Medical students are often equipped with two tuning forks. One tests hearing at a certain frequency and the other tests the sensation of vibration on the skin. This latter might seem a bit unusual; wouldn't a prod with a finger do just as well for testing the sense of touch? You need to test both, actually. "Crude" touch and vibrational touch are relayed to the brain via two different paths in the spinal cord, the spinothalamic tract and dorsal column respectively. A deficit in either is an important diagnostic sign of damage to the nervous system.
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| Example drawings from a patient with contralateral neglect syndrome |
TIL: The evolutionary age of the brain can be determined by the number of cell layers. The neocortex is the most recent to evolve with six layers. The archicortex of the hippocampus has only four layers and the paleocortex only three. Accordingly, the neocortex is only found in higher mammals while the archi- and paleocortices are also present in more primitive animals.
If you damage the visual association areas of the brain you can have a deficit whereby you can't recognize the things you see.
If you damage the somesthetic association area you can have a deficit where you literally ignore anything on one side of your vision. It's not that you can't see it or that you don't know what it is, but that you cannot focus your attention on it. This works for body parts too. You might see that your left arm is there but you think it's not your problem, as if it were someone else's arm.
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