How the selfish brain organizes its supply and demand

Abstract

During acute mental stress, the energy supply to the human brain increases by 12%. To determine how the brain controls this demand for energy, 40 healthy young men participated in two sessions (stress induced by the Trier Social Stress Test and non-stress intervention). Subjects were randomly assigned to four different experimental groups according to the energy provided during or after stress intervention (rich buffet, meager salad, dextrose-infusion and lactate-infusion). Blood samples were frequently taken and subjects rated their autonomic and neuroglycopenic symptoms by standard questionnaires. We found that stress increased carbohydrate intake from a rich buffet by 34 g (from 149 ± 13 g in the non-stress session to 183 ± 16 g in the stress session; P < 0.05). While these stress-extra carbohydrates increased blood glucose concentrations, they did not increase serum insulin concentrations. The ability to suppress insulin secretion was found to be linked to the sympatho-adrenal stress-response. Social stress increased concentrations of epinephrine 72% (18.3 ± 1.3 vs. 31.5 ± 5.8 pg/ml; P < 0.05), norepinephrine 148% (242.9 ± 22.9 vs. 601.1 ± 76.2 pg/ml; P < 0.01), ACTH 184% (14.0 ± 1.3 vs. 39.8 ± 7.7 pmol/l; P < 0.05), cortisol 131% (5.4 ± 0.5 vs. 12.4 ± 1.3 μg/dl; P < 0.01) and autonomic symptoms 137% (0.7 ± 0.3 vs. 1.7 ± 0.6; P < 0.05). Exogenous energy supply (regardless of its character, i.e., rich buffet or energy infusions) was shown to counteract a neuroglycopenic state that developed during stress. Exogenous energy did not dampen the sympatho-adrenal stress-responses. We conclude that the brain under stressful conditions demands for energy from the body by using a mechanism, which we refer to as “cerebral insulin suppression” and in so doing it can satisfy its excessive needs.

Beliefs about willpower determine the impact of glucose on self-control

“…We do not doubt that glucose is the major fuel of cerebral processes (14,37). Indeed, because the brain cannot afford to run out of glucose, the body contains redundant mechanisms to ensure its supply (14,19,38).…”

Overweight Adolescents and Life Events in Childhood

“…41,42 Previous work has also shown that under conditions of stress, the brain triggers changes in metabolism that can lead to excessive weight gain. 43 Strengths of our study include its relatively large, prospective, and socioeconomically and geographically diverse sample. Of the studies that measured negative life events as we did, 7,10,13 our study included the most detailed measure.…”

The "selfish brain" hypothesis for metabolic abnormalities in bipolar disorder and schizophrenia

“…80 Stressed individuals, however, show these neuroglycopenic symptoms even at normal blood glucose level, corresponding to a state of energetic deficit in the brain. 41 Interestingly, individuals have also been reported to develop mood symptoms after a stressful experience, and these were, as were neuroglycopenic symptoms, reversed after energy supplementation. 41 Energy deficit disrupts normal brain functions; therefore, brain homeostasis is directly linked to the system's capacity of achieving energetic balance.…”

“…Previous studies have shown that acute mental stress increases brain energy consumption by 12%. 42 In the study by Hitze et al, 41 exposure to stress increased the intake of carbohydrates, but not of fat and protein. Carbohydrate consumption, as expected, increased blood glucose, however with no subsequent increase in insulin among stressed individuals.…”

“…Systemically, there is activation of the hypothalamic-pituitary-adrenal (HPA) axis and of the sympathetic nervous system (SNS), which together inhibit the absorption of glucose in the periphery, increasing its availability to the CNS and promoting an increase in appetite and food intake. 39 This theory was tested by Hitze et al, 41 who exposed individuals to a stressful situation and subsequently to a buffet with different types of food. Blood samples were collected throughout the study.…”