Final answer:
The C4 dermatome is tested by applying a light touch to various locations on the skin in that specific region, such as the medial surface of the forearm and fingers.
Step-by-step explanation:
Dermatomes are regions of skin that are innervated by a specific spinal nerve and connect to the cortical region where somatosensation is perceived. To test for the C4 dermatome, you would apply a light touch of the soft end of a cotton-tipped applicator to various locations on the skin in that specific region. For example, the C4 dermatome corresponds to the medial surface of the forearm and extends out to the fingers.