Receptive Field Properties of Single Units From the Visual Projection to the Ipsilateral Tectum in the Frog

Abstract

The receptive field characteristics of single visual units in the ipsilateral tectum of the frog were investigated. In contrast to units in the contralateral tectum, ipsilateral units all responded to small visual stimulus objects and gave a sustained response to a small stationary black disk. Inhibition of this sustained response by a moving edge some distance from the ERF could be demonstrated and was more marked than with contra-lateral units. Some of the deeper ipsilateral units, in addition to the properties already mentioned, were excited by decremental dimming of the background illumination. The type of behaviour known as 'changing contrast detection' (class 3 units) in the contralateral tectum was not found ipsilaterally. The main projection of the retinal ganglion cells in the frog is to the contra-lateral optic tectum. Stimulation of the eye by light will, however, also produce electrical activity in the ipsilateral tectum [Rensch, 1955; Zagorul'ko, 1957]. Gaze [1958] and Gaze and Jacobson [1962] showed that this projection of the visual field upon the ipsilateral tectum was retinotopically arranged and Keating and Gaze [in preparation] have recently reinvestigated the fibre pathways concerned. The present paper reports the receptive field properties of single visually-excited units recorded from the superficial layers of the ipsilateral tectum. A preliminary report of this work has appeared elsewhere [Gaze and Keating, 1967]. METHODS The methods used were the same as in the immediately preceding paper. RESULTS The receptive field characteristics of 210 single units in the visual projection to the ipsilateral tectum have been investigated in 19 normal frogs. The excitatory receptive fields (ERFs) of most units studied were 5-8° across. It was not possible to subdivide the units into classes based on their differential responses to moving or stationary objects since, in contrast to contralateral units, the ipsilateral units display remarkably uniform field properties. The units respond to movement of small disks or edges 2-10° in size but do not respond to movement of larger objects across the field. This lack of response to larger objects is attributed to the presence of an inhibitory surround to the ERF. Perhaps the most obvious feature of all the ipsilateral units is their * Barry Stevens Memorial Fellow, Mental Health Research Fund. 143 I-. 144 G(aze anid Keating, responise to a standing, edge birought inito the ERF and lheld there stationcarv. In response to suclh 1a stinmulus the units'slhow sustainied firing, tlle duratioln of a BG cff BG cn (.) c _I (> 15~ BG off BG on d sec. Fic. 1. A unit found on the surface of the ipsilateral tecttum. (a) Sustained response to a 3° disk held stationary within the receptive field. 'I'he stus-tained iesponse is ihihibited by a transient step to darkness anid reappears on re-illumination of the stationary disk. The photocell moinitors the level of backgroulnd illuminationl. (b) The unit shows Ino response to changes in background illuminlation alone. (c) The un...

The role of the dorsal thalamus in visual processing and object selection: a case of an attentional system in amphibians

“…Background‐ and context‐dependent effects on the spike discharge of tectal neurons have been reported in several studies in anurans (Grüsser‐Cornehls et al. , 1963; Gaze & Keating, 1970; Tsai & Ewert, 1988). In the study of Plethodon by Schülert & Dicke (2005), suppression of spike discharges on presentation of a cricket dummy (the SI, also used in the present study) inside the ERF of a tectal neuron was found when another prey stimulus was moved outside the ERF.…”

Spatial and Temporal Organization of the Binocular Input to Frog Optic Tectum

“…A topographical representation of the superior portion of the anterior binocular visual field has been found on the rostral optic tectum in which an exact retinal correspondence of the two multi-unit, monocular receptive fields was reported [Gaze and Jacobson, 1962], The ipsilateral tectal projection is not a direct retinal projection but is thought to be derived, multisynaptically, from the contralateral tectum [Keating and Gaze, 1970], Earlier single-unit studies have characterized some of the properties of the direct contralateral fibers and the ipsilateral afferents, but without consideration of the spatial and temporal relationships between the two [Maturana et al, 1960;Grusser and Grusser-Cornehls, 1970;Gaze and Keating, 1970]. The demonstration of binocularly-driven neurones deep in the rostral optic tectum [Fite, 1969] suggests the possibility of a functional capacity for binocular vision in the frog, although stereoscopic depth perception has yet to be proven or disproven [Fite, 1974;Ingle, 1972].…”

Isthmotectal axons maintain normal arbor size but fail to support normal branch numbers in dark‐reared Xenopus laevis

“…It is possible that rostrocaudal gradients play little or no role in the placement of these arbors and that a random process, assisted by spontaneous activity in local tectal circuitry, helps to establish the arbors and to maintain TZ size. There may be considerable amounts of spontaneous activity in the axons of dark‐reared animals, particularly because several classes of both retinotectal and isthmotectal axons fire at high levels in response to low light levels under normal circumstances (Gaze and Keating,1970; Chung et al,1974), and isolated adult retinas display spontaneous ganglion cell firing in the dark (J.A. Demas, H.L.…”