Brain Switches Utilitarian Behavior: Does Gender Make the Difference?
et al. (2010) Brain Switches Utilitarian Behavior: Does Gender Make the Difference? PLoS
ONE 5(1): e8865. doi:10.1371/journal.pone.0008865
Brain Switches Utilitarian Behavior: Does Gender Make the Difference?
Manuela Fumagalli 0
Maurizio Vergari 0
Patrizio Pasqualetti 0
Sara Marceglia 0
Roberta Ferrucci 0
Simona Mrakic-Sposta 0
Stefano Zago 0
Giuseppe Sartori 0
Gabriella Pravettoni 0
Sergio Barbieri 0
Stefano Cappa 0
Alberto Priori 0
Alessandro Antonietti, Catholic University of Sacro Cuore, Italy
0 1 Dipartimento di Scienze Neurologiche, Universita` di Milano , Milano , Italy , 2 Centro Clinico per le Neuronanotecnologie e la Neurostimolazione, Fondazione IRCCS Ca` Granda - Ospedale Maggiore Policlinico , Milano , Italy , 3 Unita` Operativa di Neurofisiopatologia Clinica, Fondazione IRCCS Ca` Granda - Ospedale Maggiore Policlinico , Milano , Italy , 4 Unita` Operativa di Neurologia, Fondazione IRCCS Ca` Granda - Ospedale Maggiore Policlinico , Milano, Italy, 5 Associazione Fatebenefratelli per la Ricerca (AFaR) , Ospedale ''San Giovanni Calibita'' Fatebenefratelli - Isola Tiberina , Roma, Italy, 6 Dipartimento di Psicologia Generale , Universita` di Padova , Padova , Italy , 7 Dipartimento di Scienze Sociali e Politiche, Universita` di Milano , Milano , Italy , 8 Centro di Neuroscienze Cognitive, Universita` Vita-Salute San Raffaele , Milano, Italy, 9 Dipartimento di Neuroscienze , Istituto Scientifico San Raffaele , Milano , Italy
Decision often implies a utilitarian choice based on personal gain, even at the expense of damaging others. Despite the social implications of utilitarian behavior, its neurophysiological bases remain largely unknown. To assess how the human brain controls utilitarian behavior, we delivered transcranial direct current stimulation (tDCS) over the ventral prefrontal cortex (VPC) and over the occipital cortex (OC) in 78 healthy subjects. Utilitarian judgment was assessed with the moral judgment task before and after tDCS. At baseline, females provided fewer utilitarian answers than males for personal moral dilemmas (p = .007). In males, VPC-tDCS failed to induce changes and in both genders OC-tDCS left utilitarian judgments unchanged. In females, cathodal VPC-tDCS tended to decrease whereas anodal VPC-tDCS significantly increased utilitarian responses (p = .005). In males and females, reaction times for utilitarian responses significantly decreased after cathodal (p,.001) but not after anodal (p = .735) VPC-tDCS. We conclude that ventral prefrontal tDCS interferes with utilitarian decisions, influencing the evaluation of the advantages and disadvantages of each option in both sexes, but does so more strongly in females. Whereas cathodal tDCS alters the time for utilitarian reasoning in both sexes, anodal stimulation interferes more incisively in women, modifying utilitarian reasoning and the possible consequent actions. The genderrelated tDCS-induced changes suggest that the VPC differentially controls utilitarian reasoning in females and in males. The gender-specific functional organization of the brain areas involved in utilitarian behavior could be a correlate of the moral and social behavioral differences between the two sexes.
Practical issues are issues over which people are prepared to
fight and kill one another; and it may be that unless some way is
found of talking about them rationally and with hope of
agreement, violence will finally engulf the world . Although
philosophers recognized the importance of moral thinking for
mankind, the biological basis of utilitarian behavior, the guiding
psychological processes and underlying neurophysiological
mechanisms remain unclear.
The moral judgment task is an experimental tool designed to
evaluate moral reasoning by presenting various types of moral and
non-moral dilemmas . Subjects are required to respond to each
item with a utilitarian or non utilitarian answer. In general terms,
a utilitarian choice aims to obtain the maximum advantage and
the minimum disadvantage, implying a personal gain, even at the
expense of damaging others. Although lesional and neuroimaging
studies have suggested that the ventral prefrontal cortex has a
pivotal role in decisional processes [2,3,4,5,6,7,8,9,10], no data
have yet shown whether interfering directly with this area, for
example by applying brain stimulation, influences human
utilitarian judgments. Transcranial direct current stimulation
(tDCS) is a non-invasive technique for modulating brain activity
[11,12,13,14,15,16] that has already provided interesting
information on decisional processes such as risk taking [17,18], social
interaction  and lying [20,21].
Current evidence on how non-invasive brain stimulation
influences social and non-social decision-making comes also from
another brain stimulation technique widely used in neuroscience,
transcranial magnetic stimulation (TMS). Repetitive TMS (rTMS)
delivers short magnetic pulses that penetrate the skull and disrupt
neural processing in a non-invasive way . Apart from their
differing underlying mechanisms, tDCS and TMS differ also in the
focality of simulation: whereas TMS coils come in different sizes
and configurations and can stimulate a scalp area of about
25 mm2, tDCS uses large electrodes measuring about 2500 mm2
to maintain a low current density on the scalp. Although neither
tDCS nor TMS raise safety concerns, whereas rTMS is
recommended for experiments investigating neurophysiological
effects on specific brain circuits, tDCS is suitable for investigating
modulatory effects on nonspecific neuronal populations . TMS
has already been used to study the role of the dorsolateral
prefrontal cortex (DLPFC) in decision-making applying TMS
before subjects did the Ultimatum Game [24,25]. Right DLPFC
TMS increased reaction times for rejecting unfair offers  and
reduced subjects rejection of their partners intentionally unfair
offers, suggesting that subjects are less able to resist the economic
temptation to accept these offers . Two neuroeconomic studies
demonstrate also that right DLPFC TMS induces significantly
riskier decisions in a gambling paradigm  and decreases the
values assigned to food stimuli .
Intensive research into human decisional processes over the
years shows that genders differ in moral behavior [28,29,30,31],
females having superior empathic ability [32,33] and males being
more prone to physical and verbal aggressiveness [34,35]. Crime
statistics report that females account for only 67% of inmates,
irrespective of nationality, culture, religion and age [36,37,38].
Although previous tDCS and rTMS experiments have already
linked the prefrontal cortex to fairness , lie [20,21] and
risktaking behavior [17,18], they did so using money-based tasks.
Although money has a strong reward and motivational drive,
human behavior is motivated also by other non-material factors,
such as emotions, family affections, respect for life, non-violence,
care and responsibility, fairness and equality, freedom and
courage, cooperation and trust, honesty and openness. No tDCS
or rTMS studies have yet investigated whether testing designed to
assess non-material factors might advance our knowledge on
human decision-making and behavior. Nor did previous studies on
the neural basis of morality consider the important variable,
gender [2,4,6,7,39]. Understanding the biological basis of
utilitarian reasoning would have philosophical, sociological and
In this study we tested whether neurostimulation influencing
cortical excitability in the ventral part of the anterior frontal lobe,
hereafter defined as the ventral prefrontal cortex (VPC), elicits changes
in utilitarian judgments and whether gender-related responses to
tDCS underlie the gender-related differences in utilitarian
thinking. To do so, in 60 healthy subjects we delivered anodal
and cathodal tDCS to the VPC (VPC-tDCS). To test the
specificity of our findings, in 18 subjects we then delivered tDCS
also over the occipital cortex (OC-tDCS). Before and after tDCS
mood was assessed using visual analog scales  to ensure
comparable mood conditions, and participants did the moral
judgment test consisting of non moral (NM), impersonal moral
(IM) and personal moral (PM) dilemmas  to assess various
material and non material factors influencing human behavior and
Baseline Performance in the Moral Judgment Task
Utilitarian responses. Even though type of education
(human sciences or life sciences) and religion (catholic or non
catholic) had no influence on the proportion of utilitarian
responses (education: p = .396, religion: p = .835, interaction:
p = .301) in our sample, life sciences studies were more frequent
in males than in females (58% vs. 33%; chi-square = 5.080, df = 1,
p = .024) and catholic religion more frequent in females than in
males (60% vs. 53%; chi-square = 1.238, df = 1, p = .266). To
control for their potentially confounding effects we therefore
included education and religion as covariates in the subsequent
Wald chi-square test disclosed a clear effect for type of dilemma
(Wald chi-square test = 493.9; df = 2, p,.001). The post hoc
sequential Sidak procedure showed that each pairwise comparison
was significant (NM vs. IM, NM vs. PM and IM vs. PM: p,.001;
hereafter each post hoc p-value refers to the Sidak adjustment for
multiple comparisons). The Wald test also disclosed a significant
interaction between type of dilemma and sex (Wald
chisquare test = 6.892; df = 2, p = .032), because females and males
gave similar responses for NM dilemmas (p = .965) and IM
dilemmas (p = .982) but significantly dissimilar PM judgments
(p = .007). At baseline males gave significantly more utilitarian
responses to PM dilemmas than females (Table 1).
Reaction times. Similarly to utilitarian judgments, neither
type of education nor religion influenced the reaction times (RTs;
education: p = .438, religion: p = .972, interaction: p = .461) but
given their association with sex, to control for their potentially
confounding effects were entered as covariates in the subsequent
The Wald test disclosed a clear effect of type of dilemma (Wald
chi-square test = 106.3; df = 2, p,.001). The post hoc sequential
Sidak procedure showed that each pairwise comparison was
significant (p,.001): RTs values were for NM, lowest for IM and
in between for PM (mean RTs: 4726 ms, 3559 ms and 4019 ms).
The Wald test also indicated that RTs could be modulated by the
type of response (utilitarian or non-utilitarian). Precisely, although
the p-value for type of response failed to reach the significance
threshold of .05 (Wald chi-square = 3.458, df = 1, p = .063), the
interaction type of response x type of dilemma was significant
(Wald chi-square = 49.932, df = 2, p,.001). This interaction could
be explained by computing the differences in RTs between
utilitarian and non-utilitarian responses in the three types of
dilemma: the difference was negative for NM (mean RTs for
utilitarian responses: 4445 ms; mean RTs for non-utilitarian
responses: 6380 ms; utilitarian , non-utilitarian, p,.001),
nonsignificant for IM (mean RTs for utilitarian responses: 3451 ms;
mean RTs for non-utilitarian responses: 3866 ms; utilitarian =
non-utilitarian, p = .855) and significantly positive for PM (mean
RTs for utilitarian responses: 4653 ms; mean RTs for
nonutilitarian responses: 3738 ms; utilitarian . non-utilitarian,
p,.001; Tables 1 and 2).
The Effects of tDCS on the Moral Judgment Task
Utilitarian responses. When pre-post tDCS changes were
considered (entering Time as within-subjects factor), the Wald
test in the 78 studied subjects disclosed a significant Sex x Type of
tDCS x Site of tDCS x Time interaction (Wald chi-square
test = 7.645; df = 2; p = .022), mainly due to the Sex x Type of
tDCS x Time interaction for VPC (Wald chi-square = 6.255;
df = 2; p = .044) and to the non-significant interaction for OC
(Wald chi-square = 2.538; df = 2; p = .281).
The significant Sex x Type of tDCS x Time effect in the VPC
group was not dependent on type of dilemma (Sex x Type of
tDCS x Type of dilemma x Time interaction, Wald
chisquare = 4.414, df = 4, p = .353), indicating that it can be described
by collapsing the three types of dilemmas. Whereas in males
neither anodal nor cathodal tDCS affected responses (Wald
chisquare = 0.860; df = 2; p = .650; after anodal: p = .551, after
cathodal: p = .574), in females two different patterns appeared,
as indicated by the significant effect of Type of tDCS x Time
interaction (Wald chi-square = 9.270; df = 2; p = .010): more
precisely, anodal tDCS significantly increased and cathodal tDCS
decreased, though not significantly, utilitarian responses (p = .005
and p = .209). In summary, VPC-tDCS changed utilitarian
judgment only in females. The changes took opposite directions:
4565,9 (227) 3115,9 (133) 3274,5 (136) 91%
4330,6 (268) 3217,9 (280) 3574,5 (267) 86%
5069,7 (267) 3655,8 (159) 4018,9 (197) 83%
4402,9 (405) 3371,9 (290) 4140,7 (445) 86%
4247,3 (223) 3513,9 (192) 4145,3 (281) 83%
5783,6 (594) 3655,8 (386) 4047,1 (308) 92%
4951,9 (246) 3900,8 (206) 4594,1 (295) 85%
4830,4 (437) 4317,3 (327) 4753,5 (473) 87%
Mean Reaction Times (SE) in ms
4233,5 (221) 2709,3 (118) 3358,6 (224)
3540,4 (188) 2630,4 (144) 2602,6 (157)
4238,4 (194) 3016,8 (132) 3569,1 (203)
4103,7 (332) 3455,4 (502) 3331,3 (261)
4077,4 (230) 3130,8 (187) 3108,8 (161)
4827,1 (468) 3074,8 (227) 4463,4 (506)
4423,6 (241) 3146,1 (182) 3650,9 (220)
4064,7 (318) 3252,3 (454) 4156,3 (586)
F: females; M: males; SE: standard error of the mean; NM: non moral dilemmas; IM: impersonal moral dilemmas; PM: personal moral dilemmas; VPC: tDCS over the Ventral
Prefrontal Cortex; OC: tDCS over the Occipital Cortex.
anodal tDCS induced a significant increase and cathodal tDCS a
non-significant decrease (Fig. 1).
The changes after OC stimulation were not significant per se
(Time main effect, Wald chi-square = 0.236, df = 1, p = .627)
nor did they differ according to type of stimulation (Wald
chisquare = 2.083, df = 2, p = .353; Table 1).
Reaction times. Considering pre-post tDCS changes
(entering Time as within-subjects factor), RTs were only
significant per se (Wald chi-square test = 35.165; df = 1; p,.001),
owing to the significant overall reduction after stimulation (from
4008 ms to 3542 ms, p,.001; Table 1). None of these changes
were dependent on other considered factors; in particular, the type
of response (utilitarian or non-utilitarian) had to be taken into
account because it intervenes in significant double and higher
order interactions. For this reason, we ran the Generalized
Estimating Equations (GEE) procedure separately for utilitarian
and non-utilitarian responses.
When we investigated RTs for non-utilitarian responses, besides
the overall reduction indicated by the significant Time effect
(Wald chi-square = 14.722; df = 1; p,.001), two interactions were
significant: Sex x Type of tDCS x Time (Wald
chisquare = 7.582; df = 2; p = .023) and Type of dilemma x Type
of tDCS x Time (Wald chi-square = 14.422; df = 4; p = .006).
These effects were nevertheless non-specific insofar as the site of
stimulation (VPC or OC) played no role (for each interactive term
including this factor, p..132).
Conversely, considering RTs for utilitarian responses, Site of
tDCS was found as significant term when its interactions were
Reaction Times (SE)
Mean Non Utilitarian
Reaction Times (SE)
Reaction Times (SE)
Mean Non Utilitarian
Reaction Times (SE)
sex stim type stim site
F: females; M: males; SE: standard error of the mean; NM: non moral dilemmas; IM: impersonal moral dilemmas; PM: personal moral dilemmas; VPC: tDCS over the Ventral
Prefrontal Cortex; OC: tDCS over the Occipital Cortex.
evaluated. Starting with the higher order ones, the interaction
Sex x Site of tDCS x Type of tDCS x Time was significant
(Wald chi-square = 6.469; df = 2, p = .039). These data suggest that
the reliable effect found in overall RTs is due to RTs for utilitarian
responses. To interpret this interaction, we conducted separated
analyses according to the stimulation site. Whereas RTs for
utilitarian responses after OC-tDCS decreased to a similar extent
after anodal or cathodal tDCS (Type of tDCS x Time: Wald
chi-square = 0.195, df = 1, p = .659) and without further
dependence on sex (Sex x Time: Wald chi-square = 1.261, df = 1,
p = .261; Sex x Type of tDCS x Time: Wald chi-square = 1.392,
df = 2, p = .498), RTs for utilitarian responses after VPC
stimulation changed according to the time and type of tDCS
(Type of tDCS x Time: Wald chi-square = 8.529, df = 1,
p = .003). Sidak comparisons indicated that the RTs reduction
was significantly larger after cathodal than after anodal tDCS
(p,.001 and p = .735). Differently from the proportion of
utilitarian responses, no evidence was found of sex modulation
(interactive terms involving Sex were consistently
non-significant; Table 2).
Subjective mood rating. Neither the mood nor happiness
VAS differed between genders (Mood: F(1,68) = 3.53; p = .065;
Happiness: F(1,68) = .10; p = .754), or differed according to the type
of stimulation (Mood: F(3,68) = .68; p = .579; Happiness:
F(3,68) = 1.42; p = .256), nor were significant differences found in
the interaction Type of tDCS x Sex (Mood: F(3,68) = .23;
p = .877; Happiness: F(3,68) = .56; p = .646). Hence, subjects did the
moral judgment task before and after tDCS in comparable mood
The main finding is that neurostimulation influencing cortical
excitability in the VPC elicits changes in utilitarian judgments.
When we applied tDCS to the VPC but not when we applied it to
the OC, we also identified distinct gender-related differences in
utilitarian responses to moral as well as non-moral dilemmas.
These differences might help to explain the known gender-related
differences in human utilitarian reasoning. We also found a
significant reduction in RTs for utilitarian responses after cathodal
VPC-tDCS, regardless of type of dilemmas and of sex. These
findings acquire strength because they come from a study
investigating utilitarian judgments by tDCS in a large study
sample, 78 subjects, balanced for sex and age and controlled for
religious beliefs and type of education.
Our tDCS study using the moral judgment task to assess various
material and non-material factors influencing human behavior
and decisions therefore advances current knowledge on
decisionmaking processes and utilitarian judgment.
Baseline Performance in the Moral Judgment Task
The analyses of baseline RTs confirmed Greene et al. (2001)
study, showing that utilitarian responses are slower than
nonutilitarian responses specifically in PM dilemmas, but not in NM
and IM dilemmas. Whereas these baseline RTs differences are
independent of gender, we found significant gender-related
differences in utilitarian responses studied before tDCS. These
results are in line with the observation that males differ from
females in cognition, decisional processes [41,42,43], moral
judgments [28,30] and in brain activation patterns during moral
tasks . These differences are independent of cultural factors,
such as education levels and religious beliefs.
The gender-related differences in utilitarian responses we found
before applying tDCS agree well with current knowledge.
Genderrelated differences in cognitive and behavioral processes are
associated with functional and structural gender differences in the
brain [44,45,46], especially in the frontal lobe [47,48,49], an area
also involved in moral behavior [2,3,5,6,7,9,10]. In their study
assessing altruistic cooperativeness, Yamasue et al. (2008) found
that the greater cooperativeness in females correlated with larger
gray matter volumes in the social brain regions such as the
bilateral inferior frontal cortex. A remarkable gender-related
difference has been found also in the frontal lobe
neurotransmitters related to behavior [50,51]. Finally, hormones greatly
influence behavior and their receptor distribution differs between
sexes in the brain structures involved with cognition . The
gender-related difference we found in the performance of the
moral judgment task therefore fits in well with anatomical,
functional, neurochemical and neuroendocrinological evidence of
gender-related differences in brain areas involved in moral
Effect of VPC-tDCS on Utilitarian Judgments
Whereas tDCS left response patterns to the moral judgment
task in males unchanged, in females anodal VPC-tDCS increased
the utilitarian responses for all types of dilemmas tested. Also,
cathodal VPC-tDCS reduced RTs for utilitarian responses in both
males and females. We therefore conclude that anodal and
cathodal tDCS both interfere with rational decisions, or rational
evaluation of the advantages and disadvantages of each option in
both sexes, but do so more strongly in females. Our experiments
indicate that tDCS-induced changes in utilitarian reasoning are
site-specific and that both anodal and cathodal VPC-tDCS
differentially modified subjects performance in the moral
judgment task, suggesting that the effects are specific and depend
on factors other than skin perception. Equally important, the
tDCS-induced changes we observed are not related to mood
changes or cultural factors.
In our experiments the charge flows ventrally from the
prefrontal surface to the right arm, thereby most probably
stimulating the most ventral portion of prefrontal cortex. Because
skull resistivity is higher than scalp resistivity, most of the current
delivered by tDCS gets shunted through the scalp. The current
density in the scalp also tends to decrease with the distance
between electrodes. As Nathan et al. (1993) confirmed, the current
density generated in the cortex by the stimulation decreases
rapidly with depth i.e. it decreases by one order of magnitude in
8 mm . Also, intra-operative results show that eliciting a motor
evoked potential by directly stimulating the human brainstem
requires a current density of about 29 mA/cm2 . For these
reasons, it is unlikely that charge flows in the brainstem and
structures other than the cerebral cortex below the stimulating
electrode. tDCS might, however, also influence neighboring
cortical areas. Even if the main effect on cortical excitability is
localized beneath the stimulating electrode , we cannot totally
exclude the possibility that tDCS also modulates other areas of the
prefrontal cortex (directly, but also indirectly). Hence,
notwithstanding possible tDCS-induced changes in other brain areas, we
believe that tDCS induces its most important effect by modulating
the VPC below the stimulating electrode.
Explaining why tDCS affects utilitarian responses in a
genderspecific manner and RTs in both sexes is challenging. The female
susceptibility to the effects of anodal VPC-tDCS we found in
utilitarian responses could arise in several ways. For example, the
gender-related effects of tDCS on utilitarian judgments might
agree with the known gender specificity in the effects of cathodal
and anodal tDCS on brain excitability [55,56,57]. Yet if they do,
we find it hard to explain why none of the previous studies on the
influences of brain stimulation on decisional processes reported
gender-related effects [17,18,19].
A further more conjectural possibility is that the female
tendency towards altruism is also more easily modulated by
external factors. Hence whereas altruism in males is
preprogrammed, in females it might be more sensitive to changes in brain
plasticity. According to this hypothesis, tDCS influences utilitarian
judgments in females but not in males, who responded to brain
stimulation only with a reduction in RTs. This hypothesis fits in
with the behavioral differences existing between genders during
life: whereas in males altruistic behavior has no need to change
during life, in females it has to change in relation to behavioral
changes linked to reproduction and parental care . This
gender-related difference in altruisms sensibility to external factors
is also supported by the known gender-related anatomical and
functional differences in the brain structures controlling behavior
and decision making. In females, a greater propensity to altruistic
behavior correlates with a larger-sized inferior frontal cortex ,
so that reducing ventral prefrontal activity with tDCS could mean
enhancing the cognitive and rational control of behavior.
Functional neuroimaging data with moral tasks also support
a gender-related pattern of brain activation. For example, Harenski
et al. (2008) found a greater activation of posterior cingulate cortex
and anterior insula in females, and a greater activation of the
inferior parietal cortex in males. Because the VPC is tightly linked to
the cingulate cortex, tDCS over the VPC could indirectly modulate
activity in the cingulate cortex. In conclusion, the differential
sensitivity to tDCS in males and females could reflect gender-related
anatomical, functional and neurochemical differences in the brain
areas involved in utilitarian behavior. Moreover, even if gender,
which also includes educational aspects, is a crucial factor for tDCS
efficacy, socio-economic status and personal education might be
relevant too. The relative importance of biological and social factors
remains an interesting question for future researches.
A central point to clarify is how anodal and cathodal tDCS
differentially modify utilitarian choices. Anodal stimulation could
do so by inducing excitatory effects on the underlying cerebral
cortex [11,13,59]. This possibility notwithstanding, even if in
studies investigating tDCS-induced changes in primary cortices
anodal stimulation delivered close to neurons depolarizes the
neuronal membrane and cathodal stimulation hyperpolarizes it,
cognitive studies leave the relation between polarity and the
effects on the neuronal membrane unclear . In accordance
with this point of view, in our study anodal tDCS had the same
effect as a lesion in the ventral portion of the frontal cortex. In
their study, Koenigs et al. (2007) described lesioned patients as
characterized by deficits in decision-making tasks, namely they
produced an abnormally utilitarian pattern of judgments on
moral dilemmas endorsing highly emotionally aversive behaviors
despite an undamaged social knowledge of normative conduct
. Our results nevertheless showed that cathodal tDCS
decreased RTs for utilitarian responses but left the proportion
of utilitarian responses unchanged. Indeed, it decreased, albeit
not significantly, utilitarian responses in females. These data are
congruent with the study by Knoch et al. (2008) who showed that
cathodal tDCS on the prefrontal cortex reduces the propensity to
punish unfair behavior in the Ultimatum Game . In this task,
punishing unfair behavior means rejecting an unfair offer in order
to obtain a fairer proposal. This is a utilitarian behavior because
the subject aims to achieve a personal gain, even at the expense of
damaging others. Hence cathodal and anodal tDCS both induce
a functional brain system imbalance through the same
mechanism. However, whereas cathodal tDCS alters the time of
utilitarian reasoning in both sexes, anodal stimulation interferes
more incisively, modifying utilitarian reasoning and its possible
consequent actions, also in a gender-specific way. Insofar as the
ventral part of the frontal lobe is phylogenetically older than the
dorsolateral part , it might be more related to defence of the
individual and to survival than to social interaction and
Among other possible explanations, besides influencing cortical
excitability, tDCS could induce neurochemical changes in the
brain that could involve several neurotransmitters . Dopamine
is important for behavior, motivation and decision-making .
Parkinsons disease, characterized by reduced dopamine
production in the brain, is associated with impaired decisional processes
. Anodal VPC-tDCS might therefore alter the outcomes of
utilitarian decision-making processes by enhancing prefrontal
dopamine. Yet, because dopamine is an anionic catecholamine
that during electrophoresis migrates toward the anode, anodal
VPC-tDCS could increase dopamine levels in the frontal lobe,
influencing the reward circuit and ultimately altering decisional
processes, increasing the rate of utilitarian responses. Interestingly,
the gender-specific effects of VPC-tDCS in our experiments agree
with the female-specific features of the dopaminergic system in the
frontal cortex [50,51]. Although this is a theoretical hypothesis,
emerging data in humans support the interaction between tDCS
and the dopaminergic system [66,67].
The gender-related differences in utilitarian responses we found
in this study using the moral judgment task in healthy subjects are
a good starting-point for explaining criminal behavior. Mental
illness the inability to distinguish good from bad reflects
immoral reasoning. Our study provides evidence showing that
males are by nature more utilitarian than females, and that
noninvasive brain stimulation more easily and incisively alters
feminine than male utilitarian thinking, thus confirming the
prevalence of criminal behavior in males. Future studies designed
to investigate the possibility of modulating morality and
utilitarianism could better account for criminal behavior and male
propensity to violate the law.
Materials and Methods
Seventy-eight healthy subjects (38 men and 40 women)
participated in the study (Table 3). All participants spoke native
Italian, were right handed and had no history of medical,
neurological, or psychiatric disorders. Also, all subjects were
without acute or chronic central nervous system-affecting
medication. All participants gave their written informed
consent and the procedures had the approval of the ethical
committee. The experimental procedure was in accordance
with the declaration of Helsinki.
Transcranial Direct Current Stimulation (tDCS)
tDCS (2 mA, 15 minutes) was delivered by a constant current
electrical stimulator (Eldith, Ilmenau, Germany) connected to a
pair of electrodes. Two different electrode montages were used. In
60 subjects (30 males), the active electrode was placed bilaterally
on forehead, just above the eyebrows, and fixed with a pair of
goggles, while the reference electrode was placed over the right
deltoid muscle. In this montage, because the portion of the current
not shunted through the scalp enters the skull below the
stimulating electrodes  and is directed to the lowest-impedance
path towards the reference electrode, placed on the right arm ,
the charge flows ventrally from the prefrontal surface to the right
arm, thereby almost certainly stimulating the most ventral portion
of prefrontal cortex. In 18 volunteers (8 males), the active electrode
was placed over the occipital cortex (OC). Both groups of
stimulation were in turn subdivided in two groups, anodal and
cathodal. Subjects were unable to distinguish anodal or cathodal
tDCS. Because preliminary experiments showed that during
VPCtDCS subjects reported a mild itching sensation and a metallic
taste, we did not use sham stimulation but we only compared
anodal vs. cathodal tDCS.
To avoid confounding biases arising from two electrodes with
opposite polarities over the scalp, we used a non-cephalic reference
electrode for tDCS [20,60,70]. This montage allowed us to
evaluate selectively the effect of scalp stimulation over a
welldefined cortical area avoiding possible interference due to
polarization of other cortical structures near the reference scalp
electrode that can confound the source of tDCS effects. The
noncephalic reference electrode montage also yielded reproducible
data during and after polarization without inducing effects related
to brainstem activation . The electrodes used for tDCS were
thick (0.3 cm), saline-soaked synthetic sponges (scalp electrode
54 cm2; deltoid electrode 64 cm2). Because the skin on the
forehead is sensitive, stimulation at 2 mA for 15 min could induce
Non Human Life
Catholic Catholic Sciences Sciences
VPC-tDCS 25.7 (1.033) 53%
Females VPC-tDCS 23.7 (0.573) 60%
OC-tDCS 25.1 (1.407) 37.5%
OC-tDCS 22.2 (0.696) 70%
Values are mean (standard error of the mean). VPC-tDCS: tDCS over the Ventral
Prefrontal Cortex; OC-tDCS: tDCS over the Occipital Cortex.
reddening and because the bone under the prefrontal electrode is
thick we used a wide active electrode surface.
We ramped the current up over the first 8 s of stimulation and
down over the last 8 s. To guarantee safety we applied a current at
a density of 0.0037 mA/cm2 and delivered a total charge of
0.034 C/cm2. These criteria are far below the threshold for tissue
damage . Subjects were tested before tDCS and after it ended.
Moral Judgment Task
We used a set of 60 dilemmas  translated into Italian. In
accordance with Greene et al. (2001) and Fumagalli et al. (2009),
these dilemmas were classified into 20 non-moral (NM), and two
classes of moral scenarios subdivided into impersonal moral
(IM, n = 18) and personal moral (PM, n = 22) dilemmas.
The 60 dilemmas were randomly divided into two 30-item
alternate versions of the test (10 NM, 9 IM and 11 PM for each
version). These two versions were administered in a
counterbalanced order, half of the subjects receiving version 1 at baseline and
version 2 after tDCS, and half receiving the opposite order of
administration. Each dilemma was presented in a series of three
screens of text. The first two screens each displayed a paragraph
describing the context and details of the dilemma. The third
screen posed a question about a hypothetical action related to the
scenario (Would you in order to ?). Participants were
allowed to read through screens 1 and 2 at their own pace,
pressing the space-bar to advance to the next screen. In the third
screen, they were allowed no more than 25 s to read the final
question screen and respond by pressing the left (yes) or the right
(no) button on the mouse (Fig. 2). Subjects were instructed to
respond as fast and accurately as possible. Stimuli were presented
on a PC screen using E-Prime Version 1.1.
Each dilemma used could be solved by responding Yes or No,
hence in each dilemma one of the two possible responses is
utilitarian, whereas the other is non-utilitarian. An example of a
moral dilemma is the following: A runaway trolley is heading down the
tracks toward five workmen who will be killed if the trolley proceeds on its
present course. You are on a footbridge over the tracks, in between the
approaching trolley and the five workmen. Next to you on this footbridge is a
stranger who happens to be very large. The only way to save the lives of the
five workmen is to push this stranger off the bridge and onto the tracks below
where his large body will stop the trolley. The stranger will die if you do this,
but the five workmen will be saved. Would you push the stranger on to the
tracks in order to save the five workmen? In this dilemma, Yes is a
utilitarian response, whereas No is the non-utilitarian response.
The utilitarian alternative, requiring a Yes response, consists of
pushing the stranger in front of the trolley, so that even if one
person is killed, five are saved. The cost-benefit analysis suggests
that the most overall utility is to sacrifice one person rather than
five. This response is classified as utilitarian because, according to
Greene et al. (2001, 2002, 2004) and Koenigs et al. (2007), it
allows subjects to maximize aggregate welfare, often overcoming
the emotional response against inflicting direct harm to another
After an initial practice run, consisting in four examples of
nonmoral scenarios to familiarize subjects with the task, subjects were
tested before tDCS and thereafter. Subjects were randomly
subdivided into four groups: anodal and cathodal VPC-tDCS
and anodal and cathodal OC-tDCS (Fig. 3).
Subjective Mood Rating
To control the influence of tDCS on mood, before and after
tDCS we administered two 100-mm visual analog scales : a
mood VAS (0 corresponding to good mood and 100
corresponding to bad mood) and a happiness VAS (0 corresponding to
sadness and 100 corresponding to happiness). Subjects were asked
to describe their current affective condition by marking the lines
The database was constructed with information on subjects
responses for each dilemma. For each item, the response of a given
subject, a given stimulation (anodal, cathodal VPC-tDCS and
anodal, cathodal OC-tDCS) and a given time (pre, post tDCS) was
coded as 0 (non-utilitarian) or 1 (utilitarian) and the corresponding
RT was entered.
We used the GEE model in line with Koenigs et al.  study
because this model allowed us to analyze behavioral data fully. It
also avoided wasting information given by the single response and
the single RT to a given item and, instead of aggregate data
computing the proportion of utilitarian responses or the mean of
RTs, we analyzed the whole dataset with a unified statistical
approach. In particular, GEE models allowed us to assess the
significance of main and interactive effects of Type of tDCS, Site
of tDCS, Gender, Type of dilemma and Time as predictors
(factors) on utilitarian responses and RTs measures, taking into
account within-subject dependence. Specifically, a binary logistic
function was used to analyze the utilitarian responses as dependent
variables. Conversely, when RTs were the dependent variable, a
Gaussian distribution was assumed, with a log link function to
obtain a better fit to Gaussianity (typically and also in our study,
RTs follows an almost log-normal distribution).
First, we analyzed data obtained before stimulation. When RTs
were the dependent variable, the binary variable utilitarian
responses was entered as an additional factor because RTs could
change according to utilitarian/non-utilitarian responses as well as
to the interaction between utilitarian responses and the other
To assess the effect of tDCS, the Time factor was added to
the model and its main effect as well its interaction with the other
factors and covariates were evaluated. Because the subjects were
also classified by their type of education (all being graduated, the
major distinction was between life sciences and human sciences)
and by their religion (catholic vs. non catholic), the model took into
account potential confounding from these two factors.
To assess the effect of tDCS on mood, we computed the
differences (after-before tDCS) and tested them in a three-way
within subjects analysis of covariance (ANCOVA) with tDCS
(anodal, cathodal VPC-tDCS and anodal, cathodal OC-tDCS)
and gender (males, females) as factors and education and religion
as covariates for mood VAS and happiness VAS.
The authors wish to thank Prof. Marc Hauser for his advice on a
preliminary version of the manuscript.
Conceived and designed the experiments: MF FM RF SZ GS SC AP.
Performed the experiments: MF MV FM RF SMS. Analyzed the data: PP
SM AP. Wrote the paper: MF PP SM SZ GS GP SB SC AP.
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