Prefrontal Cortex and Executive Function Flashcards
What brain region plays a central executive role?
PFC
What kind of processing is automatic behaviour produced by?
Bottom-up
A reflex is where you act before making a conscious decision to do so thus perception of thoughts leading up to the decision is false
Classical view of sensory processing
behaviourist
Brain does not create meaning
Perception is a ‘bottom-up’ process
Early, reflex decisions are fast but can ‘short-circuit’ potentially adaptive responses
Sequential stages reconstruct features to represent objects
Neural representation will show similar changes as you progress up the
processing hierarchy
The world is created de novo again and again
Open to behaviour ‘stalling’ when presented with ambiguous input cues
activating more than one internal representation
Problems with the bottom up strategy
Inflexible and potentially maladaptive
Top-down processing
Main task of cognition being the guidance of intrinsic goal-directed & rewarded behaviour (latter are learnt through experience)
Successful outcome then relates not to the accurate representation of the world but rather the generation of appropriate actions
Internal brain states should conform to ‘action-oriented pointers’ (not object representations) – deals with ambiguous input through access to internal states and intentions, knowledge of immediate and future goals and memory of past successes.
For cognitive control, systems must have:
Access to information from many brain systems
Ability to encode the goal-relevant relationships between them
Flexibility through learning (‘complex learning’)
Capacity to deal with gaps in time between events/cues/actions (working memory) – and ‘pause/resume’ to allow new, more vital processes
In cognitive control, systems must be able to select:
Which sensory, motor and memory processes are active at any given moment (cognitive resource allocation)
Why is it important in cognitive control to be able to select which processes are active at any given moment?
Limited number of controlled behaviours that can be active simultaneously (in contrast to automatic behaviours)
Why is finite allocation of resources to a small number of tasks inefficient?
Trade-off between information processing and depth of analysis allows elaborate analysis of a situation
Allows individuals to stay ‘on track’ – processing irrelevant information increases chance of distraction – attention = control.
What does the meaning og top down/ bottom up depend on?
Experimental context: Anatomical Cognitive Contextual Dynamic (anatomical hierarchy not an absolute requirement)
Stephen Grossberg’s active brain model
Feedback has a role in focusing selective attention to important elements of the environment
Adaptive filtering of inputs
Predictive signals for expected (learned) patterns (priors)
Compare actual vs expected, amplify match, inhibit mismatch
Divisions of the primate PFC
Dorsolateral, ventrolateral and orbital sub-regions - but these represent at least 18 distinct areas (Brodman)
Anatomy of the primate PFC
Areas forward of motor cortex (Brodmann 4 and 6) are considered prefrontal
PFC = Brodmann areas 8-13, 44-47
Can also be defined as the region of cortex supplied by the mediodorsal nucleus of the thalamus (n.b. This does not apply to rodents)
The PFC is connected directly to every distinct functional unit of the brain
Connectivity of the PFC (the great integrator)
diagram
Sensory – most PFC regions have inputs from 2+ sensory association/multimodal regions
Motor – Area 46 may be particularly important for motor output. Connections to premotor planning regions (e.g., supplementary motor area) as well as striatum
“Limbic” – Direct and indirect (via thalamus) connection to hippocampus/MTL, amygdala and hypothalamus.
Anatomically, PFC is well placed to synthesise internal and external information to provide complex behaviour
SWRs
Sharp-wave ripples are fast (short duration) oscillation sequences that can be seen ‘riding’ on sharp waves in hippocampus. Groups of pyramidal cells fire during SWRs
Function of spikes in SWR ripples?
Spikes in SWR ripples can fire to ‘predict’ order of upcoming movement (“fwd. replay”) or ‘in reverse’ to ‘recall’ that movement once finished (“rev. replay”)
Replay of experiences during SWR in SWS
Come back to
CA1-PFC cell pairs
Cells in PFC fire within c.100ms of cells in CA1 hippocampus only during SWS and not REM sleep
CA1-PFC cell pairs show coherent activity…
…only during SWR events durings SWS
Phineas Gage
Mad major medial PFC damage
Major personality change, loss of cognitive control, ability to perform complex tasks intact, dysexecutive syndrome
Dysexecutive syndrome
Lack ability to form sensible long-term (unseen) concerns and goals
Tests for PFC damage/disinhibition
Stroop task
Wisconsin card sort task (able to learn rule but perseverate when rule changed, stimulus bound behaviour)
Tower of London task (many more moves than necessary- forward planning deficits)
Iowa Gambling Task
Subject turns over 1 card at a time, each turn has a ‘win’
Some turns ALSO have a ‘loss’
‘Wins’ for 2 decks (A and B) are of larger
amounts than for the other 2 decks (C
and D)
However, the ‘losses’ for A and B are
more frequent and larger than those for
C and D
Thus, the optimal long-term strategy is
to stick with C and D even though ‘wins’ on A and B are larger
Iowa Gambling Task and PFC damage
Come back to
Iowa Gambling Task: Amygdala vs PFC damage
Come back to
PFC lesions experiment in marmosets
Marmosets trained to criterion on I, E and R
task rules
Lesion either lateral or orbital PFC
Lateral PFC lesions inhibit re-learning of E rule
Orbital lesions inhibits re-learning of R rule Neither lesion affects I rule re-learning
Deficit is specific to inhibiting a previously- acquired responses
Similar to WCST in human PFC patients
Dorsal vs Ventral vs Orbital PFC lesions
Come back to
Object Self-Ordered Task and PFC Lesions
Previous result suggest a dissociation of function:
Dorsal PFC-Spatial memory (parietal input) Ventral- Object memory (sensory input, e.g., IT) Orbital PFC- Inhibitory control (limbic input)
However; dorsolateral lesions DO produce deficit in some non-spatial tasks – e.g., object self- ordered task
orbital lesions produce impairments on both spatial and non-spatial reversal tasks
Neurophysiology of PFC
Anatomical connectivity of PFC is reflected in the responses of PFC neurons
PFC neurons respond to visual, auditory, tactile and gustatory stimulation (and memory for these) as well as voluntary movement
The first PFC recordings in Macaque were made in the 1970s by the Fuster and Nikki labs
Recordings showed that many PFC neurons maintained information about spatial or object cues during delay periods
Responses of PFC Neurones in Delay Tasks
Neurones show a memory for visual field location.
Such responses resistant to visual directors in preferred location (unlike sensory cortex neurones)
Responses may depend on DAeric signal from VTA that predicts reward (DA antagonists blocks delay activity)
Responses of PFC Neurones in Rule-Based Tasks
Response of PFC neurons is highly dependent on the rule NOT the stimuli
Differential responding to associative vs object matching (similar for other task combinations)
Macaques can also generalise rules to novel situations
Coding can be flexible- responses adapt to new contingencies
PFC neurones code for…
…categories
Delayed PFC with morphs
come back to
