Resisting the Power

of Temptation

sThe 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 Self-Control 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-ControlLeads 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