The purpose of this study was to investigate the ways in which stroke-induced posterior parietal cortex (PPC) lesions affect reactive postural responses and whether providing auditory cues modulates these responses.
Seventeen hemiparetic patients after stroke, nine with PPC lesions (PPCLesion) and eight with intact PPCs (PPCSpared), and nine age-matched healthy adults completed a lateral-pull perturbation experiment under noncued and cued conditions. The activation rates of the gluteus medius muscle ipsilateral (GMi) and contralateral to the pull direction, the rates of occurrence of three types of GM activation patterns, and the GMi contraction latency were investigated.
In noncued pulls toward the paretic side, of the three groups, the PPCLesion group exhibited the lowest activation rate (56%) of the GMi (P < 0.05), which is the primary postural muscle involved in this task, and the highest rate of occurrence (33%) of the gluteus medius muscle contralateral–activation-only pattern (P < 0.05), which is a compensatory activation pattern. In contrast, in cued pulls toward the paretic side, the PPCLesion group was able to increase the activation rate of the GMi to a level (81%) such that there became no significant differences in activation rate of the GMi among the three groups (P > 0.05). However, there were no significant differences in the GM activation patterns and GMi contraction latency between the noncued and cued conditions for the PPCLesion group (P > 0.05).
The PPCLesion patients had greater deficits in recruiting paretic muscles and were more likely to use the compensatory muscle activation pattern for postural reactions than the PPCSpared patients, suggesting that PPC is part of the neural circuitry involved in reactive postural control in response to lateral perturbations. The auditory cueing used in this study, however, did not significantly modify the muscle activation patterns in the PPCLesion patients. More research is needed to explore the type and structure of cueing that could effectively improve patterns and speed of postural responses in these patients.
From the School and Graduate Institute of Physical Therapy, College of Medicine (Y-HL, P-FT), Graduate Institute of Brain and Mind Sciences, College of Medicine (P-FT), and School of Occupational Therapy, College of Medicine (K-CL), National Taiwan University, Taipei, Taiwan; Department of Physical Medicine and Rehabilitation (Y-HL, K-CL, LL), Physical Therapy Center (P-FT), Department of Medical Imaging (Y-HW), and Department of Neurology (J-SJ), National Taiwan University Hospital, Taipei, Taiwan; Department of Physical Therapy, University of British Columbia, Vancouver, British Columbia, Canada (JJE); and Department of Physical Medicine and Rehabilitation, Taipei Medical University Hospital, Taipei, Taiwan (S-CC).
All correspondence and requests for reprints should be addressed to: Pei-Fang Tang, PT, PhD, School and Graduate Institute of Physical Therapy, College of Medicine, National Taiwan University, Floor 3, No. 17, Xuzhou Rd, Zhongzheng District, Taipei, 100, Taiwan, Republic of China.
Supported by the National Health Research Institutes grants NHRI-EX95-9210EC and NHRI-EX96-9210EC.
Presented at the Annual Conference of Taiwan Stroke Society in 2013.
Financial disclosure statements have been obtained, and no conflicts of interest have been reported by the authors or by any individuals in control of the content of this article.