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Helen Ruth Clemo, Giriraj Sharma, Brian Allman, Alex Meredith; Auditory projections to visual cortex: synaptic basis for multisensory processing in ‘unimodal’ visual neurons. Journal of Vision 2007;7(9):864. doi: 10.1167/7.9.864.
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© ARVO (1962-2015); The Authors (2016-present)
Neurophysiological studies in our lab have recently documented the multisensory properties of ‘unimodal’ visual neurons in the cat posterolateral lateral suprasylvian (PLLS) cortex, a retinotopically organized area involved in visual motion processing. These results showed that a large proportion (80%) of ‘unimodal’ visual neurons in the PLLS had their visual responses facilitated by the presence of an auditory stimulus. The present study used neuroanatomical methods to examine the cross-modal connectivity of the PLLS that may underlie this physiological effect. Adult cats (n=17) were anesthetized and, using sterile surgical techniques, biotinylated dextran amine (BDA) was injected into one of the following auditory cortical areas: AAF, AI, and PAF. Standard cytochemical procedures were used to visualize the transported tracer and a PC-based digitizing microscope was used to plot the location of labeled axon terminals. In each case, labeled boutons were identified in the region of the PLLS in a consistent pattern. Terminal label was the most concentrated at the outer lip of the sulcus, corresponding to the location of the auditory cortical area DZ. However, the label became progressively reduced with depth along the lateral bank, until few labeled axons were found near the fundus. This gradient among auditory terminals closely mirrors the distribution of bimodal and auditory-facilitated visual neurons, where bimodal neurons were primarily encountered in the transition between the visual PLLS and the auditory DZ, while the auditory-facilitated neurons were encountered at progressively deeper locations in the sulcal bank. Therefore, the gradient of projections from different auditory cortices to the PLLS may not only underlie the synaptic basis for multisensory processing here, but also the differential distribution of different forms of multisensory processing observed in this visual structure.
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