The human brain is bombarded with all kinds of information, from the memory of last night's delicious dinner to the instructions from your boss at your morning meeting. But how do you "tune in" to just one thought or idea and ignore all the rest of what is going on around you, until it comes time to think of something else? Researchers at the Kavli Institute for Systems Neuroscience and Centre for the Biology of Memory at the Norwegian University of Science and Technology (NTNU) have discovered a mechanism that the brain uses to filter out distracting thoughts to focus on a single bit of information. Their results are reported in xxx issue of Nature.
Think of your brain like a radio: You're turning the knob to find your favourite station, but the knob jams, and you're stuck listening to something that's in between stations. It's a frustrating combination that makes it quite hard to get an update on swine flu while a Michael Jackson song wavers in and out. Staying on the right frequency is the only way to really hear what you're after. In much the same way, the brain's nerve cells are able to "tune in" to the right station to get exactly the information they need, says researcher Laura Colgin, who was the paper's first author. "Just like radio stations play songs and news on different frequencies, the brain uses different frequencies of waves to send different kinds of information," she says.
Gamma waves as information carriers
Colgin and her colleagues measured brain waves in rats, in three different parts of the hippocampus, which is a key memory center in the brain. While listening in on the rat brain wave transmissions, the researchers started to realize that there might be something more to a specific sub-set of brain waves, called gamma waves. Researchers have thought these waves are linked to the formation of consciousness, but no one really knew why their frequency differed so much from one region to another and from one moment to the next.
Information is carried on top of gamma waves, just like songs are carried by radio waves. These "carrier waves" transmit information from one brain region to another. "We found that there are slow gamma waves and fast gamma waves coming from different brain areas, just like radio stations transmit on different frequencies," she says.
You really can "be on the same wavelength"
"You know how when you feel like you really connect with someone, you say you are on the same wavelength? When brain cells want to connect with each other, they synchronize their activity," Colgin explains. "The cells literally tune into each other's wavelength. We investigated how gamma waves in particular were involved in communication across cell groups in the hippocampus. What we found could be described as a radio-like system inside the brain. The lower frequencies are used to transmit memories of past experiences, and the higher frequencies are used to convey what is happening where you are right now."
If you think of the example of the jammed radio, the way to hear what you want out of the messy signals would be to listen really hard for the latest news while trying to filter out the unwanted music. The hippocampus does this more efficiently. It simply tunes in to the right frequency to get the station it wants. As the cells tune into the station they're after, they are actually able to filter out the other station at the same time, because its signal is being transmitted on a different frequency.
The switch