In my understanding parametric modulation gives you areas with 
significant correlation (positive or negative) of BOLD and your 
modulator - so I am not sure if you can say that attention is modulating 
PFC activity - it might be also that PFC activity modulates attention.

Regards

Marek



W dniu 2016-08-15 o 16:32, Colin Hawco pisze:
> In regards to1)
>
> If you do a one-sample t-test on the parametric modulator column, yes, this shows regions in which the change in BOLD signal as related to (modulated by) the attention score you input.
>
> As a side note, p-mods are orthogonal to the HRF/task effects, so you can find activity  realted to the p-mod in regions which do not show overall task effects.
>
> In regards to 2), the correct interpretation is:
> During the decision process, the trial-by-trial attentional modulation effect on putamen activity was correlated with subject's age.
>
> Good luck!
>
> Colin Hawco, PhD
> Neuranalysis Consulting
> Neuroimaging analysis and consultation
> www.neuranalysis.com
> [log in to unmask]
>
>
>
> -----Original Message-----
> From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] On Behalf Of Mike
> Sent: August-13-16 6:22 AM
> To: [log in to unmask]
> Subject: [SPM] Interpretation of parametric modulation
>
> Hi,
>
> I have two questions regarding parametric modulation.
> (1) My first-level model had 3EVs. I added a parametric modulator (attention level) in one of these EVs (i.e., the regressor of interest), which corresponds to the trial-by-trial attention level during the decision period. If I use contrast 1 for this parametric regressor in the second-level analysis (one-sample t test in SPM) and identified that prefrontal cortex (PFC) was significant, that means PFC activity is parametrically modulated by subject's trial-by-trial attention level during the decision process. Is this correct?
>
> (2) Following (1). I totally have 20 subjects. In the second-level analysis (using the first-level t contrast of the parametric regressor, not the first-level t contrast of the EV itself) described in (1), I entered each subject's age as a covariate. Then I used contrast 1 to search for positive correlation with age and I identified putamen. What is the correct interpretation? (A) During the decision process, putamen activity is not only modulated by trial-by-trial attention but also correlated with subject's age; (B) During the decision process, the trial-by-trial attentional modulation effect on putamen activity was correlated with subject's age.
>
> Thanks. Mike

-- 
Marek Wypych PhD
Laboratory of Brain Imaging (LOBI)
Neurobiology Center
Nencki Institute of Experimental Biology
Pasteur 3, 02-093 Warsaw, Poland
Tel.: +48 22 5892 550
http://lobi.nencki.gov.pl/