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Abstract:
Abstract: The selection of alternatives is a prominent
property of prefrontal cortex (PFC) underlying decision-making and
behavior on the Wisconsin Card Sorting Test. It has been
hypothesized that attentional selection in PFC is a two-stage
process, consisting of an early stage of enhancing all alternatives
and making them available for selection (prospective set forming)
and a later stage of a directed bias towards a single alternative
and a reduction of activation of unselected alternatives.
Attentional selection is compromised with dopamine depletion in
PFC, leading to perseverative behavior. We attempt to show that
perseveration is a direct consequence of failure of prospective set
formation. We implemented a network model according to the
two-stage process model, consisting of recurrently connected
attractors and a contextual selection system. The presence of
dopamine in the network changes several crucial parameters, such as
spike frequency adaptation, synaptic depression and reliability of
spiking for D1 receptors at excitatory neurons. D2 receptor
activation depolarizes interneurons, thus increasing inhibitory
firing. We could show that dopamine depletion in the network
compromises the maintenance of spiking activity within an
attractor, thus inhibiting prospective set formation. In this
scenario, impairment of attentional set shifting under dopamine
depletion is not contingent upon target-specific enhancement of
suppression, but a result of the inability to maintain
representations in working memory during an early preparatory
process.
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