Time to face language: Face-related words trigger ultra-rapid activity in the right fusiform gyrus

GARCIA AM; ADOLFI F; HESSE E; MIKULAN E; SEDEÑO L; IBANEZ A

Congreso; 18th World Congress of Psychophysiology; 2016

According to the embodied cognition framework, word meaning depends on fast reactivations of sensorimotor circuits engaged by relevant extralinguistic experiences. Despite abundant compatible evidence, this view has been ardently criticized because most reported effects lack fine-grained neuroanatomical precision and are not rapid enough to rule out post-comprehension (e.g., imagery) effects. To address both issues, we profited from the excellent spatio-temporal resolution of intracranial recordings to assess whether face-related words yielded early resonance in the highly specialized fusiform face area (FFA). Methods: Participants performed a semantic decision task on words denoting facial body parts, non-facial body parts, and familiar objects. Direct cortical recordings were obtained from implanted semi-rigid, multi-lead electrodes. We defined two regions of interest (ROIs), one comprising key FFA hubs (right fusiform, ventral/rostral lingual, and calcarine gyri) and another one including temporal areas implicated in lexico-semantic processing (posterior middle temporal, rostral angular, and supramarginal gyri). Time-frequency charts for each word type were obtained by analyzing the digitized signals via a windowed Fourier transform. Significant power increases and decreases across time against baseline values were analyzed with Monte Carlo permutation tests combined with bootstrapping. Also, logistic regression analyses were performed to evaluate whether power activity across each trial predicted stimulus type. Results: Relative to names of non-facial body parts and objects, words denoting facial body parts yielded significant activation increases in both ROIs at low frequencies (0-20 Hz). This effect was stronger and earlier in the FFA (125-250 ms) than in the temporal (175-400 ms) ROI. In addition, logistic regressions based on such activity patterns classified each word type with more than 70% accuracy. Discussion: Our findings unambiguously show that face-related words trigger very rapid embodiment effects within neural hubs specialized for face perception. The time course of activity across ROIs further indicates that word comprehension first engages embodied mechanisms and then leads to further operations in more general (arguably amodal) semantic networks. Moreover, this is the first demonstration that words denoting specific body parts recruit functionally specialized circuitry beyond the somatosensory cortex. In sum, our results provide robust empirical constraints for neurofunctional models of language. [Work partially supported by CONICET, CONICYT/FONDECYT Regular (1130920), COLCIENCIAS (1115-545-31374 and 1115-569-33858), FONCyT-PICT 2012-0412, FONCyT-PICT 2012-1309, FONDAP 15150012, and INECO Foundation.]