Moderate hypoglycaemia after learning does not affect memory consolidation and brain activation during recognition in non-diabetic adults

In a sweet mood? Effects of experimental modulation of blood glucose levels on mood-induction during fMRI

Glucose is the primary source of energy for the human brain. Previous literature has shown that varying blood glucose levels may have a strong impact on behaviour, subjective mood, and the intensity of the BOLD signal measured in fMRI. Therefore, blood glucose levels varying even within the normal range may interact with cognitive and emotional processing as well as BOLD signal. Here, in a placebo-controlled, double-blind crossover study on 20 healthy women, we show that overnight fasting, compared to an elevated glucose condition, influences brain activation and the affective state during mood induction. Results indicate that our brain may compensate for low glucose levels during fasting by stronger recruitment of the brain areas relevant to the task at hand. Additionally, we systematically tested the effect of prior cognitive effort on behavioural and neural patterns and found that elevated activation is only associated with maintained performance as long as no prior cognitively challenging task is administered. Prior cognitive effort leads to deteriorated performance and a further increase in emotion-associated brain activation in the pregenual anterior and posterior cingulate, the superior frontal gyrus, and the pre-SMA. These results are in line with the strength model of self-regulation. Our results corroborate the strength model of self-regulation and extend it to affect regulation processes. Additionally, our observations suggest that experimentally controlling for fasting state or glucose levels may be beneficial, especially when studying processes that involve self-regulation.

The effects of acute hypoglycaemia on cognitive function in type 1 diabetes

Throughout life with type 1 diabetes mellitus people with the condition are exposed to multiple episodes of hypoglycaemia associated with insulin therapy. Hypoglycaemia affects several domains of cognitive function. Studies in non-diabetic adults and in people with type 1 diabetes have shown that almost all domains of cognitive function are impaired to some degree during acute hypoglycaemia, with complex tasks being more greatly affected.

The specific cognitive functions of attention and memory are both profoundly impaired during hypoglycaemia. These cognitive processes are fundamental to the performance of many day to day tasks. Their impairment disrupts everyday life and raises safety concerns for the pursuit of activities such as driving.

Mood and emotion are also negatively affected by hypoglycaemia, resulting in tense tiredness, while motivation is reduced, and anger may be generated in some individuals. Hypoglycaemia can cause embarrassing social situations, and may lead to chronic anxiety and depression in people with type 1 diabetes.

At present few therapeutic measures can modify or ameliorate the effects of hypoglycaemia on cognitive function, so instigation of measures to prevent exposure to hypoglycaemia is of major clinical importance, while preserving good glycaemic control.

Brain activation during working memory is altered in patients with type 1 diabetes during hypoglycemia

OBJECTIVE

To investigate the effects of acute hypoglycemia on working memory and brain function in patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging during euglycemic (5.0 mmol/L) and hypoglycemic (2.8 mmol/L) hyperinsulinemic clamps, we compared brain activation response to a working-memory task (WMT) in type 1 diabetic subjects (n = 16) with that in age-matched nondiabetic control subjects (n = 16). Behavioral performance was assessed by percent correct responses.

RESULTS

During euglycemia, the WMT activated the bilateral frontal and parietal cortices, insula, thalamus, and cerebellum in both groups. During hypoglycemia, activation decreased in both groups but remained 80% larger in type 1 diabetic versus control subjects (P < 0.05). In type 1 diabetic subjects, higher HbA(1c) was associated with lower activation in the right parahippocampal gyrus and amygdala (R(2) = 0.45, P < 0.002). Deactivation of the default-mode network (DMN) also was seen in both groups during euglycemia. However, during hypoglycemia, type 1 diabetic patients deactivated the DMN 70% less than control subjects (P < 0.05). Behavioral performance did not differ between glycemic conditions or groups.

CONCLUSIONS

BOLD activation was increased and deactivation was decreased in type 1 diabetic versus control subjects during hypoglycemia. This higher level of brain activation required by type 1 diabetic subjects to attain the same level of cognitive performance as control subjects suggests reduced cerebral efficiency in type 1 diabetes.

Is hypoglycaemia dangerous?

Tight glycaemic control (TGC) for patients treated in an intensive care unit ICU is associated with an increased risk for hypoglycaemia. Since hypoglycaemia mainly occurs in the sickest patients, no matter whether TGC is applied or not, it might be a marker for severity of illness or a harmful event in itself. Furthermore, it remains a matter of debate whether harmful effects of hypoglycaemia outbalance the clinical benefits of TGC. This review focusses on the clinical manifestations of hypoglycaemia in the critically ill and highlights its potential short- and long-term consequences specifically concerning neurocognitive function.