regress_basis_multi dmBLOCK- negative values

Hello!

I am running into some difficulties when determining which regress_basis_multi option to use for our analysis. The data is from a social incentive delay (SID) task where people anticipate varying levels of social reward or no reward, and depending on a successful response to a cue, receive that reward or not. Because there are individual differences in response timing, we used dmBLOCK. However, after extracting activation in our primary ROI, we are getting negative beta values in all conditions of interest (when based on our past samples/SID literature we would expect to get positive values). In a previous sample using the same task, we ran into this same issue and found that when WAV was used (outside of proc) the values were positive but were negative when using dmBLOCK, which made us wonder whether there was some sort of scaling issue when using dmBLOCK.

I am wondering if/why dmBLOCK could be contributing to negative values and if you have any recommendations for how to possibly correct this?

Thank you!

For each task condition, what is the duration range across trials? What is your research hypothesis about the task conditions?

Our hypothesis is that striatal activation will be greater during reward vs. no reward conditions. We're primarily interested in the anticipation of social reward conditions.

Duration ranges:
anticipation of no reward: 2.33-3.07 seconds (range: 0.73)
anticipation of low reward: 2.38- 3.07 (range: 0.68)
anticipation of high reward: 2.29-3.07 (range: 0.78)

Thanks!

You may consider using dmUBLOCK rather than dmBLOCK, as detailed here. Directly estimating the hemodynamic response using a deconvolution approach, as outlined in this blog post, could be a valuable alternative to assuming a fixed shape and might yield more accurate and improved results.

Gang Chen