placebo) predicted the performance of the mean RAT, a multiple linear
regression analysis was conducted and found the overall regression non-significant, F
(2,61) = 0.160, p = .85, R2 = 0.05, f2 = 0.05.
High versus low creativity participants
To investigate whether modafinil had similar effects on the RAT as reported by Farah
et al. (2009) on adderall, a median split was carried out on participants’ responses to the
CPS questionnaire, and those above the median (8 > ) were classified as high in creativ-
ity baseline trait, and those below the median (Journal of Creative Behavior
To test the hypothesis of whether baseline of creativity (high vs. low) and drug (mod-
afinil vs. placebo) had an effect on creativity performance, a two-way ANOVA using drug
(modafinil vs. placebo) 9 creativity baseline (high vs. low) as independent variables, and
the RAT scores as a dependent variable was conducted, and found a significant drug and
creativity baseline interaction, F(3,60) = 5.318, p = .023, d = 0.80 (Figure 5). Modafinil
participants low in creativity trait had significantly higher RAT scores (M = 6.85,
SD = 3.39; 95% CI: 5.53–8.2) than those high in creativity trait (M = 4.27, SD = 3.0;
95% CI: 2.4–6.0; Figure 5).
A further one way ANOVA confirmed a significant difference between the high
and low creativity participants on modafinil, F(1,31) = 4.638, p = .04, d = 0.80; simple
effects confirmed the finding that the modafinil participants scoring low on trait base-
line creativity were improved in their responses on the RAT, while modafinil partici-
pants high in trait creativity were impaired on the task.
DIVERGENT THINKING OF CREATIVITY
ATTA flexibility scores
To test the hypothesis of whether there was a significant difference between the mod-
afinil and the placebo group on the performance of the flexibility scores in the divergent
FIGURE 5. The effect of drug on high and low creativity participants on the RAT. In the
modafinil group, participants low in trait creativity were significantly
improved by modafinil, relative to participants high on creativity baseline
trait (p = .04). Error bars represent the SEM.
11The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
thinking task, a one-way ANOVA was conducted on the ATTA flexibility scores and
found a main effect of drug for total flexibility, F(1,57) = 23.23, p < .01, d = 1.5, and a
main effect of drug for mean flexibility F(1,57) = 23.23, p < .01, d = 1.29 (Figure 6).
Participants on modafinil (M = 0.77, SD = 0.37; 95% CI: 0.63–0.92) had significantly
lower mean flexibility scores, relative to participants on placebo (M = 1.195, SD = 0.28;
95% CI: 1.0–1.30).
ATTA elaboration scores
To test the hypothesis of whether there was a significant difference between the mod-
afinil and placebo group on the performance of the divergent thinking task a one-way
ANOVA was conducted and found a trend toward significance of drug on mean elabora-
tion, F(1,57) = 3.903, p = .053, d = 0.56, and a marginal effect of drug on total elabora-
tion, F(1,57) = 3.788, p = .056, d = 0.55. Participants on modafinil had marginally
significantly lower elaboration scores (M = 1.90, SD = 0.7; 95% CI: 1.6–2.2) relative to
participants on placebo (M = 2.41, SD = 1.1; 95% CI: 1.98–2.83; Figure 7).
FIGURE 6. The effect of drug on the mean flexibility scores on the ATTA. Participants
on placebo obtained significantly more mean flexibility scores on the task
relative to those on modafinil (p < .01). Error bars represent the SEM.
12Journal of Creative Behavior
FIGURE 7. The effect of the drug on the mean elaboration scores on the ATTA. On
average, participants on placebo were marginally significantly better on
elaboration scores relative to those on modafinil (p = .053). Error bars
represent the SEM.
To test the hypothesis of whether creativity personality trait and drug condition
(modafinil or placebo) predicted mean elaboration scores and mean flexibility scores
from the ATTA, separate multiple linear regression analysis were conducted and found
the regressions marginally significant for elaboration, F(2,56) = 2.826, p = .068,
R2 = 0.132, f2 = 0.15, and significant for flexibility, F(2,56) = 12.17, p < .01, R2 = 0.30,
f2 = 0.42, respectively.
To test the hypothesis of whether there was a significant difference between the
modafinil and the placebo group on the overall mean of the ATTA divergent thinking
scores, a one-way ANOVA was conducted and found a significant effect of drug on
the ATTA mean scores, F(1,57) = 23.30, p < .01, d = 1.3. Participants on modafinil
(Mean, 6.3, SD = 2.6; 95% CI: 5.3–7.4) had significantly lower mean divergent thinking
scores relative to participants on placebo (M = 9.5, SD = 2.3; 95% CI: 8.6–10.4;
Figure 8).
To test the hypothesis of whether creativity personality trait and drug condition
(modafinil or placebo) predicted the overall mean ATTA performance, a multiple linear
regression analysis was conducted and found the regression significant, F(2,56) = 12.46,
p < .01, R2 = 0.30, f2 = 0.42. Creativity personality baseline trait did not predict the
mean ATTA performance (b = 0.14) and was not significant (t = 1.19, p = .2; 95% CI:
13The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
FIGURE 8. The effect of the drug on the mean divergent scores on the ATTA. On
average, participants on placebo were marginally significantly better on
divergent thinking scores relative to those on modafinil (p < .01). Error bars
represent the SEM.
0.077 to 0.30), while drug condition was a significant negatively predictor of the
mean ATTA performance (t = 4.167, Beta = 2.885, p < .01).
This analysis shows that the creativity baseline trait itself was not a significant
predictor of the mean divergent thinking performance but that drug, namely modafinil
administration, was a significant negative predictor of the divergent thinking perfor-
mance as measured by the ATTA.
High and low creativity group
To test the hypothesis of whether creativity baseline trait (high vs. low) and drug con-
dition (modafinil or placebo) had a significant effect of main divergent thinking scores, a
planned comparison ANOVA was conducted and was found to be significant, F
(3,55) = 8.985, p < .01, d = 1.26. There was a main effect of drug condition on ATTA
mean creativity performance, F(1,55) = 19.82, p < .01, d = 0.87, no effect of creativity
baseline on ATTA mean creativity performance, F(1,55) = 2.35, p = .13, d = 1.28, and
14Journal of Creative Behavior
no significant interaction between creativity baseline and drug condition, F(1,55) = 0.57,
p = .45, d = 0.66.
To further investigate the main effects of drug, a posthoc analysis revealed that
participants high in creativity who were on modafinil (M = 6.76, SD = 3.0, 95% CI:
5.0–8.4) had a significant lower mean ATTA scores compared with participants on
placebo (M = 10.28, SD = 2.2, 95% CI: 9.0–11.5), t(23) = 3.33, p = .03 (two tailed)
95% CI: 1.33–5.7. Similarly, participants low in creativity baseline trait who were on
modafinil (M = 6.23, SD = 3.0; 95% CI: 5.1–7.3) had a significant lower mean ATTA
scores compared with participants on placebo (M = 8.7, SD = 2.2; 95% CI: 7.4–10.0),
t(32) = 2.91, p = .006 (two tailed) 95% CI: 0.75–4.24 (Figure 9). This suggests that
modafinil had a uniform negative effect on the performance of the ATTA scores
regardless of the participants’ creativity baseline trait.
AUT
To test the hypothesis of whether there was a significant difference between the mod-
afinil and placebo on the AUT, a one way ANOVA was conducted and was found to be
FIGURE 9. The effect of drug on the mean ATTA scores in the high and low creativity
group. In both the high and the low creativity groups, participants on
placebo obtained significantly more mean ATTA scores relative to those on
modafinil (p < .01). Error bars represent the SEM.
15The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
not significant, F(1,60) = 0.00, p = .99, d = 0.001. Regression analysis using creativity
baseline trait and drug as predictors of creativity performance was found to be not signif-
icant, F(2,59) = 0.267, p = .76, R2 = 0.095, f2 = 0.10.
PM and LD
To test the hypothesis of whether there was a significant difference between the mod-
afinil and placebo on the PM and the LD, a one-way ANOVA was conducted for both
tasks and found no significant effect for both analyses, F(1,58) = 0.3, p = .6, d = 0.002; F
(1,58) = 0.001, p = .10, d = 0.14, respectively.
Regression analysis using creativity baseline trait and drug as predictors of creativity
performance found no significant effect for both tasks, F(2,58) = 0.05, p = .9, R2 = 0.13,
f2 = 0.14; F(2,58) = 0.622, p = .541, R2 = 0.147, f2 = 0.17, respectively.
DISCUSSION
The aim of this study was to investigate the effects of modafinil on reliable measures
of divergent and convergent thinking tasks of creativity in healthy volunteers. For the
convergent thinking tasks, the results show that modafinil had a marginally positive
effect on the GEFT. There was no main effect of drug on the RAT. Hence, overall,
modafinil had no main effect on the convergent thinking tasks of creativity.
When the creativity personality trait scores and drugs treatment were combined to
see whether they predicted the convergent thinking performance, the results from the
regression analysis showed no significant effect, highlighting that the interaction
between creativity personality trait and drug treatment (either modafinil or placebo)
did not predict the performance of the convergent thinking tasks.
To investigate whether modafinil had similar effects on the RAT as was reported by
Farah et al. (2009) for adderall, when participants were divided into high and low crea-
tivity group, using a median split analysis, improvements were seen in the RAT by mod-
afinil, but only for participants who had low creativity personality trait at baseline
relative to participants who had high creativity personality trait at baseline.
Similarly, Farah et al. (2009) reported improvements of performance on adderall in
participants who were, at baseline, below the median of performance on the RAT
when they were on placebo. The results from the current study are consistent with
earlier evidence suggesting that psychostimulants impair performance in participants
who are high in cognitive function whereas they might improve performance in those
with low cognitive function (e.g., patients diagnosed with ADHD). For example, the
DA agonist, bromocriptine, improved the performance of executive function tasks in
individuals with low working memory capacity, but impaired performance of those
with high working memory capacity (Kimberg, D’Esposito & Farah, 1997). The results
from the RAT are further consistent with the empirical evidence showing that those
with lower baseline of working memory performance are moderately improved by
psychostimulants (Mehta, Goodyer & Sahakian, 2004; Randall, Shneerson & File,
2005).
When the effects of modafinil on the performance of the divergent thinking task
as measured by the ATTA were investigated, modafinil significantly reduced both the
mean flexibility performance and the total mean divergent thinking performance.
When the drug and creativity baseline trait were added together to see whether they
16Journal of Creative Behavior
together predicted the performance of the task, the results showed that, while the
regression analysis for the creativity personality trait was not significant, modafinil
was a significant negative predictor of the divergent thinking performance. The results
suggest that modafinil significantly reduced the performance of the divergent thinking
task, and this was independent of the participants’ creativity personality trait. These
findings are consistent with recently reviewed evidence suggesting that in non-ADHD
adults, psychostimulant may actually impair performance of tasks that require adapta-
tion and flexibility (Advokat, 2010).
Interestingly, the results from the other cognitive experiments, which are not reported
here, showed that modafinil failed to improve the CANTAB Paired Associate Learning
task, which assesses short-term memory, and the Digit Span test (from the Wechsler IQ
test), that assesses auditory memory. Modafinil also impaired word retrieval, as measured
by the Hayling Sentence Completion Task, which assesses response initiation, response
inhibition, and language retrieval (Mohamed & Lewis, submitted). Furthermore, partici-
pants on modafinil reported significantly increased subjective pleasure as measured by a
visual analogue scale for mood. These subjective increases in pleasure were independent
of the actual performance of the creativity and cognitive tasks. On a task of motivational
reinforcement learning, modafinil increased latency of response, and impaired the learn-
ing of motivational contingencies associated with positive reward. Taken together, these
results suggest that in healthy individuals, modafinil might have some subtle negative or
nuanced effects on different cognitive processes, particularly by reducing performance in
the domains of higher order cognitive processes such as convergent and divergent think-
ing of creativity. Hence, these results argue against the notion that modafinil is a general
cognitive enhancing drug.
It is likely that modafinil did not have robust effects on all the creativity tasks because
it modulates not only DA but it also increases other multiple neurotransmitters including
norepinephrine, serotonin, and glutamate in several regions of the brain, including the
PFC, hippocampus, hypothalamus, and the striatum (see Minzenberg & Carter, 2008).
An alternative explanation of the lack of the robust effects of modafinil on all the cre-
ativity tasks could be that the study was a small-scale trial with small to moderate effect
size because of the small number of participants that were tested. Hence, the findings
from this study are not conclusive and should be interpreted with caution. It is impor-
tant that further trials are conducted to investigate the effects of modafinil on divergent
and convergent thinking tasks of creativity.
LIMITATIONS
Although the findings from this study are consistent with Farah et al. (2009)’s study
and with previous psychopharmacology research, the results from the RAT should be
interpreted with caution. This is because median split analyses are problematic as they
split groups arbitrarily and assume that the high and low creativity group were inherently
different. However, the participants in the placebo and in the modafinil group who par-
ticipated in this study were demographically similar. Moreover, the regression analysis,
which inquired whether the combination of creativity trait and drug effect predicted the
performance of the RAT, did not show significance. Hence, in order to replicate Farah
et al.’s (2009) findings, it is important to investigate further the effects of modafinil on
the RAT with a large number of participants.
17The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
Moreover, apart from the ATTA, most of the divergent thinking tasks were not signifi-
cant. Furthermore, contrary to the second hypothesis, apart from the RAT, modafinil did
not increase creativity performance as a function of creativity baseline trait. Therefore,
although the results from this study show that modafinil significantly reduced divergent
thinking of creativity in healthy individuals, they are not conclusive enough to determine
the effects of modafinil on creativity in healthy individuals. Hence, future studies need to
collect more data to gain a clear understanding of the effects of modafinil on creativity.
Furthermore, as dose dependent effects of modafinil on the creativity tasks were not
investigated, future studies need to investigate the effects of 100–400 mg of modafinil on
creativity tasks.
CONCLUSIONS
The current study investigated the effects of modafinil on highly reliable divergent and
convergent thinking tasks on creativity. Modafinil had no main effect on convergent
thinking tasks as measured by the GEFT and the RAT. However, a median split analysis
showed that modafinil participants low in creativity trait had significantly higher RAT
scores than those high in creativity trait.
Modafinil significantly reduced flexibility and marginally reduced elaboration as mea-
sured by the ATTA. Modafinil significantly reduced the overall performance of the
ATTA, which assessed divergent thinking process of creativity. The main creativity per-
sonality trait did not interact with the drug effects to predict creativity performance.
Rather, modafinil administration was a significant negative predictor on its own in the
divergent thinking performance.
The results from this study suggest that, rather than acting as a general cognitive
enhancer, modafinil has more subtle negative or nuanced effects on different cognitive
processes, particularly in the domains of convergent and divergent thinking of creativity.
However, the results need to be interpreted with caution and replicated with a large sam-
ple of participants.
REFERENCES
Advokat, C. (2010). What are the cognitive effects of stimulant medications? Emphasis on adults with atten-
tion-deficit/hyperactivity disorder (ADHD). Neuroscience & Biobehavioral Reviews, 34, 1256–1266; doi:10.1016/
j.neubiorev.2010.03.006.
Baba, Y. (1982). An analysis of creativity by means of the Remote Associates Test for Adult Revised in Japanese
(JARAT FORM A). Japanese Journal of Psychology, 52, 330–336.
Ballon, J., & Feifel, D. (2006). A systematic review of modafinil: Potential clinical uses and mechanisms of action.
Journal of Clinical Psychiatry, 67, 554–566.
Baranski, J.V., Pigeau, R., Dinich, P., & Jacobs, I. (2004). Effects of modafinil on cognitive and meta-cognitive per-
formance. Clinical Trial Comparative Study. Humuan Psychopharmacology, 19, 323–332; doi:10.1002/hup.596.
Bardo, M.T., Donohew, R.L., & Harrington, N.G. (1996). Psychobiology of novelty seeking and drug seeking behav-
ior. Behavioural Brain Research, 77, 23–43; doi:10.1016/0166-4328(95)00203-0.
Batey, M., & Furnham, A. (2008). The relationship between measures of creativity and schizotypy. Personality and
Individual Differences, 45, 816–821; doi:10.1016/j.paid.2008.08.014.
Batir, A. (2009). Creativity induced by Dopamine Agonists in Parkinson’s Disease: Abstract. MDs 13th Interna-
tional Congress of Parkinson’s Disease and Movement Disorders: Abstract Mo-163. Presented June 8, 2009.
Beal, M.F. (2001). Experimental models of Parkinson’s disease. Nature Reviews Neuroscience, 2, 325–334.
18Journal of Creative Behavior
Carson, S.H., Peterson, J.B., & Higgins, D.M. (2005). Reliability, validity, and factor structure of the creative
achievement questionnaire. Creativity Research Journal, 17, 37–50; doi:10.1207/s15326934crj1701_4.
Chen, C.R., Qu, W.M., Qiu, M.H., Xu, X.H., Yao, M.H., Urade, Y., & Huang, Z.L. (2007). Modafinil exerts a
dose-dependent antiepileptic effect mediated by adrenergic [alpha]1 and histaminergic H1 receptors in mice.
Neuropharmacology, 53, 534–541; doi:10.1016/j.neuropharm.2007.06.017.
Claridge, G., & McDonald, A. (2009). An investigation into the relationship between convergent and divergent
thinking, Schizotypy, and autistic traits. Personality and Individual Differences, 49, 794–799.
Cropley, A.J., & Mansley, G.W. (1969). Reliability and factorial validity of the Wallach-Kogan creativity tests. British
Journal of Psychology, 60, 395–398.
Dewett, T., & Gruys, M.L. (2007). Advancing the case for creativity through graduate business education. Thinking
Skills and Creativity, 2, 85–95; doi:10.1016/j.tsc.2007.04.001.
Douglas, V.I., Barr, R.G., Desilets, J., & Sherman, E. (1995). Do high doses of stimulants impair flexible thinking in
attention-deficit hyperactivity disorder? Journal of the American Academy of Child and Adolescent Psychiatry, 34,
877–885; doi:10.1097/00004583-199507000-00011.
Eysenck, H.J. (1995). Genius: The natural history of creativity. Cambridge, UK: Cambridge University Press.
Farah, M., Caroline, H., Sankoorikal, G., Smith, M.E., & Chatterjee, A. (2009). When we can enhance cognition
with Adderall, do we sacrifice creativity? Psychopharmacology (Berl), 203, 541–547.
Flaherty, A.W. (2005). Frontotemporal and dopaminergic control of idea generation and creative drive. The Journal
of Comparative Neurology, 493, 147–153; doi:10.1002/cne.20768.
Fodor, E.M., & Greenier, K.D. (1995). The power motive, self-affect, and creativity. Journal of Research in Personal-
ity, 29, 242–252; doi:10.1006/jrpe.1995.1014.
Franke, A., Bagusat, C., Dietz, P., Hoffmann, I., Simon, P., Ulrich, R., & Lieb, K. (2013). Use of illicit and prescrip-
tion drugs for cognitive or mood enhancement among surgeons. BMC Medicine, 11, 102; doi:10.1186/
1741-7015-11-102.
Gibson, C., Folley, B.S., & Park, S. (2009). Enhanced divergent thinking and creativity in musicians: A behavioral
and near-infrared spectroscopy study. Brain and Cognition, 69, 162–169; doi:10.1016/j.bandc.2008.07.009.
Goff, T. (2002). Abbreviated Torrance test for adults manual. Bensenville, IL: Scholastic Testing Service.
Gough, H.G. (1979). A creative personality scale for the Adjective Check List. Journal of Personality and Social Psy-
chology, 37, 1398–1405; doi:10.1037/0022-3514.37.8.1398.
Greely, H.T. (2006). The Social effects of advances in neuroscience: Legal problems, Legal Perspectives. In J. Illes
(Ed.), Neuroethics: Definining the issues in theory, practice, and policy (pp. 246–263). New York: Oxford Univer-
sity Press.
Guilford, J.P. (1957). Creative abilities in the arts. Psychological Review, 64, 110–118; doi:10.1037/h0048280.
Hamilton, M.A. (1982). “Jamaicanizing” the Mednick Remote Associates Test of creativity. Perceptual and Motor
Skill, 55, 321–322.
Heilman, K.M., Nadeau, S.E., & Beversdorf, D.O. (2003). Creative innovation: Possible brain mechanisms. Neuro-
case, 9, 369–379; doi:10.1076/neur.9.5.369.16553.
Hennessey, B.A., & Amabile, T.M. (2010). Creativity. Annual Review of Psychology, 61, 569–598; doi:10.1146/annu-
rev.psych.093008.100416.
Kaduson, H.G., & Schaefer, C.E. (1991). Concurrent validity of the Creative Personality Scale of the Adjective
Check List. Psychological Reports, 69, 601–602; doi:10.2466/pr0.69.6.601-602.
Katz, A.N., & Pestell, D. (1989). Attentional processes and the finding of remote associates. Personality and Individ-
ual Differences, 10, 1017–1025; doi:10.1016/0191-8869(89)90252-3.
Kaufman, J.C., & Sternburg, R.J. (2006). The International Handbook of Creativity. Cambridge: Cambridge Univer-
sity Press.
Kim, K.H. (2011). The APA 2009 Division 10 debate: Are the Torrance tests of creative thinking still relevant
in the 21st century? Psychology of Aesthetics, Creativity, and the Arts, 5, 302–308; doi:10.1037/a0021917.
Kimberg, D.Y., D’Esposito, M., & Farah, M.J. (1997). Effects of bromocriptine on human subjects depends on
working memory capacity. NeuroReport, 8, 3581–3585.
Lowe, C., & Rabbitt, P. (1998). Test/re-test reliability of the CANTAB and ISPOCD neuropsychological batteries:
theoretical and practical issues. Neuropsychologia, 36, 915–923.
Martindale, C., & Dailey, A. (1996). Creativity, primary process cognition and personality. Personality and Individ-
ual Differences, 20, 409–414; doi:10.1016/0191-8869(95)00202-2.
Mednick, S. (1962). The associative basis of the creative process. Psychological Review, 69, 220–232; doi:10.1037/
h0048850.
19The Effects of Modafinil on Convergent and Divergent Thinking of Creativity
Mehta, M.A., Goodyer, I.M., & Sahakian, B.J. (2004). Methylphenidate improves working memory and set-shifting
in AD/HD: Relationships to baseline memory capacity. Journal of Child Psychology and Psychiatry, 45, 293–305.
Mignot, E., Nishino, S., Guilleminault, C., & Dement, W.C. (1994). Modafinil binds to the dopamine uptake carrier
site with low affinity. Sleep, 17, 436–437.
Minzenberg, M.J., & Carter, C.S. (2008). Modafinil: A review of neurochemical action and effects on cognition.
Neuropsychopharmacology, 33, 1477–1502.
Mohamed, A.D. (2014). Reducing creativity with psychostimulants may debilitate mental health and well-being.
Journal of Creativity in Mental Health, 9, 146–163; doi:10.1080/15401383.2013.875865.
Mohamed, A.D., & Sahakian, B.J. (2012). The ethics of elective psychopharmacology. The International Journal of
Neuropsychopharmacology, 15, 559–571; doi:10.1017/S146114571100037X.
Nevo, B.L.I. (1978). Remote Associates Test: Assessment of creativity in Hebrew. Megamot, 24, 87–98.
Norman, C., & Berger, M. (2008). Neuroenhancment: Status quo and perspectives. European Archives of Psychiatry
and Clinical Neuroscience, 258, 110–114.
Plucker, J.A., & Renzulli, J.S. (1999). Psychometric approaches to the study of human creativity. In R.J. Sternberg
(Ed.), Hanbook of creativity (pp. 35–64). New York: Cambridge University Press.
Qu, W.-M., Huang, Z.-L., Xu, X.-H., Matsumoto, N., & Urade, Y. (2008). Dopaminergic D1 and D2 receptors are
essential for the arousal effect of modafinil. Journal of Neuroscience, 28, 8462–8469; doi:10.1523/jneurosci.
1819-08.2008.
Randall, D.C., Shneerson, J.M., & File, S.E. (2005). Cognitive effects of modafinil in student volunteers may depend
on IQ. Pharmacology Biochemistry and Behaviour, 82, 133–139.
Reuter, M., Roth, S., Holve, K., & Hennig, J. (2006). Identification of first candidate genes for creativity: A pilot
study. Brain Research, 1069, 190–197.
Rose, L.H., & Lin, H.-T. (1984). A meta-analysis of long-term creativity training programs. The Journal of Creative
Behavior, 18, 11–22; doi:10.1002/j.2162-6057.1984.tb00985.x.
Rosenthal, R., & Westreich, L.M. (2010). Cosmetic psychopharmacology: Drugs that enhance wellbeing, performance
and creativity. Cambridge: Cambridge University Press.
Solanto, M.V., & Wender, E.H. (1989). Does methylphenidate constrict cognitive functioning? Journal of the Ameri-
can Academy of Child and Adolescent Psychiatry, 28, 897–902; doi:10.1097/00004583-198911000-00014.
Turner, D., Robbins, T., Clark, L., Aron, A., Dowson, J., & Sahakian, B. (2003). Cognitive enhancing effects of
modafinil in healthy volunteers. Psychopharmacology (Berl), 165, 260–269; doi:10.1007/s00213-002-1250-8.
Volkow, N., Fowler, J.S., Logan, J., Alexoff, D., Zhu, W., Telang, F., Wang, G.-J., Jayne, M., Hooker, J.M., Wong,
C., Hubbard, B., Carter, P., Warner, D., King, P., Shea, C., Xu, Y., Muench, L., & Apelskog- Torres, K. (2009).
Effects of modafinil on dopamine and dopamine transporters in the male human brain: Clinical implications.
Journal of the American Medical Association, 301, 1148–1154; doi:10.1001/jama.2009.351.
Wallach, M.A., & Kogan, N. (1965). Modes of thinking in young children: Holt. New York: Rinehart and Winston.
Walsh, J.K., Randazzo, A.C., Stone, K.L., & Schweitzer, P.K. (2004). Modafinil improves alertness, vigilance, and
executive function during simulated night shifts. Sleep, 27, 431–439.
Wang, G.-J., Volkow, N.D., Fowler, J.S., Logan, J., Pappas, N.R., Wong, C.T., et al. (1999). Reproducibility of
repeated measures of endogenous dopamine competition with [11C]raclopride in the human brain in response
to methylphenidate. Journal of Nuclear Medicine, 40, 1285–1291.
Weinstein, S., & Graves, R.E. (2001). Creativity, schizotypy, and laterality. Cognitive Neuropsychiatry, 6, 131–146.
White, H.A., & Shah, P. (2006). Uninhibited imaginations: Creativity in adults with Attention-Deficit/Hyperactivity
Disorder. Personality and Individual Differences, 40, 1121–1131; doi:10.1016/j.paid.2005.11.007.
Witkin, H., Oltman, P., Raskin, E., & Karp, S. (2002). Group embedded figures test manual. Redwood City, CA:
Mind Garden.
Wong, Y., Gorman, S., MCCormick, G., & Grebow, P. (1998). Single-dose pharmacokinetics of modafinil and
methylphenidate given alone in and in combination to healthy male volunteers. Journal of Clinical Pharmacol-
ogy, 38, 276–82.
Ahmed Dahir Mohamed, University of Cambridge
Correspondence concerning this article should be addressed to Dr Ahmed Dahir Mohamed, Chartered Psychologist
and Elected Academic Life Member, Clare Hall, Herschel Road, Cambridge CB3 9AL, United Kingdom. E-mail:
ahmed.mohamed@cantab.net
20You can also read
