Modulation of Neuronal Activity in Superior Colliculus by Changes in Target Probability

Abstract

Complex visual scenes require that a target for an impending saccadic eye movement be selected from a larger number of possible targets. We investigated whether changing the probability that a visual stimulus would be selected as the target for a saccade altered activity of monkey superior colliculus (SC) neurons in two experiments. First, we changed the number of possible targets on each trial. Second, we kept the visual display constant and presented a single saccade target repeatedly so that target probability was established over time. Buildup neurons in the SC, those with delay period activity, showed a consistent reduction in activity as the probability of the saccade decreased, independent of the visual stimulus configuration. Other SC neurons, fixation and burst, were largely unaffected by the changes in saccade target probability. Because we had monkeys making saccades to many locations within the visual field, we could examine activity associated with saccades outside of the movement field of neurons. We found the activity of buildup neurons to be similar across the SC, before the target was identified, and reduced when the number of possible targets increased. The results of our experiments are consistent with a role for this activity in establishing a motor set. We found, consistent with this interpretation, that the activity of these neurons was predictive of the latency of a saccadic eye movement and not other saccade parameters such as end point or peak velocity.

Learning and production of movement sequences: Behavioral, neurophysiological, and modeling perspectives

“…Also, (2) the strength of activation of a stroke representation predicts its order of production, and (3), as the sequence is pmduced, the representations arc serially deleted at the times that the corresponding strokes arc cnaetcd. Several studies (Averbeck et a!., 2002;Basso & Wurtz, 1998;Cisek & Kalaska, 2002) also give evidence for (4) partial activity normalization. The amount of activation that is spread among the plans grows more slowly than the number of plans (in the sequence), and eventually stops growing.…”

Drivers from the deep: the contribution of collicular input to thalamocortical processing

“…Consequently, the well-known visuomotor map in the intermediate layers of the SC was targeted (Robinson, 1972), assuming that the point of divergence occurs after the SC. In addition to the increase in activity just preceding a saccade that was emphasized with respect to the SC-MD-FEF pathway, many of the neurons in the intermediate layers of the SC also have delay activity related to gradual selection of the saccade to be made (Glimcher and Sparks, 1992;Dorris and Munoz, 1995;Basso and Wurtz, 1998;Bell et al, 2004). Such selection-related activity occurs at the same time that neuronal activity in visual areas of the cortex is enhanced during attentional tasks (Reynolds and Desimone, 1999;Ghose and Maunsell, 2002).…”

Linking reward expectation to behavior in the basal ganglia

“…That is, it seems possible that the activity measured in the caudate during the BST did not reflect reward context per se but, rather, a more general anticipation of an impending eye movement. This kind of anticipation is known to be represented in oculomotor areas including the superior colliculus [12,13] and parts of the parietal cortex [14] and is sensitive to target uncertainty: lower the uncertainty and increase the anticipation. To test this idea, Lauwereyns and colleagues used a second task that eliminated target uncertainty by flashing a cue indicating where the saccade target would appear.…”