Biology Reference
In-Depth Information
obtained absence of attentional modulation of neocortical responses with latencies that do
not exceed 100 ms. This model can also help understanding of the mechanisms
underlaying attentional disorders.
Keywords:
attention, visual processing, basal ganglia, synaptic plasticity, dopamine
Figure 1. Simplified scheme of associative and limbic cortico - basal ganglia -thalamocortical loops
involved in processing of visual information. BG, basal ganglia nuclei; MDN and RN, mediodorsal and
reticular thalamic nuclei; Intralam, intralaminar; SC, superior colliculus; SNc, substantia nigra pars
compacta; VTA, ventral tegmental area; DA-dopamine. Arrows - excitatory inputs; thin lines with
rhomb - weak inhibitory inputs; chain lines with arrow - dopaminergic inputs
I
NTRODUCTION
Visual attention is necessary for selection of high priority information and filtering out
irrelevant information since many different visual objects cannot all be processed
simultaneously. The role of visual attention consists of not so much in the exact and full
description of the world, as in intensifying a hierarchical ascending of signals in visual
cortical fields (Treue, 2003). Attention that influences both ascending and descending streams
of visual processing is controlled by a distributed network wherein the higher order areas in
the prefrontal cortex (PfC) generate top-down signals that are transmitted via feedback
connections to the visual areas and then to the first stage in visual processing, lateral
geniculate nucleus (LGN) (Kastner and Pinsk, 2004). According to commonly accepted
mechanism, focus of attention generates a column of the enlarged cortical inputs to the LGN,
and simultaneously suppresses surrounding activity by GABA inhibition (Montero, 2000;
Zikopoulos and Barbas, 2006). This inhibition is performed by the reticular thalamic nucleus
