Abstract

Objective: Early nocturnal sleep enhances the consolidation of declarative memories acquired during prior wakefulness. Patients with type 1 diabetes mellitus (T1DM) frequently experience hypoglycemic episodes during sleep. We investigated whether short-lasting hypoglycemia during early nocturnal sleep affects the sleep-associated consolidation of declarative memories.

Research Methods: Sixteen T1DM patients and 16 healthy subjects matched for age and BMI were tested. On one condition, a linear fall of plasma glucose to 2.2 mmol/l was induced within 60 min by infusing insulin during early sleep. On the control condition, euglycemia (> 3.86 mmol/l) was maintained throughout the night. In the morning, subjects recalled word-pairs learned in the preceding evening. To assess mood and attention, a symptom questionnaire, an adjective check list and the Stroop test were applied. Also, auditory event related brain potentials (ERP) were recorded.

Results: Following euglycemia, subjects recalled 1.5 ± 0.5 more word-pairs than following hypoglycemia (P < 0.01), remembering 2.0 ± 0.6 more word-pairs than at immediate recall before sleep (P = 0.002). Across the hypoglycemic night, no such gain occurred (+0.5 ± 0.6 words; P = 0.41). Hypoglycemia during sleep also impaired mood (P < 0.05), but did not affect attention. Effects were well comparable between T1DM patients and healthy controls.

Conclusions: Our findings indicate specific sensitivity of declarative memory consolidation during sleep to rather short episodes of mild hypoglycemia. This effect may disable memory processing in T1DM patients prone to nocturnal hypoglycemic episodes and underlines the importance of considering sleep as a critical period in the treatment of these patients.