Sequential evolution of cortical activity and effective connectivity of swallowing using fMRI.

Swallowing consists of a hierarchical sequence of primary motor and somatosensory processes. The temporal interplay of different phases is complex and clinical disturbances frequent. Of interest was the temporal interaction of the swallowing network. Time resolution optimized functional magnetic resonance imaging was used to describe the temporal sequence of representation sites of swallowing and their functional connectivity. Sixteen young healthy volunteers were investigated who swallowed 2 ml of water 20 times per run with a repetition time for functional imaging of 514 ms. After applying the general linear model approach to identify activation magnitude in preselected regions of interest repeated measures analysis of variance (rmANOVA) was used to detect relevant effects on lateralization, time, and onset. Furthermore, dynamic causal modeling (DCM) was applied to uncover where the input enters the model and the way in which the cortical regions are connected. The temporal analysis revealed a successive activation starting at the premotor cortex, supplementary motor area (SMA), and bilateral thalamus, followed by the primary sensorimotor cortex, the posterior insula, and cerebellum and culminating with activation in the pons shortly before subsiding. The rmANOVA revealed that activation was lateralized initially to the left hemisphere and gradually moved to the right hemisphere over time. The group random effects DCM analysis resulted in a most likely model that consisted of inputs to SMA and M1S1, bidirectionally connected, and a one-way connection from M1S1 to the posterior insula.

Brain imaging correlates of recovered swallowing after dysphagic stroke: A fMRI and DWI study.

Neurogenic dysphagia frequently occurs after stroke and deglutitive aspiration is one of the main reasons for subacute death after stroke. Although promising therapeutic interventions for neurogenic dysphagia are being developed, the functional neuroanatomy of recovered swallowing in this population remains uncertain. Here, we investigated 18 patients post-stroke who recovered from dysphagia using an event related functional magnetic resonance imaging (fMRI) study of swallowing. Patients were characterized by initial dysphagia score (mild to severe), lesion mapping, white matter fractional anisotropy (FA) of the pyramidal tracts, and swallowing performance measurement during fMRI scanning. Eighteen age matched healthy participants served as a control group. Overall, patients showed decreased fMRI-activation in the entire swallowing network apart from an increase of activation in the contralesional primary somatosensory cortex (S1). Moreover, fMRI activation in contralesional S1 correlated with initial dysphagia score. Finally, when lesions of the pyramidal tract were more severe, recovered swallowing appeared to be associated with asymmetric activation of the ipsilesional anterior cerebellum. Taken together, our data support a role for increased contralesional somatosensory resources and ipsilesional anterior cerebellum feed forward loops for recovered swallowing after dysphagia following stroke.