Periaqueductal gray (PAG) matter is a column of gray matter that surrounds the cerebral aqueduct of Sylvius in the midbrain. The PAG extends from the superior border of the midbrain (which forms the posterior aspect of the floor of the third ventricle), inferiorly towards the fourth ventricle and the superior medullary velum. The mesencephalic nucleus and the mesencephalic root of the trigeminal nerve are found lateral to the PAG. The oculomotor nerve nucleus and the nucleus of Edinger–Westphal are found anterior to the PAG.
The PAG participates in the spinomesencephalic tract by way of descending modulation of nociceptive transmission. Recent research has demonstrated that the PAG is involved in the primary-process emotional networks (those subcortical functions that constitute the primary affective processes in the mammalian brain) and contributes to neural circuits for empathy.
- 1. Wiberg M, Westman J, Blomqvist A. Somatosensory projection to the mesencephalon: an anatomical study in the monkey. J. Comp. Neurol. 1987;264 (1): 92-117. doi:10.1002/cne.902640108 - Pubmed citation
- 2. Gebhart GF. Descending modulation of pain. Neurosci Biobehav Rev. 2004;27 (8): 729-37. doi:10.1016/j.neubiorev.2003.11.008 - Pubmed citation
- 3. Panksepp J, Panksepp JB. Toward a cross-species understanding of empathy. Trends Neurosci. 2013;36 (8): 489-96. doi:10.1016/j.tins.2013.04.009 - Free text at pubmed - Pubmed citation
- 4. ten Donkelaar HJ. Clinical Neuroanatomy. Springer Berlin Heidelberg. ISBN:B00F777QGC. Read it at Google Books - Find it at Amazon