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Spatiotemporal Origin of Bursts and Reliable Spikes Generated by Neurons in V1 Jonathan D. Victor, Ferenc Mechler, Daniel S. Reich, Keith P. Purpura Department of Neurology and Neuroscience Weill Medical College of Cornell University and Laboratory of Biophysics The Rockefeller University Support: EY09314, GM07739, EY07138, NS01677, NS36699 Spatiotemporal origin of reliable spikes and spikes in bursts • Reliable spikes (and spikes in bursts) are disproportionately effective in signaling the visual input, as filtered by the receptive field. • For most neurons, reliable spikes are preferentially generated by particular receptive field components. • Receptive fields have distinct subregions that differ in spike generation characteristics. Experiment y receptive field structure spike generation X m-sequence cross-correlate neural response (multiple identical trials) vs. all spikes vs. bursts (3 spikes within 11 msec) vs. reliable spikes (spikes in at least 4 of 16 trials, within same 3.7-msec bin) Spatiotemporal receptive field map constructed from all spikes 18 to 37 msec 41 to 59 msec 63 to 81 msec 85 to 104 msec 107 to 126 msec 129 to 148 msec simple cell 35/1 Spatial Profiles (Per-event normalization) 1.8 all spikes simple cell 35/1 63 to 81 msec reliable bursts spikes average gain change (n=38): 1.49 +/- 0.37 (1 SD) Spatiotemporal receptive field map constructed from all spikes 22 to 41 msec 44 to 63 msec complex cell 34/20 67 to 85 msec 89 to 107 msec Spatial Profiles (Per-event normalization) 2 all spikes reliable spikes complex cell 34/20 44 to 63 msec 67 to 85 msec Spatial Profiles (Per-event normalization) 2 all spikes complex cell 35/9 44 to 63 msec reliable bursts spikes average gain change (n=38): 1.49 +/- 0.37 (1 SD) Spatial Profiles (Best-fit normalization) 0.8 complex cell 33/1 all spikes 59 to 92 msec reliable bursts spikes average shape change (fraction of unexplained variance): 0.43 +/- 0.32 (1 SD) units with significant shape changes: 30/38 Relationship of Spike Probability to Reliable-spike Probability average across trials spike probability reliable-spike probability 0.15 r(t) r(t) p(t) coincidences across trials t t 0 0 p(t) 0.15 spike probability p(t) behavior of spike generator drive distribution drive probability Size of Cross-correlation Depends on Best Linear Fit to the Behavior of the Spike Generator mean probability of spikes best-fit line drive Sensitivity on a per-event basis = (slope of best-fit line)/(mean probability of events) Effect of Spike Selection on Gain reliable spikes high threshold r(t) p(t) all spikes gain ratio =1.25 drive r(t) p(t) drive drive drive low threshold r(t) p(t) gain ratio =1.65 gain ratio =1.99 drive drive drive d(t) receptive field structure spike generation spike probability p(t) coincidences across trials r(t) average across trials reliable-spike probability r(t) p(t) • Looking at reliable spikes is the same as appending a nonlinearity. • For linear-> static nonlinear systems driven by (nearly) Gaussian noise, this can produce an apparent change in overall gain, but not a change in receptive field profile. receptive field subregion 1 drive d1(t) receptive field subregion 2 drive d2(t) receptive field subregion 1 drive d1(t) receptive field subregion 2 drive d2(t) change in per-event sensitivity of RF but no change in shape change in per-event sensitivity of RF and change in shape Summary • Reliable spikes (and spikes in bursts) are disproportionately effective in signaling the visual input, as filtered by the receptive field. • For most neurons, reliable spikes are preferentially generated by particular receptive field components. • Receptive fields have distinct subregions that differ in how threshold relates to gain and noise. • Spatial selectivity is supported by subregions with a high threshold relative to their intrinsic gain. Two Phenomena in Spatiotemporal Maps of Cortical Receptive Fields: Does spiking confer special properties on kernels? Are some spikes more special than others? Jonathan D. Victor, Ferenc Mechler, Daniel S. Reich, Keith P. Purpura Department of Neurology and Neuroscience Weill Medical College of Cornell University and Laboratory of Biophysics The Rockefeller University Support: EY09314, GM07739, EY07138, NS01677, NS36699 Spatiotemporal Origin of Reliable Spikes and Spikes in Bursts • Do reliable spikes (or spikes in bursts) carry a special message? • Are these spikes generated by specific areas within the receptive field? • What does this have to do with the statistics of spike generation? Factoring the Problem: “Drive” and “Spike Probability” drive d(t) receptive field structure spike generation average across trials spike probability reliable-spike probability 0.15 r(t) r(t) p(t) coincidences across trials t t 0 0 p(t) 0.15 Summary • Reliable spikes (and spikes in bursts) are disproportionately effective in signaling the visual input, as filtered by the receptive field. • For most neurons, reliable spikes are preferentially generated by particular receptive field components. • To account for this observation, receptive fields have distinct subregions that differ in spike generation characteristics. • These observations are compatible with both Poisson and non-Poisson spike train statistics.