The Projection of the Rat's Visual Field on the Cerebral Cortex

Abstract

The rat's visual field is represented on the cortex of each cerebral hemisphere within a primary visual area, visual field to the rat's right side upon the left hemisphere, and vice versa. The pattern of the representation has been determined electrophysiologically. The part of the visual field commanded by both eyes together, which is ahead of the animal, secures a larger representation upon the cortex in proportion to its size than the rest of the field, which is commanded by only one eye.There is evidence that a second smaller representation exists immediately lateral to the primary area.THE rat is a mammal with laterally directed eyes, widely used in laboratory studies involving visual discrimination. Where and how its visual field is projected upon the cerebral cortex was determined by Lashley [1934] who used anatomical methods to demonstrate the arrangement quadrant by quadrant. The present account describes an electrophysiological investigation of the same question. METHODSEighteen hooded rats weighing from 170 g. to 300 g. were used, and also some albino rats for comparison. The hooded rats were more satisfactory; their visual acuity, tested by their discrimination of gratings, is approximately two to four times better than that ofalbino rats [Lashley, 1930]; this difference occurs in part because the albino iris excludes light poorly. When the image on the back of the excised albino rat eye is photographed from behind the eye, the optimum exposure time varies less than 100 per cent when the pupil area is varied by a factor of 100, which suggests that a large amount of light is entering through the iris. It is impracticable to photograph the image on the back of the excised eye of a hooded rat, since the image is dispersed by the pigment present in the choroid.Anaesthesia was induced with ether and continued with a-chloralose (British Drug Houses), 140 mg./kg. given intraperitoneally. 160 mg. a-chloralose was dissolved in 20 ml. water at 100TC. and the required volume immediately cooled to 40TC. and injected. Further doses were given as required after about 5 hr. to maintain aniesthesia. In some preliminary experiments [Sefton and Swinburn, 1964], paraldehyde (1 ml./kg.) was injected intraperitoneally instead of chloralose. Satisfactory anaesthesia was obtained for 12-14 hr. with chloralose, and longer with paraldehyde.A polythene endotracheal cannula was inserted through an incision in the trachea and threaded up through the mouth and then down into the lower trachea; the neck incision could then be closed and a stable airway was available from mouth to trachea. Oxygen was administered by a fine tube within the cannula at about 3-5 ml./min., which exceeds the resting oxygen consumption of the rat [Simpson-Morgan, 1965].

The primary visual system of the rat: A primer of its anatomy

“…More recently, the primary visual area has been defined by the transport of radioactively labeled proteins (Drager, 1974) and electrophysiological map-PRIMARY VISUAL SYSTEM OF THE RAT 163 ping (Adams & Forrester, 1968;Montero, 1973;Montero, Rojas, & Torrealba, 1973). In each of these cases, the presented data show quite good agreement with the earlier anatomical observations of K.S.…”

“…With the same eye the image of a human hand 2 meters distant was easily recognizable and the outlines of buildings and the movements of automobiles two blocks away could be traced." However, it should be noted that Lashley's observations were based on images formed on the sclera, which is somewhat behind the actual receptors so that his estimates are somewhat in error (Adams & Forrester, 1968). Nonetheless, the rat clearly possesses an optical system capable of detailed vision and certainly is not hypermetropic as sugested by Vincent (1912).…”

Interaction of Egocentric and World-Centered Reference Frames in the Rat Posterior Parietal Cortex

“…6) and the population tuning for ECD was distributed nonuniformly to the sides of the rat (mean vector ϭ 91°, p Յ 0.01) with a tendency to cluster toward the central visual fields of each eye ( Fig. 7C; Adams and Forrester, 1968). Given this observation, we hypothesized that the PPC might have a role in the online control of goal-directed navigation.…”

“…C, Tuning for the population of cells with ECD properties is distributed to the sides of the rat (mean vector ϭ 91°, p Յ 0.01; left hemisphere green; right hemisphere orange). Black semicircles indicate approximate rat visual field (Adams and Forrester, 1968). Note, some cells with tuning toward the periphery of the visual field wrap to the opposite visual field so that the mean tuning direction is behind the rat and outside of the visual field (e.g., A # 3 and Fig.…”

Second and third visual areas of the cat: interindividual variability in retinotopic arrangement and cortical location

“…In rodents (Thompson, Woolsey & Talbot, 1950;Adams & Forrester, 1968;Hughes, 1971;Driger, 1975) V2 is a mirror image of VI. In monkeys V2, the representation of the horizontal meridian is split into two branches which K. ALBUS AND R. BECKMANN Zeki, 1969Zeki, , 1977van Essen & Zeki, 1978).…”