The Organization of Orientation Selectivity Throughout Macaque Visual Cortex
A double-label deoxyglucose technique was used to study orientation columns throughout visual cortex in awake behaving macaques. Four macaques were trained to fixate while contrastreversing, stationary gratings or one-dimensional noise of a single orientation or an orthogonal orientation were presented, during uptake of [ 14 C]deoxyglucose ([ 14 C]DG) or [ 3 H]DG, respectively. The two orthogonal stimulus orientations produced DG-labeled columns that were maximally separated in the two isotope
... aps (interdigitated) in four areas: V1, V2, V3 and VP. The topographic change from interdigitated to overlapping columns occurred abruptly rather than gradually, at corresponding cortical area borders (e.g. VP and V4v, respectively). In addition, the data suggest that orientation column topography systematically changes with retinotopic eccentricity. In V1, the orientation columns systematically avoided the cytochrome oxidase blobs in the parafoveal representation, but converged closer to the blobs in the foveal representation. A control experiment indicated that this was unlikely to reflect eccentricitydependent differences in cortical spatial frequency sensitivity. A similar eccentricity-dependent change in the topography of orientation columns occurred in V2. In parafoveal but not foveal visual field representations of V2, the orientation columns were centered on the thick cytochrome oxidase stripes, extended into the adjacent interstripe region, but were virtually absent in the thin stripes. Materials and Methods Surgery and Training Procedures in this experiment were similar to those described previously (Geesaman et al., 1997; Vanduffel et al., 2000) . Four male rhesus monkeys (Macaca mulatta) were restrained in a primate chair. The head of each monkey was fixed in place with a stainless steel device. Eye positions were measured using the scleral eye-coil technique. All operations were performed under ketamine anesthesia (10 mg/kg Ketalar® i.m., Parke-Davis, Brussels), supplemented with xylazine (0.5 mg/kg Rompun®, Bayer, Brussels). During the eye-coil surger y, anesthetics (0.2 mg Unicaine®, Bournonville Pharma, Braine-l'Alleud), antibiotics (150 mg Lincocin®, Upjohn, Puurs), corticosteroids (2 mg Celestone®, Schering-Plough, Brussels), and a vasoconstrictor (5 µg Levorinine®, Sterop, Brussels) were locally administered. Antibiotics (50 mg/kg i.m. Kefzol®, Lilly, Brussels) were given daily during the week following each surgery. The fourth monkey received analgetics for 3 days after the implantation of the catheter (5 mg/kg i.m. Tramadol, Dolzam®, Zambon, Brussels). The surgical procedures conformed to the American and European Guidelines for the care and use of laboratory animals. The monkeys were water-deprived during the period of testing, and behavioral control was achieved using operant conditioning. The monkeys were rewarded with drops of apple juice for maintaining fixation within a square-shaped central fixation window (1-2 on a side for training, 3 during the DG experiment). Multiple rewards within a given trial of maximally 64 s were given at gradually decreased intervals to encourage longer fixation by the monkey. The goal of this fixation paradigm was to have the monkeys viewing the CRT screen as consistently as possible during the period of DG uptake. The health status of the monkeys was closely monitored throughout the deprivation period.