Loss of temporal lobe beta power in young adults with type 1 diabetes mellitus.

Cognitive defects have been reported in type 1 diabetes mellitus with possible correlation to recurrent episodes of hypoglycemia. The purpose of the present study was to identify signs of brain dysfunction with quantitative EEG in adults with insulin-dependent (type 1) diabetes. Patients (n = 49) with type 1 diabetes and controls (n = 51) were recruited. All patients had good glycemic control, no diabetic polyneuropathy and a minor history of severe hypoglycaemia. EEG was recorded for 15 min following a standardized protocol, power spectra were obtained from 236-584 s of artefact-free EEG from each subject and EEG was repeated in diabetic patients after 3 and 9 months. The most pronounced finding was a loss of fast oscillations (alpha, beta and gamma activity) in both posterior temporal regions, with p< 0.001 for beta and p< 0.05 or 0.01 for alpha and gamma activity in the diabetes patients. A decrease in beta activity was also present bilaterally in the anterior temporal and occipital regions (p< 0.05 or 0.01). The alpha peak frequency was lower in patients than in controls, with reductions bilaterally in the temporo-central regions (p< 0.01). These changes were not found to correlate to a previous history of hypoglycaemia. The alpha and beta power showed a high test-retest reliability at both 3 and 9 months (0.88-0.92). The focal decrease in temporal lobe fast activity suggests that these brain regions are preferentially affected by type 1 diabetes. This abnormality may be related to the mechanism underlying the cognitive dysfunction described in diabetes.