P 190. Role of the cerebellum and the supplementary motor area in anticipatory postural adjustments in humans

Abstract

Introduction Understanding of the pathophysiology of gait and balance is an issue of public health, both in the elderly and patients with neurological disease, due to the increased morbidity and mortality associated to these disorders. Functional imaging studies obtained in healthy subjects who imagine to be standing or walking ( Jahn, 2008 , Snijders, 2011 ) or in a cortical activity study during induction of destabilization ( Nadeau, 2007 ) suggest the supplementary motor area (SMA), the posterior parietal cortex, the dorsolateral prefrontal cortex, the basal ganglia, the cerebellum and the midbrain are involved in postural control and locomotion in humans. Patients with a lesion of the cerebellum or SMA have problems with balance and walking such as walking called ataxic. Objectives We studied the role of the cerebellum and SMA in postural control during the initiation step in 10 healthy subjects before and after functional inactivation (using inhibitory repetitive transcranial magnetic stimulation, rTMS) of the cerebellum or SMA. Materials and methods The initiation step was studied using a force platform on which the subject stood upright. Reflective markers were positioned at the joints of both legs; their position was monitored in real time using infrared cameras (VICON system). The electromyographic activity of the Soleus and Tibialis anterior muscles of both legs was recorded. The rTMS, delivered as a theta burst stimulation ( Huang, 2005 ) was used to functionally inactivate the cerebellum or the SMA. The stimulation protocol consisted in conditions: functional inactivation of the cerebellum, functional inactivation of the SMA, and sham stimulation applied either on the SMA or on the cerebellum. Results In spontaneous walking condition, inhibition of the SMA induced a significant increase in the duration of anticipatory postural adjustments (0.47 ± 0.06 s vs. 0.51 ± 0.05 s, p Conclusion The preliminary data obtained in our study suggest that the SMA and the cerebellum have a different role in the initiation of walking, with a predominant control of the preparatory phase for the SMA and motor coordination in the implementation phase for the cerebellum.