Resisting the Power
of Temptations
The Right Prefrontal Cortex and
Self-Control
Knock, D. & Erst, F. (2007). Resisting the power of
temptations: The right pre-frontal cortex and self-control.
Ann. N.Y. Acad. Sci. 1104: 123–134
Deciding not to succumb
to all of our desires
Deciding not to succumb
to all of our desires
• The ability to override immediate urges is
relevant for adaptive individual decision
making AND contributes to harmonious social
interactions
• 2 studies reveal the importance of inhibition in
the process of decision making
• Claims that the capacity to resist temptation
depends on the activity of the right PFC
Transcranial Repetitive
Magnetic Stimulation (TMS)
• Brain stimulation technique that involves placing a
small coil of wires on the scalp and applying a brief
electric current to discrete brain areas via pulsed
magnetic fields on the corresponding scalp
location.
• Depending on the repetitive transcranial magnetic
stimulation frequency (rTMS), TMS may either
excite the brain area or inhibit neural activity
• High Frequency rTMS : Excites cortical function
• Low Frequency rTMS : “virtual lesion” disruption of
cortical function
Benefits of TMS Usage
• Studies involving patients with right sided
lesions of the prefrontal cortex:
• Reveals that the resistance to the immediate
self interests is often greatly diminished in
people with PFC damage, particularly for
patients with right sided lesions
• Limitations:
• Limited opportunity for experimental
manipulations
• Possibility of functional reorganization after
brain lesion may affect result interpretations
• Low number of patients
Benefits of TMS Usage
• Functional imaging studies
• Suggest that the right PFC may be specially
important for self regulation and self control or
behavioral adjustments
• Limitations
• Only passively measure brain activity with a specific
task
• Do not reveal a causal relationship between changes
in brain activity and their respective behavioral
consequences
• Thus, A direct investigation of such a causal brain–
behavior relationship would require a controlled
manipulation of brain activity where the impact on
behavior or cognition can be quantified.
Benefits of TMS Usage
• TMS technique allows for a controlled
manipulation of brain activity where the
impact on behavior or cognition can be
quantified
• Application of this technique can be on healthy
individuals, because it causes a transient
change in cortical functioning
• Here, TMS was used to examine weather self
control can be modified in healthy individuals
in the context of both individual and social
decision
Study 1
• Individual Decision Making: Diminished SelfControl Leads to Increased Risk-Taking
Behavior
“Virtual Lesion Study”
• Purpose: to investigate
hemispheric asymmetries in
risk taking behaviors
• Healthy volunteers
• Low frequency rTMS to the
left or right dorsolateral
prefrontal cortex (DLPFC)
• Administered a risk task
Risk Task: Gambling
Paradigm
• Provides a measure of risk taking
• Subjects have to decide between a relatively
safe choice and a risky choice
• Safe choice provides a low reward with a higher
probability
• Risky choice provides a higher reward with a
lower probability
Risk Task: Gambling
Paradigm
• Presented with 6 pink or blue boxes
• # of pink and blue boxes varied from trial to trial
• Asked to find the winning token behind one of the 6
boxes by selecting the color of the box they thought
the winning token was behind
Risk Task: Gambling
Paradigm
• Subjects were told that each box, regardless of color,
was equally likely to hide the winning token
• Thus, the likelihood of finding the winning token was
directly related to the ratio of blue to pink boxes
Risk Task: Gambling
Paradigm
• Subjects are rewarded or penalized depending if they
pick the correct color box or not
• Larger Reward/Penalty is associated with the high risk
prospect (i.e. the color with the # of fewer boxes
• Smallest Reward/Penalty is associated with the low risk
prospect
Risk Task: Gambling
Paradigm
• Subjects are rewarded or penalized depending if they
pick the correct color box or not
• Correct Choice – addition of number of points
associated with that particular scenario
• Incorrect Choice- subtraction of the same amount of
points
Risk Task: Gambling
Paradigm
• Figure Above shows that the subject chose an
incorrect choice that results in the subtraction of 90
points
Results
• Subjects stimulated over the right
DLPFC were more likely to choose
the high risk prospect than those
stimulated over the left DLPFC or
those who received the sham
stimulation
• Thus, individuals display a
significantly stronger preference
for the risky prospect, choosing
the larger potential reward even
at risk of greater penalty,
following the disruption of the
right, but not left, DLPFC
Possible Alternative
Explanations of rTMS Effect
• Task requires subjects to measure the ratio of
the pink and blue boxes and take into account
the expected value of the 2 options
• It may be that subjects receiving right
prefrontal rTMS are impaired at calculating the
riskiness of the choices
AND/OR
• May be impaired at integrating information
about the consequences of different choices
Study 2
• Social Decision Making: Diminished Self-Control
Leads to Selfish Behavior
 The human species in unique to the extent that
social norms that constrain the unrestricted pursuit of
self interest govern behavior
Overcoming the self’s natural, impulsive nature
requires self-control
The Ultimatum Game
(UG)
• Provides a useful tool for studying the neural
mechanisms of self control in the context of
social decision making
• Illustrates the tension between:
• economic self-interest and fairness goals
The Ultimatum Game
(UG)
• A bargaining game
• 2 anonymous individuals, a proposer and a
responder, must agree on the division of a given
amount of money.
• Proposer  can make 1 suggestion to the
responder on how the given amount of money is
split between them by making him an offer
• Responder 
• Accept : each player keeps the amount of money
the proposer allocates
• Reject : neither player receives any money
Conflict within the
Responder to LOW offers
• Tension between economic self-interest and
fairness goals
• Economic self interest drives responder =
acceptance of low offers
• Fairness goals drive responder = feels the need
to reject
Previous Research
• Strong evidence for rejecting low offers if the
stake is as high as 3 months’ income
• Rejection rates up to 80% for offers below 25%
of the available money
Previous Research:
Neuroimaging study
• Anterior insula and
DLPFC are activated
when responders
decide whether to
accept or reject an
unfair offer
Previous Research:
Neuroimaging study
• Anterior insula –
involved in the
evaluation and
representation of
negative emotional
states
Previous Research:
Neuroimaging study
• Right and left DLPFC
• More strongly activated when subjects face unfair offers
• Areas thought to be involved in:
• Executive control
• Goal maintenance
• Inhibition of proponent responses
• All these functions of relevant to the Responder
• Because of the competing goals: fairness goals and self interest
• Which should be maintained, or given priority?
• Which motivational impulse should be restrained?
Current study
• Understanding if the DLPFC is crucial for the
responders’ decisions
• Sample:
• 17 subjects – low frequency rTMS to right DLPFC
• 17 subjects – low frequency rTMS to left DLPFC
• 17 subjects- sham (control group)
• Stake Size = CHF 20 (CHF 1 ~ $0.80)
• Proposer offer strategy: 10, 8, 6, or 4
• 10 is fairest offer, 4 is most unfair offer
Current study
• If DLPFC is involved in overriding selfish
impulses that drive a subject toward
acceptance of unfair offers, low-frequency to
this brain region should INCREASE the
acceptance rate of unfair offers relative to the
sham stimulation condition.
• Focus on acceptance behavior of the most
unfair offer of 4, because the tension between
fairness and self interest is greatest
RESULTS
Results
• Results suggest that who received right
prefrontal TMS are less able to resist the
economic temptation to accept unfair offers
• Thus, right DLPFC is involved in overriding self
interest motives
Interpretation of Results
• Right DLPFC is causally involved in a network that
modulates the relative impact of fairness motives and
self-interest goals on decision making
• Indication that the capacity for restraint depends on the
activity level of the right PFC
• In response override, one must stop a prepotent response
to a stimulus because : response must me withheld, or a
less prepotent response it more appropriate
• Thus, displaying self-control and not being slaves of our
emotional impulses, temptations and desires.
• This allows us to be more socially adequate