Neural correlates of motor imagery of gait in amyotrophic lateral sclerosis

Introduction Gait impairment is understudied and poorly characterised in amyotrophic lateral sclerosis (ALS), despite increasing evidence of considerable extrapyramidal and cerebellar dysfunction. Objective The objective of this study is to assess gait imagery specific-networks and functional adaptation in ALS. Patients and methods Seventeen ALS patients with lower motor neuron predominant (LMNp) disability, fourteen patients with upper motor neurons predominant (UMNp) disease and fourteen healthy controls performed a dual motor imagery task on fMRI; normal and precision. Study-group specific activation patterns were evaluated during motor imagery of gait. Additional voxel based functional connectivity analyses were carried out using the supplementary motor area, cerebellum and striatum as seed regions. Results Our data revealed a significant increase in imagery time in UMNp patients compared to controls and LMNp during imagined gait. UMNp patients exhibited decreased SMA, DLPFC and superior parietal lobule activation and increased orbitofrontal, parietal and cerebellar signal during imagined locomotion. Increased functional connectivity of the striato and parieto-cerebellar circuits was also demonstrated. Additional activation was detected in the insula and cingulate cortex. Discussion The results suggest functional reorganisation in ALS. The study showed that LMNp patients exhibit similar activation patterns to healthy controls during motor imagery of both normal and precision gait. Interestingly, UMNp patients exhibit significantly longer imagery time when they imagined walking on a narrow path (precision gait) and demonstrated gait network alterations compared to LMNp patients and healthy controls. Conclusion Enhanced striato- and parieto-cerebellar networks in UMNp ALS patients are likely to represent a compensatory response to impaired postural control. Activation of insular and cingulate regions suggest that fear of falling is an implication of gait disturbance in ALS.