Because leptin is released by fat cells, scientists think its presence in the blood is likely a signal to the brain that the animal is in an environment where there is plenty of food and no need to conserve energy. The new work suggests that low levels of leptin alert the brain to the malnourished state of the body, causing the brain to go into an energy-saving mode.
“These results are extremely satisfying,” said Julia Harris, a neuroscientist at the Francis Crick Institute in London. “It is not so common to obtain such a beautiful find that is so in line with the existing understanding”,
An important implication of the new findings is that much of what we know about how brains and neurons work may have been learned from brains that researchers unknowingly put into energy-saving mode. It is very common to limit the amount of food available to mice and other laboratory animals weeks before and during neuroscience research to motivate them to perform tasks in exchange for a food reward. (Otherwise, animals would often rather just hang out.)
“A really profound impact is that it clearly shows that food restriction affects brain function,” Rochefort said. The observed changes in the flow of charged ions may be especially important for learning and memory processes, she suggested, because they depend on specific changes taking place at the synapses.
“We have to think very carefully about how we design experiments and how we interpret experiments if we want to ask questions about the sensitivity of an animal’s perception or the sensitivity of neurons,” Glickfeld said.
The results also raise brand new questions about how different physiological states and hormone signals might affect the brain, and whether different levels of hormones in the bloodstream might cause individuals to see the world differently.
Rune Nguyen Rasmussen, a neuroscientist at the University of Copenhagen, noted that people differ in their leptin and general metabolic profiles. “Does that mean that even our visual perception – although we may not be aware of it – actually differs between people?” he said.
Rasmussen cautions that the question is provocative, with few solid hints for the answer. It seems likely that the mice’s conscious visual perceptions were affected by food deprivation, as there were changes in the neuronal representations of those perceptions and in the animals’ behavior. We can’t know for sure, though, “because this would require the animals to be able to describe their qualitative visual experience to us, and of course they can’t,” he said.
But so far, there is also no reason to believe that the energy-saving mode of the visual cortical neurons in mice, and its impact on perception, will not be the same in humans and other mammals.
“These are mechanisms that I think are really fundamental to neurons,” Glickfeld said.
Editor’s note: Nathalie Rochefort is a board member of the Simons Initiative for the Developing Brain, which is funded by the Simons Foundation, the sponsor of this editorially independent journal. Maria Geffen is a member of Quanta’s advisory board.
Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation, whose mission is to advance public understanding of science by covering research developments and trends in mathematics and the natural and life sciences.
This post The brain has a ‘low-power mode’ that dulls our senses
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