Audition Promenade round Cochlea autour Cochlée oreille ear organ of Corti oreille ear CRIC Montpellier Remy Pujol U254

	Auditory pathways
	Overview / Development and plasticity
	Drawings: S. Blatrix

Auditory messages are conveyed to the brain via two types of pathway: the primary auditory pathway which exclusively carries messages from the cochlea, and the non-primary pathway (also called the reticular sensory pathway) which carries all types of sensory messages.

Primary auditory pathways

Schematically, this pathway is short (only 3 to 4 relays), fast (with large myelinated fibers), it ends in the primary auditory cortex.
The pathway carries messages from the cochlea, and each relay nucleus does a specific work of decoding and integration.

For details, see the zoom.

I
n human, the primary auditory cortex (3) is located in the temporal area (2) within the lateral sulcus (1).

Non-primary pathways

From the cochlear nuclei, small fibers connect with the reticular formation where the auditory message joins all other sensory messages. The next relay is in the non-specific thalamus nuclei before the pathway ends in the polysensory (associative) cortex. The main function of these pathways, also connected to wake and motivation centers as well as to vegetative and hormonal systems, is to select the type of sensory message to be treated first. For instance, when reading a book while listening to a record, this system allows the person to pay attention alternately to the most important task.

For details, see the zoom.

Sensation and conscious perception

Conscious perception requires the integrity of both types of pathways. For instance, during sleep the primary auditory pathway functions normally, but no conscious perception is possible because the link between reticular pathways and the wake and motivation centers is inactive. Conversely, trauma affecting the cortex may suppress the conscious perception, while the continuing integrity of the non-primary pathways may result in vegetative reflex reactions to a sound. Also, because the brain stem and midbrain are intact, Preyer reflexes are still present.

For details, see the zoom.