What Causes Frequent Brain Zaps?

My husband has been experiencing head zaps for at least 4 years, and had a CT scan which was negative at that time, recently these zaps have become more severe and frequent and have moved from the right side of his head to the left. Last week he had one and experienced tingling down his right cheek. He does not take any antidepressants or meds that may cause these sensations in others. His family doctor has sent hime on for another scan, could this be a tumour if it was not originally found in a CT scan previously?