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Shih-Cheng Yen, Jonathan Baker, Charles Gray; Heterogeneity in the responses of adjacent neurons to natural stimuli in Cat striate cortex. Journal of Vision 2007;7(9):326. doi: 10.1167/7.9.326.
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When presented with simple stimuli like bars and gratings, adjacent neurons in striate cortex exhibit shared selectivity for multiple stimulus dimensions, such as orientation, direction and spatial frequency. This has led to the idea that local averaging of neuronal responses provides a more reliable representation of stimulus properties. However, when stimulated with complex, time-varying natural scenes (i.e. movies), striate neurons exhibit highly sparse responses. This raises the question of how much response heterogeneity the local population exhibits when stimulated with movies. We investigated this question by simultaneously recording the responses of groups of neurons in cat striate cortex to the repeated presentation of movies using silicon probes in a multi-tetrode configuration. We found, first, that the responses of striate neurons to movies were rare and brief - significant response events in single cells occurred approximately only 5% of the time, with a median duration of 53 ms. Significant joint response events in pairs of nearby cells were even more rare, occurring 0.3% of the time, with a median duration of 39 ms. Secondly, striate neurons exhibited both high lifetime and high population sparseness, with median values of 81% and 70% respectively. Nearby cells appeared to contribute fairly uniformly to the coding of visual stimuli, as revealed by an average value of 0.5 for the area under the scree plot. Thirdly, the PSTH correlation between pairs of adjacent neurons recorded on the same tetrodes (median: 0.18) and pairs recorded by different tetrodes (median: 0.11) were found not to be significantly different (p=0.132), indicating that pairs of adjacent neurons exhibited as much heterogeneity in their responses as pairs separated by 150 um. These findings demonstrate that complex natural scenes evoke highly heterogeneous responses within local populations, suggesting that response redundancy in a cortical column is substantially lower than previously thought.
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