Supplementary motor area (SMA):
- important in programming and initiating complex motor sequences involving bilateral hand coordination, postural preparation and distal extremity movement
- global akinesia that is worse contralaterally
- sudden recovery a few days later, but with a persistent reduction in contralateral motor activity
- subtle sequelae within weeks to months after surgery
- Complete SMA syndrome – as contralateral hemiplegia with or without mutism
- Partial SMA syndrome – contralateral hemiparesis and/or speech hesitancy
- reduction of spontaneous movements and difficulty performing voluntary motor acts to command contralateral limbs
- tone in the limbs is maintained or increased
- serial automatic motor (like walking) activities are relatively unaffected
- speech deficits may be seen
- hemineglect and dyspraxi or apraxia involving contralateral limbs
- usually recover motor function over a variable time period from one to a few weeks
- good long-term prognosis
Proposed mechanisms of modulation of the SMA in normal subjects, SMA syndrome, PD and tics.
The SMA can both positively and negatively modulate the contralateral SMA. In normal conditions this tonic interhemispheric balance may result in both initiation and inhibition of movements.
In the SMA syndrome this balance is disturbed, leading to temporary lack of movements (akinesia) of the contralateral limbs and irreversible deficits of bimanual alternating movements. The functional schemes are projected on a coronal MNI brain section. = denotes unchanged modulation, < denotes decreased modulation, > denotes increased modulation.
Ryu, Ju Seok, Min Ho Chun, and Dae Sang You. ‘Supplementary Motor Area Syndrome And Flexor Synergy Of The Lower Extremities’. Ann Rehabil Med 37.5 (2013): 735. Web. 24 Sept. 2015.
Front. Hum. Neurosci., 28 November 2014 | http://dx.doi.org/10.3389/fnhum.2014.00960. Insights from the supplementary motor area syndrome in balancing movement initiation and inhibition. A. R. E. Potgieser, et al.