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 (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.

Functional Resilience of the Neural Visual Recognition System Post-Pediatric Occipitotemporal Resection

“…At the same time, despite the apparent integrity of the neural profile, the OTC patients’ visual recognition ability is statistically inferior to that of controls for face and object recognition, as demonstrated previously 30–32 . OTC patients’ behavioral profiles appear to reflect that visual recognition may stringently require the maintenance of representations across two hemispheres to render typical recognition, or in other words, two hemispheres are better than one.…”

“…B e havior. Designs of the (a) Cambridge Face Memory Test 44,45 (figure adapted from Croydon et al) 44 , (b) Cambridge Bicycle Memory Test 46,47 (figure adapted from Dalrymple et al) 47 , and (c) word recognition task 30,48 (figure adapted from Dundas et al) 48 . (d) Mean accuracy for each group (boxplots) and individual participant (overlaid, randomly jittered point plots) by task (recognition of faces, objects, words).…”

“…All models included group (the key predictor of interest) and age (the primary covariate, expected to affect each dependent variable 12,30,75 ). In approximating fixed effects, the maximum log-likelihood criterion was optimized 76 , and the Bound Optimization by Quadratic Approximation algorithm was applied 77 .…”

“…That patients with resections that include occipital and/or temporal cortex have seemingly intact CS ROIs [20][21][22] does not necessarily imply that the neurons in these regions are tuned for stimulus exemplars. Indeed, while patients with a single OTC perform surprisingly well on recognizing individual faces and words (average accuracy about 85%), their exemplar-specific performance is still statistically inferior to TD controls [30][31][32] , perhaps due to compromised neural profiles for stimulus individuation.…”

“…For all participants, CS and RS is measured in response to faces, objects, and words, and participants' behavioral abilities are characterized as well. If OTC patients do not evince RS in the TD range, this may offer a direct explanation for patients' previously reported behavioral difficulties [30][31][32] . If RS is intact but visual behaviors are not, this may suggest that the documented behavioral deficits in visual recognition are less a consequence of impairment of the integrity of stimulus-specific neural representation than they are a consequence of constraining processes to a single hemisphere (and hence, revealing the necessity of a second hemisphere).…”