Effects of Acute Insulin-Induced Hypoglycemia on Spatial Abilities in Adults With Type 1 Diabetes

OBJECTIVE

To examine the effects of acute insulin-induced hypoglycemia on spatial cognitive abilities in adult humans with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Sixteen adults with type 1 diabetes underwent two counterbalanced experimental sessions: euglycemia (blood glucose 4.5 mmol/l [81 mg/dl]) and hypoglycemia (2.5 mmol/l [45 mg/dl]). Arterialized blood glucose levels were maintained using a hyperinsulinemic glucose clamp technique. During each session, subjects underwent detailed assessment of spatial abilities from the Kit of Factor-Referenced Cognitive Tests and two tests of general cognitive function.

RESULTS

Spatial ability performance deteriorated significantly during hypoglycemia. Results for the Hidden Patterns, Card Rotations, Paper Folding, and Maze Tracing tests were all impaired significantly (P ≤ 0.001) during hypoglycemia, as were results for the Cube Comparisons Test (P = 0.03). The Map Memory Test was not significantly affected by hypoglycemia.

CONCLUSIONS

Hypoglycemia is a common side effect of insulin therapy in individuals with type 1 diabetes, and spatial abilities are of critical importance in day-to-day functioning. The deterioration in spatial abilities observed during modest experimental hypoglycemia provides novel information on the cerebral hazards of hypoglycemia that has potential relevance to everyday activities.Hypoglycemia is a common side effect of insulin treatment of diabetes. Strict glycemic control limits the development and severity of vascular complications of diabetes, but hypoglycemia is a frequent consequence. Strict glycemic control can increase the incidence of severe hypoglycemia by threefold (1). Hypoglycemia has an adverse effect on cognitive functions, as the human brain relies solely on glucose as its source of energy (2). It has a pronounced effect on complex cognitive tasks both in diabetic and nondiabetic individuals, whereas simple mental tasks are relatively unaffected (2). Cognitive function deteriorates when arterialized blood glucose concentrations decline to <3.0 mmol/l (3–6). Simple and choice reaction times, speed of mathematical calculation, verbal fluency, attention, memory, and psychomotor function have all been demonstrated to be affected during hypoglycemia (7–10). The recovery of different aspects of cognitive function may vary from between 40 and 90 min after restoration of blood glucose to normal (2,11).Whereas hypoglycemia impairs many domains of cognitive function, the effect of hypoglycemia on spatial cognitive abilities has not been investigated in detail, although spatial ability is undoubtedly a component of some of the tests used to assess other aspects of cognition (12). Spatial abilities may be defined as the ability to generate, retain, retrieve, and transform or manipulate structured visual images to orientate and interpret the surrounding environment. In real-life terms, spatial ability is concerned with how human beings deal with issues concerning two- and three-dimensional objects, space, navigation, and pathfinding. Practical daily cognition often involves inferring how shapes and objects will appear and function when they are rotated or otherwise oriented or viewed differently. In everyday interactions with the environment, this process is very important, with particular relevance for complex tasks such as driving and map reading. A large variety of mental tests are available for the assessment of spatial abilities. Largely, these tests can be separated into tests of spatial perception, namely the ability to determine spatial relations despite distracting information; spatial visualization, which is the ability to manipulate complex, multistep spatial information; and mental rotation, which is the ability to rotate two- or three-dimensional figures in one''s mind (13). The present study was designed to investigate the effects of acute insulin-induced hypoglycemia on spatial abilities in adults with type 1 diabetes, using a well-characterized battery of spatial tests that incorporate all of these components of spatial cognition.