Executive functions Flashcards
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”.
Do homo sapiens have a larger PFC than other animals?
- the relative size of PFC is in humans (as proportion of total brain volume) higher than in mammals below great apes….
delayed development of Prefrontal Cortex
- late developed area (not fully developed in teenagers, they tend to have problems with temptations/controlling actions)
- cognitive capacities related to it appear later in life
The Role of Prefrontal Cortex
- Figuring out what to control so that you can reach your goals
(It does not have a direct outcome for movement!)
-Conflict monitoring
-Error monitoring (Anterior Cingulate Cortex) (not part of PFC!)
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.
What is wrong with Phineas Gage?
- cognitive neuroscience folklore
- P.G. had an accident in which his PFC got damaged
- he could speak, but his personality changed after the accident:
- he had problems executing plans: sticking to them or changing them
- problems with regulation of emotions -> he was impulsive
What are Executive functions?
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]
Prefrontal Lobotomy
- invented from Moniz
- severing connections between PFC and limbic system
- was executed in more than 80.000 cases of schizophrenia and depression (also by Walter Freeman)
- argumentation: patients would became happy after the lobotomy, but they also became duller and apathetic
- patients probably got worse in tasks require planning and set shifting
Possible definitions of PFC
- based on functional properties:
regions of PFC don’t elicit movement when stimulated - based on anatomical properties:
projection zone of mediodorsal thalamic nucleus
Informations converge in PFC
- PFC is a multimodal convergence zone:
- Auditory cortex
- posterior parietal cortex (planned movements, spatial reasoning, and attention)
- motor structures
- inferior temporal cortex (part of the ventral stream => representation of objects, places, faces, and colors)
- medial temporal structures (recognition of faces, audio-visual and emotional recognition)
lesions in PFC
non-emotional aspects:
1.) slowing of thoughts and loss of spontaneity
(spontaneity = starting an action plan from within)
2.) perseveration errors: (card sorting example)
- deficiencies in foresight and planning
-> stability and flexibility can be affected: perseveration and distractibility errors
Subdivision/Anatomy of PFC
- orbitofrontal and ventral regions (emotional processing)
- lateral regions (executive functions)
- anterior cingulate cortex
(does not really belong to PFC by anatomy, but its not a motor area either: -> involved in conflict processing)
Wisconsin Card Sorting Task: set shifting
- 1950: PFC as control region for temporal lesions
- detecting and applying new rules during the card game
- test of perseveration
Tower of London
- the task tests for executive dysfunctions, especially: planing deficits
- test was used to detect PFC lesions back in the day
(today: neuroimaging techniques)
Stroop interference
easy: reading words
difficult naming colors
Model: central executive
- by Tim Shallice 1980 (one of the fathers of cog neuro)
- psychological model:
From the perceptual system certain triggers can trigger certain behavior patterns. - The “contention scheduling” detects competition in a goal conflict: if you can not follow your action plan (drive your car, while something is in the way) the “supervisory attentional system” steps in
- but there is also a direct pathway from perceptual system to effector system/movement: driving your car, while speaking to a friend.
- contention scheduling: for routine situations
- supervisory attentional system: for non-routine situations -> PFC involved in detecting a conflict
Model: bias signals from PFC
- by Miller & Cohen, 2001
- idea: in Shallice’s central executive model behavior seems hardwired, but we can shift our actions
- bias signals from PFC establishes flexibility of stimulus-response mapping. (how you respond to a stimuli.)
When I’m at my friends, I don’t pick up her phone, when it’s ringing. - not transmissive, but modulatory
action plans in macaque lateral PFC I
- by Assad et al., 2000
- single cell recordings from rhesus monkeys performing different tasks (spatial, object, associative)
- monkeys have to memorize the stimuli and make a saccade
- finding: different responds with cue period to different tasks
- interpretation: one neuron implements one kind of task
-> problem: we can not interfere from the activity of a single cell to the whole population of neurons
Selection between tasks / Cohen’s model
- naming color or read the word (no conflict like in stroop task)
- same stimulus input, but the information flow gets configured in two different ways
- 2 sensory representations and a goal representation
- biasing the sensory level of processing and you get a stronger response in that direction
Action plans in human lateral PFC
- by Bode & Haynes, 2009
- how goals are encoded in the brain
- changing the link between stimulus and response
- classification techniques allows to look at the population of voxels
- information about the action plan is in the lateral prefrontal cortex: where sensory stimuli is transformed to an action plan
Action plans in monkey’s lateral PFC II
- Assad et al., 1998
- links between cues and saccade: interaction effect
- cell is not only modulated by saccade movement or wether its a face or traffic light
- but its modulated by a non-linear combination of the two
Troubleshooting: Error related negativity (ERN) in Anterior Cingulate Cortex (ACC)
- The ERN by Gehring et al. 1993
- by Hester et al., 2004:
HHSHH: Eriksen flanker task with hand thermometer
(speed vs. neutral vs. accuracy)
