Hi!! I agree with Elena. The only thing that I will add is for the case, if you want to be more sure you can do exploratory behavior test which measures normal daily activity of rats such as licking, rearing, ambulatory activity, stereotypic activity e.t.c. It can again depend upon the basis of experiments you want to perform with rats(rota rod for muscle test, tail flick for sensitivity test, for stress there are several social behavioral test, for memory testing there are several mazes test like morris water, Y maze, T maze). Regarding EEG waves recording, for each wave there is certain range you can analse that whether the recording of waves lies in that range or not. If it lies, then recording is normal, provided that again you have to be very sure about the movement of rat while recording. Since, it the result changes with the activity of rat. In nutshell, a bit complicated because you have to acclamatize your rat to sit in same condition before you do any experiment with it. Generally, if rat is not normal then you get several clusters in recording but its a general overview.

Thanks a lot for your suggestion

As Lena said, that depends upon your Vet within your institutional animal research committee. Some IRB protocols are stringent some or bit lenient. However, as a researcher, everyone has a ethical responsibility act in an acceptable international standard. Every laboratory animal behave in certain manner, which constitute as a normal behavior: visually normal and healthy, active, friendly, licking, grooming, etc. As Abhi pointed out, they should also be eating and drinking normally and not loosing weight gradually or abruptly. Proper cage maintenance also needs to be carried out in order to keep the animals healthy. All these must be noted in your record book for future reference. Once you do this for a while, you would start to realize that you can easily tell if the animal is doing well or exhibiting any sickness behavior.

With regards to the question on EEG, I am not sure if you talking about scalp EEG or intracellular recording (cortical recording). The EEG waveform varies in continuous recording. First, you need to familiarize with them. Secondly, among others; age of the animal, brain activity variation under different depth of anesthesia (DOA), Diurnal variations, and low frequency electromagnetic field (EMF), could also influence how the EEG might look like. Above all, you need to familiarize with how the EEG artifacts will look like.