task 3 Flashcards
BASAL GANGLIA LOOPS AND MEANINGFUL BEHAVIOR.
● Through this spiral of inputs & outputs between striatum and midbrain Dopamine neurons, information can flow from
1. limbic to
2. cognitive to
3. motor circuits
● THIS Provides a mechanism by which motivation and cognition can influence motor decision-making processes & appropriate responses to environmental cues
Expressed behaviors are the result of a combination of complex information processing that involves all of the frontal cortex
cools results
- Task switching is related to the left frontal lobe as damage here leads to increased switch costs in the task switching procedure
- Frontal lobes are not uniquely responsible for deficits in task switching as demonstrated by Parkinsons patients. Since parkinsons is primarily caused by dopamine depletion.
- Parkinsons patients showed the most switch cost in the cross-talk conditions. Thus switching deficit was only present when the stimuli primed the competing task set and was not random.
BG and decision making
BG is more important than the Neocortex in decision making since,
1. when cortex was removed in cats they were still able to engage in decision making.
- BG was there before the neocortex so that’s why it is more vital in decision making, dealing with the behavior
- As seen in Cools article: BG is very much involved in cognition.
- The connection between striatum and cortex is more important than the cortex itself.
The basal ganglia does contribute to the operations of WM through gating
The basal ganglia does contribute to the operations of WM through gating
- Input gating to update WM:
D1-receptor go-cells of the BG are triggered when useful info becomes available in the environment. These in turn facilitate recurrent thalami-prefrontal information flow to update the WM. No go cells are in turn triggered by distracting sensory representations. Updating is thus prevented.
- Output gating to select info within WM:
The Biased competition model of prefrontal function suggests that some info residing in WM might be distracting to the action at hand, since not all info in WM can be relevant at the same time. Thus the BG-mediated gating system selects the ouput from within WM.
rostral area (pre PMd) rostral area = output gating
Role of (dorsal) Striatum
Role of (dorsal) Striatum
- Integrate different states and compare them with one another
- This is done by each sensory system casting a “vote” for which pathway should be more active
- Common value of these “votes” are used to guide behavior
- Both pathways are active at the same time in both hemispheres
The pathways compete against one another on whether subject should move left or right, hence why Lee etc calls this the “Left or Right orienting paradigm”
basal ganglia input gating
1) Input gating
- cortically represented stimulus could cause Go cells to fire, via corticostriatal projections à facilitate thalamic-prefrontal information flow for working memory updating
updating is favored (and stable maintenance prevented)
- distracting sensory representations à trigger NoGo cells and so would have negligible thalamoprefrontal influence
updating is prevented (and stable maintenance favored)
basal ganglia output gating support
o 3 sequentially presented and completely reorderable stimuli: 2 item stimuli and 1 context stimulus that specified which of the two items would be relevant for responses
o All items showed sustained recruitment of a relatively caudal sector of frontal cortex (dorsal premotor cortex (PMd))
o A somewhat more rostral area (pre-PMd) transiently increased recruitment specifically when context was provided last and was therefore implicated output gating
basal ganglia and reallocation
o Predicted utility of irrelevant items correlated with activation in ventral striatum, while predicted utility of relevant items correlated with recruitment of frontal regions (3c and d)
ballot box and bg
Thus, the BG serves as a “ballot box” in which all the sensory, cognitive and motivational modalities can cast their “vote”. Additionally, the hyperdirect pathway (Cortex → STN → SNr/GPi) could serve as a bias to favor a specific action.
→ The movement with the ‘most votes’ will be most likely executed
This model suggests that the 2 pathways can be active at the same time, which evidence supports. The classical model cannot explain co-activation of the 2 pathways because it is either a “go-signal” → initiation of movement OR a “stop-signal” → termination of movement.
Direct pathway
Pro contralateral vote & Against ipsilateral vote
Indirect pathway
Against contralateral vote & Pro ipsilateral vote
Activity generated by striatal inputs (cortex, amygdala, thalamus, hippocampus) represent the state of the world (present and past) and can be integrated and compared in the striatum to guide behaviour 4
The striatum participates in reward-related decision making and action selection across species. Value signals change flexibly as a function of the rewards associated with available choices.
go/nogo model
Proposes the BG as a “gating” system: Regulation of input to and output from WM capacity.
- Direct pathway: Through D1 signals ‘opening of the gate’ to facilitate information flow from a specific modality
o Go cells
o Controls contralateral side
- Indirect pathway: Through D2 signals ‘closing of the gate’ to block information flow from a specific modality
o No-go cells
INPUT: As a gate, the BG can control the thalamo-cortical information flow to keep the WM capacity updated and not overfilled with useless information. Example: Visually presented target vs. distractor stimulus:
Target stimulus causes “Go cells” in cortico-striatal connections to fire → information about the target is updated into the WM. This favors update over maintenance of prior information.
difference pasr compacta & reticula
o Pars compacta: mediodorsal portion, contains dopaminergic cells that project to the striatum and other nuclei of the BG
o Pars reticulata: ventrolateral portion, major output nuclei of the BG
ventral and central Basal ganglia
Overall, ventral regions of the basal ganglia play a key role in reward and reinforcement and are important in the development of addictive behaviours and habit formation.
More central basal ganglia areas are involved in cognitive functions, such as procedural learning and working memory tasks
- Cerebral cortex
- Thalamus
- Brain stem (primarily the dopaminergic cells)
project to stratum and terminate
Terminate in a topographic manner:
- dorsolateral striatum receives cortical input from sensory-motor areas
- central striatum receives input from associative cortical areas
- ventromedial striatum receives input from limbic areas
Corticostriatal connections
Corticostriatal terminals are distributed in a patchy manner that is topographically organized (see figure). The VS is associated with emotion, the caudate nucleus with cognition, and the putamen with sensorimotor function (remember: there is no clear boundary between VS and DS, the separation between caudate nucleus and putamen is only structural).
rostral straiaztal region
The rostral striatal region might be a hub for vmPFC, OFC, and dACC to connect with dorsal & lateral PFC regions that integrate motivational, reward, and cognitive control information
o Convergence facilitates value computations across domains
Some striatal regions, particularly posterior and lateral portions, receive inputs from only a few prefrontal regions, and therefore they may serve more specialized computational roles.
