The instant you hear a cellphone ring, your brain reacts in a unique way - if the ringtone matches that of your own phone.
Anja Roye of the University of Leipzig in Germany and colleagues recorded the text-alert tones of 12 volunteers, then played them all the tones, at the same volume and in a random order, while recording their neural activity via scalp electrodes.
In the first trial, volunteers watched a muted, subtitled film while listening to the tones. In the next trial there was no film to distract the volunteers, but they were told to press a button when they heard their own ringtone. In the final trial, they were asked to pick out an assigned ringtone belonging to another participant.
As you might expect, brain areas linked to hearing and memory retrieval lit up when participants heard their own ringtone or the one they were assigned. However, after just 40 milliseconds, more neurons were active when volunteers heard their own ringtone than someone else's, even if this was the one they were assigned (The Journal of Neuroscience, DOI: 10.1523/jneurosci.1113-10.2010).
Roye says this suggests that our brains store "templates" for our own ringtones, allowing it to distinguish quickly between familiar and unfamiliar tones.