Visual Receptive Fields of Neurons in Inferotemporal Cortex of the Monkey

Neuvons in inferotemporal cortex (area TE) of the monkey had visual receptive fields which were very large (greater than 10 by 10 degrees) and almost always included the fovea. Some extended well into both halves of the visual field, while others were confined to the ipsilateral or contralateral side. These neurons were difjerentially sensitive to several of the following dimensions of the stimuluis: size and shape, color, orientation, and direction of movement. Evidence from neuropsychological, electrophysiological, and anatomical experiments suggests that inferotemporal cortex in the monkey is involved in visual function. Removal of inferotemporal cortex produces a severe impairment in learning visual discriminations but does not affect visual acuity, the integrity of the visual fields, or discrimination learning in other modalities (1). Visual evoked responses may be recorded from macroelectrodes on inferotemporal cortex (2), and single neurons in inferotemporal cortex are responsive to visual but not auditory stimulation (3). Inferotemporal cortex receives afferents from prestriate cortex and from the pulvinar (4), and both these structures are known to respond to visual stimuli (5, 6). In order to analyze further the role of inferotemporal cortex in vision, we studied the response of single neurons in inferotemporal cortex to presentation of a variety of visual stimuli. The results presented here are based on seven Macaca mulatta weighing 3.4 to 8.2 kg. Two days before the start of recording they were implanted, under aseptic conditions and Nembutal anesthesia, with the base of an Evarts microdrive and with two bolts for subsequent fixation of the head (7), and then returned to their home cage. At the start of the recording session, the animals were anesthetized with intravenous Surital for the duration of a tracheotomy and then immobilized with a continuous intravenous infusion of gallamine triethiodide in a solution of 5 percent dextrose in lactated Ringer's (Abbott Laboratories), artificially respired, and anesthetized with a mixture of 30 percent oxygen and 70 percent Fig. 1. (Top) Side view of right hemi/ sphere of Macaca mnulatta. The dots on inferotemporal cortex show approximate 4, \site of entry of microelectrode passes. The passes in which the cells with receptive fields illustrated in Figs. I to 3 were recorded are designated with the letters A to E. (Middle) Coronal section through pass D, A B C DE illustrating the approximate locations of cells whose receptive fields are shown below or in Fig. 2. A, Allocortex; ce, central / Jsulcus; Cd, caudate nucleus; Cl, claustrum; GLD, lateral geniculate body; H, hippoGLD I D-1 campus; ip, intraparietal sulcus; 1, lunate D2/sulcus; la, lateral fissure; oi, inferior occipD-2 ital sulcus; Pu, putamen; ts, superior D-3 temporal sulcus; TA, TE, and TH desigD4 \nate cytoarchitectonic areas of von Bonin D-4 and Bailey (9). (Bottom) Size and position A *of receptive fields of three neurons recorded on pass D. Each rectangle is the largest rectangle oriented parallel or at 45 de-grees to the meridians of the visual field, which could be fitted entirely within each receptive field. In each case, the stimuli Lused to define the field were the most adeD -1 D-3 D-4 quate found. The cross in each figure represents the horizontal and vertical meridians of the visual field. The right visual 30 0 30Q field (which was always ipsilateral to the electrode) is shown on the right of each vertical meridian. All receptive fields shown are for the left eye. Unit DI, receptive field plotted with 1by 5-degree blue bar. Unit D-3, plotted with 1by 5-degree white bar, and 5by 10-degree dark rectangle. Unit D-4, plotted with 1by 5-degree white bar. The receptive field for Unit D-2 is shown in Fig. 2. The scale is in degrees of visual angle. 1303 on S etem er 4, 2019 http://sce.sciencem agorg/ D ow nladed fom nitrous oxide. Throughout the recording session the CO., content of the expired air was maintained between 3.5 and 4.2 percent, and rectal temperature was maintained at 370 to 39°C. The pupils were dilated with 0.3 percent scopolamine hydrochloride and covered with contact lenses selected with a slit retinoscope to bring the eyes in focus at a Polacoat tangent screen 57 cm away to an accuracy of + 0.5 diopter. The fovea and center of the blind spot of each eye was projected onto this screen with a reversible ophthalmoscope to an aCCuracy of about 0.5 degree. The position of the eyes was repeatedly checked throughout the experiment and virtually never drifted more than 2 degrees between readings. Glass-coated platinum-iridiuLm microelectrodes (8) were advanced with an Evarts microdrive (7). The signal from the microelectrode was led into a Grass P51 preamplifier (time constants, 3 and 0.03 msec) by way of a HIP 511 probe