Hi Michael,

A few things:
1) Matt’s point about the increased activation estimates in visual cortex is a 
good one. There is increased signal in occipital cortex in functional 
connectivity analyses that do not assume a response shape. In part, this may 
result from the back of the head being closer to the head coil than other brain 
regions (because participants are laying down).
2) To the best of my knowledge, the HCP consortium has not ventured to 
recommend a single, ideal HRF for use in task fMRI analysis. In fact, I’d wager 
that most people in the consortium expect the hemodynamic response to vary 
across brain regions and across people in such a way that there is no single 
ideal canonical HRF.
3) We chose the double-gamma during very early analysis of HCP pilot data. 
Using 2.5s TR data, the default double-gamma showed zstat maps with slightly 
higher statistical significance at the group-level than the default gamma HRF 
(in Feat). The double-gamma also seemed to be used more widely in the 
literature, in part due to the commonly observed undershoot at the end of the 
hemodynamic response (see Glover, 1999). We made this choice in piloting, and 
stayed with it for analysis of the Phase II HCP. We did not re-evaluate HRFs in 
the fast TR HCP data.
4) In HCP tfMRI, we utilized blocked designs. Blocked designs are good for 
detecting the response, but are not good for estimating the shape of the 
response function. It may follow that differences between canonical HRFs will 
matter less for blocked designs, but I don’t know if anyone has looked at that 
systematically.
5) If you’re referring to analysis of your own data using an event-related 
design, your best bet will likely be using a basis set. FSL has FLOBS, folks at 
Wash U tend to use FIR basis sets, but there are others out there as well. 
There are quite a few papers out there to help you choose between those basis 
sets. However, I’m not sure it would make much sense in the context of a 
blocked design.

Hope this all helps!
--Greg

____________________________________________________________________
Greg Burgess, Ph.D.
Staff Scientist, Human Connectome Project
Washington University School of Medicine
Department of Psychiatry
Phone: 314-362-7864
Email: gburg...@wustl.edu

> On Sep 22, 2016, at 12:25 PM, Glasser, Matthew <glass...@wustl.edu> wrote:
>
> BOLD fluctuations are generally stronger on the occipital cortex
> (independent of the chosen HRF).  See for example the attached functional
> CNR map (BOLDVariance / UnstructuredNoiseVariance).
>
> Peace,
>
> Matt.
>
> On 9/21/16, 7:29 PM, "hcp-users-boun...@humanconnectome.org on behalf of
> Michael Dreyfuss" <hcp-users-boun...@humanconnectome.org on behalf of
> mdreyfus...@gmail.com> wrote:
>
>> Hello,
>>
>> What kind of basis function are you recommending for tfMRI data?I have
>> been using double-gamma HRF but I notice that the signal is always
>> strongest in occipital cortex, so I was wondering if this is not optimal
>> for other regions. If so, do you have a more customized recommendation
>> that would better fit HRF functions in other parts of the brain to detect
>> signal there?
>>
>> Thank you,
>> Michael
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>
>
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> <BOLDCNR.png>


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