Yeah, EEG is much harder than pulse detection, myography, GSR, ECG, etc. because the electrical fields from the brain are weak compared to electrical noise in the environment.
It is not that big of a hassle to wear a Holter monitor for continuous ECG monitoring for a month (w/ only 3 electrodes compared to the usual 12 lead ECG you would get in the clinic) but ambulatory EEG is a bigger deal
In the lab we are able to see EEG waves when doing ABR in a non-electrically isolated environment pretty easily. I think that if the electrodes can be implanted under the skin next to the skull in a way that the animal wouldn't be trying to remove them all the time that some reasonable data can be gleaned and separated from intermittent environmental noise. We do use filters after all.
It is not that big of a hassle to wear a Holter monitor for continuous ECG monitoring for a month (w/ only 3 electrodes compared to the usual 12 lead ECG you would get in the clinic) but ambulatory EEG is a bigger deal
https://www.epilepsy.com/diagnosis/eeg/ambulatory
If the OP had an infinite budget the right way to do it would be to implant an ECG detector such as
See
https://www.hopkinsmedicine.org/health/conditions-and-diseas...
This device looks like it makes EEG a lot easier
https://www.hopkinsmedicine.org/health/conditions-and-diseas...
See also
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10563901/