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The old idea of five senses is obsolete.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 provide 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).
