Incidences: Synesthesia, which is not considered a disease, is believed to affect at least 1 in 2,000 people. It might be genetic, with left-handed people more commonly affected. Many sufferers tend to have an above-average intelligence level.
Unique: Synesthetes generally don’t know that anything is “wrong.” They recognize their condition early in life, but they don’t realize what they are experiencing is unique. When they do, they may pity non-synesthetes for having one-dimensional sensory experiences.
Proof: Imaging and behavioral studies have shown significant evidence of synesthesia. These studies include functional MRI scans and the test of genuineness.
Case report: In 2005, the International Association for the Study of Pain reported that a 49-year-old man with neuropathic pain in his elbow, wrist and fingers said certain odors increased his pain by super-imposing an electric shock-like pain to his existing pain. Psychophysical testing revealed that unpleasant odors exacerbated the pain. Functional MRI scans showed increased activation of pain following an unpleasant odor. The increased pain and associated neural activations may be related to the phenomenon of synesthesia.

