Distracting attention in phobic postural vertigo normalizes leg muscle activity and balance

Abstract

Objective:To examine the triggering causes of inadequate neuromuscular regulation of posture and subjective imbalance in patients with phobic postural vertigo (PPV), a subtype of functional dizziness.Methods:Postural performance was assessed by center-of-pressure displacements and surface EMG of lower-limb muscles (the tibialis anterior and soleus) in 10 patients with PPV and 10 healthy controls under 4 stance conditions: standing with eyes open or closed and with or without an additional cognitive dual task. The level of muscle cocontraction and the characteristics of open- and closed-loop postural control were analyzed.Results:At baseline (i.e., standing with eyes open without dual task), patients exhibited increased muscle cocontractions (p = 0.003), which were further associated with increased open-loop diffusion activity (p = 0.022) and a lowering of the primary feedback threshold for closed-loop control (p = 0.003). However, postural performance of patients improved considerably and normalized to that of healthy controls when performing an additional dual task.Conclusions:PPV is characterized by a dissociation of subjective postural instability and objectively maintained balance capabilities. The dual-task effects on balance in patients with PPV indicate that this dissociation might result from an increased attention to postural adjustments at baseline, which is normally required only during demanding balance situations. This internal focus on balance control promotes an inappropriate neuromuscular regulation of posture, with increased muscle cocontractions, higher short-term body sway, and an oversensitivity to external stimuli. However, if patients are distracted, muscle cocontractions and balance control normalize. Such distraction may therefore be an effective coping strategy for preventing PPV attacks in susceptible patients.