There is no difference, that are exactly the same. If you look at your contrasts, you will see they are mathematically identical, save a *-1. 

There is no way to see a "difference in deactivation", that isn't how contrasts work. They provide you a mathematical comparison, the interpretation of which is up to you. 

For my part, I always plot the contrast estimates of my activations of interest and see what they look like. I recently had an example where there were differences between a patient and control group in a group t-test, in both directions (patients > controls and controls > patients). But when plotting the contrast estimates, what I found was that patients just never showed a non-zero beta value )as a group) in these areas! So the cases of patients > controls was actually controls having a negative beta value, not that the patient group was activating that brain area while controls were not (is one interpretation). 

Long story short, contrasts are statistics, interpretation is up to you. Run the contrast and plot the Beta values. 

On 2 February 2014 21:50, Natalia Yakunina <[log in to unmask]> wrote:

Dear experts,

I would like to see the difference of deactivation maps of two different conditions (C1 and C2) using paired t-test. However, paired t-test on negative contrasts gives the same result as paired t-test on positive contrasts with the reverse order,  e.g. -C1>-C2 is the same as C2>C1. Is there a way to see the difference in deactivation?

Thank you.

Sincerely,

Natalia