“This might make you feel dizzy; hold onto the arm-rests, just in case.”
With these instructions, the doctor proceeded to inject a cup of cold water steadily into my classmate’s ear . Disconcerting. Surprising. This is the field of neurological investigation.
Sure, neurologists use conventional imaging techniques like MRI and CT, but they also have an arsenal of tests up their sleeves that are more unique. Some date back more than one hundred years. Others are cutting edge. From my superficial viewpoint, however, they all have one thing common: There’s something just odd about them!
The technique I was describing is called ‘Caloric Stimulation’. Water injected into the ear canal tricks the vestibular system (your ear’s system for maintaining balance) into thinking that you are turning either to the left, or to the right, depending on the temperature of the water. The response you look for is compensatory movement of the eyeballs. Like most predators, when we move our heads, our eyes reflexively move in the opposite direction so that they remain fixed on the same target. Since the reflex relies on brainstem functioning, neurological diseases that impair the brainstem can affect this reflex. Caloric Stimulation is therefore used to assess normal or disease functioning of the brainstem.
Now if you thought Caloric Stimulation smells a little bit like a dorm-room prank, wait till you hear about Nerve Conduction Studies. The purpose of NCS is to assess the health of nerves beyond the spinal cord, for example in your arms, or in your legs. Nerves communicate with electrical energy. So, to interrogate the nerves directly, neurologists pull out their stimulators (reminiscent of cattle prods, or police tasers) and deliver electric shocks through the skin. They measure the speed of electrical impulse through the nerves, and also contraction of the muscles that the nerves enervate. Nerve disease and muscle disease can both be detected by NCS.
One surprising fact, is that there exists a wide range of sensitivity to electrical stimulation. Some people handle being electrocuted better than others. Among our small group, one classmate could easily withstand more than 100 times the amount of electrical energy than the most sensitive classmate (who swore in severe pain at even small shocks!). Both fit within the wide range of normal sensitivity.
Perhaps the oddest neurological investigation of all: Electroencephalography (EEG). Straight from the movies, this is the test where a bundle of electrodes are placed over your shaved scalp, and your brain-waves are plotted with spiky lines on graph. EEG literally reads your mind. Now if only it could read thoughts! But brain activity, even plotted neatly on a graph, is more than a little confusing to read. EEG is used to diagnose various types of seizure, and sleep disorders.
