Abnormal bias in subjective vertical perception in a post-stroke astasia patient

[Purpose] Post-stroke astasia is an inability to stand without external support despite having sufficient muscle strength. However, the dysfunction underlying astasia is unclear. We tested the hypothesis that astasia is the result of an abnormal bias in vertical perception, especially subjective postural vertical (SPV), mediated by somatosensory inputs. [Subjects and Methods] A patient with a right posterolateral thalamus hemorrhage had a tendency to fall toward the contralesional side during standing after 8 weeks of treatment. SPV, standing duration, and physical function were evaluated before and after a 1 week standard rehabilitation baseline period, and after a 1 week intervention period, where standing training requiring the patient to control his body orientation in reference to somatosensory inputs from his ipsilateral upper limb was added. [Results] SPV was biased toward the contralesional side before and after the 1 week baseline period. However, SPV improved into the normal range and he could stand for a longer duration after the intervention period. [Conclusion] This case suggests that abnormal SPV is one of the functional mechanisms underlying astasia, and it indicates the effectiveness of standing training with somatosensory information to improve abnormal SPV and postural disorders.