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Differential functional reorganization of ventral and dorsal visual pathways following childhood hemispherectomy
Vladislav Ayzenberg1, Michael C Granovetter2, Sophia Robert3
1Department of Psychology, University of Pennsylvania, PA, USA; Department of Psychology and Neuroscience Institute, Carnegie Mellon University, PA, USA.
Insights
Pediatric brain hemispherectomy patients show remarkable visual pathway reorganization. The ventral visual pathway demonstrates greater functional plasticity than the dorsal pathway after hemispherectomy.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Cognitive Neuroscience
Background:
- Hemispherectomy surgically removes or disconnects one brain hemisphere to treat drug-resistant epilepsy.
- Pediatric patients often retain significant perceptual abilities despite extensive visual pathway loss.
Purpose of the Study:
- To investigate the functional reorganization of ventral and dorsal visual pathways to the contralateral hemisphere after childhood hemispherectomy.
- To compare the plasticity of the ventral and dorsal visual pathways post-hemispherectomy.
Main Methods:
- Functional magnetic resonance imaging (fMRI) was used in pediatric patients who underwent hemispherectomy.
- Patients completed tasks targeting the ventral (word, face perception) and dorsal (tool, global form perception) visual pathways.
- Lateralized brain responses were analyzed to assess pathway function and reorganization.
Main Results:
- Greater evidence of functional reorganization was observed in the ventral visual pathway compared to the dorsal pathway.
- These findings were consistent across patients, ruling out disease or age-related factors.
- The ventral pathway showed more plasticity than the dorsal pathway following hemispherectomy.
Conclusions:
- The ventral visual pathway exhibits greater functional reorganization and plasticity than the dorsal pathway after childhood hemispherectomy.
- The dorsal pathway's earlier maturation may limit its developmental window for plasticity.
- These results highlight differential plasticity between visual processing streams following major brain surgery.
Abstract:
Hemispherectomy is a surgical procedure in which an entire hemisphere of a patient's brain is resected or functionally disconnected to manage seizures in individuals with drug-resistant epilepsy. Despite the extensive loss of both ventral and dorsal visual pathways in one hemisphere, pediatric patients who have undergone hemispherectomy show a remarkably high degree of perceptual function across many domains. In the current study, we sought to understand the extent to which functions of the ventral and dorsal visual pathways reorganize to the contralateral hemisphere following childhood hemispherectomy. To this end, we collected fMRI data from an equal number of left and right hemispherectomy patients who completed tasks that typically elicit lateralized responses from the ventral or the dorsal pathway, namely, word (left ventral), face (right ventral), tool (left dorsal), and global form (right dorsal) perception. Overall, there was greater evidence of functional reorganization in the ventral pathway than in the dorsal pathway. Importantly, because ventral and dorsal reorganization was tested within the very same patients, these results cannot be explained by idiosyncratic factors such as disease etiology, age at the time of surgery, or age at testing. These findings suggest that because the dorsal pathway may mature earlier, it may have a shorter developmental window of plasticity than the ventral pathway and, hence, be less malleable after perturbation.
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