A 58 year old man attends clinic with his wife. His wife describes three episodes in the past three weeks during which the patient has had ‘twisting of the right side of his face, followed by stiffening for his right arm before he collapses to the ground jerking.’ The episodes last two minutes and then it is 30 minutes until he is back to his normal self. Examination is unremarkable. What is the single most appropriate investigation to arrange?