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Brain Cells Need to Follow Specific Rhythms for Proper Functioning

by VR Sreeraman on  April 29, 2009 at 12:41 PM Research News   - G J E 4
 Brain Cells Need to Follow Specific Rhythms for Proper Functioning
Two studies at Stanford University have revealed that brain cells need to follow specific rhythms for proper brain functioning.

Such rhythms are apparently not working in tandem in diseases like schizophrenia and autism.
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But, the new studies have shown that precisely tuning the oscillation frequencies of certain neurons can affect how the brain processes information and implements feelings of reward.

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"A unifying theme here is that of brain rhythms and 'arrhythmias'," Nature quoted Karl Deisseroth, MD, PhD, associate professor of bioengineering and of psychiatry and behavioral sciences and senior author of both papers, as saying.

An arrhythmia, according to cardiologists, is a seriously irregular heartbeat.

The new findings suggest that, like the cells that keep the beat of the heart (or the coxswain on a rowing team that calls out the rhythm of the strokes), certain brain cells can orchestrate oscillations that ultimately help govern behaviour of other cells that are guided by those rhythms.

In the first study, the researchers focused on neurons in mice that produce a protein called parvalbumin.

Researchers have hypothesized that these neurons drive "gamma" brain waves that oscillate at a frequency of 40 times a second (or Hertz), and might affect the flow of information in the brain.

However, this has not been proved till date, because no one could selectively control the neurons and see the resulting effect on the information flow, or oscillations.

"But this is exactly the kind of thing now that we can address using optical methods," said Deisseroth.

Now, the researchers have developed a technique, called optogenetics, in which specific cells could be genetically engineered and could be controlled by pulses of visible light.

The team did this with parvalbumin neurons in mice and found that by exciting or inhibiting them, they could produce or suppress "gamma" waves and see a marked change in the "bit rate" or quantity of information flowing through brain circuits.

Deisseroth added: "The final outcome of this is that parvalbumin neurons and gamma oscillations work together to enhance the flow of real information in the brain."

And the potential link to disease comes from the fact that in autism the gamma oscillations appear to be present at the wrong intensity, while in schizophrenia there appear to be too few parvalbumin neurons.

In the second study, researchers investigated the effect of controlling the oscillations of neurons that emit the brain chemical dopamine and aimed to see if varying the oscillations led freely behaving mice to sense varying levels of reward.

For the study, they optogenetically engineered dopamine neurons in a specific area of the brains of the mice and then placed the mice into a box with three chambers in a row.

Initially, none of the mice had a predictable preference for which chamber to occupy.

But, later, the researchers exposed them to two days of conditioning in which their engineered dopamine neurons were exposed to high-frequency pulses of light while in a chamber on one end, and low frequency pulses while in the chamber on the other end.

Specifically, the mice were split into two groups in which the different stimuli were associated with opposite ends of the box. Finally, the mice were placed in the middle chamber and exposed to no further light pulses.

Each of the mice preferred to return to whichever chamber it was in when its dopamine neurons were subjected to the high-frequency light pulses, indicating that firing dopamine neurons at high-frequency rhythm correlates with stronger reward learning.

In some sense, the papers suggest that people who aren't thinking clearly or feeling happy might just be out of step, or rather have brain cells that quite literally don't have rhythm.

The first study was published in Nature, while the second one was published in Science.

Source: ANI
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