See in line responses below.

Best Regards, 

Donald McLaren, PhD

On Mon, Apr 18, 2016 at 7:09 PM, Joelle Zimmermann <[log in to unmask]> wrote:

Hi Donald,

I'm coming back to this, just want to clarify something..

I mentioned (in my email above), that improvements in performance across time reflect decreases in neural activity (in a one-sample t-test).

This was related to the -1 that you used at the first level.

 

Then, I go on to show that the slope of this relationship (between performance and neural activity) is different in younger and older adults. I'm wondering, since I show deactivations related to improvements in performance in the one-sample t-test, is this also the case for the two-sample t-test comparing young and older adults? 

You didn't show deactivations are related to improvements. All you have shown is a negative relationship. This shouldn't be confused with activity below baseline.

In the two sample test, you are comparing the negative slopes. If Y>O, then the negative slope is greater (more negative) in young compared to old. 

 

Can I say that the slope of the relationship between performance and specifically neural DEACTIVATIONS (since I show deactivations in the one-sample, not activations), is different by age?

No. You are looking at the slope. The slope does not tell you anything about the activations or deactivations relative to baseline.

 

Thanks,

Joelle

On Fri, Apr 15, 2016 at 1:47 PM, MCLAREN, Donald <[log in to unmask]> wrote:

You can test if their slopes are different. The t-test you did was for the slope of the PM. You just can't use the phrase "closeness" as you are testing the slope.

Best Regards, 

Donald McLaren, PhD

On Fri, Apr 15, 2016 at 10:52 AM, Joelle Zimmermann <[log in to unmask]> wrote:

Hi Donald,

Thanks for your help. Could you please clarify your second point?

Additionally, I conduct a 2-sample t-test, forwarding the first-level PM contrasts to the second-level, comparing young and old subjects. Here I find young>old gives me some interesting task-related regions. Am I correct to say that young adults' neural activations are more closely tied to behavioral performance than for old adults?

No. You can say that the slope of the relationship is different, but you can't conclude that the relationship is stronger as you only have the slope at the group level.

Is there a (another?) way to test differences between young and old subjects in terms of how their behavior performance (parametric modulator) modulates to their neural activations?

Thanks,

Joelle

On Thu, Apr 14, 2016 at 8:11 PM, MCLAREN, Donald <[log in to unmask]> wrote:

See below.

Best Regards, 

Donald McLaren, PhD

On Thu, Apr 14, 2016 at 4:36 PM, Joelle Zimmermann <[log in to unmask]> wrote:

Hi SPMers,

I am looking at the relationship between neural activity and behavioral performance, and was hoping for some insight for correct interpretation of a particular analysis.

On the first level, I have a model with my fMRI signal (first column), my behavioral performance as a parametric modulator (second column), and my 6 motion regressors. I am interested in the behavioral parametric modulator, so I put a contrast over the second column.

When I forward these individual subject contrasts to the second level, and do a one-sample t-test to look at group, with t-contrast [-1], I find certain task-related regions show significance. Would it be correct to say that the behavioral performance modulates neural activity, with improvements in performance across time reflecting decreases in neural activity in these certain regions?

Yes.

 

Additionally, I conduct a 2-sample t-test, forwarding the first-level PM contrasts to the second-level, comparing young and old subjects. Here I find young>old gives me some interesting task-related regions. Am I correct to say that young adults' neural activations are more closely tied to behavioral performance than for old adults?

No. You can say that the slope of the relationship is different, but you can't conclude that the relationship is stronger as you only have the slope at the group level.

 

Thanks in advance,

Joelle