Science Topics – 100
Our study showed that the perception of touch relied on two signals: one from the skin to the brain and the other within the brain itself. The second signal relayed the first signal from a lower-level brain area to a higher area and then boomeranged it to the lower level. The higher brain area was required for touch perception, and its inactivation rendered mice unable to use the sensations in their footpads to discriminate different floor textures.
We observed the brains of mice after touching their paws and saw immediate activity in the sensory cortex, which is the brain area that receives signals from the skin. Unexpectedly, we recorded a second slower source of activity that was tens of milliseconds after the first. We investigated the source of this second activation and found that the high-level motor cortex received information from the sensory cortex and sent it back to the sensory cortex. These findings indicated that, for tactile perception, the flow of information from the skin to the brain required communication from not only the periphery to the brain but also a reverberation between two brain areas.
While it was previously thought that one signal from the skin to the brain was sufficient to produce touch sensation, this study revealed that, without the second signal, mice could not feel or use the incoming sensory information. These results suggested that they might not have been able to perceive the differences in texture. In order to investigate this idea, we trained mice to distinguish two different floor textures, rough or smooth, by associating one of them with a food reward. When we prevented the second signal by shutting off the responsible neurons with light-activated optical genetic technology, the mice could not distinguish the differences in floor texture.
Our results showed that a reverberant neural circuit from the sensory cortex to the higher motor cortex was required for the perception of touch. We speculate that this two-stage circuit design may be a safety mechanism that ensures continuous accurate perception, even when an animal is distracted by their other senses, such as when humans are feeling a steering wheel while they are concentrating on the road. This form of perception, which involves an external signal, and its internal rebound, may extend to other senses. We may find that the communication between brain areas refines perception to result in more accurate and integrated behavior.
Satoshi Manita†, Takayuki Suzuki†, Chihiro Homma, Takashi Matsumoto, Maya Odagawa, Kazuyuki Yamada, Keisuke Ota, Chie Matsubara, Ayumu Inutsuka, Masaaki Sato, Masamichi Ohkura, Akihiro Yamanaka, Yuchio Yanagawa, Junichi Nakai, Yasunori Hayashi, Matthew E. Larkum & Masanori Murayama, "A Top-Down Cortical Circuit for Accurate Sensory Perception", Neuron. 2015 Jun 3;86(5):1304-16.
Laboratory for Behavioral Neurophysiology, Brain Science Institute, RIKEN