Because leptin is released by fat cells, scientists believe that its presence in the blood probably signals to the brain that the animal is in an environment where there is plenty of food and no need to conserve energy. New work suggests that low leptin levels alert the brain to the body’s malnutrition, putting the brain into low-power mode.
“These results are unusually satisfying,” said Julia Harris, a neuroscientist at the Francis Crick Institute in London. “It’s not that common to get such a beautiful finding that is so consistent with existing understanding,”
A significant implication of the new findings is that much of what we know about how the brain and neurons work may have been learned from brains that researchers have unwittingly put into low-power mode. It is extremely common to restrict the amount of food available to mice and other experimental animals for weeks before and during neuroscience studies to motivate them to perform tasks in exchange for a food reward. (Otherwise, animals would often prefer to just sit.)
“One 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 could be particularly relevant to learning and memory processes, she suggested, because they rely on specific changes occurring at synapses.
“We have to think really 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 a neuron,” Glickfeld said.
The results also raise entirely new questions about how other physiological states and hormonal signals can affect the brain, and whether different levels of hormones in the bloodstream can cause individuals to see the world a little differently.
Rune Nguyen Rasmussen, a neuroscientist at the University of Copenhagen, noted that people differ in their leptin and overall metabolic profiles. “So does this 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 firm indications of an answer. It seems likely that the mice’s conscious visual perceptions were affected by food deprivation because there were changes in the neural representations of those perceptions and in the animals’ behavior. We can’t know for sure, however, “because that would require the animals to describe their qualitative visual experience to us, and they obviously can’t do that,” he said.
But for now there is also no reason to think that the low-power regime activated by 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 Brain Development Initiative, funded by the Simons Foundation, sponsor of this editorially independent magazine. Maria Geffen is a member of the advisory board for Quanta.
Original story reprinted with permission from Quanta Magazine, editorially independent publication Simmons Foundation whose mission is to improve public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.