The Executive Brain, Lecture 10 Flashcards
What is executive function?
Executive function refers to a set of complex cognitive processes that allow individuals to optimize their performance in situations that require the operation of a number of cognitive processes. It involves control processes that enable an individual to optimize performance, requiring coordination of basic cognitive processes. Executive function is presumed necessary for ‘controlled’ behavior in contrast to ‘automatic’ behavior. It is not tied to a specific cognitive domain such as memory, language, or perception.
What are the disorders of executive function?
Disorders of executive function can result in difficulty with decision making, multi-tasking, organizing, planning and prioritizing, paying attention, starting tasks and staying focused on them to completion, self-monitoring, understanding different points of view, regulating emotions, and regulating social behavior.
Phineas Gage and executive function
Phineas Gage was a respected foreman working on the Rutland and Burlington railroad in San Francisco who suffered a non-fatal traumatic brain injury. After the injury, Gage experienced changes in his behavior, including impulsive decision making, impaired planning, and poor regulation of social behavior. A modern reconstruction of the damage from his skull showed damage in the left orbitofrontal/ventromedial region and the left anterior region. This case contributed to the understanding of the role of the prefrontal cortex in executive function.
Prefrontal cortex and functional specialization
Disorders of executive function used to be called ‘frontal lobe disorders’. Now, executive function is linked to the prefrontal cortex (PFC), a part of the frontal lobe. The PFC has three cortical surfaces: lateral, medial, and orbital. There is functional specialization within the PFC. For example, Friederici et al. (2006) found that Brodmann area 44 (BA44) is involved in processing hierarchical structures and sequencing, while Brodmann area 45 (BA45) is involved in semantic control and working memory. Other studies have linked activity in the anterior cingulate cortex (ACC) to conflict detection of taboo spoonerisms (Wagner-Altendorf et al., 2020).
Task-setting and problem solving:
Problem solving is related to general measures of intelligence, while task-setting involves starting with a goal and finding a solution.
Tests include Tower of London, Cognitive Estimates, and FAS test (letter fluency).
Patients with damage to the left anterior PFC take longer to complete Tower of London, while those with damage to left dorsolateral PFC have poorer letter fluency and fewer novel strategies.
Accuracy of lesion identification with CT scans is a potential issue.
Overcoming potent or habitual responses:
This aspect of executive function is related to inhibition, which reduces the likelihood of a particular thought or action.
Tests include the Stroop test, which requires inhibiting the automatic response of reading the word in favor of naming the ink color.
Patients with lesions in left ventrolateral PFC have more false positives to distractors, while those with lesions in right superior medial regions have slower reaction times and decreased correct responses.
Neural correlates include fMRI to relate lesion location to reaction times, false positives, and false negatives.
Overcoming Habitual Responses
Tests: Stroop; Go/No-Go
Patients with lesions in ventrolateral PFC show impaired monitoring of performance and more variability in reaction times
Patients with lesions in superior medial area show difficulty in response inhibition and more false alarms
Evaluation: Not all models of executive function rely on inhibition, but instead consider biasing activation signals. A bias towards the correct answer may be needed rather than inhibition of the incorrect answer.
Wisconsin Card Sorting Test and Reaction Times
The test involves matching a card to one of four reference cards with varying shape, number, and color
Minimal change in reaction times between No-switch and No-switch trials
Big difference in reaction times between No-switch and Switch trials, known as the Switch Cost
Switch Cost reflects a slowing of response time due to discarding a previous schema and setting up a new one
Bilinguals show a greater Switch Cost when switching from their weaker language to their dominant language, indicating inhibiting the more complex schema has a cost
Task-Switching Neural Correlates
Study with 38 healthy controls and 41 patients with focal PFC lesions
Patients grouped based on lesion location: Left lateral, Right lateral, Inferior medial, and Superior medial
Task-switching effects on reaction time and errors, including trial type, congruent/incongruent button press, and delay of cue on the screen
Patients with lesions in different areas show varying levels of impairment in task-switching performance
Prefrontal cortex (PFC)
The prefrontal cortex (PFC) is involved in several executive functions such as task-setting, problem-solving, response inhibition, and task-switching. The Supervisory Attentional System (SAS) is a model consisting of a set of tasks and behaviors (schemas) and a biasing mechanism to activate/inhibit these according to current goals. Reaction times are slowest for the SM group, with a greater switch cost than controls. Error rates are highest for the IM group, linked to lesions in the ventral orbitofrontal cortex and medial and orbitofrontal PFC.
What did evaluation tests of executive function show?
Evidence from lesion studies is highly dependent on the nature of the task and any modifications and how patients with lesions are grouped. Sometimes, individuals with damage to the PFC can pass standard laboratory tests despite exhibiting impairments in real-world behavior. Tests developed coincidentally as we learned more about neural correlates of executive function.
What are the two types of control processes?
Hot vs. Cold Control Processes. Control processes differ based on the stimuli processed. Different neural correlates exist in the PFC for hot stimuli (orbitofrontal, which has connections with posterior affective areas) and cold stimuli (lateral frontal cortex, which has connections with posterior sensory/motor areas). Reversal learning is a hot control process, and set shifting (task-switching) is a cold control process.
What did a study on marmoset monkeys suggest?
A double dissociation between brain areas responsible for hot and cold control processes. Lesions in either the orbitofrontal cortex or lateral frontal cortex led to different deficits in the adaptation to new rules. Individuals with PFC lesions may be impaired in the real-world (hot) or spared in laboratory tests of executive function (cold).
What does the Somatic Marker Hypothesis propose?
That emotional and bodily states associated with previous behaviors are used to influence decision making. Emotional events (e.g., a risky situation) store “somatic markers” in memory, believed to be stored in the orbitofrontal/ventromedial PFC. The somatic markers may be unconscious or conscious, and retrieving that event reinstates the somatic marker. This guides behavior, making a response more or less likely.
What is the Iowa Gambling Task?
The Iowa Gambling Task is used to test the SMH. Subjects are given a “loan” of $2000 and must choose a card from one of four decks each round. They receive either a gain or a penalty, and the decks have different returns over the entire test: A + B = BAD; C + D = GOOD. Healthy controls learn to switch from bad decks to good decks and show anticipatory skin conductance response when selecting from “risky” decks during the game. Patients with orbitofrontal PFC lesions – fail to switch from bad decks to good decks. Do not show anticipatory skin conductance response when selecting from risky decks. Show intact performance on other tests of executive function (Stroop, WCST).
