H Kennedy

The influence of eccentricity on receptive field types and orientation selectivity in areas 17 and 18 of the cat

The premise that different visual cortical areas fulfil distinct functional roles leads one to suspect differences in their neuronal properties. We have investigated the spatial properties of areas 17 and 18 neurons of the cat as part of a more extensive study aimed at exploring the influence of stimulus movement parameters. In the original description of areas 17 and 189,1°, differences in receptive field (RF) types between the two areas were taken as an indication that serial processing took place at this level. Subsequent studies 7,13,14,21, which however excluded the representation of central vision or were limited to either 17 or 18, have shown that RF types in these two areas are more similar than initially described. Here we compare RF types and dimensions, orientation selectivity and ocular dominance of areas 17 and 18 neurons recorded over a range of eccentricities including neurons with RFs near the fixation point. The experiments were carried out on 13 anesthetized (N20/O2; 70 ~ :30 ~ ) and paralyzed cats (details of procedure are given elsewhereZ6). Single units were studied qualitatively with hand-held stimuli on a plotting table placed at 86 cm from the cat. The RF dimensions were measured from the minimum discharge field plotted according to Kato et al. 11 with a narrow moving slit of light (0.1-0.4 °) after optimization of the stimulus parameters. Preferred orientation and width of orientation tuning were hand plotted with long moving light or dark bars except for hypercomplex cells where shorter bars of optimal length were used. Only criteria related to the dimension or organization of the RFs were used for classification since functional properties such as velocity sensitivity or sharpness of orientation tuning may differ between areas 17 and 18. Three criteria were used to classify neurons: (1) the spatial disposition of subregions; (2) the width of the discharge region for a narrow moving slit, and (3) the absence or presence of end-zone

Functional changes across the 17–18 border in the cat

SummaryChanges in velocity sensitivity, receptive field (RF) position, and RF size were investigated in long oblique penetrations crossing the 17–18 border. The penetrations were histologically reconstructed and the border determined by cytoarchitectonics. In cortex subserving central and paracentral vision change in velocity sensitivity allowed a reasonable physiological identification of the 17–18 border. The physiological border correlates well with the histological border zone, best with its medial edge. Changes in RF position and RF size are of little use for physiological identification of the border in this region. In this cortical region area 18 representation of the vertical meridian (VM) has a high magnification factor. In cortex subserving peripheral vision, the change in velocity sensitivity was small and the change in RF position coincided with the cytoarchitectonics.

Behavioural and Neurophysiological Correlates of Visual Movement Deprivation in the Cat

The paradigm that we shall use in this chapter is the influence of sensory restriction on the development of the physiology of the visual and visuo-motor system. Conclusions drawn from this work are pertinent to the understanding this work are pertinent to the understanding of neural mechanisms operant in the normal animal. We have used a quantitative approach which is particularly interesting in that it provides, in mechanistic terms, a description of neuronal deficits in deprived animals. Before proceeding to an overview of our work, we shall situate the selective rearing paradigmboth historically and in the context of recent advances in the study of the epigenetic processes governing neural development.

Rf structure and visual cortical latencies

AbstractResponse latency to moving slits was measured from the spatial lag-velocity plots (Bishop et al., 1971) of areas 17 and 18 neurons recorded in anaesthetized (N2O/O2) and paralysed cats. The 480 neurons for which latency information was available were also classified into S, B, C & A families (Orban & Kennedy, 1981; Orban, 1984). In area 18 there was little difference in the average latency between the four families. In area 17, large field cells (A & C families) had shorter latencies than cells with narrow fields (S and B families). However when the comparison was limited to cells with equal velocity sensitivity (more precisely with similar upper cut-off velocity), all four families had similar average latencies both in areas 18 and 17. Within the S and A families, cells having a single OFF subregion (S1 or Al OFF cells) had significantly longer latencies than those having a single ON subregion (SI or Al ON cells) or those having ON and OFF subregions (A2 or S2 cells). These results show (a) that ...