Lobectomy or, in extreme cases, hemispherectomy, involves the removal of part or all of a cerebral hemisphere as a means of treating certain intractable conditions (e.g. epilepsy). Despite the radical nature of this procedure, the resulting visual deficits can undergo impressive improvement over time, especially when the procedure is conducted at an early age. Surprisingly, rather little exploration has been directed at elucidating the mechanisms supporting this remarkable display of neural plasticity. The goal of this research is to characterize the remapping of visual processing in both cortical and subcortical regions from pre- to post-surgery and longitudinally thereafter, using (and correlating) fine-grained behavioral and neuroimaging methods (univariate and advanced multivariate techniques) in a relatively large group of children who have undergone posterior cortical resection.
We first aim to characterize the reorganization of retinotopic cortex, by mapping meridians and by population receptive-field (pRF) modeling. One intriguing hypothesis that motivates this investigation concerns the ability of the intact occipital lobe to develop sensitivity over time to the affected ipsilateral hemifield. Second, at the level of extrastriate cortex, we will characterize the selectivity and topography associated with the recognition of visual categories such as faces, houses, objects and word forms during task and during resting state scans. The ability of a single hemisphere to cope with multiple categories is indicative of important adjustments in the architecture of high-level object recognition and successful recognition may be mediated by a more compact integration of visual representations underlying different categories. Third, we propose to explore functional and structural changes in the profile of subcortical structures (e.g., pulvinar/superior colliculus) as a potential mechanism for the cortical changes, and will examine structural connectivity between early and later cortical regions and subcortical structures using tractography methods. Last, we will examine patterns of recovery as a function of key variables such as age at test and at surgery, presurgical cognitive level and side of lesion. This last factor is particularly relevant for understanding hemispheric dominance, effects of lateralization and postsurgical reorganization. In sum, our investigation constitutes an unprecedented examination of a radical case of cortical remapping at the single case and aggregated group level. The degree and the manner by which there is restitution of visual function following drastic reduction in the available neural resources can shed light on the boundary conditions of plasticity. Understanding lobectomy and its consequences offers unique insights into neural plasticity that can contribute significantly both to a basic science understanding of the visual system and to translational approaches (possible rehabilitation methods and guidelines for surgery).
The overarching goal of this proposal is to examine the organization and recovery of visual functions following large posterior cortical resections in childhood. Cutting-edge psychophysical and neuroimaging procedures, as well as novel analytic approaches, will be employed to elucidate the nature and changes in topography and selectivity of the cortical and subcortical visual system pre- and post-surgery (and longitudinally thereafter), and the mechanisms that give rise to the restitution of function. Examining the consequences of such resections provides a rare but highly informative window into neural plasticity that can contribute significantly both to a fundamental understanding of the visual system and to clinical and translational application (possible rehabilitation methods and guidance for surgical protocols).
| Liu, Tina T; Nestor, Adrian; Vida, Mark D et al. (2018) Successful Reorganization of Category-Selective Visual Cortex following Occipito-temporal Lobectomy in Childhood. Cell Rep 24:1113-1122.e6 |
| Liu, Tina T; Behrmann, Marlene (2017) Functional outcomes following lesions in visual cortex: Implications for plasticity of high-level vision. Neuropsychologia 105:197-214 |
