Early activation of the primary somatosensory cortex without conscious awareness of somatosensory stimuli in tumor patients

The primary sensory cortex has usually been regarded as a necessary step in the information processing stream leading to conscious awareness. Recently , it has been proposed that that higher order associative areas rather than the primary sensory areas are the neural basis of conscious perception. In two patients with tumors near the central region we recorded magnetic soma tosensory evoked fields. Magnetic source imaging revealed early (40 ms) neu ral activation in primary somatosensory cortex and absence of later (> 60 m s) neural activation in the primary and associative areas in these patients . None of the patients showed conscious awareness of somatosensory stimuli applied to the corresponding body site although the first component of the evoked field was within normal limits. The time course of the magnetic resp onses and additional evidence on intensity ratings of somatosensory stimuli suggest that early activity in the primary somatosensory cortex is not suf ficient for conscious experience to emerge. (C) 2001 Elsevier Science Irela nd Ltd. All rights reserved.