How to differentiate attentiveness, arousal and memory via gamma oscillations
You'd need to "shut down arousal" to give a causal dissociation of arousal and memory reactivation, right?

E.g.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3174240/

Then you'd need to define what do you mean by "memory activation", physiologically, and record there simultaneously with the above. This will introduce additional difficulty in a mouse due to its small size, -- depending on where do you want to record when looking for "memory activation".

However, you may try using a simpler to implement EEG screw to get the oscillations https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5802558/

But the above link is for a rat, and you'd have to confirm in the literature that you can get the gamma through an EEG screw in a mouse. Also consider that in conjunction with your search for the area where you want to record the gamma.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5333145/

which itself is tied to the experimental design (task) that captures "memory activation".

During training, and for validation you may employ a proxy for arousal in a form of pupil dilation. 
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3612940/
There you again need to confirm  if someone has successfully used this measure in a mouse (the link is for humans, and it's possible in rats too).