The organization and post‐natal development of area 18 of the cat's visual cortex.

Abstract

SUMMARY1. We made extracellular recordings from 1176 single units in area 18 of adult cats and kittens aged between 7 days and 10 weeks, and from 137 single units in area 17 in kittens aged between 12 days and 10 weeks.2. All cells examined in area 18 of adult cats were visually responsive, 84 % being orientation selective, 9 % orientation biased and 700 non-oriented. Orientation columns and ocular dominance columns were identified. There was an over-all bias towards horizontal and vertical in the distribution of preferred orientations in the rostal part of area 18, where we were recording.3. In area 18 of 7-day-old, visually inexperienced kittens the majority of cells (60 %) were visually unresponsive; the remainder were either non-oriented (250) or orientation biased (15 %), and no orientation-selective units were found. Nevertheless there seemed to be a rudimentary columnar system, even in the youngest animals, in that orientation-biased cells tended to occur in clusters with neighbouring neurones having similar orientation preferences. In normal animals of 3 weeks and younger we found that the distribution of preferred orientations of a sample of neurones in area 18 with receptive fields scattered over much of the left lower quadrant of the visual hemifield was biased to oblique orientations. 4. As in adult cats, most cells in area 18 in young kittens were binocularly driven, and periodic alternation of dominance along oblique penetrations, characteristic of ocular dominance columns, was sometimes seen, even at the earliest ages.5. Many of the developmental changes that we observed in area 18 occurred during the first 4 post-natal weeks. Orientation selectivity, orientation tuning, directionality and responsiveness of neurones matured rapidly over this period. The proportions of simple and complex cells were similar in kittens aged 4 weeks or more to those in adult cats, whereas prior to this most neurones that displayed an orientation preference appeared to be immature simple cells.6. A laminar analysis revealed that very few units in the superficial layers (I, II and III) in area 18 are visually responsive in kittens during their first and second weeks, but orientation selectivity rapidly develops during the third week. By contrast, even in very young, visually inexperienced kittens, the majority of neurones found in deeper laminae (IV, V and VI) are visually responsive and a few of them * To whom correspondence should be addressed.C. BLAKEMORE AND D. J. PRICE already show an orientation preference; however, the subsequent appearance of larger proportions of orientation-selective cells in these lower layers is a more prolonged process than in upper laminae.7. Comparison of the development of areas 17 and 18 suggests that, although the processes of maturation are generally similar in the two regions, there are some differences, which may be related to differences in the types of afferent input.

Development of Y‐axon innervation of cortical area 18 in the cat.

“…Milleret et al (1988) report that the percentage of binocularly activated cortical neurones increases dramatically from 33 to 72 % between 2 and 4 weeks of age with a further increase to 76% at adult. Blakemore & Price (1987) find very little change in binocularly activated cortical cells during the postnatal development of area 18 (100 vs. 95% in 1-week-old kittens vs. adult cats). Although the quantitative expression of the changing fraction of binocular cells varies somewhat between laboratories, it seems clear that the physiological development of binocularity in area 18 does not mirror that in area 17.…”

“…Although recent reports have described the postnatal development of receptive field properties of neurones in cortical area 18 (Blakemore & Price, 1987;Milleret, Gary-Bobo & Buisseret, 1988), little is known of the structural development of this cortical area and its major thalamic input. This lack of information is surprising since area 18 offers several distinct advantages for understanding the ontogeny of visual processing and of general cerebral cortex development.…”

Effects of dark‐rearing on the development of area 18 of the cat's visual cortex.

“…The positions of areal borders were located in Nissl-stained (Garey, 1971) and cytochrome-oxidase-stained (Price, 1985c) sections, and cortical laminae were defined in cytochrome-oxidase-stained material following the scheme described in Blakemore & Price (1987). The term 'c.o.…”

“…A retinotopic map of the contralateral visual hemifield has been described in area 18 in adult cats (Tusa, Rosenquist & Palmer, 1979) and in young kittens (Blakemore & Price, 1987), and such an organization is presumably also present in dark-reared kittens, since the eccentricity of receptive field centres in the visual field increased with distance from the area 17/18 border, in coronal planes that ran orthogonal to this boundary. Visual deprivation, for as long as 12 weeks, does not appear to disrupt the retinotopic organization of those neurones that are visually responsive, in at least the rostral part of area 18.…”

“…Induction and maintenance of anaesthesia and paralysis, assessment of the animal's anaesthetic state, surgical procedures, optical preparation, electrophysiological recording methods, the strategy for sampling single units, receptive field classification and the technique of histological reconstruction were all identical to those described in the previous paper (Blakemore & Price, 1987).…”