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Publications scientifiques sur la vision

Visual receptive fields of single cells in the pigeon’s optic tectum

Jassik-Gerschenfeld and Guichard. 1972, Brain Research

Abstract Three hundred and ninety-four units within the optic tectum of pigeons were studied using extracellular recording. According to their receptive field properties, they were classified in 4 major classes. (1) Concentrically organized fields (6%), composed of a center ‘on’ and an antagonistic surround ‘off’, or the reverse. The center and the surround had identical spectral sensitivities. Motion of a white or black spot across the center-surround evoked equally strong responses for all directions of movement. (2) Cells with homogeneous ‘on’ or ‘off’ fields (1.3%) respond well to flashes of light, but have no antagonistic surround. (3) Movement selective cells (72%) respond preferentially to moving stimuli, and poorly or not at all to static spots. According to the size of their receptive fields these were classified as ‘small’ (2°), ‘middle’ (5°) and ‘large field’ (31°). Cells with ‘large fields’ were always found at the deepest part of the electrode penetration (1100 μm to 1400 μm). (4) Directionally selective cells (21%) respond optimally to motion of the spot in one direction ‘preferred’ and not to movement in the opposite direction ‘null’. They were always recorded in the superficial range of penetration, above 1000 μm. Although the cells in the pigeon's optic tectum seem to be preferentially stimulated by moving objects, directional selectivity appears to be a characteristic of the superficial tectal layers. These results, together with other studies, suggest that the ‘output’ of the pigeon's tectum might carry directionally coded signals.

Localization of directionally selective and movement sensitive cells in the optic tectum of the pigeon

J. Guichard, Vision Research – VISION RES, 1975

Most of the cells of the pigeon optic tectum are highly sensitive to an object moving through their receptive fields (Holden. 1969; Jassik-Gerschenfeld, Minois and Conde-Courtine 1970; Jassik-Gerschenfeld and Guichard. 1972). In previous papers (Jassik-Gerschenfeld et ai.. 1970; Jassik-Gerschenfeld and Guichard. 1972), we reported that these tectal units could be ctassified into two major groups: movement sensitive (72 per cent) and directionally selective cells (21 per cent). Movement sensitive cells are excited by a spot moving in any direction within the receptive field. Directionally selective cells, which are already present at the retinal level (Maturana and Frenk, 1963) respond optimally to a spot moving in a preferred direction and are inhibited by motion in the opposite direction. The bird’s optic tectum consists of alternating layers of cells and fibers which have been grouped from outwards to inwards into six strata: I-Opticum. 2-Griseu.m et Fibrosum Supeficiale, 3-Griscum Centrale. 4-Album Centraie, %Griseum Periventriculare. 6-Album Periventriculare. The aim of the present work was to determine whether there is any correlation between the responses properties of a unit and the tectal stratum in which it is found. To this purpose, the positions of both directionally selective and movement sensitive cells within the tectal strata were located by means of electrophoretic marking of the microelectrode path. The preparation of the animal. the recording system and the methods of stimulation were described in the previous papers (Jassik-Gerschenfeld et al., 1970: Jassik-Gerschenfeld and Guichard. 1972) and will be only summarized here, Pigeons (Cohba ticia) were paratysed with a continuous intravenous infusion of Flaxedil (14 mg/ml. 0.95 ml/H) and artificially ventilated by unidirectional airflow. Particular care was taken to block conduction of nociceptive impulses by using local anesthetics (Xylocaine) at all pressure points and incisions. The laternl surface of the left optic tectum was exposed and the dura was opened. A tungsten filament projector mounted on an adjustable tripod was used to explore the right visual fieid with moving spots of various shapes and sizes. Glass micropipettes filled with a saturated solution of methyl blue were used to record and to mark the recording sites. Extracellular action potentials were led through a cathode follower to oscilloscope and audiomonitor. An oscillograph camera was used to record the unit activity. The microelectrodes were mounted onto a mechanical microdrive fitted with a micrometer. They were at all times advanced horizontally so that the penetrations were performed within a 20” radius from the projection of the area centralis (Hamdi and Whitteridge. 1954). Arrival of the microelectrode tip at the tectal surface was controlled microscopicaiiy and signaled on the oscilloscope by a marked reduction of the background noise. At this point the micrometer reading was taken as zero. For the histological reconstruction of the electrode tracks, two or three marks were placed at various intervals along the penetration path. by electrophoretic injection of methyl blue dye (Thomas and Wilson, 1966). One of the marks was always piaced at the end of the penetration. The recording positions were later identified in frontal brain sections stained with fuchsin. The plane of the sections was parallel to the electrode track. A total of 227 cells were studied in 20 penetrations. Fig. 1(a) shows a histological reconstruction of the microelectrode track after one of such penetration. An electrode penetrating approximately perpendicular to the tectal surface encountered cells that had receptive fields located roughly in the same region of the visual field. so that the fields of individual units showed a great degree of overlap [Fig. l(c)]. Receptive fields became larger with increasing depth of penetration pig. l(c)] ; only a few exceptions were found to this trend [for example. unit number 7 in Fig. I(c)]. The receptive field properties of the nine units recorded along the penetration reconstructed in Fig. I(a) shown in Fig. I(b). Units number 1 and number 3 were directionally selective while all the others were movement sensitive cells. The directionally selective units, which had different preferred direction of motion, were located in the Stratum Griseum et Fibrosum Superficiale. Table 1 shows the distribution of 191 movement sensitive and 36 directionally selective cells in the different tectai strata. It is clear from this table that directionally selective cells are located exclusively in the Stratum Griseum et Fibrosum Superficiale and that movement sensitive cells are distributed throughout all tectal strata. The Stratum Griseum et Fibrosum Superficiale has been divided into IO layers by Cowan, Adamson and Powell (1961). Therefore it was of interest to try to determine in w.hich layer each cell could be located. Movement sensitive and directionally selective…