title: Parallel input makes the brain run faster.
abstract: In serial sensory processing, information flows from the thalamus via primary sensory cortices to higher-order association areas. However, association cortices also receive, albeit weak, direct thalamocortical sensory inputs of unknown function. For example, while information proceeds from primary (SI) to secondary (SII) somatosensory cortex in a serial fashion, both areas are known to receive direct thalamocortical sensory input. The present study examines the potential roles of such parallel input arrangements. The subjects were presented with median nerve somatosensory stimuli with the instruction to respond with the contralateral hand. The locations and time courses of the activated brain areas were first identified with magnetoencephalography (MEG). In a subsequent session, these brain areas were modulated with single-pulse transcranial magnetic stimulation (TMS) at 15-210 ms after the somatosensory stimulus while electroencephalography (EEG) was recorded. TMS pulses at 15-40 ms post-stimulus significantly speeded up reaction times and somatosensory-evoked responses, with largest facilitatory effects when the TMS pulse was given to contralateral SII at about 20 ms. To explain the results, we propose that the early somatosensory-evoked physiological SII activation exerts an SII-->SI influence that facilitates the reciprocal SI-->SII pathway - with TMS to SII we apparently amplified this mechanism. The results suggest that the human brain may utilize parallel inputs to facilitate long-distance cortico-cortical connections, resulting in accelerated processing and speeded reaction times. This arrangement could also allow very early top-down modulation of the bottom-up stream of sensory information.
authors: MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA 02129, USA. raij@nmr.mgh.harvard.edu
authors: Tommi
authors: T
authors: Raij
authors: Jari
authors: J
authors: Karhu
authors: Dubravko
authors: D
authors: Kicić
authors: Pantelis
authors: P
authors: Lioumis
authors: Petro
authors: P
authors: Julkunen
authors: Fa-Hsuan
authors: FH
authors: Lin
authors: Jyrki
authors: J
authors: Ahveninen
authors: Risto J
authors: RJ
authors: Ilmoniemi
authors: Jyrki P
authors: JP
authors: Mäkelä
authors: Matti
authors: M
authors: Hämäläinen
authors: Bruce R
authors: BR
authors: Rosen
authors: John W
authors: JW
authors: Belliveau
mesh_terms: D000328:Adult; D001921:Brain / Q000502:physiology*; D004558:Electric Stimulation; D004569:Electroencephalography; D005071:Evoked Potentials / Q000502:physiology; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D006801:Humans; D008279:Magnetic Resonance Imaging; D015225:Magnetoencephalography; D008297:Male; D008475:Median Nerve / Q000502:physiology; D008606:Mental Processes / Q000502:physiology*; D011597:Psychomotor Performance / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology; D050781:Transcranial Magnetic Stimulation