Review of Classic Single Unit Recordings from SI Barrel cortex

Andrew Hires

• What are the response properties of neurons in SI barrel cortex?

Experimental Setup

• 21 Adult Rats (308 cells)• General Anesthesia for surgery

– Pentobarbital + atropine, recover 4-5hr

• IM d-tubocurarine to paralyze muscles• Glass microelectrodes 7-12Mohm with fast green,

3M KCl• Oscillatory and ramp hold stimuli from a

polygraph motor– 1-2mm displacement, 15-100mm/s^2.

• Generally, histograms are 15 repetitions

Unit WaveformsRegular Fast Spiking

Layer 4 15-50 /s spont firingTimecourse 2x faster than RSSmaller amplitude that shrinks during burstsBroad directional selectivity

Layer 2-6 1-15/s spont firingMore reliable evoked firing up to 40Hz750-3000uVL4 - Sharp spatial tuning (<90 degrees)

Evoked Spike EntrainmentRegular Fast Spiking

Layer 4

Evoked Spike EntrainmentRegular Fast Spiking

Typically first pulse only, max 1AP/cycleSome frequency tuning

Typically every pulse, burst/cycle

15 stims8Hz 20Hz 40Hz 8Hz 20Hz 40Hz

Deflection Response Examples

FSU w/ inhibition

20Hz?

A-E = Different RSUs

Direction Selective Transient Direction Selective Maintained Transient & Maintained

Stimulus Intensity - ResponseSingle Unit example of common pattern

Directional Tuning

Spontaneous Rate

Away from Rest

Towards Rest

12 UnitsGenerally 2mm displacement

Transient

Steady-State

FSUs

SimilarAcross whiskers

SimilarAcross Stim style

Layer specific distribution of single/multiwhisker units

Location via lesion, dyes, currentsSingle Whisker UnitsII/III = 61%IV = 85%V/VI = 36%

Rows

Same

Diff

Whiskers

2

>3

Half the units had surround activation

Spatial distribution of responsive whiskers between rows

If 2, then same rowIf 3+ then multirow

• How does SI spatially integrate information from vibrissa in a layer specific manner?

Experimental Setup

• 16 Adult Rats (124 cells)

• General Anesthesia for surgery– Pentobarbital + atropine, recover 4-5hr

• IP gallamine triethiodide + pancuronium bromide to paralyze muscles

• Glass microelectrodes 7-12Mohm with fast green, 3M NaCl

• Orthogonal piezos on tube, 2-5 tubes on whiskers– 1mm displacement, 200ms, 100-135mm/s^2.

Response suppression in a multiwhisker responsive unit

10 stims1ms bins

Sweep angle

Suppression Integration Window in SI

Suppression Integration Window in Trigeminal Ganglion

Suppression Timecourse in Cortex vs. Trigeminal Ganglion

Order of deflection matters

Asymmetry of surround inhibition

• PW = C2.

• SWs = C1, C3

• Suppression greater C3-> C2 lesser C1->C2

Principal vs. Surround Suppression

Symmetric vs. Asymmetric Inhibitory SurroundSymmetric Asymmetric

Directional selectivity of suppression

PW excitation

SW inhibition

How do the response characteristics of S1 thalamcortical projection neurons

differ from their targets?

Experimental Setup

• 26 Adult Rats – 242 RSU, 135 TCU

• General Anesthesia for surgery

– Ether + Pentobarbital

• Fentanyl anesthesia

• Glass microelectrodes 7-12Mohm with fast green

• Guide hole triangulation of barrel

• Double Barrel 3M NaCL / HRP

Thalamocortical vs. Regular spiking

TCU : Minimal surround inhibitionBroader multiwhisker sensitivity

Spontaneous firing rate

TCU: Much higher spike rates

Response dynamics

TCU : Similar spikes per deflection onsetMore spikes per offsetHigher rates in the 33% slowly adapting units

Strong Directional selectivity in TCUs

Directionally consistentReponds to ON one way,OFF opposite way

TCUs more directionally consistent

Increasing selectivity

TCU : More selective off responses

TCUs show less surround inhibition

Directional tuning of TCU inhibitionSW excitatory response required SW excitatory response not required

TCU surround inhibition more directionally tuned than RSUs

Inhibitory receptive field comparison

RSU – Single WhiskerRSU – Multi WhiskerTCU – Single WhiskerTCU – Multi Whisker

Fast spiking unit exampleMinimal surround inhibitionBroad multiwhisker sensitivity

Cell class comparisonSpontaneous & Transient spike rate

Proportion / Rate ofsustained activity

Proportion of cells Proportion of cells

Grand Mean Responses

What is the timing and propagation of signals from whisker through cortical

layers and across cortical columns

Experimental Protocol

• Adult Rats

• Urethane anesthesia

• Localization by dye staining and CO

• Carbon fiber microelectrodes (382 cells)

• Modal latency was measured from the major peak in the latency histogram, providing this peak was 3+ counts.

• 3+ cells / penetration (min 1 in IV)

Latency Contours

• Spatial contour of all cells active for a latency

Lateral spread of excitation

Modal latency with column depth

Example PSTH for IV, Va, Vb

Intra-cortical latency measurement

Modal Latency – PW, Layer IV

Paired latency differential – Same Column

Paired latency differential Near Neighbor Whisker

Paired latency differential Far Neighbor Whisker

Center-surround response magnitude by layer

Schematic propagation of excitation