Postural reflexes evoked by tapping forehead and chest

We investigated whether a tap with a reflex hammer to the forehead can elic it responses in the leg muscles and whether vestibular stimulation is the c rucial prerequisite for eliciting these responses. We also measured the pos tural changes caused by the tap and by the compensatory, presumably reflex- like reactions of the subject. Tap-evoked activity of leg muscles was easil y elicited during upright stance in normal subjects and was also seen in tw o subjects without vestibular function. The pattern of muscle activation cl early showed a counteraction to the tap-evoked perturbation of stance. Taps applied to the chest elicited similar reflexes. Since these two conditions imply a different activation of the vestibular apparatus, the vestibular i nput alone cannot account for the observed leg muscle reflexes. We suggest that multisensory reflex pathways that integrate vestibular and propriocept ive inputs account for these reflexes.