Gating system
Involves the basal ganglia being a gate that regulates the passage of information from one neural circuit to the other
–> this way it solves action selection problems
e.g. Can be applied to motor system as well as WM (motor vs PFC)
Name the traditional role of the medium spiny neurons in motor gating.
(Go vs No-go cells)
- Go cells facilitate recurrent thalamo-cortical information flow
- -> opens gate - No-go cells block this info flow
- -> close gate
THUS: planned motor action triggers activity in go cells via corticospinal projection
- at the same time alternative action plans trigger no-go cells
e.g. thalamus –> motor neurons –> movement
Updated view of the role of medium spiny neurons in motor gating.
Both types of cells are co-active when initiating motor movement and do not work independently
Input gating of WM
- Go cells facilitate recurrent thalami-prefrontal info flow for WM updating
- -> when useful info becomes available in the environment - No-go cells are triggered by distracting sensory representations
- -> updating thus prevented
Output gating of WM
Biased competition model of prefrontal function
–> info residing in WM actively biases behavior
THUS: not all info in WM might be relevant and might interfere with action at hand
Solution to the biased competition model of PF function
Humans are capable of selecting info from within WM
–> BG-mediated gating mechanisms select the outputs of WM
How is WM reallocated when the already-stored info later turns out to be irrelevant ?
Name the 3 possibilities.
- Active removal process is necessary
- Passive decay
- Irrelevant representations linger until they are overwritten with new info
Input, output & reallocation of WM items.
- Input
- -> what items go into WM - Output
- -> what items can be used - Re-allocation
- -> what items can be eliminated because they become obsolete
Cognitive deficits in people suffering from Parkinsons disease
Set shifting abilities
–> ability to alter behavior according to changes in the dimensional relevance of stimuli
Task-set switching procedure
Requires the subjects to switch between letter- and digit-naming tasks on every second trial
–> each stimulus consisted of 2 closely adjacent characters presented side by side
Cross-talk condition
Task-set switching procedure
Stimulus contains
- both a letter and a digit
- -> character relevant to competing task + actual relevant one - or the relevant character adjacent to neutral character/symbol
- -> e.g. “#”
THUS: Filtering of irrelevant information is needed to perform well on this task
No cross-talk condition
Task-set switching procedure
Stimulus consists of attributes only associated to the relevant task
–> filtering of irrelevant info is NOT required
The striatum can be divided into several subdivisions. Name them.
Dorsal, ventral + central striatum
Dorsal striatum
Consists of
- Caudate nucleus
- Putamen
–> which are separated by internal capsule
AND: receives input from sensory motor areas
- Nucleus accumbens
Ventral striatum
Consist of
- Nucleus accumbens
- Medial + ventral Caudate and putamen
AND: receives input from limbic areas
Where does the striatum receive its input from ?
- Cerebral cortex
- -> topographic input - Thalamus
- Brain stem
- -> dopaminergic cells
BUT: input from cortex + thalamus terminate in general topographic manner
Where does the striatum send its output to ?
- Pallidal complex
- -> Globus pallidus external, internal segment (GPi, GPe) + ventral pallidum - Substantia nigra
- -> pars reticulata vs compacta (SNr, SNc)
Name the main striatal cells.
- Projection neurons
- -> Medium spiny neurons (95%) - Interneurons
Direct cortico-basal ganglia pathway
- Output from the GPi and SNr
- to Thalamus
- Cortex
Indirect cortico-basal ganglia pathway
- Output from GPe and VP
- to subthalamic neucleus
- GPi
Hyperdirect pathway
STN receives direct projection rom all parts of the frontal cortex
