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Background and Hypotheses
Recovery of motor function after cerebral ischemic infarction, occurring over weeks or months, is most probably due to reorganization of the underlying neuronal networks (7). Both common and subject-specific patterns have been described (9;10). Functional imaging studies in subjects with subcortical ischemic infarction revealed that patients with poor recovery were more likely to recruit a number of motor-related brain regions in addition to those seen in the control group during a motor task, whereas patients with more complete recovery were more likely to have “normal” task-related brain activations (8). In a longitudinal functional magnetic resonace imaging (fMRI) study Jaillard et al. (3) demonstrated the re-emergence after stroke of activity during a finger motor task in the intact dorsal M1 rather than the ventral M1, supporting a “vicarification" model of stroke recovery. Moreover, stroke patients participating in constraint-induced movement therapy show an enlargement of the motor output area in the affected hemisphere after therapy (4).
In most functional brain imaging studies, stroke patients performed mainly pure motor tasks. However, during daily activities more complex sensorimotor tasks like writing, placing pegs in holes or tactile object exploration are needed. Using a somatosensory discrimination paradigm to employ tactile exploration of shape, patients recovering from stroke have shown reduced activations in cortical areas, enhanced premotor activations and abnormal contralesional activations (9;10). Recently we have shown, that the intraparietal sulcus and superior parietal lobule are important relay nodes for information processing during somatosensory discrimination (1;5;6). Moreover, we have characterized functional systems involved in somatosensory discrimination by superimposing cytoarchitectonic maps on activation fields and brain lesions in the postcentral gyrus and superior parietal lobule (2;6). Considering the needs of daily activities, the significance of sensory deficits for the reorganization of neuronal networks and its relation to motor recovery remains to be clarified.
We postulate that patients with and without involvement of somatosensory cortices of right or left hemispheres recruit different networks during recovery from hand paresis. Correlating neurobehaviour with specific cerebral activation patterns, we will be able i) to describe the interference of elementary sensory and haptic information processing with recovery of motor function and vice versa; and ii) to differentiate between specific haptic information processing of sensorimotor activities in the right and left hemispheres.

Experimental design and methods
We will investigate 40 patients repeatedly during recovery from sensorimotor stroke. Cerebral activation patterns of sensorimotor activity during manipulation and somatosensory discrimination tasks will be assessed with event-related blood oxygen level-dependent (BOLD) fMRI at early and late chronic stages. All fMRI data will be analyzed with SPM5 as i) individual analysis of each patient, ii) categorical group analysis and iii) principal component analysis. The affected sensory cortices will be mapped using recently defined cytoarchitectonic areas of the postcentral gyrus and the superior parietal lobule. To avoid perfusion related variances of the BOLD response, additional arterial spin labeling (ASL) cerebral blood flow will be measured. fMRI activation patterns will be used as seeding points to determinate the white matter tracts, connecting these areas, with diffusion tensor imaging (DTI). The video-monitored task performances will be correlated with the lesions and the specific activation patterns.

Importance of the project
Despite strong efforts and advances in acute stroke management, residual sensorimotor deficits have a major impact on functional capability. Severe disability affects at least a third of all stroke patients during daily activities. Different motor skills depend highly on sensorimotor integration and sensory information processing. Thus, demonstration and categorisation of cerebral reorganisation over time in the sensory domain, related to recovery, may have considerable consequences for rehabilitation programmes employing e.g. physio- or ergotherapy. New therapeutic approaches can only be developed when these mechanisms are better described and understood.

References
1. Hartmann,S. Die Untersuchung der funktionellen Verknüpfung von Hirnregionen während der taktilen Exploration von Objekten. Hauptkomponentenanalyse eines Stimulationstestes mittels funktioneller Kernspintomographie. Thesis/Dissertation 2007.
2. Hoemke,L., Amunts,K., Boenig,L., Fretz,C., Binkofski,F., Zilles,K., and Weder,B. (2007). Analysis of lesions in patients with unilateral tactile agnosia using cytoarchitectonic probabilistic maps. Submitted.
3. Jaillard,A., Martin,C.D., Garambois,K., Lebas,J.F., and Hommel,M. (2005). Vicarious function within the human primary motor cortex? A longitudinal fMRI stroke study. Brain. 128, 1122-1138.
4. Liepert,J. (2005). Transcranial magnetic stimulation in neurorehabilitation. Acta Neurochir.Suppl. 93, 71-74.
5. Stoeckel,M.C., Weder,B., Binkofski,F., Buccino,G., Shah,N.J., and Seitz,R.J. (2003). A fronto-parietal circuit for tactile object discrimination: an event-related fMRI study. Neuroimage. 19, 1103-1114.
6. Stoeckel,M.C., Weder,B., Binkofski,F., Choi,H.J., Amunts,K., Pieperhoff,P., Shah,N.J., and Seitz,R.J. (2004). Left and right superior parietal lobule in tactile object discrimination. Eur.J.Neurosci. 19, 1067-1072.
7. Ward,N.S., Brown,M.M., Thompson,A.J., and Frackowiak,R.S. (2003). Neural correlates of motor recovery after stroke: a longitudinal fMRI study. Brain. 126, 2476-2496.
8. Ward,N.S., Brown,M.M., Thompson,A.J., and Frackowiak,R.S. (2003). Neural correlates of outcome after stroke: a cross-sectional fMRI study. Brain. 126, 1430-1448.
9. Weder,B., Knorr,U., Herzog,H., Nebeling,B., Kleinschmidt,A., Huang,Y., Steinmetz,H., Freund,H.J., and Seitz,R.J. (1994). Tactile exploration of shape after subcortical ischaemic infarction studied with PET. Brain. 117, 593-605.
10. Weder,B. and Seitz,R.J. (1994). Deficient cerebral activation pattern in stroke recovery. Neuroreport. 5, 457-460.