Journal Club Mouse Somatosensory Cortex SII

Andrew Hires

12.5.2008

Mouse Somatosensory Cortex SII

• Where is it?

• What is its structure?

• What is its response characteristics?

• What is its function?

Location of SII

"Gran Torino"

4mm2

4mm2

Carvell & Simons 1986 Sens & Motor Res

• Sodium pentobarbital

• Tungsten microelectrodes– Normal to pia, 300-450um (III, IV) most vigor

• Poking, brushing, tapping glass

Somatosensory response map in SIIWhole body somatotopic mapLarger receptive fields“head up” orientation map

• Only contralateral input in whisker areaSI to SII transition and whisker area

Subdivisions of SII

Carvell & Simons 1986

Whiskers are most medialFace is 54% of SII, Whiskers are 16% of SIIAuditory overlap in lateral and caudal areas (not in whisker)

SII cytoarchitecture• No barrels

• Thickening of cortex

• Diffuse IV, less uniform lamination of V

SII inputs• Thalamic Input

– POm (latency coding), VPMvl– Paralemniscal pathway– Parallel stream

• Cortical Input– Major from SI– Also surrounding cortical areas

Chakrabarti & Alloway 2006- SII Injections

• Retrograde tracers into SII (and MI)– Diamidino yellow, true blue – CTb, BDA, Fluoro Gold

• 50 degree from midline

• 1200-1400, 1000, 800um below pia

Promiscuous SII Inputs• Big injection

• SI Input from barrel and septa

MI has septa preference, SII does not

Broadly somatotopic input to SII

• Same pattern in various layers

SII has few inputs from layer IV SI

SII and MI injections• MI prefers border of septal and barrel

Do individual SI cells project to both?

Yes.

Thalamic input of SII and MI somewhat intermingled

VPMvl projections

• Pierret et al. 20 (19): 7455. (2000)

Kwegyir-Afful & Keller - Rat SII physiology

• Halothane -> fentanyl, or urethane

• Extracellular platinum, quartz ins, trodes

• Manual whisker stim

• 8 dir piezo stim, 50x angle– 1cm from base– 200ms ramp and hold– 1Hz

Kwegyir-Afful & Keller - 2004

SII vs. SI spiking properties• SII latency = across layers, SI-IV

• ~9ms

• Rate < SI

Stimulus dependent firing in SII

90% 10%

Large receptive fields in SII

• 5-12 whiskers per recording site

Layer V neuron

“Primary” vs. “Accessory” whiskers?

• Top 3 ave whisker amp sig dif from rest

SII angular tuning examples

Cat 6 selective Cat 0 selective

SII more angularly selective than SI

• VI more selective than other layers– But not significant

Summary of SII response properties

Additional SII findings

• Evoked activity in SII is lower– Preference for multiple whisker stimulation?– Preference for active whisking? (Paralemniscial)

• RSU = FSU magnitude– Less feed forward inhibition

• Nearly all are rapidly adapting neurons

• Inactivation of SI in cat does not block SII– Does block in primate (hierarchal or subdivisions)– Driving input is from thalamus? SI input modulates?

What is SII’s function?

• Receives lemniscal and paralemniscal input– Whisking frequency and external stimulus

• Context integration in stimulus detection?

• Spatial distributed feature analysis?

• Size of objects (# of whiskers struck)