Two Types Of Brain Cells

Your own brain thwarts diet with 'feed me' signals

When dieters starve themselves of calories, they starve their brain cells as well. New research finds that these hungry brain cells then release "feed me" signals, which drive hunger, slow metabolism and may cause diets to fail.

When the researchers created mice whose brain cells couldn't send out the signals, or appetite-increasing proteins, and these mice were leaner and ate less than normal after being starved.

"We generated a mouse that lacked this process in these neurons," study researcher Rajat Singh, of Albert Einstein College of Medicine in the Bronx, New York, said. "What we find is these mice eat less in response to a starvation challenge; they are leaner and they are healthier."

The starvation mechanism and feelings of hunger produced by these neurons is signaled through a process called autophagy (which literally means "self-eating") in which the cell breaks down its used parts. It does this to recycle the used parts, but also to harvest energy.

Most brain cells keep their autophagy at a steady level and don't respond to starvation. These appetite-sensing neurons are different, the researchers found, and are now the only known brain cells to ramp up autophagy in times of starvation.

This increased breakdown increases cellular levels of compounds called free fatty acids. Higher levels of fatty acids signal these special brain cells to release the appetite-inducing protein, which is called agouti-related peptide (AgRP).

"These neurons sense nutrients in the body and tell the body it's time to eat, time to stop eating ," Singh told LiveScience. "When you are hungry, there is this process in the brain that gets upregulated and that makes you eat."

Body Odd: Why diet food is so unsatisfying

Turning down appetite When the researchers turned off autophagy in the hypothalamus of mice, AgRP levels stayed low, as did levels of free fatty acids. These changes stopped the hunger signaling during times of starvation. When compared with normal mice, the mutant mice were about 10 percent leaner, were able to burn more energy, were more active and also ate less after food was withheld.

Living in Flatland « The Connectome

In other words, mice (and probably humans) measure distance mainly on a same plane  that’s level with their eyes. Like a broken odometer , our place and grid cells simply don’t “clock” vertical movement. As far as those cells are concerned, we might as well be living in Flatland .

The upside of this is that when it comes to horizontal movement – such as navigating a maze – mice and men can  keep a detailed memory for specific spots, and  orient themselves very precisely relative to other locations. Unless you’re like me, that is, and need GPS to find your way from the front door to the driveway.

Anyway, what does all this lack of height-sensing mean for those with vertigo – or just your basic acrophobia ? Well, as Jeffery points out, we clearly do have some instinctive sense of “very high” as opposed to “a little high” – but exactly how our brains encode that difference isn’t quite as well understood.

It’s likely that our sense of height has more to do with depth perception, and with an instinctive fear of visible drop-offs , than with any sense of personal distance or location – in other words, we aren’t able to use our bodies to sense how much higher we’re climbing, but we can look down/out and see that the ground ahead is farther away than we’d like it to be. Thus, one way to calm vertigo is simply to close your eyes .

Without that visual feedback, you’ll be back to  Flatland in no time.

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