Brain Sciences 3

Question 1

Describe the study on self control in decision making involves modulation of vmPFC

Answer 1

We used functional magnetic resonance imaging to monitor brain activity while dieters engaged in real decisions about food consumption.

1- Activity in vmPFC was correlated with goal values regardless of the amount of self-control.

2. It incorporated both taste and health in self-controllers but only taste in non–self-controllers.
3. Activity in DLPFC increased when subjects exercised self-control and correlated with activity in vmPFC.

Question 2

Describe study on Effects of Medial Orbitofrontal Cortex Lesions on Self-Control in Intertemporal Choice

Answer 2

Self-control was examined in patients with lesions to the medial OFC.
* Patients made more impulsive preference reversals during intertemporal choice
* Patients showed disrupted reward valuation
* Results support neural models of self-control

Key findings:
1. mOFC lesions disrupt choice-free valuation ratings
→ Causal evidence for a role of the mOFC in reward
valuation
2. mOFC damage indeed decreases self-control during intertemporal choice
3. The effect of mOFC damage on intertemporal choice depends on the actual self-control demands

Question 3

Describe Study on Lateral prefrontal cortex and self-control in intertemporal choice.

Answer 3

1. Disruption of function of left, but not right, lateral prefrontal cortex (LPFC) with low-frequency repetitive transcranial magnetic stimulation (rTMS) increased choices of immediate rewards over larger delayed rewards.
2. rTMS did not change choices involving only delayed rewards or valuation judgments of immediate and delayed rewards, providing causal evidence for a neural lateral-prefrontal cortex–based self-control mechanism in intertemporal choice.

Question 4

Give an example of an experiment using fMRI to test temporal discounting between a HC and LC option.

Answer 4

Demo : an fMRI experiment :
* Intertemporal choice task: repeated choices between a smaller-but-sooner and a larger-but-later option
* Different amounts and delays at each trial
* 48 choices per participant, performed in the MRI

1st level = predicting time series :
In each voxel, the time course of the BOLD signal is generated by:
- Onset of event (a choice)
→ modulation of neuronal activity by cognitive variable (subjective value)
→ neuronal activity leads to hemodynamic response function (blood goes to vmPFC)
→ adding observation noise (because no measure is perfect)
→ observed signal (the BOLD time series)
We use regression analysis to revert this! In other words, we try to predict the BOLD time series by
inferring the mental processes that are ongoing, based upon our information of the experiment.

We use regression analysis to revert this! In other words, we try to predict the BOLD time series by
inferring the mental processes that are ongoing, based upon our information of the experiment.We do this regression of all time points independently in each voxel → one beta per voxel and subject!

fMRI : Second level analysis :
After significance testing, we get a statistical map: Main effect subjective value :
* red: p<0.05
* FWE corrected yellow: p<0.001 uncorrected

Question 5

Describe stroop effect and why it happens.

Question 6

What is hyperbolic discounting and what is the model used in class?

Answer 6

prefering immediate smaller rewards over bigger delayed rewards. and time inconsistency.

Whereas an exponential curve has a constant discount rate, a hyperbolic discount curve has a higher discount rate in the near future and lower discount rate in the distant future.

example of time inconsistency: 50 today vs 100 in 6 months, prefer 50 today
BUT 50 in 3 months vs 100 in 9 months, prefer 100 in 9 months.

Even if we made the second decision, once TODAY arrives, then we change back our minds even though the time is the same (6 months) because now we are regretting the choice. Hence, WE ARE TIME-INCONSISTENT.

SV= R/ 1 + k*D and pLC= 1 / 1 + e ^ (-1/beta *(svlc-svhc))

Find one value for k and β per participant to best explain behavior. With these parameters, we compute the subjective value (SV) for each option in each trial. We think
that the vmPFC encodes this subjective value.

Question 7

Machband effect

Answer 7

The Machband describes an effect where the human mind subconsciously increases the contrast between two surfaces with different luminance.

Mach banding is caused by lateral inhibition of the receptors in the eye. As receptors receive light they draw light-sensitive chemical compounds from adjacent regions, thus inhibiting the response of receptors in those regions.

Receptors directly on the lighter side of the boundary can pull in unused chemicals from the darker side, and thus produce a stronger response. Receptors on the on the darker side of the boundary, however, produce a weaker effect because of that same migration.