task 2 Flashcards
Lateral PFC:
Association between cue, reward and voluntary actions
dlpfc & vlpfc
DLPFC: Representing and maintaining of contextual information
VLPFC: Learning, maintaining and implementing rules
pic
- The PFC is linked to most brain regions (cortical and sub-cortical)
- The PFC indirectly biases “lower-level” streams of information such as attention-to-motor effector (see 2.2) according to task rules
task rules
- Task rules are learned associations of cue-action-reward (in the broadest sense) used to anticipate consequences of responses / select the appropriate response
- This learning process is the result of “rewards” from the limbic system after actions taken; the reward is more important if unexpected or surprising
- Associations can be chained together or stored (see 2.5, 2.6)
- In reality, many rules can lead to contradiction. That is why the integration of the perceived context is important
goals and rewards
Since monkeys are trained with rewards, their sustained activity (ventral PFC, lateral PFC & orbito-frontal cortex) also reflects their expectation of a reward. There are also areas that differ in activity depending on the type of reward. Sustained activity in the lateral PFC can code for both spatial location and reward. This suggests integration in this area of information about the current sensory stimuli and expected outcomes.
In humans, the orbito-frontal cortex is also responsible for expectancies. Humans also show activity in the frontal polar cortex when they expect high rewards and when they perform difficult WM tasks. This suggests that in humans, this area integrates memory-related activity and reward expectancy.
The study by Pochon et al. ( see above) and the study by Sakai et al.
suggest that what is special about sustained activity in prefrontal area 46 might not be simply the maintenance of sensory information but also the prospective use of that information.
Task contingencies
Task contingencies = The logical structure of a given task (if the light is green, cross the street)
Prefrontal neurons indeed show conjunctive tuning for learned associations between cues, rules, actions and rewards. They can therewith describe the principles needed to achieve a particular goal.
lateral pic and reward
The lateral PFC is connected to limbic structures that process internal information like reward. Many of its neurons therefore show multimodal responses. The lateral PFC is therefore needed to learn associations between cues, rewards and actions. Neurons in there might only be activated by a cue when it signals reward while others do the opposite
Multimodal responses
Multimodal responses = Neural activity elicited by more than one sensory modality
pic and regularities
The PFC activity also shows that monkeys and humans can identify regularities in their experiences and construct rules and therewith convey information about the formal demands of tasks.
Keeping to a task
The sustainability of PFC activity is also important to keep your attention on something (PFC damage results in distractibility), since it allows you to maintain goal-relevant information (WM).
WM can retain information over possibly distracting events. The PFC has this ability. Sustained activity in extrastriate visual areas seems to be more easily disrupted by the presence of distractors, causing neural activity in the inferior temporal and posterior parietal cortex to no longer reflect the sample object retained in memory.
Inferior temporal cortex = A neocortical region responsible for high-level analysis of form information
Posterior parietal cortex = A region of the visual cortex thought to be involved in visuospatial, visuomotor and attentional processes
pic involvement
sustained attention
reward
top down control
Practice and automaticity
Bias signals and top-down control
PFC activity could (i.e. via selective attention) exert a top-down influence by providing an excitatory signal that biases processing in other brain systems towards task-relevant information. In voluntary shifts of attention a competitive advantage for certain cells is conferred by excitatory signals (thought to originate from the PFC) that represent the ‘to be attended’ stimulus. Neurons processing the stimulus of interest are excited and the others inhibited.
Practice and automaticity
Practice and automaticity
As task-relevant neural pathways in other brain systems are repeatedly selected by PFC bias signals, activity-dependent plasticity mechanisms could strengthen and establish them independently of the PFC. Thus, the PFC becomes less involved and we no longer need higher cognitive resources for the task.
PFC damage often impairs new learning but well-practiced tasks are not impaired (see figure 4)
The PFC remains critical for implementing task information, especially when familiar behaviours need to be changed
the pic involvement in cognition
Cognitive control stems from patterns of activity in the PFC that represent goals and the means to achieve them. Bias signals are provided to other brain structures that can flexibly guide the flow of activity along task-relevant neural pathways, so establishing appropriate mappings between inputs, internal states and outputs needed to perform a given task. The PFC is involved in representing acquired relationships between various pieces of information, a function essential for intelligent behaviour.
