Effects of flash mode and intensity on P2 component latency and amplitude

Alzheimer's disease (AD) groups manifest flash visual-evoked potential (VEP) P2 component delays compared to healthy control groups. However, using P2 latency to categorize individual patients and controls yields low accuracy. Additionally, several laboratories have failed to replicate the basic between group P2 latency findings. The sporadic failure to find the P2 delay and, when found, its failure to classify patients and controls accurately may reflect the use of non-optimal stimuli or recording sites.

This was a parametric investigation of stimulation and recording methods in healthy college students.

Using an extended recording montage of 64 electrodes, 10 stimulus conditions (5 flash intensities through open and closed eyes) were evaluated for their P2 effects.

The optimal recording site (O2) yielded the most reliable latencies and amplitudes across a range of stimulus intensities. Flash intensity did not affect P2 latency or amplitude. Flashes delivered through closed eyelids produced a flash VEP but delivery through open eyes produced a pattern VEP lacking a flash P2 component.

This accounts for the failure of some laboratories using open eyes to replicate the P2 delay in AD groups.

Optimal flash VEP conditions include closed eyes and recording from O2. Flash intensity is unimportant.