Executive functions of the frontal lobe

Question 1

What were the results of Gage’s accident?

Answer 1

• Intellectual qualities reduced, animal propensities increased
• Personality, reasoning, and capacity to understand and follow social norms had been diminished or destroyed
• Lost interest in hobbies and involvements that he previously cared about

Shows the prefrontal cortex’s involvement in emotion and cognition.

Question 2

List some main areas of the frontal lobe

Answer 2

• Prefrontal cortex
• Premotor area
• Primary motor cortex (controls voluntary body movement)
• Broca’s area (motor speech area)

Question 3

The frontal lobe is separated from the parietal lobe by the ____ sulcus and the temporal lobe by the ___ sulcus

Answer 3

The frontal lobe is separated from the parietal lobe by the central sulcus and the temporal lobe by the lateral (sylvian) sulcus

Question 4

What are the four divisions of the prefrontal cortex?

Try to envision their location on the brain.

Answer 4

• Dorsolateral PFC
• Medial PFC (orbitofrontal)
• Ventrolateral PFC
• Anterior PFC

Question 5

What percent of the cortex is the prefrontal cortex in humans?

Answer 5

29%

Question 6

List the main functions of the prefrontal cortex

Answer 6

• Goal forming
• Plan making
• Selection of cognitive skills
• Ordering of skills
• Evaluating actions as success or failure
• Emotion
• Working memory
• Task shifting (deficit perseveration)

Question 7

Describe the delayed response working memory task.

What happens when the monkey has prefrontal cortex lesions?

Answer 7

• Monkey baited with food in one well
• After delay (can’t see it), animal is allowed to retrieve food
• Food location is determined randomly
• Working memory is required in the first task because at the time the animal responds, there are no external cues indicating the location of the food.

Prefrontal lesions demonstrate selective impairment on working memory delayed response task

Question 8

Describe the delayed non-matching to sample task.

Answer 8

• Monkey originally presented with sample object with food underneath
• After variable delay the monkey is presented with original object and another object
• Over trials, different pairs of objects are presented, monkey learns that food is present under the object that differs from the sample.
• Monkeys are attracted to novelty

Recordings from the dorsolateral prefrontal cortex show that the most firing occurs during the delay

Question 9

What is the oculomotor spatial delayed response task? How is it used to study cells in the dorsolateral prefrontal cortex?

Answer 9

• Fixation period on fixation point
• Cue period
• Delay period (3 or 6 second delay)
• Response period (eye position recorded)

The accuracy of eye position is lessened after 6 seconds of delay (rather than 3).

Important: When recording specific neurons in the dorsolateral PFC, certain neurons fire much more than others when a cue is in a certain part of the visual field. The most activity is observed during the delay (hypothesized to be working memory firing)

Question 10

How was task shifting (deficit perseveration) determined to be a function of the lateral PFC?

Answer 10

Using the Wisconsin Card Sorting Task (WCST)

• Patient with damage in lateral PFC has difficulty with this
• The subject places top card on duck under one of four target cards
• Experiment indicates correct or incorrect, allow patient to learn by trial and error
• sorting rules change with ten right answers

People with lesions in lateral PFC have trouble shifting to new rules.

Question 11

How was it shown that the dorsolateral prefrontal cortex functions to organize goal directed behaviour (executive function)?

Answer 11

Recency memory is impaired in patients with dorsolateral prefrontal lesions, but item recognition memory is not impaired.