The hand is a wonderful piece of human engineering, allowing us to be dexterous and functional. In rehabilitation, there is a tendency to treat the hand like a robotic tool that primarily serves to reach and grasp, but in truth we do so much more with them than that.
1. The hand is a communicator.
For the number of times I have seen people talk on phones on the street, I have noticed that they talk as though the person is in front of them – with full hand gestures. Hand gestures are a universal part of human communication, and helps us provide clarity, flair and emphasis. It also conveys warmth, reassurance and security, like a mother caressing her child. And yet, this everyday function of the hand tends to get neglected in neurological rehabilitation and therapy, even though one could argue that it crosses the domains of speech, occupational and physical therapy.
2. The hand is a tactile beast.
The hand is home of thousands of receptors, that sense touch, size, temperature, texture, and fast and slow moving objects that slip past. This gives us the power of stereognosis, which is the ability to determine an object’s identity by feeling and appreciating its many properties. Many of the major receptors have its own receptor territory, so that when it touches something sharp, the receptor in contact fires its impulse while the neighbouring one doesn’t. This gives our brain the message that the object has a very narrow edge. Pain is then perceived by the brain after integrating these messages, in an attempt to protect us, and in fact, we don’t actually have pain receptors in our skin – only those that detect sharp and blunt. Pain is just a function of the brain’s perception.
3. The hand that moves tells us what is really happening with our body.
We all know that we use vision and touch to help us orientate us to the world, such as knowing whether the body or environment is moving at any given point in time. Think of sitting in your car, and out of corner of your eye the cars are moving slowly forward. Suddenly you think you’re rolling backwards when in fact the eyes have informed your system that you are moving relative the world.
So vision is important, and so is touch in the detection of what is moving against what. However, in an experiment done by Blanchard et al (2013), they inform us that muscle proprioception, the ability to use our muscles to move and explore, is an even more powerful sense. They explained that when we have a choice of 3 senses (vision, touch and proprioception), only proprioception can give us the most unambiguous information about the concept of where are body really is and this is particularly in the hand. The authors also state that our nervous system trusts our hand proprioception more than our eyes in depth perception, which explains why we often grope in the dark or have arms that seem to engage in our balance mechanisms when our orientation is challenged.
So whenever we see a person with an inactive hand who does not seem to have much of a concept of how their body moves in space, we are thinking about how we can create a hand that is more exploratory and purposely placed within the environment. This will involve a aligning and mobilising muscle fibres to help activate them, so as to place them in a position where the brain can believe it is apart of its overall system.
For example, we can suggest placing the non-dominant hand on the sink when brushing your teeth. Not only can it help be a physical stabiliser, but the thousands of receptors can get to work and help orientate our body so our vision can be freed up away from the effort to balance and focus on where the toothbrush is going. Furthermore, vision can also be made redundant as we are also capable of brushing our teeth in complete darkness or even when there is no mirror.
As therapists we should appreciate the power of the hand, for it is such a powerful reference for our nervous system and executive function. And without this we would not be as evolutionarily advanced as we are today.
Blanchard, C., Roll, R., Roll, J. P., & Kavounoudias, A. (2013). Differential contributions of vision, touch and muscle proprioception to the coding of hand movements. PloS one, 8(4), e62475.
Image credit: Nate Steiner