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Impairment and Recovery of Elementary Cognitive Function Induced by Hypoglycemia in Type-1 Diabetic Patients and Healthy Controls

Departments of Endocrinology and Metabolism (R.L., G.P., K.W., H.L.) and Neurology (H.G.O.M.S., H.-J.H.), Magdeburg University Medical School, 39120 Magdeburg, Germany

Address correspondence and requests for reprints to: Prof. Dr. med. Hendrik Lehnert, Dr. R. Lobmann, Otto-von-Guericke-Universität Magdeburg, Medizinische Fakultät, Zentrum für Innere Medizin, Klinik für Endokrinologie und Stoffwechselkrankheiten, Leipziger Str. 44, 39120 Magdeburg, Germany. E-mail: hendrik.lehnert{at}medizin.uni-magdeburg.de

Although neuroendocrine changes after induction of hypoglycemia, in patients with diabetes and healthy persons, are thoroughly investigated, cognitive adaptation processes are still insufficiently understood. Changes in cognitive functions are mainly investigated by psychometric tests, which represent a summation of different cognitive processes. We aimed at dissecting cognitive adaptation into single components, i.e. stimulus selection, response choice, and reaction speed during a hyperinsulinemic hypoglycemic clamp in patients with type-1 diabetes and matched healthy controls. Using novel neurophysiological analyses, the event-related potentials of early stimulus selection (selection negativity) and response selection (lateralized readiness potential) were studied, in addition to reaction time (RT). A total of 12 diabetic patients and 12 normal volunteers were studied while receiving a hyperinsulinemic hypoglycemic clamp. RTs and the event-related potentials related to stimulus selection and response selection were significantly delayed during hypoglycemia in both groups, whereas early evoked potentials (P100) were unaltered. This suggests that hypoglycemia delays stimulus selection, with the consequence that also central and motor processing are delayed. In addition, patients with diabetes showed an earlier negative shift over the frontal cortex, which, when compared with the controls, reveals better adaptation to hypoglycemia in frontal cortical brain regions. After restoration of euglycemia stimulus selection, response selection and RT returned to baseline level in the type-1 group. In the control group, however, response selection and RTs were still delayed. This suggests that type-1 patients, possibly because of the past occurrence of hypoglycemic events, might be able to better cope with the hypoglycemic state than healthy volunteers who lack such a history. In summary, our data demonstrate, for the first time, that cognitive adaptation processes to an experimental hypoglycemic episode can clearly be dissected into their single components.

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