Parallel input makes the brain run faster.

Full 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.

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Author information

Author/s: Raij, Tommi (T); Karhu, Jari (J); Kicic, Dubravko (D); Lioumis, Pantelis (P); Julkunen, Petro (P); Lin, Fa-Hsuan (FH); Ahveninen, Jyrki (J); Ilmoniemi, Risto J (RJ); Mäkelä, Jyrki P (JP); Hämäläinen, Matti (M); Rosen, Bruce R (BR); Belliveau, John W (JW);

Affiliation: MGH/MIT/HMS Athinoula A. Martinos Center for Biomedical Imaging, Charlestown, MA 02129, USA. raij(-atsign-)nmr.mgh.harvard.edu

Grants: P41 RR14075 (Agency:United States NCRR) ; R01 HD040712 (Agency:United States NICHD) ; R01 NS037462 (Agency:United States NINDS) ; R01 NS048279 (Agency:United States NINDS) ; R21 EB007298 (Agency:United States NIBIB)

Journal and publication information

Publication Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't

Journal: NeuroImage (Neuroimage), published in United States. (Language: eng)

Reference: 2008-May; vol 40 (issue 4) : pp 1792-7

Dates: Created 2008/04/14; Completed 2008/06/23;

PMID: 18353681, status: MEDLINE (last retrieval date: 11/6/2008)

Sourced from the National Library of Medicine. Abstract text and other information may be subject to copyright.

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MeSH headings (categories)

This article was linked to the MESH Headings shown below.

Adult
Brain - physiology
Electric Stimulation
Electroencephalography
Evoked Potentials - physiology
Evoked Potentials, Somatosensory - physiology
Humans
Magnetic Resonance Imaging

Magnetoencephalography
Male
Median Nerve - physiology
Mental Processes - physiology
Psychomotor Performance - physiology
Reaction Time - physiology
Somatosensory Cortex - physiology
Transcranial Magnetic Stimulation

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