In the thoracic region there is overlap between the nerves that innervate neighboring dermatomes. Thus, a lesion of one dorsal root produces hypesthesia rather than anesthesia. To get complete cutaneous anesthesia in the thoracic area, at least three adjoining spinal nerves or their dorsal roots must be affected. There is much less overlap in the extremities where borders between dermatomes are sharper. Shingles, is a herpes infection of dorsal root ganglia with skin lesions. The eruption outlines the dermatome!