Research Report
Population: Adult
Mark E. Lester, DPT, PhD, OCS, Assistant Professor, U.S. Army-Baylor University Doctoral Physical Therapy Program mark.e.lester5@gmail.com
James Cavanaugh, PT, PhD, NCS, Associate Professor, Department of Physical Therapy, University of New England jcavanaugh@une.edu
Scott Shaffer, PT, PhD, OCS, ECS, Professor, U.S. Army-Baylor University Doctoral Physical Therapy Program scott.w.shaffer.mil@mail.mil
K. Foreman, PT, PhD, Associate Professor, Department of Physical Therapy, University of Utah bo.foreman@hsc.utah.edu
Leland Dibble, PT, PhD, ATC, Associate Professor, Department of Physical Therapy, University of Utah Lee.Dibble@hsc.utah.edu
Keywords: Plasticity, Parkinson’s Disease, Vestibular, Sensory Reweighting
Purpose/Hypothesis: The ability to reweight sensory contributions to postural stability diminishes with age and is further impaired by Parkinson disease (PD). Practice-based improvements in sensory reweighting are poorly understood. We investigated whether PD or age would differentially affect acute and long-term adaptive postural responses to repeated galvanic vestibular stimulation (GVS) induced vestibular illusion during quiet stance.
Subjects: Thirty-four participants: 14 healthy young adults (HY; 25.5 yrs, 171.6cm, 73.8 kg); 9 healthy elders (HE; 63.8 years, 172.7 cm, 85.8 kg); and 11 individuals with PD (70.6 years, 173.7 cm, 81.9 kg) completed testing.
Materials/Methods: Postural responses to repeated GVS were assessed on 2 days: 15 trials on Day 1 (acquisition) and 9 trials on Day 2 (retention) during quiet stance on a force platform. Center of pressure (COP) location was recorded at 200 Hz. 6 seconds after trial initiation, a 500ms, 1.5mA GVS stimulus was applied over the mastoid processes to invoke vestibular illusion. For each trial, pre- and post-stimulation postural control was quantified in linear and non-linear terms using COP coefficient of variation (CV) and sample entropy (SaEn), respectively. Between- and within-group adaptive postural responses were evaluated for each parameter using mixed-model ANOVA with post-hoc Bonferroni-corrected comparisons.
Results: Transient, GVS-induced postural instability occurred in each group, but only the PD group had a prolonged within-trial, post-stimulation COP CV increase compared to the HY group (p=.016). Throughout acquisition and retention, all groups had post-stimulation COP CV reductions with repeated GVS exposure. However, the PD and HE groups had a relatively lower overall mean SaEn values than the HY group (p ≤ .002) and failed to show increases in SaEn with repeated exposure to GVS during acquisition and retention testing (p > .05). In contrast, the HY group had a significant post-stimulation decline in SaEn values during acquisition (p < .001) and a significant increase in SaEn values from acquisition to retention (p < .001).
Conclusions: Taken together, these results suggested that the sensory reweighting in older adults and individuals with PD, as inferred from reductions in GVS-induced postural instability, may improve with practice. However, their adaptive postural responses, as inferred by changes in the complexity of COP time series, appeared to be less robust than those of younger adults. Further investigation into the nature of this adaptive difference is warranted.
Clinical Relevance: Postural instability is a common outcome of neurologic disease. This study demonstrated that repeated exposure to an induced sensory perturbation may positively influence postural responses, presumably by altering sensory reweighting processes. However, the complexity of this response may be mediated by age and disease state. Clinicians should consider manipulating the sensory environment during balance training programs to enhance training responses and facilitate central nervous system adaptation.
Citation:
Lester, Mark E., DPT, PhD, OCS; Cavanaugh, James , PT, PhD, NCS; Shaffer, Scott W., PT, PhD, OCS, ECS; Foreman, K. Bo, PT, PhD; Dibble, Leland E., PT, PhD, ATC. Adaptive postural responses to vestibular illusion in individuals with parkinson disease and healthy controls.. Poster Presentation. IV STEP Conference, American Physical Therapy Association, Columbus, OH, July 17, 2016. Online. https://u.osu.edu/ivstep/poster/abstracts/047_lester-et-al/