Double Dissociation Between Visual Recognition and Picture Naming: A Study of the Visual Language Connectivity Using Tractography and Brain Stimulation

BACKGROUND: Study of the corticosubcortical functional anatomy of reading and picture naming. OBJECTIVE: To study the role of the left basal occipitotemporal area and its white matter pathways. METHODS: Three patients underwent awake surgery for lesions in the left basal posterotemporal region with intraoperative electrostimulations. Intraoperative testing consisted of naming, reading, and recognition of symbols. Location of the stimulation sites was obtained by comparing the surgical cavity in the postoperative magnetic resonance imaging with the tags precisely located in each one of these sites seen on intraoperative photographs. RESULTS: A double dissociation was elicited, inducing specific visual recognition and reading disturbances during stimulation in the left posterobasal temporal cortex, without naming impairment. Stimulation of the inferior part of the sagittal stratum (inferior longitudinal fascicle) generated the same response, while a specific picture-naming impairment, consisting of semantic paraphasia, was obtained when stimulating superiorly to this fascicle, over the lateral wall and roof of the ventricle (inferior fronto-occipital fascicle). CONCLUSION: We propose the existence of a dual visual language route in the left dominant hemisphere. The first pathway seems to run basally, from the occipital lobe to the posterobasal temporal cortex, mediated by the left inferior longitudinal fascicle, subserving visual recognition. The second pathway might run superiorly and more medially, from the occipital pole directly to the frontal areas, and could be underlain by the inferior fronto-occipital fascicle, involved in naming (semantic processing). Such a model might have both fundamental and clinical implications for the selection of the tasks during awake mapping as well as for postsurgical rehabilitation.