A major breakthrough has been made that provides new insights into how tinnitus, and the often co-occurring hyperacusis, might develop and be sustained. Tinnitus is largely a mystery, a phantom sound heard in the absence of actual sound. Tinnitus patients "hear" ringing, buzzing or hissing in their ears much like an amputee might "feel" pain in a missing limb. It is a symptom, not a disease, and though exposure to loud noise may cause it, some cases have no apparent trigger.