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Interleaving.
The planning module
has to retain supervisory control (Sheridan 1992)
over routinized action.
In situations requiring full evaluation of the proposed
course of action, the system might have to reach a viable
state, which could take 300 milliseconds. Routine action,
on the other hand, can be used for faster actions such as steering a bike.
The phenomena of action slips show how action breaks at the
boundaries between these two modes of action.
Neural circuitry and the thalamus
We show in the diagram the
cortical layers and the connections involved in our
scheme.
Most of the thalamus is concerned with receiving a wide range
of sensory, subcortical and cortical inputs and sending
outputs to the cortex.
It is only the limited parts,
mainly the ventral group of thalamic nuclei
that are involved in the basal ganglia loops and receive
inputs from the globus pallidus and substantia nigra.
A possible role for the thalamus
This suggests a possible role for the thalamus, namely that
it could help regulate the rapid flow of routine action,
so that once a routine course of action is
selected by the neocortex, the stream of routine
actions can flow faster than cortical decision speeds.
The cortex would send a message to the thalamus
allowing it to let this stream through.
Before this,
while the cortex is monitoring and deciding on
selecting a routine action,
the thalamus would prevent this rapid flow.
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