Combined action observation and motor imagery influences hand movement amplitude in Parkinson's disease

Abstract

Background: Action observation (AO) activates the motor system, influencing movement and increasing learning, and has been shown to improve speed and timing of movement in people with Parkinson's disease (PD). Importantly, however, effects on movement amplitude have not been quantitatively demonstrated. Additionally, motor imagery (MI) can increase behavioural and neural effects of AO, but the combined effects of AO+MI have never previously been explored in PD. The aim of this study was to investigate imitation of hand movement amplitude in people with PD following (i) AO and (ii) combined AO+MI. Methods: Twenty-four participants with mild to moderate PD and 24 healthy older adults observed and imitated videos showing a human hand moving between horizontal positions. Kinematics were recorded and modulation of vertical amplitude when replicating elevated vs. direct movements provided an index of imitation. After an initial set of AO trials, participants were instructed to engage in MI during observation for the remaining trials (AO+MI), emphasizing kinaesthetic (sensory) imagery. Results: Movement amplitude was imitated (modulated) for elevated vs. direct stimuli by both groups, and this imitation increased following MI instructions. Conclusions: These results demonstrate quantitatively for the first time that people with PD are able to modulate the amplitude of their hand movements following action observation, and that combining AO and MI increases imitation in PD. The effects parallel findings in healthy young participants, and indicate that combined action observation and motor imagery could be a promising therapeutic approach for PD. To indicate compliance with the preceding declaration and that you have obtained agreement from all of the authors of this paper to declare their compliance as well, please place an x here: _X__

The Role of Mental Imagery in Parkinson’s Disease Rehabilitation

“…Mental imagery can be performed in the absence of appropriate sensory input [ 103 , 104 ] or while the imaged stimulus is available to the imager [ 105 , 106 , 107 ]. When related to movement, mental imagery can be done with or without physical execution of the imaged movement [ 108 , 109 ] as well as while observing the movement performed by another individual or a video (aka “action observation”) [ 110 , 111 ]. A strong linear correlation exists between overt physical execution and mental imagery [ 112 , 113 ], spanning temporal (i.e., similarity in time to complete actual and imaged tasks) and spatial (i.e., activated neural pathways and brain regions) spheres [ 104 , 114 , 115 ].…”

“…The ability to mentally image gait vividly and accurately is similar in PwP and controls and does not seem to correlate with actual walking performance, though PwP may perform mental imagery tasks more slowly than controls [ 90 ]. Mental imagery speed and vividness may be enhanced through use of visual cues [ 149 ] and potentially through using action observation [ 110 , 111 ]. The preserved ability for mental imagery and use of cueing suggests that even those with poor walking performance may still be able to image walking effectively and therefore potentially benefit from mental imagery as a strategy to compensate for gait impairments [ 150 ].…”

Action Imagery and Observation in Neurorehabilitation for Parkinson’s Disease (ACTION-PD): development and pilot randomised controlled trial of a user-informed home training intervention to improve everyday functional actions

“…Despite the evidence supporting combined AO+MI approaches in healthy participants and in stroke rehabilitation as described above, only one study to date has investigated AO+MI in PD, showing increased imitation of hand movements when participants engaged in MI during AO, compared to AO alone [34]. It has been proposed that combining AO and MI may increase corticospinal excitability in people with PD, thereby enhancing pre-movement facilitation [47].…”

“…It has been proposed that combining AO and MI may increase corticospinal excitability in people with PD, thereby enhancing pre-movement facilitation [47]. Additionally, concurrent observation provides an ongoing visual input, which may facilitate the generation of motor imagery (see [25]), potentially compensating for difficulties with MI in people with PD [34]. Indeed, spontaneous MI may have contributed to the effects of previous AO interventions that did not include explicit MI instructions.…”

“…Moreover, MI training is recommended in rehabilitation guidelines from the American Stroke Association [31]. Although a smaller number of studies have investigated AO and MI in PD, AO has been found to influence movement speed and timing in reaching [32] and finger-tapping [33] tasks, as well as hand movement amplitude [34], and people with PD have shown preserved motor resonance for incidentally-observed hand actions [35]. People with PD also report similar vividness of MI to healthy controls; however, like their actual 3 movements their imagery may be slowed [36], and compensatory mechanisms may be involved, such as a greater reliance on visual processes [37,38].…”