Tactile nerve fibers

Touch is our most under-rated sense. We relish what we eat, we are intrigued or repelled by what we smell, and vision and hearing connect us to the world around us and our fellow humans. And touch? Well, it's just there, isn't it?

Actually no! When was the last time you saw a distressed child ask for more words of advice as opposed to asking for a cuddle? Touch comforts. We use it to caress and to strike, to detect (in the dark or in places we can't see into), to feel for shape, size, texture, weight, volume – and we do all this using our hands and fingers in different ways, as the diagram shows you.

Ways we use touch
Image adapted from Sekuler & Blake, 2002

Touch is not only an important sense to gain information about the world (as hearing and vision also are), it is also a very sophisticated sense using all the sensory processing strategies as do other sensory systems.

In this simulation we are going to explore three aspects of tactile processing:

  1. We'll first look at the sensory "receptive fields". A receptive field simply tells us from what part of the body a sensory neuron gets information and this is important to help us localize objects around us or on us. The RF will depend on the type of sensory neuron: for touch neurons, it's some part of the body surface; for visual neurons, some part of the retina in the eye; for auditory neurons, some part of the inner ear. In the simulation here we'll look at these receptive fields (RFs) for neurons in the hand.
  2. As that RF information flows from the neurons in the hand, through a succession of way-stations (called nuclei), up to the cortex of the brain it is altered. This is because information from different neurons is not kept separate but is often integrated. So in the second simulation we will see the structure of RFs of neurons in the cortex. By comparing these RFs to RFs for neurons in the hand from the first simulation, we can identify the pattern of integration in the brain of information originally emanating from different neurons in the hand.
  3. Sensory systems provide a lot more information than simply whether there is some there to see, hear, touch – for example, in our vision, neurons from the eye allow us to distinguish between different wavelengths of light, and this forms the basis of what is ultimately colour perception. So in this touch simulation, we will look at the information that tactile sensory neurons provide to allow us to identify the objects we touch. They do so through the timing of the electrical signals, the Action Potentials, they produce as we move our fingers carefully over an object we're trying to identify solely through touch.