The reticular formation is a set of interconnected nuclei that are located throughout the brainstem. The reticular formation is not anatomically well defined because it includes neurons located in diverse parts of the brain. The neurons of the reticular formation all play a crucial role in maintaining behavioral arousal and consciousness. The functions of the reticular formation are modulatory and premotor. The modulatory functions are primarily found in the rostral sector of the reticular formation and the premotor functions are localized in the neurons in more caudal regions.
The reticular formation is divided into three columns: raphe nuclei, magnocellular red nucleus, and parvocellular reticular nucleus. The raphe nuclei is the place of synthesis of the neurotransmitter serotonin, which plays an important role in mood regulation. The magnocellular red nucleus is involved in motor coordination. The parvocellular nucleus regulates exhalation.
It is essential for governing some of the basic functions of higher organisms and is one of the phylogenetically oldest portions of the brain.