[Characteristic event-related potentials evoked by somatosensory tasks in a patient with right-left disorientation and finger agnosia].

Event-related brain potentials associated with both somatosensory and auditory detection tasks were recorded from the scalp in a 63-year-old man with finger agnosia and right-left disorientation resulted from cerebral infarction located around the region of the left angular gyrus. In a somatosensory oddball paradigm for discrimination between the right index finger (target, P = 0.2) and the left index finger (non-target, P = 0.8), early cognitive components P100, N140 and processing negativity were observed both in the target responses and non-target responses, however, no P300 component was recorded in both paradigms. In another paradigm to discriminate the index finger (target, P = 0.2) from small finger (non-target, P = 0.8) in the right hand, no P300 was evoked and only processing negativity was recorded both in the target responses and nontarget responses. These phenomena were obtained through characteristic behavior that the patient paid attention to the target stimuli as well as non-target stimuli and mentally counted them without discrimination. In contrast, in an auditory oddball paradigm P300 was clearly demonstrated to target stimuli that the patient correctly could count. The normal appearance of P300 in auditory detection tasks strongly suggests that the neural generator for the P300 was reserved intact. These results indicate that somatosensory information processing might be disturbed at the level of sensory discrimination needed for generation of P300 in our patient. It is also proposed that the neural events for somatosensory discrimination and auditory discrimination would take separate channels each other to reach the common generator of p300 in information processing.