Slide Slam R9
Distinct Nodal Responses for Verbs in the Production Network
Nora Maerean1,2, Kiefer Forseth1, Nitin Tandon1; 1UT Health, 2Rice University
Foundational studies by Damasio (PNAS, 1993) and Tranel (Brain and Language, 2005) suggest that lesions may result in selective impairments in the ability to produce specific word classes, namely nouns and verbs, leading to the concept that the retrieval and production of words for objects and actions engage unique substrates or network components. Neuroimaging studies have examined the neural correlates underlying such functions, but the spatiotemporal dynamics that separate these two processes are not fully understood. To resolve these questions, we used electrocorticographic recordings in a large cohort during visually-cued object and action naming tasks. Recordings from intracranial surface grid and stereotactic depth electrodes (n = 10730, 93 patients), implanted for pre-surgical evaluation of epilepsy were used to characterize the cortical network dynamics during noun and verb production. Patients performed picture naming of objects and actions along with a high-level control condition of scrambled images. A surface-based mixed-effects multilevel analysis (SB-MEMA) of broadband gamma activity yielded population maps of focal activity changes relative to baseline. We explored regional dynamics in three anatomically constrained nodes within the active regions: intraparietal sulcus, posterior middle temporal gyrus, and pars triangularis. A broad cortical network was recruited for both verb and noun naming. Immediately following picture presentation, cortical activity propagated along the dorsal and ventral streams to the intraparietal sulcus (IPS) and mid-fusiform gyrus, respectively; activity in the dorsal stream was uniquely prolonged during verb production (p<0.001). Next, cortical activity was observed concurrently in posterior middle temporal gyrus (pMTG) and a constellation of frontal regions: pars triangularis and opercularis, superior frontal sulcus, and supplementary motor areas. Pre-articulatory activity was uniquely observed in pMTG during verb production (p<0.001); post-articulatory activity in this region was matched between noun, verb, and control conditions. Pars triangularis (pTri) exhibited similar temporal dynamics in both noun and verb production, but this activity was significantly enhanced during verb production (p<0.001). Finally, peaks in cortical activity were observed in mouth sensorimotor and auditory cortex following onset of articulation. We found that the production of words from these two classes recruit the same language production network, but three critical nodes possess unique dynamics selective for verbs: (1) IPS has a longer duration of activity, (2) pMTG is active prior to articulation, and (3) pTri has a higher magnitude of activity. Our results demonstrate that object and action naming networks are overlapping but differentially activated, and identify distinct focal patterns of cortical activity specific to verb naming. This comprehensive view of category-specific production networks may aid in the development of novel therapies and interventions for aphasia.