Hallucinations, while widely known of and portrayed in the media, are one of science's ongoing mysteries of the human brain. Part of the problem with pinpointing the science behind and cause of hallucinations lies in semantics; the word hallucination is more like a catchall or general term that includes any kind of real perception, be it taste, sound, sight, touch, smell, temperature or loss in balance, that does not conform to reality. An example of a classic visual hallucination is the tropical oasis: clear, sparkling water surrounded by palm fronds that an unfortunate wanderer in the desert sees in the throes of psychosis and dehydration.

Many parts of the brain and body are involved in and work together to produce sensations and perceptions, and can be placed into three main groups: cells and neurons that receive the sensory information, intermediate messenger nerves that relay the signals to your brain, and the cortices and areas of the brain that put all the information together to give you a sense of the outside world. You can further subdivide these groups according to the many different jobs and information they specialize in, for instance, for feeling and touch your body has different pathways for sensations of the skin (mechanosensation), sensations inside the body and muscles (proprioception), and several for different kinds of pain (sharp pain, throbbing pain, and burning pain).

Arguably the sense people care about and rely on the most is vision, and the pathways and components that bring to life a real-time view of the world around you are no exception to the body's rule of complexity. In the retina, or back part of the eye that receives light coming in through the pupil, there are no less than five types of neurons: the photoreceptors (rods specialize in night vision, and cones perceive color and detail), horizontal, bipolar and amacrine cells (these all form networks between rods and cones to give information on what neighboring photoreceptors are seeing), and ganglion cells that take all the information through the optic nerve, and to the brain to be decoded.

Once the nerve impulses from the retina reach the brain, in addition to sending information off to the pupils to control their dilation, the hypothalamus to control sleep and wakefulness rhythms, the layered part of the midbrain known as the superior colliculus (that governs eye movements and allows you to focus on a still or moving target), visual signals are sent on a journey

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