Cortical involvement in a gait-related imagery task: Comparison between Parkinson’s disease and normal aging
Introduction
Gait disturbance is one of the cardinal symptoms in patients with Parkinson’s disease (PD). Patients demonstrate a shuffling gait with a shortened stride, reduced overall velocity, and decreased arm swing. The progressive gait disturbance combined with postural instability deprives the patients of the ability to walk safely and increases the risk for falling. The major problem with gait disturbance is that it is poorly controlled by dopaminergic agents [1].
Studies in patients with PD of the different components of gait have been of great interest. Difficulty in gait initiation, stepping over obstacles, and gait termination compromise the ability to walk of patients with PD and predispose them to falls [2]. Gait initiation is the transition from the upright posture to the steady walking state. The task is challenging due to the volitional transition from a condition with stable support to an unstable posture during walking [3]. Patients with PD often have start hesitation when initiating gait. PD patients also demonstrate difficulty terminating gait. Therefore, they are unable to stop abruptly [4]. Furthermore, negotiating obstacles when walking is compromised in people with PD and tripping is a major risk factor for falling [5].
Non-invasive imaging studies of human cortical involvement in gait control using functional magnetic resonance imaging (fMRI) are limited. The inability to walk inside an fMRI scanner is the major reason. Gait imagery has been proposed as a novel paradigm with which to study brain activation during walking [6], [7], [8]. A recent study on real versus imagined locomotion validated the feasibility of the imagery based method [9]. To account for the inter-individual differences in motor imagery [10], one study incorporated the mental process of actively visualizing the action of walking for studying gait-related cortical activations, in addition to the imagery [11]. The rationale based on shared motor representations, which assumed a functional equivalence between intending, imagining, observing, and performing an action [7]. There is evidence that the addition of action observation would improve motor imagery [12], [13]. With an event-related design, it could be possible to determine cortical activity at different stages of gait [11].
In the current study, the cortical control over different gait-related tasks was examined in PD patients. We recruited healthy age-matched old and young adult controls in an effort to differentiate between the PD and normal aging. We included the following tasks: imagining gait initiation, stepping over an obstacle, and gait termination. Our hypothesis was that at gait initiation, PD patients would express increased activation at pre-SMA, to overcome the weakened striatum-cortical connection [14]. During stepping over an obstacle, the pathway involving the transmission of visuospatial information from the visual related area, posterior parietal lobe, then to the lateral premotor area would be activated to facilitate visuomotor coordination [15]. At gait termination, patients would have more activation in the prefrontal area to compensate for their subcortical dysfunction [16].
Section snippets
Methods
The study was approved by the institutional review board of the Chang Gung Memorial Hospital. The experiments were undertaken with the understanding and written consent of each subject.
Result
Fig. 1 shows the contrast involved in the imagery task of gait initiation (A), stepping over an obstacle (B) and termination (C). Comparisons were made between PD versus Old (yellow) and Old versus Young (red). The overlapping areas are in orange.
During gait initiation, no cluster survived the correction for FWE for activation between the PD and the Old subjects. The differences between Old and Young were in the visual related area, including right middle occipital gyrus, bilateral Middle
Discussion
Our results showed that a neural network, which involves the SMA/pre-SMA, PMd, visual and posterior parietal area, is preferentially activated during the gait-related imagery tasks. The locations of the activated regions are consistent with previous studies [11]. Furthermore, this neural network might experience modulation in a pathological state, such as PD, and during the process of normal aging.
Previous studies on the cortical mechanism underlying gait disturbance in PD reported a reduced
Conclusion
Our study provides image based evidence for pathophysiological and compensative cortical mechanisms for gait disturbance in PD and older subjects.
The study protocol could be extended to gait-related studies on subjects with other movement disorders. The results could provide a resource for potential therapeutic interventions.
Acknowledgments
This study was supported by National Science Council Taiwan (NSC100-2314-B-182-024) and Chang Gung Memorial Hospital (CMRPG371353). The authors acknowledge the support of the Molecular Imaging Centre in Chang Gung Memorial Hospital, Linkou and the use of the MR facility.
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