How are auditory signals processed in the human brain?

Auditory signals are processed in the human brain through the auditory pathway, involving several brain structures.

The processing of auditory signals in the human brain begins with the detection of sound waves by the ear. The outer ear captures sound waves and funnels them into the ear canal, where they hit the eardrum and cause it to vibrate. These vibrations are then transferred to the three small bones in the middle ear: the malleus, incus, and stapes. The stapes bone pushes on the oval window of the cochlea, a fluid-filled structure in the inner ear, causing fluid waves that stimulate hair cells.

These hair cells, located on the basilar membrane within the cochlea, convert the mechanical vibrations into electrical signals. This process is known as mechanotransduction. The hair cells are arranged in a tonotopic manner, meaning different frequencies of sound stimulate different parts of the cochlea. High frequencies stimulate the base of the cochlea, while low frequencies stimulate the apex.

The electrical signals generated by the hair cells are then transmitted to the brain via the auditory nerve, also known as the cochlear nerve. This nerve carries the signals to the cochlear nucleus in the brainstem, the first central processing centre of the auditory system. From there, the signals are sent to the superior olivary complex, which helps to localise sound by comparing the timing and intensity of signals from both ears.

The signals then travel to the inferior colliculus, which integrates auditory input with other sensory information, and then to the medial geniculate nucleus of the thalamus. The thalamus acts as a relay station, sending the signals to the primary auditory cortex in the temporal lobe of the brain.

In the primary auditory cortex, the signals are processed and interpreted as different sounds. This area of the brain is also organised tonotopically, mirroring the arrangement of the hair cells in the cochlea. This allows us to perceive and distinguish between different pitches and volumes of sound. The auditory cortex also communicates with other areas of the brain, such as the frontal lobe, to associate sounds with memories and emotions.