Cognitive impairment correlates to low auditory event-related potential amplitudes in type 1 diabetes

Type 1 diabetes may be associated with a mild decline in cognitive function and mostly in mental speed. In order to study the pathophysiology of this, we have investigated auditory event-related potentials (AERP) and their relation to cognitive function in diabetes patients. AERP was recorded in patients with type 1 diabetes (n=119) and in a healthy control group (n=61). AERP was obtained with an odd-ball and a two-stimulus paradigm. Cognitive function was evaluated in 10 domains in the patients. Patients had normal N100 latency, but a highly significant decrease in auditory N100 amplitude (p<10(-6)), which correlated with a decrease in psychomotor speed but not with function in other domains. Psychomotor speed also correlated with P300 amplitude, although P300 amplitude was only slightly decreased in the patients. Even stronger correlations were found with the parietal N100-P300 peak-to-peak amplitude, which correlated both to psychomotor speed (rho=0.61, p<10(-7)) and processing speed (p<0.005). P300 latency was increased in patients, and this correlated to low global cognitive score and older age. We conclude that the decline in psychomotor speed in type 1 diabetes is associated with a highly significant decrease in the auditory N100 peak amplitude. This association and the relatively small abnormality in P300 latency is quite different from those generally found in dementia, and suggest that the underlying defect is located in the brain stem or the white matter. Presumably small conduction defects in ascending fibers can distort the firing synchrony necessary for signal generation in the cortex.