Executive Functions Flashcards
Executive Function
Complex processes by which an individual optimizes his/her performance in a situation that requires the operation of a number of cognitive processes. [In short it is about controlling your behavior to reach your goals]
What is wrong about Phineas Gage?
He had a Prefrontal Cortex damage. After this damage his personality changed , he became more impulsive and he started experiencing problems in following plans. ( Cognitive Neuroscience Folklore)
Stability and Plasticity Dilemma
To reach your goals there has to be a balance between stability and plasticity. For stability; you have to stick your plans so that you can pursue them without distraction. However, you need certain amount of plasticity in case of any changes in the situation. PFC helps you to reach this balance !
Homunculus Problem in Executive Functioning
Who controls and monitors your behaviors? Is there a little man inside of your brain? No, there is no little man thinking inside (This is the homunculus problem) rather control may be the outcome of multiple competing biases (top down and bottom up).
Prefrontal Lobotomy (Yey or Nay)
Moniz (a doctor I think) was really into the prefrontal lobotomy (severing connections between PFC and limbic system) and it was executed more than 80.000 cases of schizophrenia and depression. Although they argued that patients became happy (?) after the lobotomy, they also became duller and apathetic. - And probably they got worse in tasks require planning and set shifting.
Executive Functions
Prefrontal Cortex
- Definition I
- Definition II
Definition I
- based on movement
- Regions of the frontal lobe that do not elicit movements when stimulated.
Definition II
- Projection zone of mediodorsal thalamic nucleus
Subdivisions of (pre)frontal cortex
Delayed development of PFC
In humans PFC obtains peak cortical thickness later than other (e.g. sensory) regions.
- Peak: ~10 years
Prefrontal cortical lesions
- The slowing of thought and loss of spontaneity
- Persevation errors - Card sorting example
- Loss of self-awareness and flat affect, especially empathy
- Deficiencies in foresight and planning
- Tendency to confabulate
- Stability and flexibility can be affected: Perseveration and distractability errors
Wisconsin Card Sorting Task
This task can be used as a measure of executive functioning. Basically, there are different rules to sort the cards (color, number, shape) and the participant should figure out which rule he/she needs to adhere. During the experiment, experimenter changes the rules of the sorting randomly and rather than explicitly saying the new rule, just say “wrong” when participant tries to sort cards by using previous rules. The goal of the participant is learning the new rule and changing his/her behavior according to it.
Task Set and Set Shifting
Task Set : The way that you can solve a problem or the way that you can reach your goal.
Set Shifting : When the rules of the game is changed or the situation changes, you may need a new task set to reach your goal. Suppressing the old task set and shifting to a new one is called “set shifting”.
Perseveration
While healthy humans (people without PFC lesions) can change their task sets when the rules of the game are changed (like in the Wisconsin Card Sorting Game), people with PFC lesion stick to their old task sets. Although their behavior does not solve the problem anymore, they just keep doing it which is called “perseveration”.
Tower of London Task
It is a task that measures executive functioning (Especially “planning”). In the task there is a “start position” and a “target position”. Participant’s goal is that reaching the target position ASAP (with less trial-error). Participant should plan his/her behavior to do this with minimum number of moves. [It is difficult since some of your movements should go against to your goal first to reach your goal in the end]. People with PFC lesion do this with a lot of moves which shows that they can’t plan beforehand but try to reach their goals by relaying on trial-error.
Executive Control Models
(PS: Look at the page 8 in the slides).
Executive control model shows how the perceptual information used to reach your goals. “Trigger data base” part decides what to do in each condition. After that part, information goes to “Scheme Control Units”. In here there is a competition (which one is going to be used) between Contention Scheduling (Which is used for routine operations) and “Supervisory Attentional System” (which is necessary to decide what to do in a novel, non-routine situation). At the end information reaches “Effector System” (purpose processing unit involve in schema operation in both action and thought).
Bias Signals from PFC
PFC is not an essential part in stimulus-response pathways. (without PFC you can still perform). BUT, without PFC, your stimulus-response chains will be hard-wired, without no flexibility. Therefore, PFC controls the way how a certain stimulus creates a certain response. (so it biased the action due to the certain stimuli and it has a “modulatory function”)
Stroop Test and PFC Relationship
During the Stroop test, both name of the word and the color of the word are activated. You need to suppress one of them to reach your goal. (If you need to say the color of the word, you should suppress the urge to say the name of it- which is difficult since we are over-trained to read things-Top down bias-). For the goal setting part, PFC is crucial.
Action Plans in Human Lateral PFC
fMRI studies show that both “Parietal Cortex” and PFC are important in action plans of humans. Two of them have a role in establishing the map between the stimulus and behavior.
Free Will and Libet Experiment
The famous experiment is about measuring the time differences between “readiness potential”, “my decision to move” and the actual movement. Participants are free to move their hands whenever they want. Before doing any movement, our muscles get ready to move (this is readiness potential) and this potential is measured by EEG during the experiment. The key point of the experiment is that, participants should say when they decided to move their hands (they used a chamber full of dots moving around it, participant says the place of the dot when they’ve decided to move their hand). When they looked at the time difference between participant’s decision (-200 ms before movement) and readiness potential (-500 ms before movement), It seems like our muscles are getting ready to move before we decide moving. So do we say that our brain knows what we are going to do before we decide ? Is this mean that there is no free-will and everything is deterministic ? Be critical and don’t jump into the conclusions. The debate still continue. Further research showed that we can predict the behavior by looking at Lateral Frontopolar Cortex and Medial Frontopolar cortex although not perfectly. What does that mean? Does predicting something (your behavior) means that you have no control over it ?
Executive Functions
Subdivisions of the Frontal Lobes
- Prefrontal Cortex
- Lateral prefrontal cortex (LPFC)
- Frontal polar region (FP)
- Orbitofrontal cortex (OFC)
- Medial frontal cortex (MFC)
- when compared to other primate species, the expansion of prefrontal cortex in the human brain is more pronounced in the white matter
- the frontal lobe’s expansion is related to the emergence of the complex cognitive capabilities that are especially pronounced in humans
Prefrontal Cortex Is Necessary for Working Memory but Not Associative Memory
- delayed-response task
- recency memory + study
Delayed-response tasks
- In the simplest version, a monkey is situated within reach of two food wells. At the start of a trial, the monkey observes the experimenter placing a food morsel in one of the two wells (perception). Then the two wells are covered, and a curtain is lowered to prevent the monkey from reaching toward either well. After a delay period, the curtain is raised and the monkey is allowed to choose one of the two wells and recover the food.
- Although this appears to be a simple task, it demands one critical cognitive capability: The animal must continue to represent the location of the unseen food during the delay period (working memory). Monkeys with lesions of the lateral prefrontal cortex do poorly on the task
Recency Memory
- the ability to organize and segregate the timing or order of events in memory
- In a recency discrimination task, participants are presented with a series of study cards and every so often are asked which of two pictures was seen most recently. For example, one of the pictures might have been on a study card presented 4 trials previously, and the other, on a study card shown 32 trials back. For a control task, the procedure is modified: The test card contains two pictures, but only one of the two pictures was presented earlier. Following the same instructions, the participant should choose that picture because, by definition, it is the one seen most recently.
- Note, though, that the task is really one of recognition memory. There is no need to evaluate the temporal position of the two choices. Patients with frontal lobe lesions perform as well as control participants on the recognition memory task, but they have a selective deficit in recency judgments. The memory task can be performed by evaluating if one of the stimuli was recently presented—or perhaps more relevant, if one of the stimuli is novel. The recency task, though, requires working memory in the sense that the patient must also keep track of the relationship between recently presented stimuli. This is not to suggest that the person could construct a full timeline of all of the stimuli—this would certainly exceed the capacity of working memory. But to compare the relative timing of two items, the frontal lobes are required to maintain the representations of those items at the time of the probe. When frontal lobes are damaged, this temporal structure is lost.
Physiological Correlates of Working Memory
- fusi form face area
- A working memory system requires a mechanism to access stored information and a way to keep it active.
- In the delayed-response studies, single-cell recordings from the prefrontal cortex of monkeys showed that these neurons become active during the delayed-response task and show sustained activity throughout the delay period
- Within the lateral prefrontal cortex, cells characterized as “what,” “where,” and “what–where” were observed
- “what” cells responded to specific objects, and this response was sustained over the delay period.
- “Where” cells showed selectivity to certain locations.
- In addition, about half of the cells were “what–where” cells, responding to specific combinations of “what” and “where” information. A cell of this type exhibited an increase in firing rate during the first delay period when the target was the preferred stimulus. Moreover, the same cell continued to fire during the second delay period if the response was directed to a specific location
- the activity of these PFC cells is dependent on the monkey using that information to obtain a response. That is, the activity of the PFC cells is task-dependent. If the animal only has to passively view the stimuli, then the response of these cells is minimal right after the stimulus is presented and entirely absent during the delay period
- These cellular responses by themselves do not tell us what is represented by this protracted activity. It could be that long-term representations are stored in the prefrontal cortex, and the activity reflects the need to keep these representations active during the delay. Patients with frontal lobe lesions do not have deficits in longterm memory, however, so this hypothesis is unlikely. An alternative hypothesis is that prefrontal activation reflects a representation of the task goal, and as such, serves as an interface with task-relevant long-term representations in other neural regions. This latter hypothesis jibes nicely with the fact that the prefrontal cortex is extensively connected with postsensory regions of the temporal and parietal cortex.
fusi form face area
When the stimuli were presented, either during the encoding phase or for the memory probe, the BOLD response was much stronger in the FFA than in the prefrontal cortex
Processing Differences Across Prefrontal Cortex
- nbaxck task
- Michael Petrides (2000) suggests a model of working memory
- information held in the posterior cortex is activated, retrieved, and maintained by the ventrolateral PFC (e.g., the standard percentage for a tip)-
- then manipulated with the relevant information (e.g., the price of the dinner) in more dorsal regions of lateral PFC, enabling successful attainment of the goal.
n back task
- With n-back tasks, it is not sufficient simply to maintain a representation of recently presented items; the working memory buffer must be updated continually to keep track of what the current stimulus must be compared to
- Activation in the lateral prefrontal cortex increases as n-back task difficulty is increased, a response consistent with the idea that this region is critical for the manipulation operation
Hierarchical Organization of Prefrontal Cortex
- It has been proposed that the frontal pole is essential for integrating the specific contents of mental activity into a general framework
- Work focused on the anterior–posterior gradient across the PFC suggests that activation patterns follow a crude hierarchy: For the simplest of working memory tasks, the activation may be limited to more posterior prefrontal regions or even secondary motor areas. When such contingencies are made more challenging by changing the rules from one block of trials to the next, activation extends even farther in the anterior direction.
As a heuristic, we can think of PFC function as organized along three separate axes (see O’Reilly, 2010):
- A ventral–dorsal gradient organized in terms of maintenance and manipulation as well as in a manner that reflects general organizational principles observed in more posterior cortex, such as the ventral and dorsal visual pathways for “what” versus “how.”
- An anterior–posterior gradient that varies in abstraction, where the more abstract representations engage the most anterior regions (e.g., frontal pole) and the least abstract engage more posterior regions of the frontal lobes. In the extreme, we might think of the most posterior part of the frontal lobe, the primary motor cortex, as the point where abstract intentions are translated into concrete movement.
- A lateral–medial gradient related to the degree to which working memory is influenced by information in the environment (more lateral) or information related to personal history and emotional states (more medial). In this view, lateral regions of PFC integrate external information that is relevant for current goal-oriented behavior, whereas more medial regions allow information related to motivation and potential reward to influence goal-oriented behavior.
Executive Function
Goal Planing
- What three components are essential for successfully developing and executing an action plan?
- What problems could arise for patients with preforntal lesions?
What three components are essential for successfully developing and executing an action plan?
- Identify the goal and develop subgoals
- In choosing among goals and subgoals, consequences must be anticipated
- Determine what is required to achieve the subgoals
What problems could arise for patients with preforntal lesions?
- Problems can arise because of deficits in filtering irrelevant information, making it difficult to keep the eyes on the prize. Or the challenge may come in prioritizing information to help select the best way to achieve a particular goal or subgoal.
Executive Functions
Goal Planing
- Hierarchical Gradient Hypothesis
- Asymmetric processing deficits
Hierarchical Gradient Hypothesis
- Consistent with the hierarchical gradient hypothesis, more anterior regions of PFC were recruited as the task became more complex. For the simplest task, varying response complexity activated premotor cortex. When the participant had to use color to select the appropriate dimension for the response, activation was also observed in more prefrontal cortex and extended into polar frontal cortex for the most complex task.
Asymmetric processing deficits
- A key idea of hierarchy, however, is that processing deficits will be asymmetric. Individuals who fail at operations required for performance at the lower levels of a hierarchy will also fail when given more challenging tasks. In contrast, individuals who fail at tasks that require the highest levels should still be able to perform tasks that are dependent only on lower levels.
Executive Functions
Retrieval and Selection of Task-Relevant Information
- PFC as a dynamic filtering mechanism
PFC as a dynamic filtering mechanism
- working memory is more than the passive sustaining of representations. It also requires an attentional component in which the participant’s goals modify the salience of different sources of information.
- Reciprocal projections between PFC and posterior cortex provide a way for goals, represented in PFC, to maintain task-relevant information that requires longterm knowledge stored in posterior cortex.
Executive Functions
Retrieval and Selection of Task-Relevant Information
- High Filtering vs. Low Filtering
Executive Functions
Task Switching
The type of cue turned out to be critical. When a visual word cue was used to specify the task goal, patients with lateral prefrontal lesions performed similarly to the matched control participants. When a color cue was used, however, the patients were slow on the switch trials. This dissociation reinforces the idea that the prefrontal cortex is important for coordinating goal-oriented behavior. Moreover, this form of control is needed especially when the goal must be retrieved from memory. With the color cue, the patients must remember the associations between the colors and the tasks (e.g., red with digit naming). The word cues do not require this step of referring to memory.
