The effects of anterior arcuate and dorsomedial frontal cortex lesions on visually guided eye movements: 2. Paired and multiple targets

This study examined the effects of anterior arcuate and dorsomedial frontal cortex lesions on the execution of saccadic eye movements made to paired and multiple targets in rhesus monkeys. Identical paired targets were presented with various temporal asynchronies to determine the temporal offset required to yield equal probability choices to either target. In the intact animal equal probability choices were typically obtained when the targets appeared simultaneously. After unilateral anterior arcuate lesions a major shift arose in the temporal offset required to obtain equal probability choices for paired targets that necessitated presenting the target in the hemifield contralateral to the lesion more than 100 ms prior to the target in the ipsilateral hemifield. This deficit was still pronounced 1 year after the lesion. Dorsomedial frontal cortex lesions produced much smaller but significant shifts in target selection that recovered more rapidly. Paired lesions produced deficits similar to those observed with anterior arcuate lesions alone. Major deficits were also observed on a multiple target temporal discrimination task after anterior arcuate but not after dorsomedial frontal cortex lesions. These results suggest that the frontal eye fields that reside in anterior bank of the arcuate sulcus play an important role in temporal processing and in target selection. Dorsomedial frontal cortex, that contains the medial eye fields, plays a much less important role in the execution of these tasks.