Poster A14, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall
Temporal language areas appear necessary to wire up frontal cortex for language
Greta Tuckute1,2, Zachary Mineroff2, Idan Blank2,3, Hope Kean2, Evelina Fedorenko2,4,5;1University of Copenhagen, 2Massachusetts Institute of Technology, 3University of California, Los Angeles, 4Harvard Medical School, 5Massachusetts General Hospital
High-level language processing is supported by a bilateral fronto-temporal brain network, which is lateralized to the left hemisphere (LH) in most individuals. How this network emerges ontogenetically remains debated. There is general agreement that frontal cortex exhibits protracted development (e.g., Fuster, 2002), suggesting that frontal language areas must emerge later and/or mature more slowly than temporal language areas. But are temporal areas necessary for the development of the language areas in the frontal lobe, or do frontal language areas instead emerge independently? We shed light on this question through a case study of an individual (EG) born without a left temporal lobe, likely as a result of pre/perinatal stroke. We investigated the high-level language network and a control network (the domain-general multiple demand (MD) network; Duncan, 2010) in EG relative to two controls groups (n=96 and n=57) using functional localizer tasks in fMRI (Fedorenko et al., 2010). First, we asked whether the language network in the language-dominant hemisphere in EG is similar to control participants. As expected in cases of early LH damage (e.g., Lenneberg, 1967), EG had a fully functional language network in her right hemisphere (RH), comparable in topography, extent, and strength of activation to the LH language network in the control groups. Moreover, EG performed within normal range on standardized language assessments. Second, the critical question was whether EG’s intact left frontal lobe would contain language-responsive areas despite her biologically nonintact left temporal lobe. If so, that would suggest that frontal language areas can emerge without temporal language areas in the same hemisphere. If not, it would suggest that temporal language areas are critical for the emergence of the frontal ones, and that frontal inter-hemispheric connections are not sufficient to wire up the frontal cortex for language. We found that EG’s RH frontal language areas have no LH homologs: no reliable response to language were detected anywhere on the lateral surface of EG’s left frontal lobe. To ensure that EG’s left frontal lobe was functional aside from the lack of its engagement in language, we investigated the MD network, a bilateral network implicated in executive functions and goal-directed behaviors. The MD network was robustly present in EG’s right and left frontal lobes, suggesting that her left frontal cortex is capable of supporting non-linguistic cognitive functions. Thus, even though EG’s left frontal cortex supports high-level cognitive functions, no language-responsive areas were present in this area. Temporal language areas, and presumably the intra-hemispheric fronto-temporal connections, therefore appear to be critical for the emergence of frontal language areas, and frontal inter-hemispheric connections do not appear sufficient to wire up left frontal cortex for language.
Themes: Development, Disorders: Developmental
Method: Functional Imaging