The topography of the P1 component of the flash visual evoked response.

The scalp topography of the P1 component of the human flash visual evoked response was investigated by means of the biologic brain mapping system. Thirty subjects, ranging in age from 21 to 84 years, had flash visual evoked responses recorded using the standard 10-20 electrode positions referred to a balanced noncephalic reference. The subjects were divided by age into three groups: young, middle and old. A P2 component was recorded over the occipital region for all three groups and a frontal negative component was found to occur concurrently with the P2 occipital component. Neither the young or the middle age groups showed an identifiable P1 component. However this component was clearly present in the older group at 76 msec. The distribution of this component was more widespread anteriorly than the P2 component. In both the middle and the older age groups an earlier frontal negative component was present at around 75 msec; no such component was recordable in the young. This work suggests that the development of the P1 component during middle age is preceded by the development of a frontal negative component of around the same latency.