Neurones in the pontomedullary reticular formation signal posture and movement both as an integrated behaviour and independently

We have previously suggested that the discharge characteristics of some neurones in the pontomedullary reticular formation (PMRF) are contingent upon the simultaneous requirement for activity in both ipsilateral flexor muscles and contralateral extensors. To test this hypothesis we trained cats to stand on 4 force platforms and to perform a task in which they were required to reach forward with one forelimb or the other and depress a lever. As such the task required the cat to make a flexion movement followed by an extension in the reaching limb while maintaining postural support by increasing extensor muscle tonus in the supporting limbs. We recorded the activity of 131 neurones from the PMRF of 3 cats during left, ipsilateral, reach. Of these, 86/131 (66%) showed a change in discharge frequency prior to the onset of activity in one of the prime flexor muscles and 43/86 (50%) showed a bimodal pattern of discharge in which activity decreased during the lever press. Among the remaining cells, 28/86 (33%) showed maintained activity throughout the reach and the lever-press. Most cells showed a broadly similar pattern of discharge during reaches with the right, contralateral, limb. We suggest these results support the view that a population of neurones within the PMRF contributes to the control of movement in one forelimb, and the control of posture in the other forelimb, as a coordinated unit. Another population of neurones contributes to the control of postural support independently of the nature of the activity in the reaching limb.