A different part of the brain handles stronger, more imposing sensations, Moore said. The primary sensory neocortex, a particular feature of mammals, has the distinction of allowing an animal to purposely pay attention to more subtle sensations. It's the difference between the feeling of gently brushing a fingertip along a wood board to assess if it needs a bit more sanding and the feeling of dropping the wood board on a foot.
Before anything else in the paper, the researchers confirmed that mice naturally produce a 40-hertz gamma rhythm in their sensory neocortex sometimes. Then they optogenetically generated that gamma rhythm with precise pulses of blue light. Mice with this rhythm could more often detect the fainter vibrations the researchers supplied to their whiskers than could mice who did not have the rhythm going in their brains.
Control and optogenetically stimulated mice alike had been conditioned to indicated their detection of a supplied stimulus by licking a water bottle. The vibrations provided to the mice to sense covered a span of 17 different levels of detectability.
The team's hypothesis was that the gamma rhythm of the stimulated neurons, because they inhibit the transmission of sensation messages by pyramidal neurons in the neocortex with a structured periodicity, actually orders the pyramidal messages into a more coherent and therefore stronger train.
"It's not surprising that these synchronized bursts of activity can benefit signal transmission, in the same way that synchronized clapping in a crowd of people is louder than random clapping," Siegle said.
This idea suggested that the timing of the rhythm matters.
So in another experiment, Siegle, Pritchett, and Moore varied the onset of the gamma rhythm by increments of 5 milliseconds to see whether it made a difference to perception. It did. The mice showed their increased sensitivi
|Contact: David Orenstein|