Noun
The middle segment of the brain; the midbrain. Sometimes abbreviated to mesen. See Brain.
Source: Webster's dictionaryDopaminergic projections from the ventral tegmental area (bottom part of the "midbrain" or mesencephalon) to the prefrontal cortex (mesocortical pathway) and to the nucleus accumbens (mesolimbic pathway - "meso" referring to "from the mesencephalon".. Source: Internet