Browsing by Author "Bulkin, David A"

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    Distribution of eye position information in the monkey inferior colliculus.
    (Journal of neurophysiology, 2012-02) Bulkin, David A; Groh, Jennifer M
    The inferior colliculus (IC) is thought to have two main subdivisions, a central region that forms an important stop on the ascending auditory pathway and a surrounding shell region that may play a more modulatory role. In this study, we investigated whether eye position affects activity in both the central and shell regions. Accordingly, we mapped the location of eye position-sensitive neurons in six monkeys making spontaneous eye movements by sampling multiunit activity at regularly spaced intervals throughout the IC. We used a functional map based on auditory response patterns to estimate the anatomical location of recordings, in conjunction with structural MRI and histology. We found eye position-sensitive sites throughout the IC, including at 27% of sites in tonotopically organized recording penetrations (putatively the central nucleus). Recordings from surrounding tissue showed a larger proportion of sites indicating an influence of eye position (33-43%). When present, the magnitude of the change in activity due to eye position was often comparable to that seen for sound frequency. Our results indicate that the primary ascending auditory pathway is influenced by the position of the eyes. Because eye position is essential for visual-auditory integration, our findings suggest that computations underlying visual-auditory integration begin early in the ascending auditory pathway.
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    Distribution of visual and saccade related information in the monkey inferior colliculus.
    (Frontiers in neural circuits, 2012-01) Bulkin, David A; Groh, Jennifer M
    The inferior colliculus (IC) is an essential stop early in the ascending auditory pathway. Though normally thought of as a predominantly auditory structure, recent work has uncovered a variety of non-auditory influences on firing rate in the IC. Here, we map the location within the IC of neurons that respond to the onset of a fixation-guiding visual stimulus. Visual/visuomotor associated activity was found throughout the IC (overall, 84 of 199 sites tested or 42%), but with a far reduced prevalence and strength along recording penetrations passing through the tonotopically organized region of the IC, putatively the central nucleus (11 of 42 sites tested, or 26%). These results suggest that visual information has only a weak effect on early auditory processing in core regions, but more strongly targets the modulatory shell regions of the IC.
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    Systematic mapping of the monkey inferior colliculus reveals enhanced low frequency sound representation.
    (Journal of neurophysiology, 2011-04) Bulkin, David A; Groh, Jennifer M
    We investigated the functional architecture of the inferior colliculus (IC) in rhesus monkeys. We systematically mapped multiunit responses to tonal stimuli and noise in the IC and surrounding tissue of six rhesus macaques, collecting data at evenly placed locations and recording nonresponsive locations to define boundaries. The results show a modest tonotopically organized region (17 of 100 recording penetration locations in 4 of 6 monkeys) surrounded by a large mass of tissue that, although vigorously responsive, showed no clear topographic arrangement (68 of 100 penetration locations). Rather, most cells in these recordings responded best to frequencies at the low end of the macaque auditory range. The remaining 15 (of 100) locations exhibited auditory responses that were not sensitive to sound frequency. Potential anatomical correlates of functionally defined regions and implications for midbrain auditory prosthetic devices are discussed.