Tinnitus
Tinnitus is the sensation of hearing buzzing, ringing, hissing, or other such sounds, when none is present. Tinnitus can be subdivided into objective and subjective tinnitus. Objective tinnitus is noise that can be heard by another individual (e.g., a person hearing their own heartbeat which can, of course, be heard with a person with a stethoscope) and is the much rarer type of tinnitus. The predominant type of tinnitus is subjective, i.e., only the complainer hears the noise.
Tinnitus can also be described as pulsatile or nonpulsatile. Pulsatile tinnitus is the much rarer form and is a result of hearing blood flow in the head and neck area. Nonpulsatile tinnitus is the predominant form of tinnitus and is a steady tone or tones that can be present continuously or intermittently. When this tinnitus has persisted for more than 3 months, it is defined as chronic tinnitus.
It is unclear why people develop tinnitus, but it often accompanies hearing loss. Not everyone with hearing loss develops tinnitus and there are many people who develop tinnitus with no perceptible hearing loss on standard hearing tests. Noise trauma has been implicated as a leading cause of tinnitus (Axelsson and Barrenas, 1992; Penner and Bilger, 1995). There are multiple theories behind chronic nonpulsatile tinnitus, but the prevailing current thought is central auditory disinhibition, which is that the hearing centers in the brain become hyperexcited when there is a perceived decrease in hearing from the ears (Henry J, et al., 2014).
The intensity of tinnitus can vary from individual to individual and can fluctuate for each person. It can be a barely perceptible sound that does not affect a person or it can be an overwhelmingly loud sound that disturbs a person's ability to sleep or function during the day.