How Your Brain Blocks Out Unwanted Thoughts and Memories

If you don't want to think about a fight you had with your sister yesterday, a scary movie you watched recently or the source of that nasty smell on the subway, you're going to need some GABA.

A new, small study suggests that GABA, or gamma-Aminobutyric acid, plays a key role in suppressing unwanted thoughts and memories in a region of the brain called the hippocampus. GABA is a neurotransmitter, or chemical messenger, that's found throughout mammals' central nervous systems.

The new finding offers insight into how humans pull off the daily mental task of squashing down thoughts they don't want to think about, according to the study, which was published Nov. 3 in the journal Nature Communications. The study also provides clues as to what goes wrong in the brains of people with illnesses such as schizophrenia, in which people have trouble suppressing intrusive thoughts, the researchers said. [10 Things You Didn't Know About the Brain]

In the study, the researchers looked at the brains of 24 young, healthy subjects as they tried to suppress or recall memories. They found that the study participants with more GABA in their hippocampi were better at controlling which thoughts and memories popped into their minds compared with the people who had less GABA. And the less GABA that people had in their hippocampus, the less control they wielded over the wild, ceaseless churning of their minds.

But measuring the amount of GABA in a person's brain isn't exactly simple to do.

To do so, the researchers had to get clever: They employed an expensive, somewhat rare technique known as magnetic resonance spectroscopy, or MRS. Though costly and difficult to use, MRS has a key advantage over more typical brain scans: It lets researchers look at not just the general shape and density of subjects' brains but also their specific chemical content. So, with the aid of MRS, the researchers were able to sort their subjects into high-GABA and low-GABA groups.

With the technique to measure GABA levels in place, the scientists then focused on studying the subjects' abilities to suppress thoughts and memories.

Here, the researchers used a simple game. The participants were given a controller with two buttons. They were told to press the left button when certain colors showed up on the screen and the right button when other colors appeared. The participants played this game over and over until they were pressing the correct buttons without thinking about it.

But then the researchers introduced a new rule: Don't press the button if a tone sounds. This made the game much harder; the players had to control their habit of immediately pressing a button, and stop their fingers from flicking forward when the tone played just after a color appeared.

Neuroscientists use this kind of test to measure a person's control over their thoughts and memories. The players who did a better job of avoiding button pressing were assumed to have better control over their remembered impulses.

The study found that the people in the high-GABA group were significantly better at the game than the people in the low-GABA group.

So what does this mean? First, it directly links GABA in the hippocampus to the ability to suppress memories, expanding neuroscientists' understanding of how memory recall works in the brain.

The findings also suggest that mental illnesses such as schizophrenia, which are associated with low levels of GABA, might involve a lack of the basic memory-suppressing chemical tools, the researchers said in a statement.

In people with such mental health conditions, a lack of GABA may be involved in allowing unwanted thoughts and memories to overwhelm the mind, the researchers said. The new study included a small number of young, healthy people, and more research is needed to see if the findings hold up in different groups of people, as well as to better understand how GABA plays a role in memory.

Originally published on Live Science.