Abstract
Bradykinesia is the most disabling motor symptom of Parkinson’s disease (PD). The sequence effect (SE), a feature of bradykinesia, refers to the rapid decrement in amplitude and speed of repetitive movements (e.g., gait, handwriting) and is a major cause of morbidity in PD. Previous research has revealed mixed results regarding the role of dopaminergic treatment in the SE. However, external cueing has been shown to improve it. In this study, we aimed to characterize the SE systematically and relate this phenomenon to the energetic cost of movement within the context of cost–benefit framework of motor control. We used a dynamic isometric motor task with auditory pacing to assess the SE in motor output during a 15-s task segment in PD patients and matched controls. All participants performed the task with both hands, and without and with visual feedback (VF). Patients were also tested in “on”- and “off”-dopaminergic states. Patients in the “off” state did not show higher SE compared to controls, partly due to large variance in their performance. However, patients in the “on” state and in the absence of VF showed significantly higher SE compared to controls. Patients expended higher total motor energy compared to controls in all conditions and regardless of their medication status. In this experimental situation, the SE in PD is associated with the cumulative energetic cost of movement. Dopaminergic treatment, critical for internal triggering of movement, fails to maintain the motor vigor across responses. The high motor cost may be related to failure to incorporate limbic/motivational cues into the motor plan. VF may facilitate performance by shifting the driving of movement from internal to external or, alternatively, by functioning as a motivational cue.
Highlights
Bradykinesia, one of the cardinal manifestations of Parkinson’s disease (PD), means slowness of movement
Our main findings can be summarized as follows: [1] the groups were well matched in their maximum voluntary contraction (MVC). [2] The magnitude of the initial squeeze played a significant role in the degree of the decrement
(5) PDs demonstrated a higher sum of area under the curve (AUC) for the short segment compared to healthy volunteers (HVs), and this was independent of feedback and medication status
Summary
Bradykinesia, one of the cardinal manifestations of Parkinson’s disease (PD), means slowness of movement. It is the most disabling symptom and a complex phenomenon with different components [1]. Bradykinesia is assessed during repetitive sequential movements (e.g., finger tapping). The amplitude and/or speed of the movements rapidly diminishes with each repetition. This phenomenon is known as the “sequence effect” (SE) and seems unique to PD among other parkinsonian syndromes [2, 3]. The SE is an important source of morbidity in daily activities of PD patients, including handwriting, gait, and speech [3,4,5], for which dopaminergic treatment falls
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