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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. 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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slide1
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.
slide2
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.

slide3
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

slide5
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.

slide6
Layout & Identification

Deflection  transients similar to spontaneous ones.

Electrical and microscopy produced similar results.

slide7
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.

slide8
Tuning amount varied by individual.

Little individual direction tuning.

Tuning corrected for

Spiking rate.

No spatial organization for directional tuning.

slide9
Question: Sparse/Dense responses?

Conclusions:

(1) Varies trial-to-trial

(2) Varies greatly between cells.

(3) Onset-Offset active cells may vary.

slide10
Fraction active by location:

Stimulus – different.

Spontaneous – similar.

Assuming independence does not match the data.

 Correlated Activity

Subsets activated not consistent trial-to-trial.

slide11
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

slide12
Stimulus detection always > false positive.

Classification accuracy improves with population size considered.

% small errors increased with size.

% large errors decreased with size.

slide13
Summary

Spatially organized – but probalistically

Correlated spiking, but variant

No discrete subpopulations observed.

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