Answer:
Answer is EEG.
Step-by-step explanation:
EEG means electroencephalogram, and it involves the use of flats metal disc, known as electrodes, to evaluate or find the problems related to electrical activity of the brain. These flats metal disc are attached to the scalp of the brain with wires then connect with a computer to record the result.
EEG tracks and records brain wave pattern. It is used to diagnose brain and sleep disorder.
Therefore, the device used by Dr. Billings is electroencephalogram, EEG.