Following a stroke, it is important to assess a person’s perception of verticality. This assessment can help us to find what causes the bodily disorientation with respect to vertical (lateropulsion) and can guide post-stroke rehabilitation and monitor postural recovery. The visual vertical (VV) is the most commonly used test to assess verticality perception, both in research and in clinical practice. It is a simple test that consists of adjusting a luminous rod to the vertical in darkness; however, specific guidelines for use in clinical practice are lacking. Published studies have used different methodologies and the impact of these different methodologies on the assessment outcome is not well-understood. For example, should the trunk and head be free to move during the test or should they be fixed in the upright position? This question is critical for stroke survivors. It is well-known that spontaneous lateral whole body tilts are common after stroke and this may compromise their ability to sit on their own and might further impact their perception of verticality. In the present study, we aimed to analyse the impact of controlling body orientation on stroke patients’ ability to estimate VV and their ability to sit unsupported.

VV perception was assessed in 20 controls and 36 subacute patients undergoing rehabilitation after a first hemisphere stroke, under 3 different scenarios: body not fixed (trunk and head free), partially fixed (trunk fixed, head free), or both trunk and head were fixed. We quantified both trunk and head orientations and analysed VV as a function of trunk and head tilt. Patients were classified into 2 groups according to their ability to maintain (n=25) or not (n=11) an independent upright sitting posture. Our results confirmed for the first time the clinical intuition: it is spontaneous upright trunk (and not head) orientation which is necessary for recovering an independent sitting posture after stroke. This suggests that postural orientation deficits, especially trunk orientation, are a major cause of lateral postural disorders after a stroke. The level of fixation strongly affects the estimation of VV in stroke patients who have difficulties maintaining a seated posture. Our results suggest that a fixed trunk and head in the upright position was the most optimal setting for assessing VV. We proposed that measuring VV without any body fixation is only valid in patients with satisfactory balance abilities. Our results contribute to a better standardization of VV assessment to optimize its integration in research and clinical practice.

Figure. Individual mean spontaneous orientations of trunk axis and head axis. The data were classified from the most pronounced contralesional tilt (negative values) to the most pronounced ipsilesional tilt (positive values), for trunk orientation, and this order was maintained for the classification of head orientation data. (B) Visual vertical perception, orientation (mean) and uncertainty (variability) as a function of group and setting.

Publications

Piscicelli C, Barra J, Sibille B, Bourdillon C, Guerraz M, Pérennou D. (2016). Maintaining trunk and head upright optimizes visual vertical measurement after stroke, Neurorehabil Neural Repair, 30(1):9-18. https://doi.org/10.1177/1545968315583722

Piscicelli C, Pérennou D. (2017). Visual verticality perception after stroke: A systematic review of methodological approaches and suggestions for standardization. Ann Phys Rehabil Med, 11. pii: S1877-0657(16)00042-7. https://doi.org/10.1016/j.rehab.2016.02.004

About the Author

Concussion results in a wide variety of impairments such as cognitive deficits in memory, reaction time and processing speed. Moreover, post-concussion dizziness and balance impairments are found to be common and predictive of worse recovery times.  Therefore, an increasing number of patients with concussion are referred for vestibular physical therapy.
Although it is likely that cognitive and vestibular impairments after concussion are related, they have only been examined in isolation. This study examined the relationship between cognitive performance and various gait and balance measures in patients referred for vestibular physical therapy after concussion.

Our study investigated the relationship between gait and balance performance with cognitive performance in a group of 60 adolescents referred for vestibular therapy after concussion. We tested our participants on a range of functional gait and balance measures, such as the Functional Gait Assessment, Timed “UP & GO”, and Five Times Sit to Stand. Our results suggest that, after concussion, both memory deficits and impaired gait and balance can occur in individuals. Our results further show that they are associated with each other. First, we demonstrated that functional balance and gait measures were associated with worse verbal and visual memory on the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT). For example, in the figure below, we observed that better performance in visual memory (i.e. higher scores) and verbal memory was related to better performance in the Five Times Sit to Stand (i.e. less time). We also found that higher scores on the Post-Concussion Symptom Scale were associated with lower scores on the Activities-specific Balance Confidence scale and higher scores on the Dizziness Handicap Inventory.

Spatial navigation is frequently affected after concussion and is important for both gait and balance tasks as well as memory tasks. Clinicians working with patients after concussion should check whether any observed cognitive impairments might be partially attributed to declines in spatial navigation rather than an isolated memory decline. Vestibular therapists should consider giving dual-task exercises, combining balance and cognition, during the rehabilitation process to reduce the impact of cognitive performance on gait and balance function. It will be interesting to see in future studies whether the associations between cognitive and balance affect recovery trajectories after concussion.

Figure: Association between Five Times Sit to Stand Performance and Visual and Verbal Memory performance in 60 adolescents with a concussion who were referred for vestibular physical therapy. Higher visual and verbal memory scores were related to better performance on the Five Times Sit to Stand.

Publication
Alsalaheen BA, Whitney SL, Marchetti GF, Furman GM, Kontos AP, Collins MW, Sparto PJ:  Relationship between cognitive assessment and balance measures in adolescents treated with vestibular physical therapy after concussion. Clin J Sport Med. 2016. 26(1):46-52. PMCID:  PMC4856020

http://journals.lww.com/cjsportsmed/Citation/2016/01000/Relationship_Between_Cognitive_Assessment_and.7.aspx

About the Author

Threats to standing balance, such as standing at the edge of a roof or on a ladder are known to evoke fear, anxiety and arousal. Moreover, these height-induced postural threats are known to alter standing balance control. The vestibular system, or inner ear balance organ, is thought to contribute to threat-related balance changes because it is a major contributor to balance control, and because the vestibular nuclei in the brainstem are heavily interconnected with nervous system regions associated with fear, anxiety and arousal. We tested this hypothesis by examining how balance responses to electrically-generated vestibular error signals were affected by exposure to a height-induced postural threat.

Young healthy adults were exposed to two height-induced postural threat conditions; first they stood on a hydraulic lift at a ground-level equivalent condition (LOW), then they were elevated to a 3.2m-high condition (HIGH; Fig 1A). Binaural bipolar stochastic electrical vestibular stimulation (SVS; 2-25Hz) was used to evoke balance responses; balance responses were recorded with a force plate. Participants stood with their head facing either forwards or turned 90° to the right (see Fig 1A) so that vestibular-evoked balance responses were evoked in different directions (perpendicular to head orientation). We anticipated that if postural threat primes the vestibular system for balance control, then evoked balance responses would be larger and better correlated with SVS inputs while standing at height. We characterized the relationship between SVS and balance responses with time-domain correlations (‘cumulant density’); frequency-domain correlations (‘coherence’); and frequency-domain signal gain (amplitude) estimates. Height-induced postural threat led to greater correlation between the signals (larger cumulant density peaks and greater coherence; Fig 1B, C), and larger gains at all frequencies (Fig 1D).

The stronger relationship between vestibular inputs and balance response outputs in the HIGH threat condition suggests that the balance control system responds more faithfully to vestibular inputs at height. These results are similar to threat-related changes observed in other clinical measures of vestibular reflexes, and to other balance-relevant sensory systems, including muscle spindle stretch and Golgi tendon organ-Ib reflexes. We interpret these findings as evidence for context-dependent tuning of sensory-motor interactions, and speculate that this is a normal aspect of human balance control. Furthermore, a failure to adequately control such tuning processes, perhaps by either becoming hyper- or hypo-sensitive to balance-relevant stimuli under threatening or challenging situations, might contribute to poor balance performance in the elderly or in people with anxiety or neurologic balance impairments.

Publication

Horslen, B. C., Dakin, C. J., Inglis, J. T., Blouin, J.-S. and Carpenter, M. G. (2014), Modulation of human vestibular reflexes with increased postural threat. J Physiol, 592: 3671–3685. doi:10.1113/jphysiol.2014.270744

http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.2014.270744/abstract;jsessionid=A592E320B18184BF9C30F5C547B6E9C6.f02t04

About the Author