How to differentiate attentiveness, arousal and memory via gamma oscillations I am planning an experiment using mice with in vivo extracellular recordings (and maybe also optogenetic stimulation). In these kinds of experiments, the mouse is getting a reward after executing a (short term) memory involved task.

I noticed that in the papers I read, it is not really possible to know if the observed $\gamma$-oscillations (for instance), derive from memory activation, or arousal (from thinking of the reward), or from attentiveness (from trying to execute the task correctly).

Are there any ideas or a good reference for this problem of distinguishing between these related cognitive activities?

Examples of experiments with humans will also help. Maybe not directly but will give some ideas about how these notions can be separated.
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).