Tinnitus – the non-stopping auditive experience – is a well-known malady. Patients with tinnitus hear sounds even though no source of this acoustic impression is present; at least not outside of the brain. The source of the sound is in fact inside the brain, which is proven by several observations. Firstly, patients whose acoustic nerves have been severed still “hear” the sound. And secondly, the acoustic sensation is independent of the position of the ears. Both facts do not comply with regular sounds. Furthermore, EEG analysis showed that neuronal activity is altered in tinnitus patients.
In the current Question of the Week, however, I do not want to focus on tinnitus, but on another similar phenomenon: The Hum. First mentioned in the 60s of the previous century, the hum has been detected around the world. But what is this hum? People who complain about it “hear” a low-frequency humming sound similar to a diesel engine or a turbine without any physical source. But what is the difference compared to regular tinnitus? It displays some dissimilar properties like varying volumes depending on the location of the patient and modulation, e.g. it is not perceived as a single tone but more as a vibrato like sound.
So if it is not tinnitus, what is the reason for the hum? There are a variety of speculations. Most of them assign the hum to electromagnetic fields emitted by modern technology like mobile telephones of sending masts as well as Wi-Fi networks. But this cannot be the (only) case, since the hum was already described before these technologies existed. Until now, no unambiguous explanation for the hum exists, but it is mainly described in high-technology societies like Europe or Northern America. This however might just be accounted to limited data from other countries of the world. In fact, the hum is still an unsolved question and it remains unclear if it indeed has an origin which waits for its detection or if it is just the imagination of the patients.
– Andreas Neidlinger
 I. Adamchic, B. Langguth, C. Hauptmann, P. A. Tass, Front. Neurosci. 2014, 8, 284.