Abstract
Current models of cortical speech and language processing include multiple regions within the temporal lobe of both hemispheres. Human communication, by necessity, involves complex interactions between regions subserving speech and language processing with those involved in more general cognitive functions. To assess these interactions, we utilized an ecologically salient conversation-based approach. This approach mandates that we first clarify activity patterns at the earliest stages of cortical speech processing. Therefore, we examined high gamma (70–150 Hz) responses within the electrocorticogram (ECoG) recorded simultaneously from Heschl’s gyrus (HG) and lateral surface of the superior temporal gyrus (STG). Subjects were neurosurgical patients undergoing evaluation for treatment of medically intractable epilepsy. They performed an expanded version of the Mini-mental state examination (MMSE), which included additional spelling, naming, and memory-based tasks. ECoG was recorded from HG and the STG using multicontact depth and subdural electrode arrays, respectively. Differences in high gamma activity during listening to the interviewer and the subject’s self-generated verbal responses were quantified for each recording site and across sites within HG and STG. The expanded MMSE produced widespread activation in auditory cortex of both hemispheres. No significant difference was found between activity during listening to the interviewer’s questions and the subject’s answers in posteromedial HG (auditory core cortex). A different pattern was observed throughout anterolateral HG and posterior and middle portions of lateral STG (non-core auditory cortical areas), where activity was significantly greater during listening compared to speaking. No systematic task-specific differences in the degree of suppression during speaking relative to listening were found in posterior and middle STG. Individual sites could, however, exhibit task-related variability in the degree of suppression during speaking compared to listening. The current study demonstrates that ECoG recordings can be acquired in time-efficient dialog-based paradigms, permitting examination of language and cognition in an ecologically salient manner. The results obtained from auditory cortex serve as a foundation for future studies addressing patterns of activity beyond auditory cortex that subserve human communication.
Highlights
Intracranial recordings in humans have permitted evaluation of speech and language processing with unprecedented temporal and spatial resolution (e.g., Leonard and Chang, 2014; Nourski and Howard, 2015)
The second pattern was observed in anterolateral Heschl’s gyrus (HG), wherein high gamma activity was generally of lower amplitude in response to self-initiated speech compared to listening
In posteromedial HG, no significant difference was found between activity during listening to the interviewer’s questions and the subject’s answers
Summary
Intracranial recordings in humans have permitted evaluation of speech and language processing with unprecedented temporal and spatial resolution (e.g., Leonard and Chang, 2014; Nourski and Howard, 2015). A conversation, by its very nature, will engage a wide array of auditory, speech, and language areas and interface with regions engaged in higher cognitive functions This conversationbased approach has been shown to be an effective means for exploring the roles of human auditory and auditory-related cortex within the setting of clinically necessitated intracranial recordings (Creutzfeldt et al, 1989; Derix et al, 2012, 2014; see Dastjerdi et al, 2013). Auditory cortex on the lateral STG has been shown to be modulated by speech phonetic features, attention and task demands, and self-initiated vocalization (e.g., Chang et al, 2011; Greenlee et al, 2011; Mesgarani and Chang, 2012; Mesgarani et al, 2014; Steinschneider et al, 2014) While these studies have been performed in well-structured and controlled settings, it remains to be seen whether these effects can be reliably identified within the ecologically relevant context of a conversation-based paradigm.
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