P3 latency and symbol digit performance correlations in aging.

Relationships among age, P3 latency, and Symbol Digit Modalities Test (SDMT) performance were investigated for 172 subjects ranging from 20 to 79 years. Age-related increases in P3 latency were most evident for older normal subjects (greater than 55 years) and for a subset of subjects with low physical fitness levels, but were negligible for a subset of subjects with high physical fitness levels. A similar relationship was found between age and SDMT. P3 latency and SDMT performance were significantly correlated for older subjects with low fitness levels but not for young (less than 55 years) subjects or subjects with high fitness levels. Partial correlation analyses indicated a significant relationship between P3 latency and SDMT performance that was independent of age. These results agree with previous studies suggesting that P3 latency provides a sensitive measure of age- and/or health-related processes affecting CNS function and cognitive performance. Careful attention to nonpathologic subject variables and use of age-adjusted norms are important considerations for clinical use of P3 latency.