Effects of monocular strobe rearing on kitten striate cortex

Summary

Monocular deprivation in kittens does not lead to an ocular dominance shift in striate cortex if the visual stimuli do not contain contours. In the present study we sought to find out whether an ocular dominance shift is produced if the visual environment does contain contours but is devoid of motion. Six kittens were reared with one eye occluded in a visual environment that was lit only by the light of a stroboscope (2 flashes per sec). Exposure was started at 5–6 weeks of age after dark-rearing from birth and extended until 8–12 weeks of age for 8 h per day. The rest of the time was spent in total darkness. Thus, the animals were completely deprived of vision in one eye, while the other eye experienced only stationary flashing contours. Single units in area 17 of these animals were studied and compared to normally reared cats. In all six animals ocular dominance was clearly shifted towards the eye with strobe experience. The ocular dominance shift showed, however, the following interdependencies with other parameters: neurones that responded to stationary flashing test stimuli were nearly always dominated by the strobe eye; neurones that responded only to moving bars or edges remained binocular. In the normal control animals the ocular dominance distribution was similar for both groups of cells. Track analysis according to cortical lamination revealed that neurones in infragranular layers consistently showed a weaker OD shift towards the strobe eye than neurones in supragranular layers (including layer 4). Response latencies to stationary flashing stimuli were significantly shorter in the strobe-reared animals than in the normal controls. Orientation tuning was normal in all animals. Directional tuning was reduced after monocular strobe experience, but not by the same amount as described after binocular strobe rearing. The present results demonstrate that monocular visual experience reduced to stationary flashing contours is sufficient to produce on ocular dominance shift in striate cortex. This adds further support to existing notions about the role of nervous activity for changes in cortical connections. Cortical responses to afferent stimulation and the resulting correlated activation of pre- and postsynaptic neurones seem to be a prerequisite for a stabilization of synaptic connections.