Significance
Can one brain hemisphere perform the functions of the typical two hemispheres? Typically, in adults, there are right and left hemispheric biases for face and word recognition, respectively, a division of labor that emerges over development. Here, face and word recognition were examined in childhood hemispherectomy patients, who have a single hemisphere. While these patients showed above 80% task accuracy for both visual classes—surprisingly high relative to the brain volume resected—they nonetheless performed more poorly than neurotypical 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 remarkable plasticity of the developing brain but, at the same time, highlights plasticity’s constraints.
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 (median age 16.7 y) 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.
