Neural Control of Locomotion in the Decorticate Cat

The acute decorticate (thalamic) cat exhibits spontaneous locomotor hindlimb movements which can be demonstrated by observing patterns of rhythmic EMG bursts. Corresponding but simpler efferent nerve discharges can be found after suppression of all phasic afferent inputs by curarization, showing that there exists a central locomotor program. Complete deafferentation of the hindlimb, suppressing tonic afferent inflow, further simplifies the locomotor pattern: in the “knee flexors,” activity during the flexion phase disappears while activity during the extension phase remains in relation to the hip extensor function of these biarticular muscles. It might be concluded that the central program acts both directly on motoneurones and, indirectly, on flexor reflex pathways through modulation. The fusimotor activity, with its partial independence on reflex actions and its low threshold appears as a sensitive expression of the generator output. It confirms that the locomotor cycle is rather simple, with an immediate activation of flexor motoneurones and a more progressive one of extensor motoneurones, and without the strict alternation generally seen in alpha motoneurones.