The Power of Touch- Progress on a Great Sense

The Power of Touch- 

Progress on a Great Sense

In May of 2106, The New Yorker  published a deeply fascinating review of recent advances in understanding a sense that all people have, but few of us stop to consider:  touch.

http://www.newyorker.com/magazine/2016/05/16/what-the-science-of-touch-says-about-us

The article is loaded with many fun facts, but I will highlight three of them:

1.  The organization of touch 

2.  Progress in reproducing touch

3.  The essential nature of touch

The Organization of Touch

All senses in the body, including taste, vision, and hearing, are organized by the detection of a signal being translated into a nerve impulse that the brain then converts into a perception.

A word on each of these steps should be helpful, and hopefully, interesting.  Think about vision. Vision happens when light in the world is converted by our eye into an electrical nerve impulse that our brain transforms into a visual picture of the world.  This requires a special sensor that converts the light into a nerve impulse, and that would be the light-sensing cells of the retina.  When light hits these cells, they create an electrical charge that shoots down a series of nerves to the brain.  Once the pattern of electrical impulses from the eye hit the brain, the brain turns those patterns into all the extraordinary things we see.

Two more thoughts on this process:  the sensor for each sense is very specific for that sense.  The retina can only turn light into nerve impulses, it cannot do that with sound.  That is why the eye can only see, it cannot hear.   And, all nerve impulses are the same, a nerve can only be quiet or shooting an electrical signal, it is either on or off.  The nerve impulses from the tongue are the same as from the eye.   But there are literally billions of these nerves and it's their pattern that carries the information from the sensor and allows the brain to perceive.  Think of the lights on a movie marquee, each light bulb can only be on or off, and all the light bulbs are often the same.  But the pattern of their going on and off gives the sense that the lights are moving around the marquee.  Pattern causes information.

For touch, the sensor is a special nerve ending that makes a nerve fire if it is squeezed.   It turns out that if the sensor is squeezed, a nerve signal is created, which goes to the brain and creates our perception of touch.   Touch also includes the ability to sense a vibration, or temperature, but this discussion will focus on the simple notion of touch itself.    The variations of pressure allow us to sense all that we do about the world via touch.   Our fingers, and much of our skin, are able to distinguish very minute differences in texture, for example, a soft satin, or a satin that is a tiny bit stiffer.  Or more easily, the feel of wood v. glass, or a pencil point v. a pen point on paper v. cardboard.

Three observations now can be shared about the way touch is organized in our nerves and minds:

1.  The brain detects incoming signals about touch in a frequency of 1 impulse per second.  

The information that the brain manages comes in the form of waves of electricity, in particular differences in waves.   So for touch, the essential wave is a pulse of electricity that beats once a second.  Variations in this pulse actually carry the information of touch to the brain.  Interestingly this rate of electrical pulsing is essentially the same as the rate of a heartbeat.

2.  There are several separate systems of touch, itch has its very own set of nerves.  It turns out that some nerves that deliver the touch signals to the brain cover many areas of function, including pain and sensual pleasure.   But itch has a separate system of nerves exclusively devoted to delivering that message to the brain where the sense of feeling itchy actually comes alive.

3.  The general system of touch nerves can deliver different experiences of touch.  As noted above, pain and sensual pleasure touches are experienced through the same set of nerves.  But the setting of the activation of the touch signals varies.

Progress in Reproducing Touch

As the essay notes, there has been astounding progress in reproducing touch.  Perhaps the most amazing steps forward have involved the development of a pen like device that can dial up almost any touch texture.

You can set the device to create the sensation of wood, and your hand holding the "touch pen" will soon experience the sensation of touching the type of wood you selected.  Or plastic, or silk, or paper, whatever the texture, the pen will recreate the sensation of touching it.  It is designed to help people with injuries re-experience various touch sensations, but it remains extraordinary that scientists can recreate the wide variations of our experience of touch.

The Essential Nature of Touch
Perhaps one of the most interesting insights from this essay is how essential touch is.

Many people will over time suffer loss of vision or hearing, or even be born without these senses, but there are no reports of a person losing their sense of touch.    It is the least of the senses discussed, but may turn out to be fundamental to being alive and human.

There are even specialists in neuroscience who think touch is the best way to understand our consciousness, that is, our awareness of the world depends greatly on what we touch.

BOTTOM LINES

The article in The New Yorker from May, 2016 offers a rare inside look at the sense of touch.

http://www.newyorker.com/magazine/2016/05/16/what-the-science-of-touch-says-about-us

Reading it will give you amazing insights into how senses are delivered and experienced by our brains, new insights on how touch functions are organized into systems, and the great and essential role touch plays in our lives.

To your health,
Dr. Arthur Lavin

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