Since leptin is released by fat cells, the researchers believe that its presence in the blood is likely to signal to the brain that the animal is in an environment where there is plenty of food and there is no need to conserve energy. The new work suggests that low levels of leptin warn the brain about the malnourished state of the body, and switch the brain to low-energy state.
“These results are exceptionally satisfactory,” he said Julia Harris, neuroscientist at the Francis Crick Institute in London. “It is not so common to obtain such a beautiful find that is so consistent with the existing understanding,”
Does neuroscience distort?
A major 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 inadvertently put into low-power mode. It is extremely common to limit the amount of food available to mice and other experimental animals in weeks before and during neuroscience studies to motivate them to perform tasks in return for a food reward. (Otherwise, animals would often rather just sit.)
“A really profound impact is that it clearly shows that food restrictions affect brain function,” Rochefort said. The observed changes in the flow of charged ions can be particularly important for learning and memory processes, she suggested, as they depend on specific changes that occur at the synapses.
“We need to think 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 open up completely new questions about how other physiological conditions and hormone signals can affect the brain, and whether different levels of hormones in the bloodstream can make individuals see the world a little differently.
Rune Nguyen Rasmussen, a neuroscientist at the University of Copenhagen, noted that humans vary in their leptin and overall metabolic profiles. “Does that mean that even our visual perception – even though we may not be aware of it – is actually different between people?” he said.
Rasmussen warns that the question is provocative with few solid hints of the answer. It appears likely that the mice’s conscious visual perceptions were affected by food deficiency because there were changes in the neuronal representations of these perceptions and in the animals’ behavior. However, we can not know for sure, “as this would require the animals to be able to describe to us their qualitative visual experience, and they obviously cannot do this,” he said.
But so far, there is also no reason to believe that the low-power state that the visual cortical neurons in mice, and its effect 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 member of the board of Simons Initiative for the Developing Brain, 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, an editorially independent publication of Simons Fund whose mission is to increase public understanding of science by covering research developments and trends in mathematics and physical and life sciences.