Exploration of cat striate cortex during natural scene stimulation
Baker, Jonathan Lee
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The mammalian visual system evolved to process and represent objects within the complexities of the natural world to appropriately guide behavior in order to ensure survival and reproduction. Visual neuroscience has long sought to understand the neural basis of these processes, but the complexity of both the visual world and the brain has traditionally required a highly reductionist approach. The classical approach has led to the development of models of visual perception that are largely based on the analysis of how single cells within the visual system respond to simple and parametrically defined visual stimuli. However our ultimate goal is to understand how the visual system operates in the natural world. The experiments and results contained in this thesis were conducted, in part, to explore the cat's visual system during the presentation of time varying natural scenes, i.e. movies, and to attempt to validate our current working models of the visual system. Novel large-scale recording methods were employed to record from and characterize responses of large populations of cat primary visual cortex neurons during classical as well as movie stimulation. Contrary to the current models and our general understanding of how visual cortex represents information, groups of adjacent neurons responded heterogeneously to the movies presented and individual responses were very brief and highly sparse in time. The diversity and dynamics of the spiking activity was also significantly correlated with fluctuations of the ongoing local field potentials, specifically within the gamma frequency band, ranging from 25 to 90Hz. These gamma band oscillations also exhibited rich spatiotemporal dynamics throughout the movie presentations. In conclusion, time-varying natural scenes evoke response dynamics within the cat primary visual cortex not typically observed under more classical stimulus regimes. Future experimentation and the construction of biologically feasible models of visual cortex should take into account the diversity of responses observed under more natural stimulus conditions.