Spike latency code for orientation discrimination and estimation by primary visual cortical cells
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1
Ben-Gurion University, Israel
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2
Albert Einstein College of Medicine, United States
Accumulating evidence from behavioral experiments and imaging studies shows we are able to discriminate between different visual objects at a remarkable speed. The high computation speed yields a strong constraint on any possible answer to the question: how is information from one brain region communicated to another? Conventional neural coding research has ignored the temporal structure of the neural response and focused, in many cases, on the neural mean response over long timescales that are often beyond the relevant behavioral timescale. It has been suggested that the temporal structure of the neural initial response and in particular response latency are used by the central nervous system for fast communication of information between different brain regions. However, the accuracy of such a scheme has not been analyzed rigorously. Here we addressed this question in the framework of orientation coding by primary visual (V1) cortical cells of the monkey. To this end, simultaneous recordings of multiple V1 neurons over many repetitions per each orientation were performed. The spike data from these recordings were used to investigate the utility of first spike latency for encoding information about the orientation of visual stimuli. Cells in V1 are known to code for the orientation of a grating stimulus by their rate of firing. Typically, V1 cells show a maximum firing rate in response to a ’preferred orientation’. We find that many cells in the monkey V1 also show tuning of their first spike time latency to the orientation of the stimulus. Most cells have the shortest latency at the preferred orientation of their rate tuning curve. Moreover, by transforming the latency tuning curve to units of rate we find that the two tuning curves have a very similar tuning width. Using various statistical measures, we quantified the performance of a highly nonlinear readout mechanism, which estimates stimulus orientation by the preferred orientation of the cell with the shortest first spike latency, the temporal-Winner-Take-All (tWTA). In the context of a two-alternative forced-choice paradigm, we find that the tWTA discrimination accuracy is comparable to that of a conventional rate-code readout, which takes into account the total number of spikes fired by the cell in response to the visual stimulus. The accuracy of the tWTA readout can be further increased by considering a generalized n-tWTA readout, which estimates the orientation as the preferred orientation of the cell which fired the first n spikes. We find that the stimulus orientation can be estimated by n-tWTA with a relatively small bias for n>=2. The study demonstrates that a readout based on spike latency, or the first few spikes fired, may significantly improve response speed at a small cost to the accuracy of the decision.
Conference:
Computational and Systems Neuroscience 2010, Salt Lake City, UT, United States, 25 Feb - 2 Mar, 2010.
Presentation Type:
Poster Presentation
Topic:
Poster session I
Citation:
Shriki
O,
Kohn
A and
Shamir
M
(2010). Spike latency code for orientation discrimination and estimation by primary visual cortical cells.
Front. Neurosci.
Conference Abstract:
Computational and Systems Neuroscience 2010.
doi: 10.3389/conf.fnins.2010.03.00107
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Received:
21 Feb 2010;
Published Online:
21 Feb 2010.
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Correspondence:
Oren Shriki, Ben-Gurion University, Beer-Sheva, Israel, oren70@gmail.com