Cross references: K&W provides a good picture and a brief discussion of the midbrain (mesencephalon) on [K&W:53-54]. The superior colliculus of the midbrain is considered to be the site of the highest level of sensory-motor integration in the precortical brain, and its internal structure is more complex than any other part of the precortical brain. It receives direct input from the eyes and indirect input from all other sense modalities via secondary neurons from all sensory nuclei. Its primary output is to the mesencephalic locomotor region (MLR). The MLR is embedded in, and part of, the middle and upper portions of the reticular formation. It supplements the spinal locomotor generator (SLG) by controlling the movement of the four limbs in the context of side-to-side body motion which is still controlled by the SLG. Searching Pub Med <http://www.pubmed.gov> for "mesencephalic locomotor" brought up 201 references. I've included four below, just in case you're curious. None is definitive, so this appears to be an area of ongoing research. The first link leads, not only to an abstract, but also to the full article. Differential contribution of reticulospinal cells to the control of locomotion induced by the mesencephalic locomotor region. J Neurophysiol. 2003 Sep;90(3):1714-27. Epub 2003 May 7. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=12736238&query_hl=1&itool=pubmed_DocSum To link to the full article, click on the dark rectangle that says: Free full text of article at jn.physiology.org The other three links lead to abstracts. Excitatory and inhibitory postsynaptic potentials in alpha-motoneurons produced during fictive locomotion by stimulation of the mesencephalic locomotor region. J Neurophysiol. 1985 Jun;53(6):1345-55. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=4009222&query_hl=1&itool=pubmed_DocSum Controlled locomotion in the mesencephalic cat: distribution of facilitatory and inhibitory regions within pontine tegmentum. J Neurophysiol. 1978 Nov;41(6):1580-91. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=731291&query_hl=1&itool=pubmed_DocSum Role of pontine tegmentum for locomotor control in mesencephalic cat. J Neurophysiol. 1977 Mar;40(2):284-95. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=pubmed&cmd=Retrieve&dopt=AbstractPlus&list_uids=845624&query_hl=1&itool=pubmed_DocSum |