Objective: The ventrolateral nucleus of the thalamus (VL), based on its connectivity with the cerebellum and motor cortex, has long been considered to be involved with motor functions. We show that the human VL also plays a prominent role in sensory processing.
Methods: Structural magnetic resonance imaging and diffusion tensor imaging were used to localize a small lesion restricted to the right VL in a patient with contralesional sensory processing deficits. Systematic assessments of anatomic brain organization and behavioral measurements of somatosensory and visual processing were conducted at several time points after stroke.
Results: Initially, the patient was more likely to detect events on the contralesional side when a simultaneous ipsilesional event was presented within the same, but not different, sensory modality. This perceptual phenomenon, which we refer to as unisensory antiextinction, persisted for several months before transforming into a form of synesthesia in which auditory stimuli produced tactile percepts. Tractography performed on the diffusion tensor imaging data showed altered connections from the lesioned thalamus to the cerebral cortex, suggesting a neural basis for these sensory changes.
Interpretation: These results demonstrate a role for the VL in sensory processing and suggest that reorganization of thalamocortical axonal connectivity can lead to major changes in perception.