  The Superior Colliculus, a laminar structure involved in the retinotopic
mapping of the visual field, plays a cardinal role in the several cortical and
subcortical loops of the saccadic system. Although the selection of saccade
targets has long been thought to be the sole product of cortical processes, a
growing body of evidence hints at the implication of the Superior Colliculus,
firstly by the lateral connections between the neurons of its maps, and
secondly by its interactions with the midbrain Basal Ganglia, already renowned
for their role in decision making. We propose a biomimetic population-coded
race model of selection based on a dynamic tecto-basal loop that reproduces the
observed ability of the Superior Colliculus to stochastically select between
similar stimuli, the accuracy of this selection depending on the
discriminability of the target and the distractors. Our model also offers an
explanation for the phenomenon of Remote Distractor Effect based on the lateral
connectivity within the Basal Ganglia circuitry rather than on lateral
inhibitions within the collicular maps. Finally, we propose a role for the
intermediate layers of the Superior Colliculus, as stochastic integrators
dynamically gated by the selective disinhibition of the Basal Ganglia channels
that is consistent with the recorded activity profiles of these neurons.
