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Leo Lui, Maureen Hagan, Tristan Chaplin, Krystel Huxlin; MT neurons are less directional selective after chronic V1 lesions in adult marmoset monkeys. Journal of Vision 2016;16(12):1184. doi: 10.1167/16.12.1184.
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© ARVO (1962-2015); The Authors (2016-present)
The Middle Temporal Area (MT), an area important for motion perception in primates, receives most of its inputs from the Primary Visual Cortex (V1). However, in primates, MT cells continue to respond to motion stimuli presented in the scotoma 1-3 months after lesions (Rodman et al. 1989 in macaques; Rosa et al. 2000 in marmosets). Here, we further quantify these responses to determine if they are maintained chronically (>6 months) after permanent V1 damage. Maintained responsiveness in MT and corresponding dorsal stream areas has been reported to underlie visual sensations, including blindsight, after V1 lesions in monkeys and humans (Cowey 2010; Leopold 2012). We recorded from MT cells in two anesthetized adult marmosets 10-11 months following partial, unilateral V1 lesions (central 20-40 degrees). Location of each scotoma was determined by V1 recordings around the lesion border. For MT recordings, random dot motion stimuli were presented within circular apertures that approximated the neurons' receptive fields. For each cell, we computed a discrimination index (DI) based on its response to eight directions of motion (Uka and DeAngelis 2003). Sixty-six units (46 from monkey 1, 20 from monkey 2) responded to these stimuli. While directionally selective responses were found inside the scotoma, DI was significantly reduced compared 25 MT cells from two intact animals. The proportion of directionally selective cells was also reduced (54% in monkey 1, 20% in monkey 2; normal >90%). Thus, marmosets, just like old world primates, exhibit preservation of directional responses in MT after V1 lesions, but direction selectivity is decreased. This may be explained by a shift in the balance of MT's inputs towards sub-cortical regions, whose cells tend to be less directional than V1 neurons in intact animals. Decreased direction selectivity may also represent a significant constraint to restoring completely normal motion perception in chronic V1-damaged patients.
Meeting abstract presented at VSS 2016
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