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dependent modulation of the efficacy of strong and weak cortical inputs to the input basal
ganglia nucleus, striatum, and subsequent activity reorganizations in all basal ganglia nuclei,
the output basal ganglia signals (“attentional filter”) exert disinhibitory and inhibitory
influence on thalamic cells projected to neocortical neurons which initial visual activation
was strong and weak, respectively. This “filter” simultaneously favours increase of responses
of cortical neurons to attended stimulus, and decrease of responses to other stimuli. Divergent
dopaminergic projections promote the attentional enhancement of perception of different
features of the same stimulus and their binding into the entire object.
In proposed model, attention requires a release of dopamine in the striatum. Involuntary
attention is initiated by stimulus-evoked dopamine release, which is promoted by visual
activation of disinhibitory pathway through the basal ganglia to the superior colliculus that
excites dopaminergic cells. Voluntary activation of the prefrontal cortex that excites
dopaminergic cells initiates voluntary attention. Both involuntary and voluntary attention as
well as processing of visual stimulus are performed in the same loops. Attention represents a
part of sensory processing which improves its quality. However, this part of processing starts
with a time lag of approximately 100 ms from the appearance of stimulus, due to the
necessity of sensory activation of dopaminergic cells. This condition explains experimentally
obtained absence of attentional modulation of neocortical responses with latencies that do not
exceed 100 ms.
Experimental findings led to an assumption, that the role of basal ganglia in processing of
information is nonspecific in terms of stimulus modality and the cognitive context of the task
(Rektor et al., 2005). We suppose that the absence of modal specificity is the result of
uniform character of signal processing in different cortico- basal ganglia - thalamocortical
loops irrespective of the parts of cortical area, thalamic and basal ganglia nuclei included in
these loops. In our opinion, divergent dopaminergic projections may underlie well established
cross-modal attentional effects and attentional enhancement of binding. Proposed model that
provides a new insight into the role of dopamine-dependent synaptic plasticity in the
networks that include neocortex, basal ganglia and thalamus in mechanisms of visual
perception and attention can help to understand mechanisms underlaying disorders in visual
perception. For example, it explains why a lesion or degeneration of the visual striatum
causes some deficits in visual perception (Jacobs et al., 1995).
This work was supported by the Russian Foundation for Basic Research, Grant 08-04-
00218a
R
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