Saccadic Target Selection Deficits after Lateral Intraparietal Area Inactivation in Monkeys

Abstract

We investigated the contribution of the lateral intraparietal area (LIP) to the selection of saccadic eye movement targets and to saccade execution using muscimol-induced reversible inactivation and compared those effects with inactivation of the adjacent ventral intraparietal area (VIP) and with sham injections of saline into LIP. Three types of tasks were used: saccades to single visual or memorized targets, saccades to synchronous and asynchronous bilateral targets, and visual search of a target among distractors. LIP inactivation failed to produce deficits in the latency or accuracy of saccades to single targets, but it dramatically reduced the frequency of contralateral saccades in the presence of bilateral targets, and it increased search time for a contralateral target during serial visual search. In the latter task, the observed deficits might reflect either an ispilateral bias in saccadic search strategy or an attentional impairment in locating a target among flanking distractors within the contralateral field. No effects were observed on any of these tasks after VIP inactivation. These results suggest that one important contribution of LIP to oculomotor behavior is the selection of targets for saccades in the context of competing visual stimuli.

Motor role of parietal cortex in a monkey model of hemispatial neglect

“…In laboratory settings, researchers have modified this task by introducing a delay between the onsets of the two targets (6,8,15,17,20). Specifically, one target appears in the right (left) part of the screen.…”

“…bias animals' choices in choice tasks (8,17). We also reversibly inactivated circuits on the medial bank of the intraparietal sulcus (PRR) to probe the contribution of these circuits to spatial choice making.…”

“…Neglect patients show difficulties with detecting or directing an action to the target presented in the hemifield contralateral to the lesioned hemisphere (2)(3)(4). The failure to detect or direct an action to a target in the contralesional hemifield, also termed "extinction," is conditioned on the presence of the competing second target; detecting or directing an action to a single visual target usually incurs little or no difficulty to a neglect patient (6,7) or to a monkey neglect model (8). The competitive, relativistic nature of the extinction phenomenon has been taken as evidence that parietal cortex is involved in choosing behaviorally relevant targets in space (9).…”

“…This debate remains, for the most part, unresolved (13). Only few parietal lesion studies explicitly tested for biases in spatial choice making (8,15,17). Of these, only one study (15) specifically aimed to distinguish the perceptual from motor deficits in spatial choice making.…”

Rapid enhancement of visual cortical response discriminability by microstimulation of the frontal eye field

“…These findings are complemented by experiments that test whether neuronal signaling in the FEF and SC is necessary for attention by inactivating these areas. Reversible inactivation of FEF neurons not only impairs saccade production (34,35) but has also been shown to increase reaction time in a covert visual search task that did not require eye movement responses (36). In addition, reversible inactivation of the SC produces deficits in target selection that cannot be attributed to a purely visual or motor impairment (37).…”