With Childhood Hemispherectomy, One Hemisphere Can Support--But is Suboptimal for--Word and Face Recognition

Abstract

The right and left cerebral hemispheres are important for face and word recognition, respectively--a specialization that emerges over human development. The question is whether this bilateral distribution is necessary or whether a single hemisphere, be it left or right, can support both face and word recognition. Here, face and word recognition accuracy in patients with a single hemisphere following childhood hemispherectomy was compared against matched typical controls. In Experiment 1, participants viewed stimuli in central vision. Across both face and word tasks, accuracy of both left and right hemispherectomy patients, while significantly lower than controls accuracy, averaged above 80% and did not differ from each other. To compare patients single hemisphere more directly to one hemisphere of controls, in Experiment 2, participants viewed stimuli in one visual field to constrain initial processing chiefly to a single (contralateral) hemisphere. Whereas controls had higher word accuracy when words were presented to the right than to the left visual field, there was no field/hemispheric difference for faces. In contrast, left and right hemispherectomy patients, again, showed comparable performance to one another on both face and word recognition, albeit significantly lower than controls. Altogether, the findings indicate that a single developing hemisphere, either left or right, may be sufficiently plastic for comparable representation of faces and words. However, perhaps due to increased competition or "neural crowding," constraining cortical representations to one hemisphere may collectively hamper face and word recognition, relative to that observed in typical development with two hemispheres. Significance StatementAdults show right and left cerebral hemispheric biases for face and word recognition, respectively, a division of labor that emerges over development. Here, face and word recognition were assessed in childhood hemispherectomy patients to study the consequences of development with a single hemisphere. While these patients showed above 80% accuracy on face and word recognition tasks, which is surprisingly high relative to the brain volume resected, they nonetheless performed more poorly than typically developing controls. Importantly, patient performance was independent of which hemisphere was removed, suggesting that their single, preserved hemisphere subserves face and word recognition comparably, albeit somewhat inferiorly relative to controls. This demonstrates the remarkable plasticity of the developing brain but, at the same time, highlights plasticitys constraints.