GARCIA adolfo Martin
congresos y reuniones científicas
Timing embodied semantics, across and within the brain: A combined EEG/iEEG study on face-related nouns
GARCÍA, ADOLFO M.; HESSE, EUGENIA; BIRBA, AGUSTINA; ADOLFI, FEDERICO; MIKULAN, EZEQUIEL; MARTORELL CARO, MIGUEL; PETRONI, AGUSTÍN; BEKINCHSTEIN, TRISTÁN; DEL CARMEN GARCÍA, MARÍA; SILVIA, WALTER; CIRAOLO, CARLOS; VAUCHERET, ESTEBAN; SEDEÑO, LUCAS; IBÁÑEZ, AGUSTÍN
Conferencia; SNL 2021 Conference; 2021
During semantic processing, the brain recruits multimodal conceptual systems and embodied mechanisms grounding modality-specific information. Yet, no consensus exists on how crucial the latter are for the inception of semantic distinctions, mainly because most research, focused on action-related words, has been undermined by potential motor artifacts. Here we combined EEG and iEEG to examine when nouns denoting facial body parts (FBPs) and non-facial body parts (nFBPs) are discriminated and individually classified in face-processing and multimodal networks. In two experiments, participants completed a semantic decision task involving 21 FBP nouns (e.g., nose) and 21 nFBP nouns (e.g., chest), matched for nine psycholinguistic variables and presented amid diverse filler items. The EEG experiment involved 25 young healthy participants. Signals were recorded online with a 128-channel system. ERP analysis of face-sensitive N170 modulations focused on two temporo-occipital four-electrode regions of interest, via Monte Carlo permutation tests (1000 permutations) combined with bootstrapping (p < .05, FRD- corrected). The iEEG experiment comprised two young patients with intractable epilepsy undergoing intracranial monitoring. Both had electrodes implanted in key hubs of the face- processing network (right fusiform, ventral/rostral lingual, and calcarine gyri) and a multimodal semantic network (angular and supramarginal gyri). Time-frequency charts were obtained to identify differential modulations between conditions in each network (across patients) for the 1-20 Hz frequency range, sensitive to both semantic and facial processing. Digitized signals were analyzed using a windowed Fourier transform. Significant power changes were analyzed across time against baseline values and between conditions with non-parametric bootstrap tests with 2000 permutations (p < .05, FRD-corrected). Multivariate pattern analyses, via support vector machines, were also used to examine the classification efficiency of signals from both patients related to FBP and nFBP words between 1 and 20 Hz, for each network separately. Finally, EEG task-related connectivity was examined in an early (0-200 ms) and a late (200-400 ms) window, considering all electrodes across the scalp, via a non-linear method called weighted Symbolic Mutual Information (wSMI). The same metric was used to calculate iEEG connectivity considering the same windows for each pair of electrodes within both networks for each patient separately. Results revealed four main patterns. First, relative to nFBP words, nouns denoting FBPs increased N170 amplitude (a key signature of early facial processing) over the right hemisphere. Second, iEEG-derived time-frequency patterns showed that FBP words triggered fast (~100 ms) activity boosts within the face- processing network, mirrored by later (~275 ms) effects in multimodal circuits. Third, iEEG recordings from the face-processing network allowed decoding ~80% of items within the first 200 ms, while classification based on multimodal-network activity only surpassed ~70% after 250 ms. Finally, EEG and iEEG connectivity between both networks proved greater in the early than the late window. Collectively, these findings indicate that semantic differentiations can spring via fast sensorimotor reenactments and rapid interplays with cross-modal conceptual systems. Accordingly, they challenge views which reject an inceptive role of embodied mechanisms in semantic processing as well as those that reduce semantic processing exclusively to embodied reactivations.