Brain Mind Center

How Many Senses?

The old idea of five senses is obsolete. The idea of an extra sixth sense is also obsolete. Not only are there multiple senses, but information from many senses tend to be mixed in the brain to figure out what is really going on. Sensors are tuned by other systems, so that receiving information is not passive, nor consistent. Sensing is a variable tuning activity that selects a few relevant signals out of many.

The basic idea behind human and other animal brains is to bring information about the outside world together with information from inside the body. In the human mind, images of the outside tend to be detailed and explicit in consciousness. In contrast, monitor images from inside the body are vague and variable. Feelings and body sensations bubble up, as if from below consciousness and disappear.

As biology students know, information from the outside enters through sense organs. Some senses are obvious:  everyone knows about vision, hearing, smell, balance, taste, touch, temperature and pain. There are more. Chemical information from the outside world has always been important to living creatures.  A fascinating array of chemical sensors and processors exist in the living world. Humans are left with a diminished chemical sensibility of the outside world and rely more on vision and hearing.

Images of the outside tend to be detailed and explicit in consciousness. Vision, hearing and smell are distance senses that inform about events far away. Sensors on the surface of the body inform about close contacts. Light touch, pressure, temperature, vibration, itch and pain are sensed by skin receptors. Movement sensors in the inner ear tell us about our orientation in space and the effects of gravity. Sensors in muscles and joints inform about our movement in space-time and provide information about contact with the ground.  Sense receptors inside the body are of various kinds and are not clearly represented in consciousness.

Inner sensors are providing information to the brain about conditions in the body and feedback information the brain about the consequences of actions taken.

Inner senses belong to two groups - the most ancient chemical kind and a more modern and rapid electronic kind. The digestive tract for example is supplied with dense innervation, an internal internet that provides electronic networking. Neural communications are sent to and from the brain via the autonomic nervous system. The dialectic of approach/avoidance is expressed in the two divisions of the autonomic nervous system; the parasympathetic network corresponds to eating, rest and pleasure; the sympathetic system corresponds to action, fight and flight.

Chemical messages are broadcast both ways by substances secreted into the blood. These circulating messages tend to have whole body effects. There are several classes of chemical messengers: hormones, peptides, neurotransmitters and cytokines (produced by immune cells).

The idea of "psychosomatic" usually involves a fuzzy logic or illogical interpretation of signals that travel between body and brain via the autonomic nervous system and via chemical pathways in the blood. Many neurotransmitters are not confined to synapses within the nervous system but also circulate and move through tissues, activating a variety of tissue responses.

The word "sense" is used an interesting way to represent ways in which we mix and package sensory experience. Dr. David Stinson, one of my medical-school teachers and life-long friend, suggested a long time ago that there were four senses: the sense of beauty, wonder, rhythm and humor. The term "sense of humor" is in common usage along with other phases such as "common sense." We mostly speak of beauty when we see someone or something that pleases us. Males will say "she's pleasing to the eye" or "she's not hard on the eyes."  The eye, as wonderful as it is, does not see, nor can the eye recognize or evaluate what is seen. The eye sends information to the visual cortex and somewhere among the millions of circuits interconnecting the occipital cortex with the thalamus and other cortical areas - we see.  The sense of beauty is a cognitive structure, perhaps a special set of evaluators that look at visual information from the point of view of one innate system or another. A heterosexual male finds a woman beautiful if she is well formed, symmetrical, healthy-looking and behaves in a feminine manner so that he knows that she has good genes and is sexually receptive.

Stinson proposed to use these senses" as elements of medical therapeutics long before others proposed their use. He recruited me to study the "sense of humor" as a therapeutic tool. At the time, I thought we should be studying a new antihypertensive drug or something useful. I was also concerned that medical colleagues would find the idea foolish (I doubted their sense of humor). As it turned out, the project was interesting and medical colleagues were receptive to the presentation that followed.

We share slapstick humor with our chimpanzee relatives who delight in rough and tumble play and are amused by falls and other mistakes made by fellows. Humans laugh when others slip, fall or otherwise embarrass themselves. Jokes are language-based version of slapstick that play on words, insult others, or reveal mistakes and misunderstandings. The person who laughs always feels more in control and safer than the person who is described in a joke. People who share jokes feel connected and leave their encounter with good feelings. A joke, well-received can diffuse aggression and anger. Self-deprecating humor also diffuses aggression and anger. Goel and Dolan scanned the brains of subjects listening to jokes. They found that semantic jokes that play on the meaning of words, such as "What do engineers use for birth control?  "their personalities" activate the  posterior temporal lobe. Puns that play on the sounds of words such as:  "Why did the golfer wear two sets of pants - he got a hole in one," activate the left inferior prefrontal cortex and insula. Quiet or inward responses to jokes activated the median ventral prefrontal cortex.

The sense of wonder and awe probably should be linked to curiosity and gratitude. A force in us connects us with the world, interests us in how the world is and what it does. We pause and feel awe when confronted with the giant forces of nature - a great wind, a thunderstorm, large waves breaking on a rocky beach. Often fear is the initial response that dissolves into awe when the danger is too great to be resisted or when we find shelter from the storm, pause and reflect.

Wonder emerges in the spaces when we stop being robotic, busy getting things and doing things. Humans attempt to re-create and contain the experiences of wonder and awe. We find large caves that echo, frighten and inspire and then build these caves out of stone and concrete. Religious buildings and ceremonies are often designed to recreate, invoke and imitate natural wonders. Music and movies simulate awe-inspiring experience in the comfort and safety of a theater or the living room at home.

See Goel, V. & Dolan, R. J. The functional anatomy of humor: segregating cognitive and affective components. Nature Neuroscience 4, 237 - 238 (2001).

Further reading: Neuroscience Notes, Intelligence and Learning, Language & Thinking

Persona Digital

Persona Digital Books is the publisher of The Human Brain, Neuroscience Notes, Intelligence & Learning and related books. Three books are available as print editions for mail delivery. All books are available as eBooks for download (PDF files).

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