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Spatial Organization of Neuronal Population Responses in Layer 2/3 of Rat Barrel Cortex

Spatial Organization of Neuronal Population Responses in Layer 2/3 of Rat Barrel Cortex. Jason N. D. Kerr, Christiaan P. J. de Kock, David S. Greenberg, Randy M. Bruno, Bert Sakmann, and Fritjof Helmchen. Take Home Points:. 1. Sparse spiking, no precise patterns.

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Spatial Organization of Neuronal Population Responses in Layer 2/3 of Rat Barrel Cortex

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  1. Spatial Organization of Neuronal Population Responses in Layer 2/3 of Rat Barrel Cortex Jason N. D. Kerr,Christiaan P. J. de Kock, David S. Greenberg, Randy M. Bruno,Bert Sakmann,and Fritjof Helmchen Take Home Points: 1. Sparse spiking, no precise patterns. 2. Spatially organized probalistic spiking patterns. 3. Position Not related direction sensitivity (unlike afferents) 4. Population coding: Each feature  many neurons. Each neuron  several features. • May facilitate integration of multiple whiskers.

  2. Mutual Information : How much information two things share. . . . . ? A measure of how knowledge about one thing reduces your uncertainty about another thing. ~ a more sophisticated correlation.

  3. Rationale: Large single cell variability. Sparse and short-lived patterns BUT could have an unambiguous pattern, but requires many neurons. (Think sample size) Methodologically: Development of spatial maps of neural activity. – normally impossible with extracellular recording.

  4. Rat Barrel Cortex • Rodent somatosensory cortex. • Single whisker  discrete structures (whisker barrels) separated by regions called septa. • Same geometric order as whiskers. • Model system for cortical columns. • Organized into layers. Layer IV (L4): individual neurons -- consistent trial-to-trial, strong directional tuning. • However, L2/L3 layer does not. 1: Woolsey and Van der Loos, 1970

  5. Methods Calcium Indictors Location of all cells Single-cell and single-spike resolution. Two-Photon Microscopy Skull exposed, optical imaging while stimulating whisker. Patch-clamp recordings – visually targeted. Random whisker deflected for 500ms. Interstim ~3-6 sec Cortex sectioned and area of WB determined. ….. Then a significant variety of analysis.

  6. Layout & Identification Deflection  transients similar to spontaneous ones. Electrical and microscopy produced similar results.

  7. Question: Spatial organization? Stimulated whisker Septa near whisker. Conclusion: (1) Depends on distance from BCC (2) Highly variable Nearby whiskers (3) For both onset & offset (4) Highly significant topology. (5) Offset ~ onset, but smaller. (6) Spontaneous: all similar.

  8. Tuning amount varied by individual. Little individual direction tuning. Tuning corrected for Spiking rate. No spatial organization for directional tuning.

  9. Question: Sparse/Dense responses? Conclusions: (1) Varies trial-to-trial (2) Varies greatly between cells. (3) Onset-Offset active cells may vary.

  10. Fraction active by location: Stimulus – different. Spontaneous – similar. Assuming independence does not match the data.  Correlated Activity Subsets activated not consistent trial-to-trial.

  11. Correlations present in spontaneous, but increased with stimulus. Distance between neurons  means little. Distance from BCC  significant meaning. For both spontaneous and stimulus. “During sensory stimulation, neighboring neurons may be bound together by common inputs.” Question: Is effect of distance to BCC on correlation a result of pairs in the BCC being packed closely? Conclusion: No. < 40µm pair distance

  12. Stimulus detection always > false positive. Classification accuracy improves with population size considered. % small errors increased with size. % large errors decreased with size.

  13. Summary Spatially organized – but probalistically Correlated spiking, but variant No discrete subpopulations observed.

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