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Subject:

Re: simple regression

From:

Daniel Simmonds <[log in to unmask]>

Reply-To:

Daniel Simmonds <[log in to unmask]>

Date:

Mon, 23 Jul 2007 12:20:15 -0400

Content-Type:

text/plain

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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.  I¹m 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

³less activation and deactivation contribute to the longer RT².



One possible interpretation for these ³conflicting² finding is that

because

of the ³less activation and deactivation² in some brain areas of

patients or

³slower² 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 ³default brain area² (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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