How brain maintains activity balance

Ever wondered how we constantly adjust and adapt our social behaviour in response to external stimuli? A mechanism in the brain automatically does that for us.

Maladjustment of this mechanism, called the E/I ratio, may result in inappropriate behaviour, finds the study.

"If this E/I balance is broken, it completely alters your perception of the world," said study co-author Massimo Scanziani, a professor of neurosciences at Howard Hughes Medical Institute.

"You will be less able to adjust and adapt appropriately to the range of stimulation in a normal day without being overwhelmed or completely oblivious.

"And E/I imbalances may be most easily noticed in social interactions because these interactions require such nuance and subtle adjusting," he added.

Researchers discovered the mechanism that involves processes that control whether a neuron relays information to other neurons or suppresses the transmission of information.

There is a constant ratio between the total amount of pro-firing stimulation that a neuron receives from the thousands of excitatory neurons that feed into it, and the total amount of red-light stop signalling that it receives from inhibitory neurons.

"Neurons in our brain drive by pushing the brake and the accelerator at the same time," said Scanziani.

"There is always a tug-of-war. It's weird but very clever. It allows the brain to exert very subtle control on our response to stimuli," he explained.

Scientists have also proposed that some neuro-degenerative diseases, such as Parkinson's and Huntington's disease, may be associated with a shift in the E/I balance.

"Now that we know how this E/I balance is regulated in a normal brain, we can begin to understand what goes wrong in the diseased state.

"It paves the way for interventions that might restore the balance in the brain," said lead author Minghan Xue from the University of California, San Diego.

In terms of clinical applications, the scientists said that neurological diseases such as autism, epilepsy and schizophrenia are believed to be a problem, at least in part, of the brain's ability to maintain an optimal E/I ratio.

The findings were published online in the journal Nature.