Investigation of choice for diagnosis of Epilepsy is?

In the evaluation of a patient with suspected epilepsy, the presence of electrographic seizure activity during the clinically evident event (i.e., abnormal, repetitive, rhythmic activity having a discrete onset and termination) clearly establishes the diagnosis. The EEG may also be helpful in the interictal period by showing ceain abnormalities that are highly suppoive of the diagnosis of epilepsy. The EEG is also used for classifying seizure disorders and aiding in the selection of anticonvulsant medications. Ref Harrison20th edition pg 2456