karppaus.infon arkistoitu foorumi

Highlights
•Food restriction results in ATP savings via reduced AMPAR currents in visual cortex

•Concurrent increases in input resistance and resting potential preserve spike rate

•These changes amplify response variability, leading to broader orientation tuning

•Supplementation with the adipocyte-hormone leptin restores visual coding precision


Summary
Information processing is energetically expensive. In the mammalian brain, it is unclear how information coding and energy use are regulated during food scarcity. Using whole-cell recordings and two-photon imaging in layer 2/3 mouse visual cortex, we found that food restriction reduced AMPA receptor conductance, reducing synaptic ATP use by 29%. Neuronal excitability was nonetheless preserved by a compensatory increase in input resistance and a depolarized resting potential. Consequently, neurons spiked at similar rates as controls but spent less ATP on underlying excitatory currents. This energy-saving strategy had a cost because it amplified the variability of visually-evoked subthreshold responses, leading to a 32% broadening of orientation tuning and impaired fine visual discrimination. This reduction in coding precision was associated with reduced levels of the fat mass-regulated hormone leptin and was restored by exogenous leptin supplementation. Our findings reveal that metabolic state dynamically regulates the energy spent on coding precision in neocortex.

A new study published in the journal Neuron suggests that long-term reductions in caloric intake send the brain into a “power-saving” mode that cuts the amount of information it transmits to consume less energy. The findings, published by researchers from the University of Edinburgh, reveal how the fuel-guzzling human brain, which is responsible for up to 20% of our body’s energy consumption despite making up only 3% of its mass, tunes itself down in energy-scarce scenarios.

This change to the brain’s activity comes at a cost. “Basically, we have found the mechanisms that explain how the brain can enter low-battery mode. You need less energy, but you also function less well,” said Prof. Nathalie Rochefort, a fellow at the University of Edinburgh’s Centre for Discovery Brain Sciences and co-author of the paper, in an interview with Technology Networks.

Among the conclusions from the study was the confirmation that prolonged semi-starvation produces significant increases in depression, hysteria and hypochondriasis as measured using the Minnesota Multiphasic Personality Inventory. Indeed, most of the subjects experienced periods of severe emotional distress and depression.[1]: 161 

The rehab phase proved to be psychologically the hardest phase for most of the men with extreme effects including self-mutilation, where one subject, Sam Legg, amputated three fingers of his hand with an axe, though the subject was unsure if he had done so intentionally or accidentally.[6] Participants exhibited a preoccupation with food, both during the starvation period and the rehabilitation phase. Sexual interest was drastically reduced, and the volunteers showed signs of social withdrawal and isolation.[1]: 123–124  The participants reported a decline in concentration, comprehension and judgment capabilities, although the standardized tests administered showed no actual signs of diminished capacity. There were marked declines in physiological processes indicative of decreases in each subject's basal metabolic rate (the energy required by the body in a state of rest), reflected in reduced body temperature, respiration and heart rate. Some of the subjects exhibited edema in their extremities, presumably due to decreased levels of plasma proteins given that the body's ability to construct key proteins like albumin is based on available energy sources.