[Homer-users] HRF inversion...any explanations?

[Scholkmann Felix]

Inverted and "abnormal" O2Hb and HHb responses could be due to (according to my experience) (i) not completely developed neuro-vascular coupling and autoregulation (one can observe this in neonates) ([1, 2]) and/or (ii) changes in hemodynamics caused by global systemic physiology or local extracerebral physiology (see for example [3, 4]).

When measuring at the temporal region of the head, also the muscle there (temporal muscle) can cause local muscle perfusion and oxygenation changes when activated (e.g. by teeth clenchin or movements of the mandibular, etc.).

And finally, there is a possibility that a "vascular steal phenomenon" was happening - a nice paper about this was published by Poublanc et al. [6].

Regards,
Felix

[1] http://www.pnas.org/content/110/11/4380.short
[2] http://www.sciencedirect.com/science/article/pii/S0079612316000376
[3] http://neurophotonics.spiedigitallibrary.org/article.aspx?articleid=2502725
[4] http://www.sciencedirect.com/science/article/pii/S1053811916304505
[5] https://en.wikipedia.org/wiki/Temporal_muscle
[6] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3776710/






From: homer-users-bounces at nmr.mgh.harvard.edu [mailto:homer-users-bounces at nmr.mgh.harvard.edu] On Behalf Of Cecile Issard
Sent: Freitag, 24. Februar 2017 12:05
To: homer-users at nmr.mgh.harvard.edu
Subject: Re: [Homer-users] HRF inversion...any explanations?

Also how old are your participants ?
You can see Meek et al. (1998) about that in neonates.

 Kiss Louah for me !
Le 23 févr. 2017 à 13:25, Cheung, Shirley <s.cheung at lancaster.ac.uk<mailto:s.cheung at lancaster.ac.uk>> a écrit :

Dear Homer2 community,

I’m experiencing some difficulty interpreting my results in Homer2. In some conditions (but not all), my HRFs are inverted where HbR is higher than HbO. My experimental procedure consists of short auditory stimuli presented in a repeated Baseline (non-alternating), Test (alternating), and Silence block order. Does anyone have an idea why HRF inversion occurs? Could it be due to the experimental design, arrangement of sources/detectors, averaging baselines/blocks incorrectly, other factors such as watching a silent video during auditory stimulus presentation, or anything else?

Also, is it possible to manually set a baseline interval in Homer2 that does not immediately precede the onset of a stimulus?

Any suggestions or explanations would be greatly appreciated, thank you!


Shirley Cheung
Leverhulme Trust Doctoral Scholar
Department of Psychology
Lancaster University, U.K.

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