this aspect of brain science is trippy cool. If you were to ever read one of my posts rather than just skip it......
Functional movement disorders
Many terms have been debated to describe “psychogenic” movement disorders. A thoughtful discussion was published in the The Lancet Neurology in 2012 by Edwards, et al. The 2002 study referenced there by Stone et al., suggests that overall patients find the term “functional” more acceptable and with less negative connotations.
This is important, because functional movement disorders have been considered to be related to psychological trauma, however epidemiologic studies do not support this (Stone 2011) (Kranick 2011). Even if they were, this would not explain what may be most striking about these conditions. Functional movement disorders are neurologically voluntary movement, but according to patients they have a decidedly involuntary feel to them.
Voluntary movement and that of functional disorders of myoclonus and tremor, involve the premotor cortex, supplementary motor area and motor cortex, which are used in motor planning and execution. When it comes to patting your head and rubbing your belly at the same time, one voluntary motor plan can interfere with another, and this is seen with movement from a functional disorder.
However, there is more to voluntary movement than execution. Research into the pathophysiology of functional movement disorders is looking into the perception of movement, and not just the mechanisms that generate it.
Imaging of patients while they are experiencing functional tremor was compared to imaging while these same patients were voluntarily imitating their tremor – meaning that the abnormal movement was being compared with decidedly normal voluntary movement in the same brain. During the abnormal movement there was hypoactivation of the temporoparietal junction, an area suspected to compare predicted and actual sensory feedback. This may give the sense the movement was involuntary. (Edward 2012).
It is theorized there is a feed-forward signal from the frontal lobes that includes the premotor and motor cortices, but also goes to the parietal lobe so planned movement can be compared to actual movement to allow for motor correction. This may also be the way a person experiences the sense of telling their body to move and receiving feedback that it did. (Edward 2012).
A neurosurgical study used electric impulses to stimulate the parietal area, and showed that low intensities gave the sense that patient wanted to move a certain part of their body, and high intensities made patients feel like they actually had moved when they hadn’t. Stimulation of the premotor region caused movement without any awareness of it. This suggests that the parietal area is responsible not only for the sense of wanting to move your body, but also with the sense that you actually did, and this may be the reason that you believe you were the one to do so. This may support the feed-forward signal theory. (Desmurget 2009).
What is presented here explores the pathophysiology of only one aspect of functional movement disorders – the sense of being involuntary. These disorders may not have hard anatomic structural abnormalities like that found in Parkinson’s, but the suffering is just as involuntary. Greater understanding of functional movement disorders may not only yield future therapies and help strengthen the therapeutic alliance, it may also help us to understand and treat other movement disorders.
References:
J Stone, W Wojcik, D Durrance et al. What should we say to patients with symptoms unexplained by disease? The “number needed to offend”. BMJ, 325 (2002), pp. 1449–1450.
Stone, J. and Edwards, M. J. How “psychogenic” are psychogenic movement disorders?. Mov. Disord., (2011), 26: 1787–1788.
Kranick, S., Ekanayake, V., Martinez, V., Ameli, R., Hallett, M. and Voon, V. Psychopathology and psychogenic movement disorders. Mov. Disord., (2011), 26: 1844–1850
Mark J Edwards, PhDa, Prof Kailash P Bhatia, MDa. Functional (psychogenic) movement disorders: merging mind and brain. The Lancet Neurology. Volume 11, Issue 3, March 2012, Pages 250–260
Desmurget M, Reilly KT, Richard N, Szathmari A, Mottolese C, Sirigu A. Movement intention after parietal cortex stimulation in humans. Science. 2009 May 8;324(5928):811-3.