title: Habituation within the somatosensory processing hierarchy.
abstract: Habituation is a basic process of learning evident in a decrement in neuronal/behavioral responses to repeated sensory stimulation. It is generally accepted that habituation affects all sensory systems in the human brain, including the somatosensory network. However, it is not clear where habituation originates within this hierarchically organized network. In this study, we examined whether habituation effects increase relatively uniformly along the processing hierarchy or rather distinctly at a particular processing stage. We addressed these questions by performing functional magnetic resonance imaging (fMRI) on 43 healthy subjects during unilateral electrical median nerve stimulation using a block design. We found a time-dependent decrease in the positive BOLD response (indicative of habituation) in all areas of the somatosensory network with the exception of Brodmann area (BA) 3b. The increase in habituation within the presumed processing stream was most pronounced between subareas of the primary somatosensory cortex (BA3b, BA1, BA2), and no further increase in habituation effects was observed in the subsequent processing stages within either the secondary somatosensory cortex or the insula. Moreover, we found a relatively strong habituation effect within the thalamus. These findings indicate that the increase in habituation along the processing hierarchy is measurable primarily between subareas of the primary somatosensory cortex, and we hypothesize that this increase originates in thalamocortical interactions early in the processing stream.
authors.affiliation: Department of Neurology, University of Jena, Jena, Germany. carsten.klingner@med.uni-jena.de
authors.forename: Carsten M
authors.initials: CM
authors.lastname: Klingner
authors.forename: Igor
authors.initials: I
authors.lastname: Nenadic
authors.forename: Caroline
authors.initials: C
authors.lastname: Hasler
authors.forename: Stefan
authors.initials: S
authors.lastname: Brodoehl
authors.forename: Otto W
authors.initials: OW
authors.lastname: Witte
mesh_terms: D000328:Adult; D001931:Brain Mapping / Q000379:methods / Q000523:psychology*; D002540:Cerebral Cortex / Q000502:physiology*; D004558:Electric Stimulation; D005260:Female; D006185:Habituation, Psychophysiologic / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008475:Median Nerve / Q000502:physiology; D013003:Somatosensory Cortex / Q000502:physiology*; D013788:Thalamus / Q000502:physiology*