Bilateral impairment of somesthetically mediated object recognition in humans.

Thirty adult patients (six in each of five groups--neurologically normal, lacunar infarct-related hemiparesis, unilateral thalamic lacunar infarction, right cortical infarction with mild left hemineglect, and extensive right cortical infarction with severe left hemineglect) were asked to perform various tasks that encompassed basic and intermediate somatosensory functions and tactile and visual object recognition. Patients with thalamic and cortical infarctions had severe impairment of contralateral hand-mediated somatosensory functions in all three categories of somesthetic tasks, although patients with cortical infarction were more impaired on the object recognition task than were patients with thalamic infarction. Patients with extensive damage to the right hemisphere and severe left hemineglect also had impairment of somesthetically mediated object recognition in the ipsilateral hand despite normal basic and intermediate somatosensory function and visually mediated object recognition analogous to unilateral tactile agnosia. All other groups had normal ipsilateral tactile object recognition.