Painless legs and moving toes from parasagittal meningioma

Radially expanding optic flow is a visual consequence of forward locomotion and supports walking, also in patients with Parkinson’s disease (PD). When presented on a display, it evokes the illusion of forward self-motion. This implies that manipulation of optic flow while walking on a treadmill enables testing the effect of this basic stimulus pattern on gait progression, independent of actual walking. As movements in PD patients are more vulnerable to external stimuli, which may lead to, for example, freezing of gait (FOG), we expected a stronger effect of manipulating optic flow in these patients than in the healthy controls (HC). Fifteen PD patients (8 right-sided symptom dominance [PD.R], 7 left-sided [PD.L]) and 10 matched HCs (mean age, 66.3 years; SD, 7.8) were tested. Patients (mean age, 64.9 years; SD, 7.7 years) were mildly affected (Hoehn & Yahr, 2.3; UPDRS III, 24.3 SD, 7.6) and did not suffer from FOG. At steady-speed walking on the treadmill, narrowing the optic flow field was expected to evoke slowing of gait with backward displacement, mimicking the effect of approaching a narrow corridor. The latter was quantified by center-of-mass calculation. Optic flow is represented by white dots in the lower half of a black screen (171 128 cm). A gradual 1.8-second transition from a wide to a narrow flow field occurred by expanding dark gray surfaces from the horizon in both upward and downward directions (condition Fw-to-Ftn), which provided the natural illusion of moving into the changing environment. Control conditions for nonspecific visual effects were the abrupt transition from wide flow to stationary dots (Fw-to-Sw) and the gradual transition from a wide to a narrow stationary field (Sw-toStn). Given right-hemisphere dominance in visuospatial processing, stronger effects were expected in PD.L. The WAIS block design test was used as a general indicator of right hemisphere function. The transition of narrowing the wide-optic flow field evoked clear gait obstruction, particularly in PD.L (Fig. 1). This suggested a relation with right hemisphere dysfunction, which was supported by the correlation between stronger gait obstruction and lower scores on the WAIS block design in the entire PD group (P1-tailed 1⁄4 .016, r 1⁄4 0.552). Although patient numbers were rather small after splitting into PD.L and PD.R groups, the novel paradigm of manipulating optic flow during treadmill gait appears to provide a promising strategy to study the effects of basic visual stimulus features on gait control. The effect particularly in PD.L is consistent with right-hemisphere dominance concerning visuomotor transformations, also in gait. Enhanced stimulus effects on movements in PD may be a consequence of reduced output from basal ganglia–thalamic circuitry to the lateral premotor cortex, leaving an overruling effect of parietally transferred visual information. As the output of basal ganglia–thalamic circuitry to medial frontal regions may be FIG. 1. Effect of narrowing optic flow on treadmill position and correlation with block design test. A: Mean backward displacement on the treadmill (with standard error) is expressed by positive values (in centimeters), comparing the mean position in the 1.8-second frame after and 1.8 seconds before transition onset in the visual display (P < .05). B: Right hemisphere involvement in backward displacement of Parkinson’s disease patients during the treadmill gait is expressed by the correlation between the block design test and the effect of the transition from a wide to narrow forward optic flow field (Fw-to-Ftn). The thick line shows the overall regression, R 5 0.305. The separate regression lines for PD.L and PD.R patients are constituted by thin dashes and dots, respectively. Abbreviations: PD.L, Parkinson’s disease with left-sided symptom dominance; PD.R, PD with right-sided symptom dominance; HC, healthy controls; Fw-to-Ftn, transition from wide-flow field to narrow flow; Fw-to-Sw, control transition of wide flow to stationary wide field; Sw-to-Stn, control transition of stationary wide field to stationary narrow field; cm, centimeters.