The patient is a adult male who was hit from behind by a police car going 45 miles an hour — while he stopped at a traffic light.  Since then he has reported episodic dizziness.  His fistula test results are negative on the day of the evaluation; he was not symptomatic that day.  His ECoG results are shown.  They were obtained using alternating polarity stimuli with TipTrodes.

• Please mark the SP and AP and estimate the ratio.