Different stimuli, different spatial codes: a visual map and an auditory rate code for oculomotor space in the primate superior colliculus.

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2014

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Maps are a mainstay of visual, somatosensory, and motor coding in many species. However, auditory maps of space have not been reported in the primate brain. Instead, recent studies have suggested that sound location may be encoded via broadly responsive neurons whose firing rates vary roughly proportionately with sound azimuth. Within frontal space, maps and such rate codes involve different response patterns at the level of individual neurons. Maps consist of neurons exhibiting circumscribed receptive fields, whereas rate codes involve open-ended response patterns that peak in the periphery. This coding format discrepancy therefore poses a potential problem for brain regions responsible for representing both visual and auditory information. Here, we investigated the coding of auditory space in the primate superior colliculus(SC), a structure known to contain visual and oculomotor maps for guiding saccades. We report that, for visual stimuli, neurons showed circumscribed receptive fields consistent with a map, but for auditory stimuli, they had open-ended response patterns consistent with a rate or level-of-activity code for location. The discrepant response patterns were not segregated into different neural populations but occurred in the same neurons. We show that a read-out algorithm in which the site and level of SC activity both contribute to the computation of stimulus location is successful at evaluating the discrepant visual and auditory codes, and can account for subtle but systematic differences in the accuracy of auditory compared to visual saccades. This suggests that a given population of neurons can use different codes to support appropriate multimodal behavior.

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10.1371/journal.pone.0085017

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Groh, JM, and J Lee (2014). Different stimuli, different spatial codes: a visual map and an auditory rate code for oculomotor space in the primate superior colliculus. PLoS One, 9(1). p. e85017. 10.1371/journal.pone.0085017 Retrieved from https://hdl.handle.net/10161/8313.

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Groh

Jennifer M. Groh

Professor of Psychology and Neuroscience

Research in my laboratory concerns how sensory and motor systems work together, and how neural representations play a combined role in sensorimotor and cognitive processing (embodied cognition).

Most of our work concerns the interactions between vision and hearing. We frequently perceive visual and auditory stimuli as being bound together if they seem likely to have arisen from a common source. That's why we tend not to notice that the speakers on TV sets or in movie theatres are located beside, and not behind, the screen. Research in my laboratory is devoted to investigating the question of how the brain coordinates the information arising from the ears and eyes. Our findings challenge the historical view of the brain's sensory processing as being automatic, autonomous, and immune from outside influence. We have recently established that neurons in the auditory pathway (inferior colliculus, auditory cortex) alter their responses to sound depending on where the eyes are pointing. This finding suggests that the different sensory pathways meddle in one another's supposedly private affairs, making their respective influences felt even at very early stages of processing. The process of bringing the signals from two different sensory pathways into a common frame of reference begins at a surprisingly early point along the primary sensory pathways.


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