Frontoparietal involvement in passively guided shape and length discrimination: a comparison between subcortical...

Fifty to 85 % of patients with sensorimotor hemiparesis following stroke encounter impaired tactile processing and proprioception. Sensory feedback is, however, paramount for motor recovery. Sensory feedback through passively guided somatosensory discrimination exercises has been used in therapy, but so far, no studies have investigated which brain areas are involved in this process. Therefore, we performed a study with functional magnetic resonance imaging (fMRI) to examine brain areas related to discriminating passively guided shape and length discrimination in stroke patients and evaluate whether they differed from healthy age-matched controls. Eight subcortical stroke patients discriminated different shapes or length based on passive finger movements provided by an fMRI compatible robot. The data were contrasted to a control condition whereby patients discriminated music fragments. Passively guided somatosensory discrimination versus music discrimination elicited activation in similar frontoparietal areas in stroke patients compared to the healthy control group. Still, patients had increased activation in the right angular gyrus, left superior lingual gyrus, and right cerebellar lobule VI compared to healthy volunteers. Conversely, healthy volunteers activated the right precentral gyrus to a greater extent than patients. In both groups, shape discrimination resulted in anterior intraparietal sulcus and premotor activation, while length discrimination elicited a more medially located parietal activation with mainly right-sided premotor activity. The current study is a first step in clarifying brain activations during passively guided shape and length discrimination in subcortical stroke patients. Research into the effects of the use of sensory discrimination exercises on brain reorganization and brain plasticity is encouraged.