1.
Review of Classic Single Unit Recordings from SI Barrel cortex<br />Andrew Hires<br />

2.
What are the response properties of neurons in SI barrel cortex?<br />

3.
Experimental Setup<br />21 Adult Rats (308 cells)<br />General Anesthesia for surgery<br />Pentobarbital + atropine, recover 4-5hr<br />IM d-tubocurarine to paralyze muscles<br />Glass microelectrodes 7-12Mohm with fast green, 3M KCl<br />Oscillatory and ramp hold stimuli from a polygraph motor<br />1-2mm displacement, 15-100mm/s^2.<br />Generally, histograms are 15 repetitions<br />

4.
Unit WaveformsRegular Fast Spiking<br />Layer 4 <br />15-50 /s spont firing<br />Timecourse 2x faster than RS<br />Smaller amplitude that shrinks during bursts<br />Broad directional selectivity<br />Layer 2-6 <br />1-15/s spont firing<br />More reliable evoked firing up to 40Hz<br />750-3000uV<br />L4 - Sharp spatial tuning (<90 degrees)<br />

5.
Evoked Spike EntrainmentRegular Fast Spiking<br />Layer 4<br />

6.
Evoked Spike EntrainmentRegular Fast Spiking<br />Typically first pulse only, max 1AP/cycle<br />Some frequency tuning<br />Typically every pulse, burst/cycle<br />15 stims<br />8Hz 20Hz 40Hz<br />8Hz 20Hz 40Hz<br />

7.
Deflection Response Examples<br />A-E = Different RSUs<br />Direction Selective Transient<br />Direction Selective Maintained<br />Transient & Maintained<br />FSU w/ inhibition<br />20Hz?<br />

8.
Stimulus Intensity - Response<br />Single Unit example of common pattern<br />

9.
Directional Tuning<br />FSUs<br />12 Units<br />Generally 2mm displacement<br />Spontaneous Rate<br />Away from Rest<br />Similar<br />Across <br />whiskers<br />Towards Rest<br />Transient<br />Steady-State<br />Similar<br />Across <br />Stim style<br />

10.
Layer specific distribution of single/multiwhisker units<br />Location via lesion, dyes, currents<br />Single Whisker Units<br />II/III = 61%<br />IV = 85%<br />V/VI = 36%<br />Whiskers<br />2<br />>3<br />Rows<br />Same<br />Diff<br />

11.
Half the units had surround activation<br />

12.
Spatial distribution of responsive whiskers between rows<br />If 2, then same row<br />If 3+ then multirow<br />

13.
How does SI spatially integrate information from vibrissa in a layer specific manner?<br />

14.
Experimental Setup<br />16 Adult Rats (124 cells)<br />General Anesthesia for surgery<br />Pentobarbital + atropine, recover 4-5hr<br />IP gallaminetriethiodide + pancuronium bromide to paralyze muscles<br />Glass microelectrodes 7-12Mohm with fast green, 3M NaCl<br />Orthogonal piezos on tube, 2-5 tubes on whiskers<br />1mm displacement, 200ms, 100-135mm/s^2.<br />

15.
Response suppression in a multiwhisker responsive unit<br />10 stims<br />1ms bins<br />Sweep <br />angle<br />

16.
Suppression Integration Window in SI<br />

17.
Suppression Integration Window in Trigeminal Ganglion<br />

18.
Suppression Timecourse in Cortex vs. Trigeminal Ganglion<br />

19.
Order of deflection matters<br />

20.
Asymmetry of surround inhibition<br />PW = C2. <br />SWs = C1, C3<br />Suppression greater C3-> C2 lesser C1->C2<br />

21.
Principal vs. Surround Suppression<br />

22.
Symmetric vs. Asymmetric Inhibitory Surround<br />Symmetric<br />Asymmetric<br />

23.
Directional selectivity of suppression<br />PW excitation<br />SW inhibition<br />

24.
How do the response characteristics of S1 thalamcortical projection neurons differ from their targets? <br />

25.
Experimental Setup<br />26 Adult Rats – 242 RSU, 135 TCU<br />General Anesthesia for surgery<br />Ether + Pentobarbital <br />Fentanyl anesthesia<br />Glass microelectrodes 7-12Mohm with fast green<br />Guide hole triangulation of barrel<br />Double Barrel 3M NaCL / HRP<br />

26.
Thalamocortical vs. Regular spiking<br />TCU : Minimal surround inhibition<br />Broader multiwhisker sensitivity<br />

27.
Spontaneous firing rate<br />TCU: Much higher spike rates<br />

28.
Response dynamics<br />TCU : Similar spikes per deflection onset<br />More spikes per offset<br />Higher rates in the 33% slowly adapting units <br />

29.
Strong Directional selectivity in TCUs<br />Directionally consistent<br />Reponds to ON one way,<br />OFF opposite way<br />

30.
TCUs more directionally consistent<br />TCU : More selective off responses<br />Increasing <br />selectivity<br />

31.
TCUs show less surround inhibition<br />

32.
Directional tuning of TCU inhibition<br />SW excitatory response required<br />SW excitatory response not required<br />

33.
TCU surround inhibition more directionally tuned than RSUs<br />

34.
Inhibitory receptive field comparison<br />RSU – Single Whisker<br />RSU – Multi Whisker<br />TCU – Single Whisker<br />TCU – Multi Whisker<br />

35.
Fast spiking unit example<br />Minimal surround inhibition<br />Broad multiwhisker sensitivity<br />

36.
Cell class comparison<br />Proportion / Rate of<br /> sustained activity<br />Spontaneous & <br />Transient spike rate<br />Proportion of cells<br />Proportion of cells<br />

37.
Grand Mean Responses<br />

38.
What is the timing and propagation of signals from whisker through cortical layers and across cortical columns <br />

39.
Experimental Protocol<br />Adult Rats<br />Urethane anesthesia<br />Localization by dye staining and CO<br />Carbon fiber microelectrodes (382 cells)<br />Modal latency was measured from the major peak in the latency histogram, providing this peak was 3+ counts. <br />3+ cells / penetration (min 1 in IV)<br />

40.
Latency Contours<br />Spatial contour of all cells active for a latency<br />

41.
Lateral spread of excitation<br />

42.
Modal latency with column depth<br />

43.
Example PSTH for IV, Va, Vb<br />

44.
Intra-cortical latency measurement<br />

45.
Modal Latency – PW, Layer IV<br />

46.
Paired latency differential – Same Column<br />

47.
Paired latency differential Near Neighbor Whisker<br />

48.
Paired latency differential Far Neighbor Whisker<br />

49.
Center-surround response magnitude by layer<br />

50.
Schematic propagation of excitation<br />