Questions: Dorsolateral Prefrontal Cortex and Cognitive Control

Question 1

During the Stroop task, a person must name the ink color of the word 'RED' printed in blue. What is the dlPFC specifically doing to support correct performance?

• A. Perceiving the color blue in visual cortex and suppressing the word-reading pathway
• B. Maintaining the rule 'report ink color, not word meaning' and sending top-down signals that bias posterior regions toward color processing
• C. Generating the motor output for saying 'blue' while inhibiting the output for 'red'
• D. Detecting the conflict between ink color and word meaning and alerting other regions to slow down

Answer: (B)

The dlPFC's role is rule maintenance and top-down biasing — it holds the current task rule in an active, accessible state and signals posterior regions to favor goal-relevant processing. It is not itself doing the perceptual processing or motor output. Option A describes what visual cortex does in response to dlPFC signals. Option C describes premotor/supplementary motor area function. Option D describes the anterior cingulate cortex's conflict-monitoring role.

Question 2

In a Stop-Signal Task study, TMS is applied to right dlPFC during a trial where the stop signal appears. What is the most direct prediction of this disruption?

• A. Reaction times on go trials will increase, because dlPFC is needed for all motor preparation
• B. Subjects will fail to perceive the stop signal, because dlPFC processes visual attention
• C. Stopping ability will be selectively impaired, because dlPFC implements the 'hold' signal that halts the pre-initiated motor response
• D. Subjects will stop more reliably, because disrupting dlPFC removes the competing go response

Answer: (C)

TMS studies disrupting right dlPFC selectively impair stopping performance — not go-trial reaction times, not perception of the signal. This is the causal evidence that dlPFC is necessary for implementing the stopping rule, not merely correlated with it. Options A and B describe functions of different regions (motor cortex, parietal cortex). Option D has the logic backwards.

Question 3

A patient with a dlPFC lesion will show performance deficits specifically on task-switching trials (where the rule changes) while performing near-normally on consistent-rule trials within the same experiment.

• T. True
• F. False

Answer: True

This selective impairment on switch trials is the hallmark dlPFC lesion finding. The dlPFC's specific contribution is rule updating and reconfiguration — replacing one rule representation with another. Consistent-rule trials can rely on more automatic or habitual processing, which is less dlPFC-dependent. The dissociation between switch and non-switch trials makes dlPFC lesion effects diagnostically specific.

Question 4

The dlPFC serves as the brain's central executive, directly performing the perceptual, mnemonic, and motor computations required for complex goal-directed tasks.

• T. True
• F. False

Answer: False

This is the key misconception. The dlPFC does not perform the computations — it maintains the rules and sends top-down signals that bias other specialized regions (visual cortex, motor areas, hippocampus) to perform those computations in a goal-relevant way. The dlPFC is a rule-maintenance and updating system, not a homunculus doing everything. This distinction explains why dlPFC lesions produce deficits in flexible behavior without wholesale loss of perception, memory, or movement.

Question 5

Why is the switch cost — the performance cost of switching from one task rule to another — larger when the previous rule was heavily practiced than when it was recently learned?

Model answer: Heavily practiced rules become more automatic and leave stronger traces in procedural memory, making them harder to suppress. Switching requires both loading the new rule into active maintenance AND actively inhibiting the old, well-learned response tendency. The more ingrained the prior rule, the more inhibitory work is needed, which takes additional time and dlPFC resources.

This question gets at the dual burden of rule switching: the dlPFC must simultaneously update its working memory representation (load the new rule) and inhibit the pull of the old, automatized response. Novel rules have weak automatic pull and are easier to displace. This is why experienced typists switching to a new keyboard layout struggle more than beginners — the old motor program is deeply practiced and must be actively suppressed rather than simply replaced.