subcortical nuclei
involved in regulating movement:
subcortical
from its output nuclei
certain brainstem nuclei
fiber tracts:
ansa lenticularis
lenticular fasciculus
thalamic fasciculus
action selection and initiation - both motor actions and 'cognitive actions'
cognitive actions, e.g. gating or releasing something into working memory
convoluted architecture - ensures that actions are not triggered accidentally
principal subcortical components of a family of circuits linking the thalamus and cerebral cortex
prefrontal circuits
limbic circuit
scaling the amplitude or velocity of movement (ks4,859)
or suppressing potentially conflicting patterns, focusing the activity for voluntary like an inhibitory surround in sensory systems
only poor evidence for basal ganglia doing skill learning
in animals without neocortex, such as amphibians, the basal ganglia form the telencephalic mechanism for determining responses
input comes into the striatum - divided into go and no-go units
from outside the basal ganglia, and also from dopaminergic substantia nigra pars compacta
through the direct pathway and indirect pathway, that have opposite effects
stimulation of the direct pathway increases the activity of the thalamus while stimulation of the indirect pathway decreases the activity of the thalamus
the balance between these pathways is all important and determines the amount of inhibitory outflow from the basal ganglia
to thalamus - tonically inhibited by internal globus pallidus ('foot on the brake')
think of it as the trigger for the response
discharge tonically at high frequency, inhibiting the thalamus ('foot on the brake')
phasically affected by direct pathway and indirect pathway
dopmainergic inputs to both pathways facilitate movements initated in the cortex
see Parkinson disease#simulations
involved in Parkinson disease (hypokinetic), Huntington disease (hyperkinetic) and hemiballismus
see also: motor disorders
can cause complex neuropsychiatric cognitive and behavioral disturbances
damage to basal ganglia:
affects all of the tasks affected by frontal damage
also affects simple probabilistic learning tasks (like the weather prediction task) that are not affected by frontal damage
involved in Brocas aphasia
basal ganglia lesions cause spatial memory impairments (like frontal cortex) (Ingle & Hoff)
visible barrier placed beside frog, then removed
delay, then large dark object looms towards frog, which leaps away
normal frogs avoided leaping into or around the barrier's previous location
frogs with basal ganglia lesions: behaved as if they failed to remember where the barrier had been, though they avoided it when it was present