Can you be more specific about patient? Basically you are seeing (undampened) inappropriate output from the vestibular nuclei. These nuclie are controlling extenor tone to the spine. Review decorticate vs decerebate posturing as it pertains to brainstem injury and recongnize that supranuclear lesions (ie. stroke) will cause a decrease in the inhibition of these postural regulatory centers. This is also the mechanism which is producing the spasticity in their the lower extremity as well.