Role of spinal premotoneurones in mediating corticospinal input to forearm motoneurones in man
Article first published online: 22 SEP 2004
The Journal of Physiology
Volume 508, Issue 1, pages 301–312, April 1998
How to Cite
Pauvert, V., Pierrot-Deseilligny, E. and Rothwell, J. C. (1998), Role of spinal premotoneurones in mediating corticospinal input to forearm motoneurones in man. The Journal of Physiology, 508: 301–312. doi: 10.1111/j.1469-7793.1998.301br.x
- Issue published online: 22 SEP 2004
- Article first published online: 22 SEP 2004
- (Received 19 May 1997; accepted after revision 1 December 1997)
- 1Evidence was sought to support the suggestion that corticospinal input can be relayed to motoneurones (MNs) via a population of interneurones (premotoneurones) in the cervical cord, and that this pathway operates in parallel with the direct monosynaptic pathway.
- 2Single motor units were recorded in forearm muscles and post-stimulus time histograms (PSTHs) of their firing pattern were constructed during voluntary activation. Weak transcranial magnetic stimulation of the contralateral motor cortex was used to produce a small facilitation in the PSTH. We then examined how the size of this peak was affected by low threshold electrical stimulation of either the homonymous muscle nerve or the musculo-cutaneous nerve at various interstimulus intervals (ISIs).
- 3Homonymous nerve stimulation had the following characteristics: (a) the cortical peak was facilitated when stimuli were timed so that both inputs arrived simultaneously at the MN; (b) the amount of facilitation was only slightly greater than the sum of the effects of each stimulus given alone; and (c) facilitation affected even the earliest bins of the cortically evoked peak. These three features are consistent with a monosynaptic input onto the MN from both sources.
- 4Stimulation of the musculo-cutaneous nerve (which has no monosynaptic connections with forearm MNs) had no effect at similar timings. It (a) produced facilitation only at longer intervals corresponding to an extra central delay of 4-6 ms; (b) always gave a significantly larger facilitation than expected from the algebraic sum of the effects of each stimulus given alone; and (c) never affected the earliest bins of the cortical peak. These features are compatible with interaction of peripheral and cortical inputs at a population of premotoneurones.
- 5These results confirm the suggestion that premotoneurones mediate part of the cortical command to MNs innervating forearm muscles.
- 6Excitation is followed by an inhibition which may almost completely suppress the cortical peak. It is suggested that cortical and musculo-cutaneous volleys also converge onto inhibitory interneurones projecting to the premotoneuronal pool.