Up close and personal with movement – a review from the experts

Here is a review that, if you are interested in how the brain controls muscles, and you are prepared to put in some hard yards, you should read. Simon Gandevia works down the corridor from me, so do Janet Taylor and Jane Butler. Nicholas Peterson doesn’t but I once had a cup of tea from the same pot. So, I am, everyday, in the presence of corticospinal greatness. What one doesn’t realise however, because they are all such modest folk, is how corticospinally great they really are. I could do a full review of this review, but I really don’t have the expertise. Here are the things that I think are most relevant to what we do as clinicians when we help people to move:

i) Motor neurones get input from many different parts of the brain, not just primary motor cortex. I think this is a great thing to remember because it gives us a mechanism by which a gaggle of factors can influence how we move. I think this is really relevant to work I did with Paul ‘The Walking Cortex’ Hodges on postural adjustments, where the expectation of back pain changes trunk muscle activation and where beliefs about back pain seem to relate to altered postural adjustment strategies. That the primary motor neurone receives corticospinal projections from frontal cortex is a lovely possible route by which beliefs can change motor output.

ii) Many corticospinal projections run to many motoneurones.  I think this is interesting too because it fits with the whole brain as an orchestra idea – each musician contributes to many tunes, just like brain motor cells contribute to lots of different movements.

iii) The whole thing is highly dynamic and can be relatively easily modified. This is, of course, what we are trying to do when we teach people new ways of moving or not moving. Sometimes it feels really really difficult to shift, but at least we know, from the likes of Nicholas, Jane, Janet and Simon, that the system is very shiftable.  Anyway, if you are up for a challenge, read this paper. You won’t regret it.

Probing the corticospinal link between the motor cortex and motoneurones: some neglected aspects of human motor cortical function.

Petersen NCButler JETaylor JLGandevia SC.

Abstract

This review considers the operation of the corticospinal system in primates. There is a relatively widespread cortical area containing corticospinal outputs to a single muscle and thus a motoneurone pool receives corticospinal input from a wide region of the cortex. In addition, corticospinal cells themselves have divergent intraspinal branches which innervate more than one motoneuronal pool but the synergistic couplings involving the many hand muscles are likely to be more diverse than can be accommodated simply by fixed patterns of corticospinal divergence. Many studies using transcranial magnetic stimulation of the human motor cortex have highlighted the capacity of the cortex to modify its apparent excitability in response to altered afferent inputs, training and various pathologies. Studies using cortical stimulation at ‘very low’ intensities which elicit only short-latency suppression of the discharge of motor units have revealed that the rapidly conducting corticospinal axons (stimulated at higher intensities) drive motoneurones in normal voluntary contractions. There are also major non-linearities generated at a spinal level in the relation between corticospinal output and the output from the motoneurone pool. For example, recent studies have revealed that the efficacy of the human corticospinal connection with motoneurones undergoes activity-dependent changes which influence the size of voluntary contractions. Hence, corticospinal drives must be sculpted continuously to compensate for the changing functional efficacy of the descending systems which activate the motoneurones. This highlights the need for proprioceptive monitoring of movements to ensure their accurate execution.

Full article at Acta Physiol (2010), 98 (4), 403-16

ResearchBlogging.org
Petersen NC, Butler JE, Taylor JL, & Gandevia SC (2010). Probing the corticospinal link between the motor cortex and motoneurones: some neglected aspects of human motor cortical function. Acta physiologica (Oxford, England), 198 (4), 403-16 PMID: 20003100

Moseley GL, Nicholas MK, & Hodges PW (2004). Does anticipation of back pain predispose to back trouble? Brain : a journal of neurology, 127 (Pt 10), 2339-47 PMID: 15282214

Moseley GL, & Hodges PW (2006). Reduced variability of postural strategy prevents normalization of motor changes induced by back pain: a risk factor for chronic trouble? Behavioral neuroscience, 120 (2), 474-6 PMID: 16719709

Comments

  1. Nice questions David. I think we are getting closer to identifying specific mechanisms as they relate to some presentations – i think the Parkinson’s research is a good example of that- and we are certainly painting a clearer picture of what is awry in people with MS complaints. Are we close to prioritising strategies….? I think we are there – it would seem to me that several approaches to rehab do this already – graded motor imagery, cognitive therapies, tactile discrimination training, Queensland-style motor control training. And ‘weighting’ the identifiable components – perhaps not. This is tricky, clearly. Finally, will we refine the methodology – i believe we will continue to refine our approaches – this is, afterall, what research is about in a way. Thanks for posting David, L.

  2. Lorimer

    Are we getting closer to identifying specific mechanisms as they pertain to clinical presentations? I,ve followed this debate for 20 years implicating each of the musculoskeletal components, the search for specific pain mechanisms, the search for the magic receptor, the search for the magic bullet cure, and the multiplicity of cortical contributions to musculoskeletal function, pain perception and behaviour.
    – Are we even close to prioritising strategies to target the cortex relative to the musculoskeletal system and “weighting” the idendifiable components of the pain experience?
    It looks (and feels) like we’re in the middle of a blunderbus approach touching all bases (which I guess is better than ignoring important elements) but do you think we may be able to refine this methodology?

    David