In fig. 3 bellow is shown the normal sound processing in the avian brain. This normal pathway passes through the cochlear nerve, enters the Hindbrain where if it is not high rising sound, continues to the Midbrain, the Thalamus, and then enters the Cerebrum where it is processed in the Auditory Cortex. If the signal is assessed as threatening, the pathway leads back to the Thalamus, where the Hypothalamic–pituitary–adrenal axis is activated and a stress hormone, corticosterone, is released. Finally, the motor centers in the hindbrain are activated and a bird reaction happens in response to the signal.