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Temporal Processing of Saccade Targets in Parietal Cortex Area LIP During Visual Search

¹Neuroscience Graduate Program, ²Centre for Neuroscience Studies, ³Canadian Institutes of Health Research Group in Sensory-Motor Systems, and ⁴Departments of Physiology and ⁵Psychology, Queen's University, Kingston, Ontario, Canada

Submitted 19 April 2006; accepted in final form 27 October 2006

We studied whether the lateral intraparietal (LIP) area—a subdivision of parietal cortex anatomically interposed between visual cortical areas and saccade executive centers—contains neurons with activity patterns sufficient to contribute to the active process of selecting saccade targets in visual search. Visually responsive neurons were recorded while monkeys searched for a color-different target presented concurrently with seven distractors evenly distributed in a circular search array. We found that LIP neurons initially responded indiscriminately to the presentation of a visual stimulus in their response fields, regardless of its feature and identity. Their activation nevertheless evolved to signal the search target before saccade initiation: an ideal observer could reliably discriminate the target from the individual activation of 60% of neurons, on average, 138 ms after stimulus presentation and 26 ms before saccade initiation. Importantly, the timing of LIP neuronal discrimination varied proportionally with reaction times. These findings suggest that LIP activity reflects the selection of both the search target and the targeting saccade during active visual search.

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