A surprising new role for motor cortex, Nature Neuroscience publication
A lion is chasing a zebra across the African savanna. For both animals, choosing the right movement at the right time is a matter of life and death. Accordingly, a large part of the mammalian brain is devoted to the control of movement: The motor cortex.
Many previous studies have investigated how neuronal activity in motor cortex might be involved in causing movements. In a new study, published on 31.10, 2016 in Nature Neuroscience, scientists from the Humboldt-Universität zu Berlin report that – surprisingly – neuronal activity in motor cortex is suppressing movement, rather than causing it.
We have long known that motor cortex is arranged like a remarkable ‘map’ of the body (see figure). We also know that important body parts, like the human hand, have a large representation in motor cortex. For different animals, different body parts are important. For example, rats live in dark tunnels and are night-active, so they must sense the world around them by moving their whiskers. Thus, the whisker-region of rat motor cortex is very large.
The group of Berlin scientists decided to investigate the neuronal activity in rat motor cortex. The scientists observed that during various forms of whisker touch (e.g. whisking during social interactions, or whisking to investigate an object), neurons in whisker motor cortex reduced their activity (see figure).
This made the scientists wonder if perhaps, when rats do not want to whisk, activity in motor cortex neurons is blocking whisker movements. And perhaps, the activity in motor cortex has to decrease in order for rats to start whisking.
To test if this might be the case, the scientists performed two additional experiments, which both agreed with their theory: Artificially increasing motor cortex activity lead to whisker retraction, as if to abort whisker touch. Similarly, artificially reducing motor cortex activity increased whisker movements, as if to engage in whisker touch.
Professor Michael Brecht, who led the study, says: “This brain region is named motor cortex because it was thought to be a kind of motor, which generates movement. For us, it was therefore incredibly surprising to see the animals generate more movements, when we blocked motor cortex. Our results show, that – at least sometimes – motor cortex is actually more like a brake.”
The discovery of such an unexpected role of motor cortex might be very important, for example when designing therapies for patients with neurological damage to the motor system.
Above:Both the human brain and the rat brain contains a ‘map of the body’ in motor cortex (marked in red). Important movements, like rat whisker movements, have a large representation in motor cortex.
Below:Activity of a single neuron (vertical lines) in whisker motor cortex is strongly suppressed during various forms of whisking behavior, in this case, during a social interaction with another rat.
Ebbesen, C.L., Doron, G., Lenschow, C. & Brecht, M. (2016) Vibrissa motor cortex activity suppresses contralateral whisking behavior. Nature Neuroscience doi:10.1038/nn.4437
Contact: Prof. Dr. Michael Brecht
Bernstein Center for Computational Neuroscience Berlin
Humboldt-Universität zu Berlin
Philippstr. 13, Haus 6
Tel: +49 (0) 30 2093 6770