Have you ever wondered why you can't tickle yourself? The problem is that your brain always knows where your fingers are going before they actually get there. So if you tickle your belly your brain thinks nothing strange or surprising is happening. However, if someone else tickles your belly using the exact same movements and pressure, you'll start . The reason tickles only work when others are involved is due to the way in which your brain is wired. When you decide to move your fingers, you initiate a series of muscle contractions and relaxations that allow your hand to reach out and touch something. During this movement, your brains need to know where your hand and arm are located in relation to the rest of your body so that you do not overreach and miss the object you're trying to touch. Thus, your sense of movement, from skin and muscle sensory systems, provides the brain with vital information during the movement to make sure everything happens in the right sequence at the right time. Thus, you cannot tickle yourself because you can never surprise your brain.

The same thing is true with speech. As you hear yourself talking you adjust the pitch and pattern of your speech to match what your brain intends to say. You introduce more volume if the room is noisy; you introduce emphasis on certain syllables in order to convey your emotions; sometimes you might alter how a word is expressed in response to the reactions of the person you're talking to. This complex processing happens very quickly thanks to the connections that formed inside your brain even before you were born. As you hear the words you are speaking echo back to your ears, one thing is certain; you know that it's your voice. What if you didn't know this? What if your brain generated words in your mind and you heard them but you did not recognize them as your own words? This condition, an auditory , is often one of the many disabling symptoms experience by people diagnosed with .

Scientists in the Netherlands recently investigated how auditory might be produced by the brain of these patients. The first thing to know about hearing is that it is mostly processed within the temporal lobe of the brain. This part of your brain lies just inside your ears. The scientists discovered that certain regions of the left temporal lobe were more active during an auditory hallucination, as compared to when the patient was not hallucinating. Essentially, the brains of hallucinating patients acted as though they were experiencing a "real" auditory experience. Their brains were generating the "voices or sounds" and they were "hearing" the sounds at the same time! Somehow the patients never made the connection that they were hearing their own voice. The patients believed that the voices were coming from someone else.

In order to understand how this happens, compare producing and hearing your own voice with producing and feeling your own tickle. Under normal circumstances, they always go together - never any surprises. Your brain always tells itself what it's about to experience. In the brains of people with schizophrenia this process seems to be malfunctioning. The scientists concluded that the brain signals originating in speech-generating regions of the brain were not bothering to tell the auditory regions that the forthcoming thought was actually self-generated. If the auditory part of the brain does not expect to hear its own voice, then any voices that are heard MUST belong to someone else.

The actual problem, for the psychology majors in the audience, which was discovered, was an anatomical error within the fiber bundle that connects speech-generating areas in the frontal lobe with auditory cortex in the temporoparietal lobe. Essentially, if you do not know with certainty that you are speaking then you will assume that the voices are talking TO you. Sadly, and sometimes tragically, due to the underlying that these patients also experience, the voices instruct the patients to do disagreeable tasks.

© Gary L. Wenk, Ph.D. Author of Your Brain on Food (Oxford University Press, 2010)