Objective: Deciphering the role of the MLR in gait and balance disorders in PD patients

Background: Lesion or dysfunction of the MLR, including the Pedunculopontine (PPN) and Cuneiform (CuN) nuclei, have been reported in PD patients with freezing of gait (FOG) and/or falls. Recent data also reported pathological modulation of the neuronal activity of the PPN during FOG episodes. However, deep brain stimulation (DBS) of the MLR failed to significantly improved FOG or falls in these patients, and the exact roles of the PPN and CuN areas in the different phases of gait in human are still unknown.

Method: Here, we recorded neural activity of the MLR in 4 PD patients operated for DBS during gait. Gait was recorded using a force plate and motion capture system, concomittantly with EMG activity of the lower limbs, patients being asked to walk for 6-8 meters, turn and go-back to its initial position (n=15-20 trials). Patients were examined with (ON) or without (OFF) dopaminergic medication. Gait parameters included the 1) gait initiation process with anticipatory postural adjustments (APA) phase, 2) self-paced forward gait with stride length, velocity, single- and double-stance phases durations, 3) turn amplitude and 4) number of FOG episodes.

Results: At the time of gait initiation, we observed a significant decrease in the beta band power (12-35Hz) and increases in the theta (4-7 Hz) and alpha (8-12Hz) bands, both in the CuN and PPN (Off-Dopa). Decreased beta band power was higher in the PPN area, whereas increased theta-alpha bands power started in the CuN area. On-dopa, modulation in the theta and alpha bands activities were lower with no changes in the beta band modulation. During forward gait, alpha rythm was synchronized with the step. Lastly, in the PPN and off medication, we found a trand for a beta desynchronisation before and during FOG, with conversely increased alpha band in the CuN area.

Conclusion: These data suggest that PPN and CuN areas may play different roles in gait phases in human, with in particular modulations of low frequency activities in the CuN area and beta band activity in the PPN that might serve as a physiological signal specific to the MLR linked with either attentional ressources or sensorimotor integration. Other studies should focus on dysfonctions related to the freezing of gait and falls to better alleviate these doparesistant symptoms

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MDS Abstracts - https://www.mdsabstracts.org/abstract/modulation-of-the-mesencephalic-locomotor-region-activity-during-gait-in-parkinsons-disease-patients/