In primary visual cortex (V1) of large mammals, intrinsic signal optical imaging has demonstrated continuous topographic maps of tuning preference. As expected for an efficient neural code, the maps of different stimulus parameters tend to overlap such that their contours run perpendicular to each other. However, the ultimate coding efficiency is dependent on the organization of both tuning preference and tuning shape at a fine spatial scale, which requires functional measurements with microscopic resolution. Here, we propose the use of two-photon imaging in macaque VI to characterize tuning diversity within the so-called hypercolumn and to measure its theoretical consequences on the overall population code. With two-photon imaging, we can measure tuning curves of multiple stimulus properties on a cell-by-cell basis across a patch of cortex that is hundreds of microns wide.
Aim 1 is to investigate relationships between each cell's tuning shape and the neighboring population of tuning curves. The experiments and analyses will help us to better understand how the cortex performs local computations that affect the tuning properties of individual neurons.
In Aim 2, we will test the impact of tuning diversity on information content within the hypercolumn. The analyses are directed toward finding possible benefits of having neurons embedded in continuous functional maps for transmitting information about the visual scene to downstream cortical areas.
In Aim 3, we will examine a related issue. We hypothesize that the cortical hypercolumn is not perfect in its coverage of stimulus properties and that this is counterbalanced by changes in tuning bandwidth. Overall, the experiments and analyses in this proposal are designed to address fundamental questions in sensory systems neuroscience using a powerful new technique.
We expect to acquire knowledge on how cortical circuits integrate sensory input so that the information can be faithfully passed on to higher level areas to create normal behavior. Many neurological disorders such as autism, attention deficit disorder (ADD), epilepsy, and schizophrenia, are poorly understood. Knowledge about normal cortical function such as basic wiring rules and the organization of functionality in the cortex is fundamental to our understanding of abnormal cortical activity.
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