Analysis of visual evoked potentials and background electroencephalographic activity in young and elderly subjects

New techniques developed in this laboratory to overcome the loss of information involved in conventional evoked potential averaging are applied here to visual evoked potential (VEP) in young and elderly normal subjects.

The techniques are based on statistical descriptions of the times and amplitudes of the electroencephalographic deflections recorded before (background) and after (evoked) a series of pattern reversal visual stimuli.

The elderly had a higher rate of background deflections at all electrode sites, but lower amplitudes at the occipital electrodes. The elderly had a lower rate of deflections during the period of evoked activity compared with the background period. The young had a higher degree of response deflection time locking and amplitude. The mean amplitude of the deflections recorded during the period of evoked activity was significantly greater in amplitude than the background deflections and greater than the amplitudes of the conventionally averaged VEP derived from the same data. Thus the lower amplitude VEPs seen in the elderly are due to their poor time locking and reduced amplification. Only 79% of the stimulus trials contributed deflections to the P1 response component in both young and elderly subjects and 63% to the N1. In young subjects, several of the new response parameters showed the presence of evoked response components that were not apparent in the conventionally averaged VEP derived from the same data.

The novel methods presented here provide a great deal of additional information that is unavailable when analyzing data using only conventional evoked potential averaging.