R imager leftright  [...-Hb]/µM Studying NIRS from infancy

uses and abuses of optical topography hellmuth obrig

uses and abuses of optical topography hellmuth obrig!!!!!

Maybe there is some abuse in the literature

Taga et al 2003

condition 1 condition2 n= nm & 850 nm 7 detectors 8 sources 20s this is a boring experiment

the imaging result is redundant imager

the interesting result is the time course stim vs. stim stim vs. rest time /s concentration change / µM

data processing event related averaging artefact removal General Linear Model approach PCA removal of global effects

Thus we can check our hypothesis by an analysis procedure

Let‘s make things complicated Iadecola et al 04

... or alternatively oversimplify the matter neuronal model blood-flow regulator oxygen- extractor venous balloon BOLD contrast

E E D D 3 s 0.01µM [deoxy-Hb] BOLD contrast ‚activation‘ is an operational term

likewise ‚deactivation‘ is an operational term

the time course is still conroversial

VEP NIRS the recoupling issue

There is a component not showing habituation

stimulusvascular-response neuronal activity vascular response flow velocity oxygenation  OD parameters want a break?

An early component of the VEP does not show habituation

transcallosal inhibition

NIRS tapping NIRS TMS Comparing excitation and inhibition of primary motor cortex

motor TMS the vascular response is similar

mmol / l time / s mmol / l oxy deoxy The time courses are qualitatively similar

motorwithout with preactivation x3 activation and inhibition cannot be discriminated

EffectCBF Spiking (on target)(local)(output) Exitation Exitation+ Inhibition Deactivation Inhibition ? Disinhibition ? Lauritzen & Gold PNAS 2003 Inverse problem of the vascular response

EEG ssVEP source detector ISS NIRS Does background activity have an influence on the vascular response?

detector oxy-Hb emitter deoxy-Hb There is a focal hyperoxygenation over the occipital region

P3O1PzO2P4 EEG NIRS 2.5 cm 10 cm 2.5 cm 5 cm electrode detector NIRS-probe electrode emitter ms 45ms 5ms 45ms 15 s experimental setup

    Neurovascular coupling?

8-12Hz 24-28Hz Alpha power is an inverse predictor of the haemodynamic response

stimulus Summation (EP /LFP) 1s ‚idling state‘ desynchronisation Modulation of evoked and spontaneous activity is mutually dependent

Use or abuse? There is a NIRS response closely linked to classical imaging methods There is changes which definitely are not related to the brain There is options to identify brain related signals Neurovascular coupling is a very general principle There are exceptions from the rule NIRS allows to investigate these deviations from a 1:1 translation