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

Abstract

SUMMARY1. We recorded extracellularly from 420 single units in area 18 in visually inexperienced kittens aged 7 days and dark-reared kittens aged between 3 and 12 weeks and from 60 single units in area 17 in dark-reared kittens aged 5 and 11 weeks.2. Visual deprivation generally depressed the maturation of area 18, although some features were affected more than others and certain developmental improvements still occurred. The percentage of visually responsive units in area 18 increased from 400 in 7-day-old kittens to about 75 % in dark-reared animals 10-12 weeks. At each age a proportion of cells was orientation biased (between 15 and 45 %) and these neurones appeared to be arranged in a crude columnar fashion. However, dark-rearing, from birth, prevented the development of a significant proportion of orientation-selective cells in area 18; no more than 5 % of neurones were orientationselective at any age. We found no major bias in the over-all distribution of preferred orientations of cells in area 18 in dark-reared kittens.3. Simple cells, which are found in area 18 even in very young, visually inexperienced kittens, persisted after dark-rearing, although most retained immature properties. Relatively few complex cells were found in area 18 in visually deprived animals.4. The majority of neurones in area 18 of dark-reared kittens were binocularly driven, many equally well by either eye; evidence for regional variation in ocular dominance (indicative of a columnar pattern) was found in these deprived animals.5. A laminar analysis in area 18 showed that percentages of non-oriented and orientation-biased cells changed little, if at all, in lower laminae (IV, V, and VI) but increased substantially in upper layers (above layer IV) in the absence of visual stimulation, over the first 12 post-natal weeks.6. A comparison of the effects of dark-rearing on areas 17 and 18 indicates that the normal development of visual responsiveness and specific receptive field properties is suppressed in both areas during the first 12 post-natal weeks. It is possible that area 17 has a greater degree of orientation selectivity than area 18 in young visually deprived kittens and this may reflect a difference in the type of afferent inputs.

Recovery of neurofilament following early monocular deprivation

“…The loss of NF-H with dark-rearing could initially be interpreted as evidence for a severe processing impairment given the importance of NF-H for maintenance of axon caliber and fast conduction velocity (Yamasaki et al, 1992 ; Ohara et al, 1993 ; Sakaguchi et al, 1993 ). Indeed the reduction of NF-H may contribute to visual system dysfunction that results from a period of dark-rearing (Blakemore and Van Sluyters, 1975 ; Buisseret and Imbert, 1976 ; Mower et al, 1981 ; Blakemore and Price, 1987 ). However, in the context of monocular deprivation, where one eye's anatomical and physiological characteristics are deeply abnormal, imposition of periods of darkness could provide a means to reduce eye-specific differences prior to introduction of normal visual experience and as a consequence enhance recovery.…”

Cortical plasticity and preserved function in early blindness

“…It is worth noting that binocular enucleation did not prevent the development of the initial crude clustering (Ruthazer and Stryker, 1996). However, binocular deprivation and blockage of afferents from the LGN reduced the density and precision of projections from area 17 to area 18 (Caric and Price, 1999, see also Blakemore and Price, 1987 Caric and Price, 1999). Therefore it seems that the initial clustering depends on spontaneous neural activity at the level of the Lateral geniculate nucleus (LGN) or cortex while the fine tuning of the clustering depends on sensory experience (Howard, 2002, see also Innocenti and Frost 1979; Innocenti et al, 1985).…”

Molecular Mechanisms at the Basis of Plasticity in the Developing Visual Cortex: Epigenetic Processes and Gene Programs

“…This notion derives from classical experiments combining sensory deprivation and electrophysiological analysis. While rearing animals in total darkness from birth delays the functional maturation of striate cortex and prolongs neuronal plasticity beyond its normal limits, 43,45,46 raising animals in an environment enriched in terms of sensory-motor activity and social stimulation accelerates visual system development and promotes a precocious closure of the CP. 47 How do Pv+ GABAergic neurons come into play in the regulation of the CP?…”