Plantar stimulation can affect subjective straight-ahead in neglect patients

The rightward orientation bias of neglect patients has been shown to be decreased by postural changes, suggesting that afferences coding the posture relative to gravity might influence the body-centred spatial reference frame. In order to test this hypothesis, we evaluated the effects of plantar stimulations on the subjective straight-ahead (SSA) of two neglect patients presenting with a strong rightward shift, as well as two non-neglect patients and three normal subjects. Vibratory or electrical stimulations were applied to the left or right plantar sole. Data showed that these manipulations influenced the SSA position in neglect patients only. The observed improvement could be explained by a direction-specific effect of vibration, in addition to a non-specific activation induced by both stimulations.