Review of Classic Single Unit Barrel Cortex Literature.

1. Review of Classic Single Unit Recordings from SI Barrel cortex Andrew Hires

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

3. 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

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

5. Evoked Spike EntrainmentRegular Fast Spiking Layer 4

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

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

8. Stimulus Intensity - Response Single Unit example of common pattern

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

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

11. Half the units had surround activation

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

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

14. Experimental Setup 16 Adult Rats (124 cells) General Anesthesia for surgery Pentobarbital + atropine, recover 4-5hr IP gallaminetriethiodide + 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.

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

16. Suppression Integration Window in SI

17. Suppression Integration Window in Trigeminal Ganglion

18. Suppression Timecourse in Cortex vs. Trigeminal Ganglion

19. Order of deflection matters

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

21. Principal vs. Surround Suppression

22. Symmetric vs. Asymmetric Inhibitory Surround Symmetric Asymmetric

23. Directional selectivity of suppression PW excitation SW inhibition

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

25. 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

26. Thalamocortical vs. Regular spiking TCU : Minimal surround inhibition Broader multiwhisker sensitivity

27. Spontaneous firing rate TCU: Much higher spike rates

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

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

30. TCUs more directionally consistent TCU : More selective off responses Increasing selectivity

31. TCUs show less surround inhibition

32. Directional tuning of TCU inhibition SW excitatory response required SW excitatory response not required

33. TCU surround inhibition more directionally tuned than RSUs

34. Inhibitory receptive field comparison RSU – Single Whisker RSU – Multi Whisker TCU – Single Whisker TCU – Multi Whisker

35. Fast spiking unit example Minimal surround inhibition Broad multiwhisker sensitivity

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

37. Grand Mean Responses

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

39. 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)

40. Latency Contours Spatial contour of all cells active for a latency

41. Lateral spread of excitation

42. Modal latency with column depth

43. Example PSTH for IV, Va, Vb

44. Intra-cortical latency measurement

45. Modal Latency – PW, Layer IV

46. Paired latency differential – Same Column

47. Paired latency differential Near Neighbor Whisker

48. Paired latency differential Far Neighbor Whisker

49. Center-surround response magnitude by layer

50. Schematic propagation of excitation