DEVELOPMENT OF THE TEMPORAL PROPERTIES OF VISUAL-EVOKED POTENTIALS TOLUMINANCE AND COLOR CONTRAST IN INFANTS

We have studied the development of the temporal characteristics of the pattern visual evoked potentials (P-VEPs) in response to contrast rev ersal of patterns of low spatial frequency (0.1 c/deg) of either pure luminance contrast (yellow-black plaid patterns) or pure colour contra st (equiluminant red-green plaid patterns) in 15 infants between 6 and 30 weeks of age. High contrast patterns were modulated temporally eit her sinusoidally at various temporal frequencies to elicit steady-stat e responses, or abruptly at a low temporal frequency to elicit transie nt responses. Analysis of both the transient and steady-state response s suggests the existence of three different mechanisms contributing to the infant and adult P-VEP responses at low, medium and high temporal frequencies. The responses at the three different temporal frequency ranges have different time constants; and develop at different rates. The low frequency response predominates at 8 weeks, where it spans the range 1-6 Hz with an apparent latency of about 230 msec, for both col our and luminance stimulation. This response increases in bandwidth an d decreases in latency progressively with age, at a similar rate for l uminance and colour contrast, up to 14 weeks. After 14 weeks, the lumi nance response undergoes major changes, with the emergence of a new re sponse with a shorter latency (about 100 msec) and a peak activity nea r 10 Hz. This mid-frequency response matures further with age, until i t dominates the whole response of the adult P-VEP to luminance contras t. It also makes a contribution to the chromatic response at frequenci es above 10 Hz, generating the characteristic double-peaked amplitude response in adults. However, its contribution is very limited below 10 Hz, where the response latency is 140 msec in adults, as it was at 14 weeks of age. A third component is evident at very high temporal freq uencies of the luminance response as early as 6 weeks, extending up to 15 Hz in 8-week-olds and up to 25 Hz for older infants. It remains ap parent up to 18 weeks, thereafter being swamped by the major mid-frequ ency response. The apparent latency of response over this frequency ra nge is about 70 msec at all ages. The development of transient P-VEPs paralleled that of the steady-state P-VEPs. At all ages there was an e arly negative component (N70) at about 70 msec, corresponding to the f ast steady-state response at high frequencies for luminance contrast. Before 14 weeks, the luminance and chromatic transient response had th e same morphology, with a single major peak of similar latency to the apparent latency of the low temporal frequency response. After this ag e, the morphology of the luminance response changed, particularly in t he first 100 msec, consistent with the emergence of the mid-frequency response. We discuss whether the high-frequency component may represen t pre- or early post-synaptic cortical activity, already mature by 8 w eeks, and how the different maturation rates of the mid and high-frequ ency components may reflect different intra-cortical circuitry for col our and luminance. Copyright (C) 1996 Elsevier Science Ltd.