Parvocellular and magnocellular visual processing in spinocerebellar degeneration and Parkinson's disease: an event-related potential study.

OBJECTIVE: We recorded event-related potentials (ERPs) using appropriate visual stimuli to establish a non-invasive method that separately investigates the parvocellular (P) and magnocellular (M) visual functions, and to evaluate the visual function in spinocerebellar degeneration (SCD) and Parkinson's disease (PD).
METHODS: Eight SCD and 10 PD patients were compared with 11 age-matched control subjects. In the P-task, subjects were required to discriminate equiluminant red (frequent) and green (rare) random dots. In the M-task, moving random dots on a rotating cylinder (frequent) and those moving irregularly (rare) were discriminated.
RESULTS: Control subjects showed an endogenous positive component at 400 ms (P400(p)) with an early exogenous negative potential (N160(p)) in the P-task. In the M-task, N160(m) and P400(m) were recorded. A deuteranope lacked P400(p) with normal P400(m). In SCD, P400(p) latency and N160(p)-P400(p) interval were increased with normal N160(p) latency. N160(m) latency was also increased while N160(m)-P400(m) interval was normal. In PD, there were no significant changes in the P-task but P400(m) latency was increased with normal N160(m) latency.
CONCLUSIONS: SCD patients may have not only abnormal higher processing in the P-pathway but abnormal fundamental processing in the M-pathway. PD may have impaired higher processing of the M-pathway with the preserved P-function.