Slide Slam J4 Sandbox Series
Intracranial electroencephalographic signatures of word retrieval in individuals with intractable epilepsy
Elizabeth J. Anderson1, Charles Dickey2,3, Katherine Andrade1, Carrie R. McDonald4, David Lee5, Leena Kansal6, June Yoshii-Contreras5, Jerry J. Shih6, Sharona Ben-Haim7, Eric Halgren6,8, Stephanie K. Ries9; 1Joint Doctoral Program in Language and Communicative Disorders, San Diego State University/University of California San Diego, San Diego, USA, 2Neurosciences Graduate Program, University of California San Diego, La Jolla, CA, USA, 3Medical Scientist Training Program, University of California San Diego, La Jolla, CA, USA, 4Department of Psychiatry, University of California San Diego, La Jolla, CA, USA, 5Department of Neurology, University of California San Diego, La Jolla, CA, USA, 6Department of Neurosciences, University of California San Diego, La Jolla, CA, USA, 7Department of Neurological Surgery, University of California San Diego, La Jolla, CA, USA, 8Department of Radiology, University of California San Diego, La Jolla, CA, USA, 9School of Speech, Language, and Hearing Sciences, Center for Clinical and Cognitive Neuroscience, San Diego State University, San Diego, CA, USA
Although language production is complex, speakers can select from more than 50,000 words in their mental lexicon to produce 2-3 words per second (Levelt, Roelofs, & Meyer, 1999). Several models have been proposed to illustrate the stages of processing during word retrieval, including Levelt et al. (1999)’s serial processing model and Dell et al. (2013)’s interactive activation model. One question that arises when adjudicating between different models is whether word retrieval processes are serial and confined to a small number of structures (Levelt et al., 1999) or interactive and widespread (Dell et al., 2013). We can probe stages of word retrieval through semantic facilitation and interference, which have previously been reported using picture-word interference with identity primes to trigger facilitation and semantically-related primes to trigger interference (Blackford et al., 2012). Previous work examining word retrieval primarily used non-invasive techniques (e.g., EEG, MEG, fMRI). Using intracranial EEG recordings is better suited to determine whether word retrieval is focal (i.e., Levelt’s model) or widespread (Dell et al., 2013) and which brain regions are involved in facilitation and interference because we can access deeper focal activities not accessible using non-invasive techniques as well as combine excellent spatial and temporal resolution. We collected intracranial stereotactic EEG in 7 individuals with intractable epilepsy undergoing invasive monitoring to identify seizure foci (mean age = 30.2 years, SD = 6.03 years). Participants named pictures superimposed with to-be-ignored distractor words that were either semantically-related, semantically unrelated, or the same identity as the image. There was a main effect of condition on reaction time (χ2(1,7) = , p = .005) and error rate (χ2(1,7) = 7.70, p =.02). Planned follow-up analyses indicated significantly slower RTs in related than identity (t = -5.43, p < .0001), marginally slower in related than unrelated (t = 2.31, p = .054), and significantly slower in unrelated than identity (t = -3.10, p = .006). Significantly more errors occurred in related than identity (Wald Z = 2.72, p=.017) and in unrelated than identity (Wald Z = 2.41, p=.041) with no significant difference between unrelated and related (Wald Z = -0.40, p=.91). In preliminary iEEG analyses with 3 participants we analyzed bipolar local field potentials and high gamma activity. There was an increased N400 amplitude for identity and related conditions, suggesting early semantic facilitation. Frontal regions (right superior and inferior frontal sulcus) contained both early facilitation (N400 window) and later (starting at 800ms) interference effects. Temporal regions (right superior temporal sulcus) contained both early facilitation (N400) and late response-related effects (peaking between 1000ms and 1400ms post-stimulus onset). Our results suggest that frontal and temporal brain regions assist with lexical activation during early stages of word retrieval, while possible later engagement of cognitive control in the frontal cortex handles effortful processing for related conditions. Future results from this ongoing study will help shed further light on the neural underpinnings of semantic facilitation and interference in speech production.