I don’t think any of us should advise you about which drugs might be affected by the various tests you are having.
I’m not sure what ncs stands for or ssep (some kind of evoked potentials I assume). And I’m unclear about what effects Keppra might have on you for example in an MRI scanner.
If you are having all the tests on the same day, I assume you’ll be checked into a ward for the day, I presume you could ask a doctor before the tests, maybe don’t take the drugs until you get there, ask then take the drugs? Or if there is enough time between now and your testing day, phone the consultants secretary and ask if you can email him/her to be forwarded on to the consultant, and ask the same question you’ve asked us.
Best of luck.