Biology Reference
In-Depth Information
T HE M AIN D ISTINCTIONS B ETWEEN P ROPOSED AND O THER M ODELS
OF A TTENTION
It was proposed that attention to an object requires the simultaneous activity of three
interconnected brain regions: the cortical site of attentional expression, the thalamic
enhancement structure, and the prefrontal area of control (LaBerge, 1997). Unlike, in our
model, attention requires the simultaneous interdependent activity in all regions of the C-BG-
Th-C loops. Reentrant signaling realizes by signal circulation in these loops but not only in
the cortico-cortical and cortico-thalamocortical loops. Formation of neural patterns
representing visual stimulus is based not only on interactions between the prefrontal and
visual cortical areas (Mechelli et al., 2004), but also on dopamine-dependent changes in
signal transductions through the C-BG-Th-C loops.
In spite of the known role of dopamine in attentional effects (Nieoullon and Coquerel,
2003; Turle-Lorenzo et al., 2006), known models of attention do not include mechanism of
dopaminergic cell activation by sensory stimulus. We have suggested such mechanism, and
proposed that excitation of dopaminergic cell requires sensory activation of the direct
pathway through the BG (Silkis, 2007).
In recent model of attention (Paul and Schyns, 2003), thalamic complex functionates in
two directions: ascending activity promotes switching of attention to significant external
signals, and descending activity supervises selection of signals participating in cognitive
perception through the network cortex - BG. Unlike, in our model the BG nuclei, which
influence transmission of signals through the thalamic complex to the neocortex, participate
in both descending and ascending pathways for attentional switching.
There is a hypothesis that signals generated by "detectors of transient processes” switch
on involuntary attention (Naatanen, 1992). These signals are determined by properties of
sensory stimulus, its novelty and intensity, and "detectors of transient processes” exist in
addition to detectors of sensory attributes. It is however unclear, what structures play the role
of such "detectors”, where and how the switching signal is generated and what is the
character of this signal. From the point of view of our model, a network that includes
striatonigral cells could execute detections of "transient processes”. A release of dopamine in
the striatum could play a role of a signal that switches on the attention. This signal is
generated by dopaminergic neurons of the SNc and VTA in response to sensory stimulation.
It was proposed (Naatanen, 1992) that selection of stimulus for voluntary attentional
perception occurs in primary cortical areas owing to comparison of a sensory input with the
representation of physical properties of stimulus - “attentional trace”. We suppose that
selection of stimulus for the best analysis occurs not only in primary, but also in other cortical
areas where the diverse stimulus attributes are processed.
C ONCLUSION
In our model, as well as in other models, the attention is a selective action directed on
searching a stimulus for the best processing. We advanced a hypothesis that this action is the
result of dopamine-dependent plastic reorganizations of neuronal activity in the visual and
limbic cortico - basal ganglia - thalamocortical loops. Owing to opposite sign of dopamine-
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