Browsing by Author "McKay, Colette M"

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    Language networks of normal-hearing infants exhibit topological differences between resting and steady states: An fNIRS functional connectivity study.
    (Hum Brain Mapp, 2024-09) Paranawithana, Ishara; Mao, Darren; McKay, Colette M; Wong, Yan T
    Task-related studies have consistently reported that listening to speech sounds activate the temporal and prefrontal regions of the brain. However, it is not well understood how functional organization of auditory and language networks differ when processing speech sounds from its resting state form. The knowledge of language network organization in typically developing infants could serve as an important biomarker to understand network-level disruptions expected in infants with hearing impairment. We hypothesized that topological differences of language networks can be characterized using functional connectivity measures in two experimental conditions (1) complete silence (resting) and (2) in response to repetitive continuous speech sounds (steady). Thirty normal-hearing infants (14 males and 16 females, age: 7.8 ± 4.8 months) were recruited in this study. Brain activity was recorded from bilateral temporal and prefrontal regions associated with speech and language processing for two experimental conditions: resting and steady states. Topological differences of functional language networks were characterized using graph theoretical analysis. The normalized global efficiency and clustering coefficient were used as measures of functional integration and segregation, respectively. We found that overall, language networks of infants demonstrate the economic small-world organization in both resting and steady states. Moreover, language networks exhibited significantly higher functional integration and significantly lower functional segregation in resting state compared to steady state. A secondary analysis that investigated developmental effects of infants aged 6-months or below and above 6-months revealed that such topological differences in functional integration and segregation across resting and steady states can be reliably detected after the first 6-months of life. The higher functional integration observed in resting state suggests that language networks of infants facilitate more efficient parallel information processing across distributed language regions in the absence of speech stimuli. Moreover, higher functional segregation in steady state indicates that the speech information processing occurs within densely interconnected specialized regions in the language network.
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    Resting-State Functional Connectivity Predicts Cochlear-Implant Speech Outcomes.
    (Ear & Hearing, 2024-07-16) Esmaelpoor, Jamal; Peng, Tommy; Jelfs, Beth; Mao, Darren; Shader, Maureen J; McKay, Colette M
    Cochlear implants (CIs) have revolutionized hearing restoration for individuals with severe or profound hearing loss. However, a substantial and unexplained variability persists in CI outcomes, even when considering subject-specific factors such as age and the duration of deafness. In a pioneering study, we use resting-state functional near-infrared spectroscopy to predict speech-understanding outcomes before and after CI implantation. Our hypothesis centers on resting-state functional connectivity (FC) reflecting brain plasticity post-hearing loss and implantation, specifically targeting the average clustering coefficient in resting FC networks to capture variation among CI users.
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    Two Independent Response Mechanisms to Auditory Stimuli Measured with Functional Near-Infrared Spectroscopy in Sleeping Infants.
    (Trend in Hearing, 2024-07-25) Lee, Onn Wah; Mao, Darren; Wunderlich, Julia; Balasubramanian, Gautam; Haneman, Mica; Korneev, Mikhail; McKay, Colette M
    This study investigated the morphology of the functional near-infrared spectroscopy (fNIRS) response to speech sounds measured from 16 sleeping infants and how it changes with repeated stimulus presentation. We observed a positive peak followed by a wide negative trough, with the latter being most evident in early epochs. We argue that the overall response morphology captures the effects of two simultaneous, but independent, response mechanisms that are both activated at the stimulus onset: one being the obligatory response to a sound stimulus by the auditory system, and the other being a neural suppression effect induced by the arousal system. Because the two effects behave differently with repeated epochs, it is possible to mathematically separate them and use fNIRS to study factors that affect the development and activation of the arousal system in infants. The results also imply that standard fNIRS analysis techniques need to be adjusted to take into account the possibilities of multiple simultaneous brain systems being activated and that the response to a stimulus is not necessarily stationary.