The Prefrontal Cortex Flashcards
Difference in PFC in different animals
It looks quite similar to the chimpanzee but there’s a lot more complexity in the folds – in the sulci and gyri in the human brain.
Thus, it seems that the PFC must be doing something important that distinguishes us from other animals
When you look at the picture of the connections between PFC and other brain regions, you can see that it is connected to …
When you look at the picture of the connections between PFC and other brain regions, you can see that it is connected to virtually every other region of the brain, which also suggests it plays a key role in human behaviour.
Who was Phineas Gage
One of the first indications of the function of the PFC was provided by the unfortunate case of Phineas Gage, a railway worker who was carrying out some explosives work on the lines when an explosion went off unexpectedly and a metal bar shot up into his face, entered his brain and exited the top of his head.
This is a reconstruction of the approximate entry and exit points based on the damage he sustained.
what is the Wisconsin Card Sorting Task
Patients are given a single card (here the one at the bottom) and must choose which of 4 decks to place the card on. They have to learn the rule governing which deck it should be placed on and continue to place different cards on the same deck according to the correct rule. The rule could be based on colour, shape, number of shapes etc. The patient must use trial and error to find the correct rule. Then, after 10 consecutive correct responses, the rule is changed and the patient must discover the new rule.
what is task-set switching
The idea is that the patient must acquire a ‘set’ for task performance, which basically means a rule or set of rules. And this set can switch repeatedly during the task.
Errors on Wisconsin Card Sorting Task pre and post surgery
Dorso-lateral prefrontal cortex seems to be involved.
Milner (1963)
what did Milner 1963 do
Patients with frontal lobe injuries showed disproportionate impairment on the task.
What these patients did was perseverate – after the rule changed, they tended to carry on responding according to the same rule.
Normal healthy people and patients with brain damage in other regions would discover the new rule with a couple of tries. However, patients with PFC lesions would simply carry on placing the card on the deck with the same colour as the single card. They would perseverate.
The conclusion was that the PFC is doing something related to inhibition - enabling flexible behaviour by inhibiting (suppressing) previously relevant, but no longer relevant, responses.
what did Shallice and Burgess do
They found that patients with frontal lobe lesions were actually surprisingly not very impaired on tasks that measure supposedly frontal executive functions.
e.g. Stroop task (attentional interference), Tower of London task (planning), even a modified WCST.
who came up w six elements task
Shallice and Burgess
what is the six elements task
• Limited total time (e.g., 10 minutes)
• Six different tasks to work on, such as picture naming, arithmetic, visual cancellation task.
• The goal is to work on all six of the tasks, and hopefully complete all six of the tasks, in the 10 minutes.
• The score is based on the number of tasks attempted, and score penalties are given for rule infractions or not spending an equal amount of time on each task.
To investigate this, Shallice and Burgess designed the 6 elements task, in which subjects had to do multiple different sub-tasks in a limited time. It wasn’t possible to complete all of the tasks so the optimal strategy was to spend a bit of time on each task and switch between the tasks.
what was foudn from the six elements task
What they found was that patients failed quite dramatically on the 6 elements task – most patients only attempted 2 or 3 of the subtasks relative to the 6 of healthy controls, and spent a dispropotionately large amount of time on each of the sub-tasks.
They theorised that the deficits on this task were due to the breakdown in a unitary supervisory system, located in the PFC
what is the The SAS model (Norman & Shallice, 1980)
The model is basically designed to explain how behaviour can operate in non-routine situations, in other words where well learned behavioural sequences are not sufficient. The WCST could be seen to be a model of this type of behaviour – the patient learns a particular rule governing responding but then has to re-learn this rule repeatedly
problems w SAS model
Homunculus’ criticism
• There is no controller at the front of the brain. Otherwise someone has to control that control. This causes infinite regression
• Who controls the controller?
• Explains what is controlled but not how control is exercised
what is cold cognition
Lateral parts of the prefrontal cortex. These are cold cognition. Doesn’t involve much emotional input
what is hot cogniton
The orbitofrontal cortex is hot- this is driven by values, emotions
what did Miyake do
In an influential study, Miyake and colleagues attempted to fractionate executive function into component variables using behavioural tasks and factor analysis.
They gave healthy subjects a variety of tasks:
what tasks did Miyake give
- Number/Letter Task (Rogers & Monsell, 1995)
- Letter Memory Task (Morris & Jones, 1990)
- Stop Signal Reaction Time Task (Logan, 1994)
what is Number/Letter Task (Rogers & Monsell, 1995)
For example, task switching – subjects have to perform two tasks – odd/even or vowel/consonant – depending on the location of the letters/numbers
Subjects are slower in switch trials than they are in repeat trials on this task.
what is Letter Memory Task (Morris & Jones, 1990)
A letter memory task that requires subjects to remember letters but also to update the letters in memory.
what is Stop Signal Reaction Time Task (Logan, 1994)
And a stop signal task requiring subjects to withhold prepotent responses. So the task is to respond as quickly as you can to the direction of the arrow but to withhold responding if you hear a loud beep after the arrow is presented.
The researchers gave subjects 9 tasks in total measuring a variety of different executive functions like these.
what did Miyake find
They then performed a factor analysis of all the tasks.
The figure here shows the 9 tasks on the left. They found that there were three very clearly distinct, latent variables that accounted for performance differences on the 9 tasks. These variables (or ‘factors’) are shown in the central part of the figure.
– shifting, which means shifting between task sets.
- updating, which means updating the contents of WM.
- And inhibition, which means inhibiting prepotent responses.
- This has been quite an influential model of executive function, and it tends to be used as a kind of template for understanding how executive functions can be fractionated.
- The idea is that any complex executive task can be accomplished by drawing on (some mixture of) these three functions.
what was Stuss & Alexander (2007) ‘s goal
Our goal was to determine whether all focal frontal lesions produced a similar impairment in cognitive supervisory control or whether lesions in different regions produced specific impairments that might or might not appear on a task depending upon the particular demands of the task
what did Stuss & Alexander (2007) do
- Tested frontal lobe patients (n = ~40) on a range of neuropsychological tasks including classic frontal tasks (WCST, Stroop), language and memory tests requiring executive functions, and attentional tests.
- Brain lesions were mapped out and location of brain damage defined by registration to a standard anatomical template
what did Stuss & Alexander (2007) find
Stuss performed a neuropsychological study where he ran a battery of tasks on patients with different focal prefrontal cortex lesions. He found some correspondence between the Miyake model and patients, as well as some differences.
Right lateral – monitoring issues – Miyake’s “updating” variable included monitoring tasks
Left lateral – task setting issues– necessary for shifting as in Miyake’s model
Convergence in medial PFC – energising. No space for inhibition. Stuss actually goes as far as to say that inhibition may not exist at the psychological level, certainly that it wasn’t a necessary concept to explain performance on the tasks they used.
No sign of inhibition in this study.