Testing is your sensory nerves

The human brain and nervous system is probably the most complex organ in nature. The brain depends on the nervous system to supply information which the brain can then use to make decisions.

Recently, my son Troels broke his arm. I have four boys, and my wife and I more or less expected one of them to break something one day. After all, boys are boys!

Unfortunately, Troels’ fracture turned out not to be as ‘standard’ as I had hoped: Both bones in the lower left arm snapped completely, and he lost senses in the little finger, indicating damage to the ulnar nerve. Troels’ case where a nerve is damaged and cause loss of senses has made me think about analogies to testing.

Xray of Troels' arm showing the steel inserts to stabilize the broken bones
Xray of Troels’ arm showing the steel inserts to stabilize the broken bones

Sensory nerves work like testers

Sensory nerves collect information, transform it lightly and transmit it. Just like testers test things, nerves sense things. Science has identified four ‘modalities’: Touch, the sense of location in space, pain, and sense of temperature. Testers have modalities too: We test for performance, usability, functionality etc.

When signals from a nerve stops, areas in the brain previously associated with processing sensory information from this particular nerve are reorganized to process sensory information from other nerves. Some claim that the brain has a lot of spare capacity, but this reorganization indicates that that is actually not the case: Neurons are not allowed to sit idle and are reused as soon as they become ‘available’.

Loosing senses in the hand is considered a severe handicap for many reasons, and one reason is that patients risk burning their hands because they are no longer warned by their senses to avoid heat.

In the same way, not testing a subsystem at all introduces a risk that serious problems will go unnoticed. This relates to the coverage problem in testing.

Diagram showing sensory nerves in the arm and hand (source: wikipedia)

Nerve cells regenerate very slowly, only about 1 mm a day, but even after the nerve itself has totally regenerated, the brain still needs to do some relearning. It will have to relearn its map of the hand. Troels is 8 so his brain is still very flexible and easily relearns, and his senses have almost completely returned to normal by now.

Nature is a fascinating source of new insights!

Troels at the hospital after having the fracture stabilized
Troels on the way home with plaster on and steel in the arm

Thanks to Jesper L Ottosen for reviewing and editing this article.

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