title: Thalamo-cortical processing of near-threshold somatosensory stimuli in humans.
abstract: Somatosensory stimuli elicit complex cortical responses that are discernible as somatosensory evoked potentials (SEPs) in scalp electroencephalographic recordings. Whereas earlier SEP components, occurring up to 100 ms after stimulus delivery, have been labeled 'preconscious', later responses have been associated with stimulus awareness. To date, how far these processes are primarily cortical or comprise additional subcortical operations remains open. Therefore, we recorded thalamic and scalp SEPs evoked by perceived as well as unperceived median nerve stimulation in neurosurgical patients with electrodes implanted into the ventral intermediate nucleus of the thalamus for deep brain stimulation. At stimulation intensities below perceptual threshold, only thalamic SEP components appeared consistently during the first 75 ms after stimulus delivery. Stimulation that was perceived by the patients elicited cortical as well as thalamic SEPs that lasted longer than 75 ms. These results indicate that the thalamus remains active after the primary propagation of a sensory signal to the cortex, and suggest that the transition from elementary to higher-order somatosensory processing is based on thalamo-cortical interactions.
authors.affiliation: Department of Neurology, CBF, Charité-University Medicine Berlin, Hindenburgdamm 30, 12203 Berlin, Germany. fabian.klostermann@charite.de
authors.forename: Fabian
authors.initials: F
authors.lastname: Klostermann
authors.forename: Michael
authors.initials: M
authors.lastname: Wahl
authors.forename: Jesko
authors.initials: J
authors.lastname: Schomann
authors.forename: Andreas
authors.initials: A
authors.lastname: Kupsch
authors.forename: Gabriel
authors.initials: G
authors.lastname: Curio
authors.forename: Frank
authors.initials: F
authors.lastname: Marzinzik
mesh_terms: D000344:Afferent Pathways / Q000502:physiology*; D000368:Aged; D002540:Cerebral Cortex / Q000502:physiology*; D046690:Deep Brain Stimulation; D004567:Electrodes, Implanted; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008875:Middle Aged; D012684:Sensory Thresholds / Q000502:physiology*; D013788:Thalamus / Q000502:physiology*; D055698:Touch Perception / Q000502:physiology*