cross-modal plasticity for sensory

Cross-modal plasticity for sensory and motor activation patterns in blind subjects E.R. Gizewski, a, * T. Gasser, b A. de Greiff, c A. Boehm, a and M. Forsting a a Department of Neuroradiology, University Hospital, Essen, Germany b Department of Neurosurgery, University Hospital, Essen, Germany c Department of Neurology, University Hospital, Essen, Germany Received 22 November 2002; accepted 11 February 2003 Abstract Experimental data on cortical reorganization in blind subjects using H 2 15 O positron emission tomography and functional magnetic resonance imaging (fMRI) showed activation of the visual cortex related to Braille reading and tactile discrimination tasks in congenitally and early blind subjects. The purpose of our study was to differentiate whether occipital activation of blind subjects during Braille reading is task specific or only triggered by sensory or motor area activation. Twelve congenitally and early-onset blind subjects were studied with fMRI during Braille reading, discriminat ing nonsen se dots, sensory stimulat ion with electromagnet ic pulse s, and finger tapping. All experiments were performed utilizing a block design with 6 active epochs alternating with 6 rest conditions lasting 34 s each. Echo-planar ima ging seq uences wit h 34 tra nsversal slices wer e per for med on a 1.5-T MR scanne r. All blind indivi dua ls rea ding Bra il le and discriminating nonsense dots showed robust activation of the primary, secondary, and higher visual cortex. Application of peripheral electrical stimuli to the reading hand revealed expected sensory activation of the primary somatosensory cortex, but no activation in the visua l cortex. Pure motor activation during finger tappi ng with the readi ng hand showed expec ted precentra l acti vation and no acti vatio n of visual cortex. In conclusion, occipital activation during Braille reading and discrimination tasks is not due to plasticity of sensory or motor function; pure motor or sensory tasks do not lead to an activation of striate cortex. The brain learns to differentiate between “finger touching” and “finger reading.” Our results suggest that activation of the visual cortex in blind subjects is related to higher and more complex brain functions. © 2003 Elsevier Science (USA). All right s reser ved. Introduction The first experimental data on cortical reorganization in blind subjects were shown by Wanet-Defalque et al. (1988) . They used fluorodeoxyglucose-position emission tomography ( 18 FDG-PET) to investigate the effects of early-onset blindness on cortical metabolism and observed an elevated glucose metabolism of the visual cortex. Since this time, the most interes ting questio n is whether this acti vity is task depend ent. Wit h H 2 15 O-PET, a task- depen dent occip ital cortex activation related to tactile processing in congenitally and earl y-bli nd subje cts was shown (Sadato et al., 1998; Buchel et al., 1998). Sadato et al. (2002) described primary and secondary visual cortex activation during Braille reading and discrimination tasks, whereas they found no activation during nondiscrimination tasks. Buchel et al. (1998b) described no activation in primary visual cortex in congenitally blind subjects during Braille reading but activation in this area in late-onset blindness. However, they found an activation of occipital areas during tactile reading tasks. The question arose about whether the occipital activation is necessary for Braille reading or an epiphenomenon re- lat ed to an increased nec ess ity for somato sensor y inp ut function. This issue has been addressed by an experiment using transcranial magnetic stimulation (TMS) to create a functional lesion in occipital brain areas during Braille reading (Cohen et al., 1997). TMS led to impairment of Braille * Corresponding author. Department of Neuroradiology, University of Essen, Hufeland str. 55, D-451 27 Essen, Germany . Fax: 49-201-723- 5959. E-mail address: [email protected] (E.R. Gizewski). NeuroImage 19 (2003) 968 –975 www.elsevier.com/locate/ynimg 1053 -811 9/03/$ – see front matter © 2003 Elsevier Science (USA). All rights reserv ed. doi:10.1016/S1053-8119(03)00114-9

cross-modal plasticity for sensory

Documents