TEMPORAL ASPECTS OF CONTRAST VISUAL-EVOKED POTENTIALS IN THE PIGMENTED RAT - EFFECT OF DARK REARING

Cortical visual evoked potentials (VEPs) in response to gratings tempo rally modulated in counterphase were recorded in normal and dark-reare d pigmented rats. Temporal modulation was either sinusoidal (0.25-15 H z, steady state condition) or abrupt (0.5 Hz, transient condition). In normals, the amplitude spectrum of contrast VEPs has two peaks (at ab out 0.5 and 4 Dz) and a high temporal frequency cut-off of the order o f 11 Hz. The VEP phase lags with temporal frequency, showing two diffe rent linear slopes for separate frequency ranges (0.25-1 Hz and 1-7 Hz ) centred on the peaks of the curve. The different slopes correspond t o apparent latencies of 500 and 136 msec, respectively. Dark rearing r educed the cut-off frequency by about 3 Hz and increased apparent late ncies by about 42 msec in the low temporal frequency range and 30 msec in the high temporal frequency range. The latency of the first peak o f transient VEPs was increased by about 47 msec. Results indicate that the frequency response of rat contrast VEPs is qualitatively similar to that of other mammals (including human), albeit shifted to a lower range of temporal frequencies. Dark rearing significantly alters the V EP temporal characteristics, suggesting that visual experience is nece ssary for their correct development. Copyright (C) 1997 Elsevier Scien ce Ltd.