Browsing by Author "Irving, Sam"

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    Cochlear implant use causes changes in the auditory cortex
    (2013) Irving, Sam; Irvine, Dexter; Shepherd, Robert; Fallon, James
    The tuning of sites within the auditory cortex changes within the first three months of cochlear implant use.
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    Effects of age on the preservation of residual hearing with cochlear implants
    (2013) Wise, Andrew; Irving, Sam; Shepherd, Robert; Fallon, James
    Chronic cochlear implant (CI) use results in a significant loss of residual acoustic hearing in some, but not all, animals. The loss occurs more rapidly in animals deafened as adults than those deafened as neonates.
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    Second spatial derivative analysis of cortical surface potentials recorded in cat primary auditory cortex using thin film surface arrays: Comparisons with multi-unit data
    (Elsevier Ltd., 2016-04) Fallon, James; Irving, Sam; Pannu, Satinderpall; Tooker, Angela; Wise, Andrew; Shepherd, Robert; Irvine, Dexter
    BACKGROUND: Current source density analysis of recordings from penetrating electrode arrays has traditionally been used to examine the layer- specific cortical activation and plastic changes associated with changed afferent input. We report on a related analysis, the second spatial derivative (SSD) of surface local field potentials (LFPs) recorded using custom designed thin-film polyimide substrate arrays. RESULTS: SSD analysis of tone- evoked LFPs generated from the auditory cortex under the recording array demonstrated a stereotypical single local minimum, often flanked by maxima on both the caudal and rostral sides. In contrast, tone-pips at frequencies not represented in the region under the array, but known (on the basis of normal tonotopic organization) to be represented caudal to the recording array, had a more complex pattern of many sources and sinks. COMPARISON WITH EXISTING METHODS: Compared to traditional analysis of LFPs, SSD analysis produced a tonotopic map that was more similar to that obtained with multi-unit recordings in a normal-hearing animal. Additionally, the statistically significant decrease in the number of acoustically responsive cortical locations in partially deafened cats following 6 months of cochlear implant use compared to unstimulated cases observed with multi-unit data (p=0.04) was also observed with SSD analysis (p=0.02), but was not apparent using traditional analysis of LFPs (p=0.6). CONCLUSIONS: SSD analysis of surface LFPs from the thin-film array provides a rapid and robust method for examining the spatial distribution of cortical activity with improved spatial resolution compared to more traditional LFP recordings.