Intracranial electrophysiology of human auditory and auditory-related cortex during speech categorization tasks

Abstract

Speech perception engages a large cortical network encompassing multiple regions within temporal and frontal lobes. This study examined spatiotemporal dynamics of speech processing using direct electrophysiological recordings from patients undergoing invasive monitoring for surgical treatment of refractory epilepsy. Words were presented in target detection tasks that required acoustic, phonemic and semantic processing. High gamma (70-150 Hz) activity was recorded directly from Heschl’s gyrus (HG), superior, middle temporal and supramarginal gyri (STG, MTG, SMG), and prefrontal cortex (PFC). Analysis focused on task effects (responses to non-target words in a control tone detection task vs. semantic categorization tasks) and target effects (target vs. non-target words in a semantic task). Responses within posteromedial HG (auditory core cortex) represented acoustic stimulus attributes, but did not show task or target effects. Non-core auditory cortex (anterolateral HG and lateral STG) primarily exhibited sensitivity to task. Auditory-related areas (MTG and SMG) and PFC showed both target and, to a lesser extent, task effects. Task and target effects were more prominent in the language-dominant hemisphere. Findings support hierarchical organization of speech processing at the cortical level, wherein acoustic, phonemic, and semantic processing are primarily subserved by core, non-core, and auditory-related cortex, respectively.