Central pattern generator
Central pattern generators (CPGs) are biological neural networks that produce rhythmic patterned outputs without sensory feedback. CPGs have been shown to produce rhythmic outputs resembling normal "rhythmic motor pattern production" even in isolation from motor and sensory feedback from limbs and other muscle targets. To be classified as a rhythmic generator, a CPG requires:
1. "two or more processes that interact such that each process sequentially increases and decreases, and
2. that, as a result of this interaction, the system repeatedly returns to its starting condition. CPGs have been found in practically all vertebrate species investigated, including human.
Anatomy and physiology
Localization
Various molecular, genetic and imaging studies have been conducted as for the localization of the CPGs. The results have shown that the networks responsible for locomotion are distributed throughout the lower thoracic and lumbar regions of the spinal cord. Rhythmic movements of the tongue, that participate in swallowing, mastication and respiration, are driven by hypoglossal nuclei, which receive inputs from the dorsal medullary reticular column (DMRC) and the nucleus of the tractus solitarius (NTS). The hypoglossal nucleus receives rhythmic excitatory inputs also from brainstem respiratory neurons within the pre-Boetzinger complex, which appears to play an important role in the origin of respiration rhythmogenesis.