 |
 |
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 Disclaimer: The materials in this e-mail are private and may contain Protected Health Information. Please note that e-mail is not necessarily confidential or secure. Your use of e-mail constitutes your acknowledgment of these confidentiality and security limitations. If you are not the intended recipient, be advised that any unauthorized use, disclosure, copying, distribution, or the taking of any action in reliance on the contents of this information is strictly prohibited. If you have received this e-mail in error, please immediately notify the sender via telephone or return e-mail.