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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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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.

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.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

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.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

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.


Rat barrel cortex

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


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

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.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

Layout & Identification

Deflection  transients similar to spontaneous ones.

Electrical and microscopy produced similar results.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

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.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

Tuning amount varied by individual.

Little individual direction tuning.

Tuning corrected for

Spiking rate.

No spatial organization for directional tuning.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

Question: Sparse/Dense responses?

Conclusions:

(1) Varies trial-to-trial

(2) Varies greatly between cells.

(3) Onset-Offset active cells may vary.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

Fraction active by location:

Stimulus – different.

Spontaneous – similar.

Assuming independence does not match the data.

 Correlated Activity

Subsets activated not consistent trial-to-trial.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

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


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

Stimulus detection always > false positive.

Classification accuracy improves with population size considered.

% small errors increased with size.

% large errors decreased with size.


Spatial organization of neuronal population responses in layer 2 3 of rat barrel cortex

Summary

Spatially organized – but probalistically

Correlated spiking, but variant

No discrete subpopulations observed.


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