The experience of "hearing" a song in your head is a phenomenon called auditory imagery or mental rehearsal. It is an internal cognitive process that allows you to recall and simulate sounds in your mind without any external auditory input. While it may seem like there are no sound waves being transmitted or received inside your head, the perception of sound in your mind is a result of complex neural activity.
When you listen to a song or any sound in the external world, your ears detect the sound waves and transmit electrical signals to your brain via the auditory pathway. However, when you imagine or recall a song in your head, it is the brain itself that recreates the perception of sound.
The process of auditory imagery involves the activation of neural circuits in the brain that are associated with auditory processing. These circuits can recreate the patterns of neural activity that would typically occur when you hear a particular sound. The brain has the ability to reconstruct and simulate sensory experiences internally based on memory, learned patterns, and cognitive processes.
Several brain regions are involved in auditory imagery, including the auditory cortex, which is responsible for processing sound information, as well as other regions involved in memory, attention, and imagination. When you mentally replay a song in your head, these brain regions work together to generate a neural representation of the sound, which is subjectively experienced as if you are hearing it.
It's important to note that while the perception of sound during auditory imagery can be vivid and detailed, it is a subjective experience and not an actual physical transmission or reception of sound waves. It is a result of the brain's ability to internally simulate and recreate auditory sensations based on stored memories and cognitive processes.
In summary, the ability to listen to a song in your head is a product of the brain's capacity to generate and simulate auditory experiences internally, using neural representations of sound based on memory and cognitive processes, rather than the actual transmission and reception of sound waves.