1.
Journal Club Mouse Somatosensory Cortex SII Andrew Hires 12.5.2008

2.
Mouse Somatosensory Cortex SII <ul><li>Where is it? </li></ul><ul><li>What is its structure? </li></ul><ul><li>What is its response characteristics? </li></ul><ul><li>What is its function? </li></ul>

3.
Location of SII <ul><li>4mm 2 </li></ul>&quot;Gran Torino&quot; 4mm 2

4.
Carvell & Simons 1986 Sens & Motor Res <ul><li>Sodium pentobarbital </li></ul><ul><li>Tungsten microelectrodes </li></ul><ul><ul><li>Normal to pia, 300-450um (III, IV) most vigor </li></ul></ul><ul><li>Poking, brushing, tapping glass </li></ul>

5.
Somatosensory response map in SII Whole body somatotopic map Larger receptive fields “ head up” orientation map

6.
<ul><li>Only contralateral input in whisker area </li></ul>SI to SII transition and whisker area

7.
Subdivisions of SII Carvell & Simons 1986 Whiskers are most medial Face is 54% of SII, Whiskers are 16% of SII Auditory overlap in lateral and caudal areas (not in whisker)

8.
SII cytoarchitecture <ul><li>No barrels </li></ul><ul><li>Thickening of cortex </li></ul><ul><li>Diffuse IV, less uniform lamination of V </li></ul>

9.
SII inputs <ul><li>Thalamic Input </li></ul><ul><ul><li>POm (latency coding), VPMvl </li></ul></ul><ul><ul><li>Paralemniscal pathway </li></ul></ul><ul><ul><li>Parallel stream </li></ul></ul><ul><li>Cortical Input </li></ul><ul><ul><li>Major from SI </li></ul></ul><ul><ul><li>Also surrounding cortical areas </li></ul></ul>

10.
Chakrabarti & Alloway 2006- SII Injections <ul><li>Retrograde tracers into SII (and MI) </li></ul><ul><ul><li>Diamidino yellow, true blue </li></ul></ul><ul><ul><li>CTb, BDA, Fluoro Gold </li></ul></ul><ul><li>50 degree from midline </li></ul><ul><li>1200-1400, 1000, 800um below pia </li></ul>

11.
Promiscuous SII Inputs <ul><li>Big injection </li></ul><ul><li>SI Input from barrel and septa </li></ul>

12.
MI has septa preference, SII does not

13.
Broadly somatotopic input to SII <ul><li>Same pattern in various layers </li></ul>

14.
SII has few inputs from layer IV SI

15.
SII and MI injections <ul><li>MI prefers border of septal and barrel </li></ul>

16.
Do individual SI cells project to both?

17.
Yes.

18.
Thalamic input of SII and MI somewhat intermingled

19.
VPMvl projections <ul><li>Pierret et al. 20 (19): 7455. (2000) </li></ul>

20.
Kwegyir-Afful & Keller - Rat SII physiology <ul><li>Halothane -> fentanyl, or urethane </li></ul><ul><li>Extracellular platinum, quartz ins, trodes </li></ul><ul><li>Manual whisker stim </li></ul><ul><li>8 dir piezo stim, 50x angle </li></ul><ul><ul><li>1cm from base </li></ul></ul><ul><ul><li>200ms ramp and hold </li></ul></ul><ul><ul><li>1Hz </li></ul></ul>Kwegyir-Afful & Keller - 2004

21.
SII vs. SI spiking properties <ul><li>SII latency = across layers, SI-IV </li></ul><ul><li>~9ms </li></ul><ul><li>Rate < SI </li></ul>

22.
Stimulus dependent firing in SII 90% 10%

23.
Large receptive fields in SII <ul><li>5-12 whiskers per recording site </li></ul>Layer V neuron

24.
“ Primary” vs. “Accessory” whiskers? <ul><li>Top 3 ave whisker amp sig dif from rest </li></ul>

25.
SII angular tuning examples <ul><li>Cat 6 selective </li></ul>Cat 0 selective

26.
SII more angularly selective than SI <ul><li>VI more selective than other layers </li></ul><ul><ul><li>But not significant </li></ul></ul>

27.
Summary of SII response properties

28.
Additional SII findings <ul><li>Evoked activity in SII is lower </li></ul><ul><ul><li>Preference for multiple whisker stimulation? </li></ul></ul><ul><ul><li>Preference for active whisking? (Paralemniscial) </li></ul></ul><ul><li>RSU = FSU magnitude </li></ul><ul><ul><li>Less feed forward inhibition </li></ul></ul><ul><li>Nearly all are rapidly adapting neurons </li></ul><ul><li>Inactivation of SI in cat does not block SII </li></ul><ul><ul><li>Does block in primate (hierarchal or subdivisions) </li></ul></ul><ul><ul><li>Driving input is from thalamus? SI input modulates? </li></ul></ul>

29.
What is SII’s function? <ul><li>Receives lemniscal and paralemniscal input </li></ul><ul><ul><li>Whisking frequency and external stimulus </li></ul></ul><ul><li>Context integration in stimulus detection? </li></ul><ul><li>Spatial distributed feature analysis? </li></ul><ul><li>Size of objects (# of whiskers struck) </li></ul>