Obstacle Avoidance amongst Parkinson Disease Patients Is Challenged in a Threatening Context

We examined whether people with Parkinson disease (PD) have difficulty negotiating a gait obstruction in threatening (gait path and obstacle raised above floor) and nonthreatening (gait path and obstacle at floor level) contexts. Ten PD patients were tested in both Meds OFF and Meds ON states, along with 10 age-matched controls. Participants completed 18 gait trials, walking 4.7？m at a self-selected speed while attempting to cross an obstacle 0.15？m in height placed near the centre point of the walkway. Kinematic and kinetic parameters were measured, and obstacle contact errors were tallied. Results indicated that PD patients made more obstacle contacts than control participants in the threatening context. Successful crossings by PD patients in the threatening condition also exhibited kinematic differences, with Meds OFF PD patients making shorter crossing steps, with decreased initiation and crossing velocities. The findings from this study lend support to the theory that PD patients rely on directed attention to initiate and control movement, while providing indication that the motor improvements provided by current PD pharmacotherapy may be limited by contextual interference. These movement patterns may be placing PD patients at risk of obstacle contact and falling. 1. Introduction Epidemiological investigation indicates that Parkinson disease (PD) patients experience more falls than either age-matched healthy controls or individuals with other neuropathologies, including spinal disorders, epilepsy, multiple sclerosis, stroke, and motor neuron disease [1]. For patients with PD, fall occurrences and increased fear of falling are frequent in situations with complex or threatening context [2], with contact with an obstacle presenting a major cause of falls among PD [1, 3]. Task demands, such as the inherent characteristics of the obstacle to be crossed as well as constraints imposed by the general environment surrounding the obstacle and task, contribute to context [4] and exacerbate motor disturbances amongst PD patients [5]. Previous studies have shown that neurotypical adults adopt conservative strategies for standing [6, 7], walking [8], and obstacle crossing [9] when behaving in a context that threatens increased physical consequences as a result of a fall. In contrast, PD patients have exhibited increased postural instability [10] and gait disturbance [11] when concurrently challenged with a cognitive or motor demand. It is probable that threatening context may exacerbate any obstacle negotiation deficits that exist for PD patients. While PD