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Transformation of Stimulus Representation along the Cortical Auditory Pathways

Presented During:

Language: Anatomy, Networks and Pathology

Thursday, June 26, 2025: 11:30 AM - 12:45 PM

Brisbane Convention & Exhibition Centre

Room: M4 (Mezzanine Level)

Poster No:

2031

Submission Type:

Abstract Submission

Authors:

Kirill Nourski¹, Mitchell Steinschneider¹, Ariane Rhone¹, Matthew Howard¹

Institutions:

¹The University of Iowa, Iowa City, IA

First Author:

Kirill Nourski
The University of Iowa
Iowa City, IA

Co-Author(s):

Mitchell Steinschneider
The University of Iowa
Iowa City, IA

Ariane Rhone
The University of Iowa
Iowa City, IA

Matthew Howard
The University of Iowa
Iowa City, IA

Introduction:

Auditory cortex on the superior temporal plane and lateral convexity are key areas in the initial stages of cortical processing of sounds. More complex perceptual representations are envisioned to occur in auditory-related cortex along the ventral and dorsal processing streams, extending into prefrontal cortex and ultimately leading to behavior. To characterize the flow of information across these stages of the auditory hierarchy that ultimately leads to sensory-driven behavioral events, we examined neural activity using intracranial electroencephalography (iEEG) during semantic categorization tasks.

Methods:

Participants were 42 neurosurgical patients undergoing iEEG monitoring for medically intractable epilepsy. Stimuli were 300 ms monosyllabic words, with participants pressing a button in response to words belonging to a target category ("animal" or "number"). We examined iEEG data by analyzing high gamma (70-150 Hz) power. Event-related band power, normalized to a prestimulus baseline within 100-200 ms prior to the stimulus onset, was measured in two windows: (1) 50-300 ms after stimulus onset and (2) 250-0 ms before motor response. Trials with reaction times of <550 ms were excluded from the analysis to avoid the overlap between the two windows. Two distinct patterns were identified: (1) significant activity in the first, but not second window ("stimulus-related") and significant activity in the second, but not first window ("behavior-related") (Fig. 1). Cortical regions of interest (ROIs) were characterized in terms of bias towards one pattern vs. the other, calculated for individual as the difference between the numbers of sites with behavior- and stimulus-related activity divided by their sum (Fig. 2).

Supporting Image: Fig1ExamplewaterfallplotsV10.png

Supporting Image: Fig2HighGammabiasMNIV7LR.png

Results:

Over 6000 recording sites across 52 ROIs were examined. Stimulus-related pattern was considerably more common than behavior-related. Behavior-related pattern was sparsely represented throughout the brain. It had the highest prevalence in the prefrontal cortex, a more limited representation in anterior temporal lobe and sensorimotor cortex, and was practically absent in the superior temporal cortex. Interestingly, despite the occurrence of behavior-related activity in sensorimotor cortex, stimulus-related pattern remained more common there. Hemispheric asymmetries were prominent in this semantic classification task. Stimulus-related activity had a higher prevalence in the right hemisphere compared to the left (left: 525/3111 sites, right: 580/3050 sites, p=0.0285; Chi-squared test). By contrast, behavior-related responses were more common in the left hemisphere than in the right (left: 63/3111; right: 29/3050; p=0.000509; Chi-squared test). Pars triangularis of the inferior frontal gyrus, middle frontal gyrus and anterior temporal lobe all had a stronger bias weighted towards behavior-related activity in the left hemisphere. Additionally, orbital gyrus had the highest bias towards behavior-related activity bilaterally. Pars opercularis of the inferior frontal gyrus exhibited a more balanced representation of the two activity patterns bilaterally.

Conclusions:

There is a transformation from stimulus-related activity in auditory cortex towards a more balanced mixture of stimulus- and behavior-related patterns in prefrontal and anterior temporal regions. This transition primarily occurs in the left hemisphere. Results reveal progressive stages of cortical auditory processing wherein sensory stimulus-driven responses are ultimately transformed into activity driving subsequent behavior. Additional studies requiring more complex semantic processing will evaluate whether these findings can be generalized or if profiles dynamically change as a function of the task.

Language:

Speech Perception ²

Perception, Attention and Motor Behavior:

Perception: Auditory/ Vestibular ¹

Keywords:

Other - High gamma; iEEG; Superior temporal gyrus

^1|2Indicates the priority used for review

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Are you Internal Review Board (IRB) certified? Please note: Failure to have IRB, if applicable will lead to automatic rejection of abstract.

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