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Cerebral CortexPrinciples of Operation$
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Edmund T. Rolls

Print publication date: 2016

Print ISBN-13: 9780198784852

Published to Oxford Scholarship Online: November 2016

DOI: 10.1093/acprof:oso/9780198784852.001.0001

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Cortex versus basal ganglia design for selection

Cortex versus basal ganglia design for selection

(p.406) 20 Cortex versus basal ganglia design for selection
Cerebral Cortex

Edmund T. Rolls

Oxford University Press

The functional architecture of the basal ganglia make an interesting comparison with the neocortex, for the basal ganglia do not use excitatory recurrent collaterals between the neurons. Instead the much evolutionarily older basal ganglia use direct inhibition between the neurons at the striatal and at the pallidal / nigral stages of processing. In comparison with cortex, this is a much safer method of selection, and of ensuring that only one output is selected, which is important in motor systems so that contradictory outputs are not attempted, for there is no risk of positive feedback becoming uncontrolled and runaway with the striatal direct mutual inhibition by neurons. The basal ganglia do have regular principles of internal connectivity between the neurons which lead to hypotheses about how it performs its computations, and this emphasizes the importance of building on the details of the anatomical and functional connectivity of neurons and networks of neurons to develop theories of how brain systems operate. This comparison helps to underscore the adaptive value of the excitatory recurrent collaterals in the cerebral cortex, for though subject to runaway excitation and instability, they provide the way that the cortex uses to implement short-term memory by continuing firing maintained by the positive feedback, and which provides a computational basis for planning ahead; for completion of a long-term memory from a partial retrieval cue; for decision-making in which the result of the decision can be maintained `on-line’ by continuing attractor-related firing, to guide actions performed on the basis of the decision; and for associating together semantic items which provide the basis for semantic structures in language.

Keywords:   basal ganglia, striatum, globus pallidus, substantia nigra, inhibition, recurrent collaterals, short-term memory, selection, stimulus-response learning, habits, planning

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