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Motor Control by Sensory Cortex

By a Whisker Every student learns that the sensory cortex is used for processing sensation and the motor cortex is used for perceiving movement. However, in the real world, this may not always be so neatly arranged. Matyas et al. (p. 1240) have found that sensory and motor fields are specialized for different types of movement, such that in mice the motor cortex controlled the forward movement (protraction) of their whiskers and the sensory cortex controlled backwards movements (retraction) of whiskers. So if a whisker hits an object, then a reasonable first reaction might be a motor command for retraction. Similarly, the motor cortex stimulates protraction for more active exploration. Hence, the sensory cortex is also motor and the motor cortex is also sensory. In an ecological context, these combined reactions offer a repertoire useful for a mouse seeking food and shelter in a complex environment. Mouse whisker movements are controlled by both the sensory and motor cortex. Classical studies of mammalian movement control define a prominent role for the primary motor cortex. Investigating the mouse whisker system, we found an additional and equally direct pathway for cortical motor control driven by the primary somatosensory cortex. Whereas activity in primary motor cortex directly evokes exploratory whisker protraction, primary somatosensory cortex directly drives whisker retraction, providing a rapid negative feedback signal for sensorimotor integration. Motor control by sensory cortex suggests the need to reevaluate the functional organization of cortical maps.