Across both groups. How to use multiple regression?
Also, you mentioned "it is consistent with lots of models". Could you give
me one or two examples?
Thanks
Jiansong
> From: Daniel Simmonds <[log in to unmask]>
> Reply-To: Daniel Simmonds <[log in to unmask]>
> Date: Mon, 23 Jul 2007 12:20:15 -0400
> To: <[log in to unmask]>
> Subject: Re: [SPM] simple regression
>
> hi jiansong,
>
> is the simple regression you are discussing in the patients, in the
> controls, or across both groups? it may be that there are different
> correlations with RT for each group (ie positive correlation in
> controls/negative correlation in patients and vice versa) and this could
> potentially indicate that the two groups are using this region
> differently (ie in one group, greater activation in this region leads to
> faster RT's, while in the other, it leads to slower RT's). this type of
> question could be answered using a multiple regression as opposed to a
> simple regression.
>
> dani
>
> Daniel Simmonds
> Developmental Cognitive Neurology
> Kennedy Krieger Institute
> [log in to unmask]
>
>>>> Jiansong Xu <[log in to unmask]> 7/23/2007 12:11 PM >>>
> Thanks. But, the problem is:
>
> Relative to control subjects, patients showed longer RT and less
> activation
> in the lateral prefrontal cortex and less deactivation in the medial
> prefrontal cortex. I©öm glad about this finding and I can claim that
> the
> less activation and deactivation exhibited by patients correlated with
> their
> longer RT than controls. Now, the RT positively correlated with the
> BOLD in
> the lateral prefrontal cortex and negatively correlated with signal in
> the
> medial cortex. Such correlation is opposite to my above interpretation
> of
> ©øless activation and deactivation contribute to the longer RT©÷.
>
> One possible interpretation for these ©øconflicting©÷ finding is that
> because
> of the ©øless activation and deactivation©÷ in some brain areas of
> patients or
> ©øslower©÷ performers, the remaining intact brain areas in patients need
> to
> work longer to compensate for the impaired brain function.
>
>
> I have another study of healthy subjects (different population from
> above
> study) with different task. It also showed greater RT positively
> correlated
> with greater signal changes in the prefrontal and parietal cortex, and
> subcortical area (thalamus and striatum) and negatively correlated
> with
> signal changes in the ©ødefault brain area©÷ (e.g., medial part of the
> brain).
> Follow your comments, these data suggest that the worse performers
> (i.e.,
> longer RT) showed greater BOLD signal increase in the positive network
> and
> greater BOLD signal decrease in the negative network, thus showed less
> functional efficiency in their brain. Is it reasonable?
>
> Best
>
> Jiansong
>
>
>
> From: "Weissman, Daniel" <[log in to unmask]>
> Reply-To: "Weissman, Daniel" <[log in to unmask]>
> Date: Mon, 23 Jul 2007 11:31:14 -0400
> To: <[log in to unmask]>
> Subject: Re: [SPM] simple regression
>
> Dear Jiansong,
>
> If I understand correctly, you've found a positive beta coefficient in
> a
> simple (across-subjects) regression in which BOLD signal is regressed
> against RT. In that case, the positive beta coefficient would indeed
> mean
> that subjects who show larger changes in BOLD signal tend to exhibit
> longer
> RT. Although this finding goes against your prediction, it is
> consistent
> with lots of models. For example, longer RT may indicate greater time
> on
> task, which results in more activity.
>
> Hope this helps,
> Daniel
>
>
> Dear Friend:
>
> I'm using simple regression to assess the correlation between BOLD
> signal
> changes and reaction time. Several clusters in the prefrontal and
> parietal
> cortex showed significant positive correlation between signal changes
> and
> RT. Does this positive correlation indicate greater signal changes
> correlated with greater RT? If so, it is opposite to my expectation of
> greater activity correlated with shorter RT. Any comments are
> appreciated.
>
> Best
>
> Jiansong
>
>
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