Dear Kalina,

There have been a number of papers and abstracts published in recent
years on this topic. Studies have characterised the haemodynamic
response in terms of both its delay and its relative magnitude. try Lai
et al., 1993 MRM 30 387-392 for an early study; Lee et al., 1995 MRM 33,
745-754 (identifying voxels with a late delay characteristic); Krings et
al., 1998 NeuroImage 7 S255. Robson et al., 1998 have also tried an
approach that excludes voxel regions with very high signal change.  

We are also interested in this problem and have been working on
statistical methods to best characterise the spatially varying magnitude
and delay parameters of the haemodynamic response.

I hope that this helps.

Regards,

Dr Debbie Hall
MRC Institute of Hearing Research
University of Nottingham
Nottingham
UK
****************************************************** 
Kalina Christoff wrote:
> 
> Dear SPM list,
> 
> Has anybody had experience trying to model explicitly (as a confounding
> variable) the part of the signal in fMRI that may be coming from large
> blood vessels? Since, to my understanding, signal from large blood vessels
> does not reflect local neural activity (and is instead influenced by
> the pooled neural activity over rather large and sometimes distant brain
> regions), it seems that it would be reasonable to try to exclude this
> variance from the activation maps.
> 
> Presumably, the signal coming from such large vessels (or at least
> large veins) has a later onset and peak, and it should therefore be
> possible, at least in principle, to model it explicitly and exclude the
> variance due it. Has anybody tried that before and what would an
> appropriate (late) onset be? Anyone's thoughts or experience would be
> greatly appreciated.
> 
> Best regards,
> -k.
> 
> _____________________________________________________________________________
> Kalina Christoff                      Email:  [log in to unmask]
>                                       Office: Rm.478; (650) 725-0797
> Department of Psychology              Home:   (650) 497-7170
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