Brain's response to attention is studied

LA JOLLA, Calif., Sept. 30 (UPI) -- U.S. scientists say reductions in the firing rates of the brain's background nerve cells occur when monkeys intensely focus on a visual stimulus.

Salk Institute researchers in La Jolla, Calif., said that finding is important because a reduction in firing rates of nerve cells not involved in the attention-demanding task contribute more to the improved attention than does the increase in firing rates of the neurons responding to the stimulus.

Until now, it had been assumed an increase in the activity of neurons responding to a stimulus was the primary cause of improvements in perceptual discrimination that result from attention, the scientists said.

The researchers recorded responses of neurons in an area of the brains of two macaque monkeys that processes visual information. Nerve responses were recorded when the monkeys were and were not directing attention to a visual stimulus.

"What we found is that attention also reduces background activity," said Jude Mitchell, first author of the study. "We estimate that this noise reduction increases the fidelity of the neural signal by a factor that is as much as four times as large as the improvement caused by attention-dependent increases in firing rate."

The research is reported in the journal Neuron.