Because leptin is released from fat cells, scientists believe its presence in the blood likely signals the brain that the animal is in an environment where food is plentiful and there is no reason to conserve energy. The new work suggests that low levels of leptin alert the brain to the body’s malnutrition state and put the brain into a power-saving mode.
“These results are unusually satisfactory,” said Julia Harris, a neuroscientist at the Francis Crick Institute in London. “It is not so common to get such a beautiful finding that is so consistent with the existing understanding,”
A key 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 have unknowingly put into sleep mode. It is common to restrict the amount of food given to mice and other experimental animals for weeks before and during neuroscience studies to motivate them to perform tasks in return for a food reward. (Otherwise, animals would often prefer to just sit around.)
“One really profound effect is that it clearly shows that food restriction affects brain function,” Rochefort said. The observed changes in the flow of charged ions could be of particular importance for learning and memory processes because they are based on specific changes at the synapses.
“We have to think really carefully about how we design experiments and how we interpret experiments if we’re going to ask questions about the sensitivity of an animal’s perception or the sensitivity of neurons,” Glickfeld said.
The findings also raise entirely new questions about how other physiological states and hormone signals might affect the brain, and whether different levels of hormones in the bloodstream might cause people to see the world slightly differently.
Rune Nguyen Rasmussen, a neuroscientist at the University of Copenhagen, found that people differ in their leptin and overall metabolic profile. “Does that mean, then, that even our visual perception — while we may not be aware of it — is actually different between people?” he said.
Rasmussen warns that the question is provocative and offers few solid clues as to the answer. It seems likely that the mice’s conscious visual perceptions were affected by food deprivation because there were changes in the neuronal representations of these perceptions and in the animals’ behavior. But we can’t know for sure, “because to do that, the animals would have to be able to describe their qualitative visual experience to us, and they obviously can’t do that,” he said.
But so far, there’s also no reason to believe that the low-power mode activated by the visual cortical neurons in mice and its effects on cognition 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, sponsor of this editorially independent magazine. Maria Geffen is a member of the Advisory Board for quantum.
Original story Reprinted with permission from quanta magazine, an editorially independent publication Simons Foundation whose mission is to improve public understanding of science by covering research developments and trends in mathematics and the natural and life sciences.