Physiology & Behavior, Vol. 24, pp. 103-109 Pergamon Press and Brain Research Publ., 1980. Printed in the U.S.A. Associative Function of the Arcuate Segment of the Monkey's Prefrontal Cortex I LINDA Z. PODBROS, JOHN S. STAMM AND FRANK J. DENARO State University of New York, Stony Brook, NY 11794 Received 28 February 1979 PODBROS, L. Z., J. S. STAMM AND F. J. DENARO. Associative function of the arcuate segment of the monkey's prefrontal cortex. PHYSIOL. BEHAV. 24(1) 103-109, 1980.--Monkeys were trained in a WGTA on two visual conditional position response (CPR) tasks. Bilateral ablations were made to the arcuate sulcus (ARC), principal sulcus (PRIN), or to cortex inferior to the principalis sulcus (IDL). The means of total errors for both tasks were ARC 161.33, PRIN 21.6 and IDL 45.25, with significantly greater ARC deficit. Findings support the view that the role of arcuate cortex is to mediate spatial-response contingencies, regardless of cue modality. Arcuate cortex Cerebral cortex Conditional position response task Frontal lobe Lesions Monkey Spatial THE findings that ablations within the monkey's principal sulcus result in marked impairment on delayed response and delayed alternation tasks [3, 4, 12] have led to investigation of the functional properties of other segments of cortex within the prefrontal dorsolateral area. Resection of the cor- tex surrounding the principal sulcus resulted in impairment on an auditory discrimination task with go versus no-go re- sponse [4] and also on a conditional position response (CPR) task that required the monkey to walk in the direction oppo- site to that of the concurrently-presented visual or auditory cue [13,14]. These lesions included the cortex in the anterior bank of the arcuate sulcus and in the strip inferior to the principal sulcus. Lesions of cortex in the principal sulcus, however, or in the premotor area [13] did not disrupt correct performance on the CPR task. More recent research has demonstrated functional dissociation among small segments of the dorsolateral area. Ablation of cortex within the ar- cuate sulcus, including both banks, resulted in marked im- pairment on a CPR task that required the monkey to choose between left and right food cups in response to a concurrently-presented auditory signal from above or below the cage [2,11], while ablation of cortex in the principal sul- cus disrupted correct performance on the delayed alternation task [2], and ablation of cortex inferior to the principal sulcus disrupted correct performance on a nonspatial successive visual discrimination task [11]. The above findings suggest that the role of arcuate cortex is to mediate selectively be- tween the different directions that are involved in the CPR tasks--the direction for orienting to the cue and that for the correct instrumental response. This explanation implies that arcuate function is not modality-specific. However, since the crucial research on arcuate function has employed CPR tasks with auditory cues, the possibility of modality-specific function for arcuate function [4] cannot be disregarded. The aim of the present experiment was to clarify this issue. Monkeys were tested on a CPR task with visual cues, where a left- or a right-choice response was contingent upon the location of the cue in the upper or the lower portion of a display panel. A second aim of the experiment was to de- termine whether the non-principalis deficits that had been found on the tasks of spatial opposition between cue and reward [3] could be attributed also to arcuate lesions. The monkeys in this study were trained on both tasks; they then sustained lesions of arcuate, pricipalis, or inferior dorsolat- eral cortex. Performance impairments on both tasks after only arcuate lesions would strengthen the interpretation that arcuate cortex is substrate for mediation of the spatial cue- response contingencies, regardless of cue modality. METHOD Subjects and Surgery Seven experimentally naive Macaque monkeys of 3.0--4.5 kg bodyweight were used. Because of the difficulties in ob- taining new monkeys, the group consisted of three rhesus (Macaca mulatta) and four cynomolgus (Macaca fas- cicularis). Surgery was performed under aseptic conditions, using pentobarbital sodium anesthesia. The skin, skull and dura were opened and cortex removed bilaterally by subpial suction. The intended boundaries for the three types of le- sions were: ARC (arcuate)---the banks and floor of both branches of the arcuate sulcus; PRIN (principalis)---the banks and floor of the principal sulcus; IDL (inferior dorsolateral)--from inferior lips of the principal sulcus to the orbital ridge, terminating anterior to the inferior arcuate branch. Following the ablation, the dura was closed with 1This research was supported in part by Grant GB-6911 from The National Science Foundation. Copyright © 1980 Brain Research Publications Inc.--0031-9384/80/010103-07502.00/0