[Cognitive and visual functions in a sample of the aged population: analysis of evoked potentials]

There are significant changes of perception and cognition during aging. Goal of this study was to investigate these functions by means of evoked potentials, and to obtain normative data in older people for comparisons with cognitive disorders in the elderly.

Twenty three healthy subjects (14 women and 9 men), aged 59 to 82 years (average 68 years), were examined for auditory event-related potentials (AERP) and somatosensory event-related potentials (SERP) using pattern reversal stimulation with large squares (1 degree 10') and small vertical bars (10'). The exogenous components N1 and P2 in both AERP and SERP exhibited significantly longer latencies and higher amplitude in response to target stimuli compared to an indifferent stimulus, a fact attributable to selective attention mechanisms (AERP: N1 delay 8 ms, p < 0.001; P2 delay 11 ms, p < 0.05; increase in amplitude N1/P2 2.2 microV, p < 0.01; SERP: N1 delay 8 ms, p < 0.05; P2 17 ms, p < 0.01; increase in amplitude N1/P2 8 microV, p < 0.001). As for the endogenous components N2 and P3, there were no latency differences between the two modalities (N2: p < 0.4; P3a: p < 02; P3b: p < 0.2). Significant correlations were found between P3 latencies AERP and SERP (r = 0.56, p < 0.01). N1, P2, N2 and P3b latencies of the AERP and P3a, P3b of the SERP correlated significantly with age. The average annual increase was 3.9 ms for P3b AERP (p < 0.01) and 3.2 ms for P3b SERP (p < 0.01). These values are markedly higher than the data reported by other authors for groups of lower average age. In the VEP, an age-related increase was seen in the N70 latency (0.6 ms/year, p < 0.05) and in the P100 latency (0.8 ms/year, p < 0.05) in response to the smaller bars stimulus and in the N140 latency (1.2 ms/year, p < 0.01) in response to the larger squares stimulus.

We confirm an age-related increase in latencies of the AERP and SERP, which is markedly higher than the increase described in other studies with younger subjects. This finding is important to keep in mind in order to avoid false positives of cognitive deficits in older patients. The latencies of later components, compared with earlier components of the VEP, AERP and SERP are more dependent on age. This may suggest that there are universal aging influences on the neuronal conduction velocity. The latencies of the P3b SERP and N2 AERP were found to be correlated with the N140 VEP with the smaller bars stimulus. These findings suggest that parameters of some waves may be modulated by certain other factors than age.