Preliminary evidence for a direct projection of the prefrontal cortex to the hippocampus in the squirrel monkey.

Unilateral partial ablations in the medial prefrontal cortex of six squirrel monkeys led to fiber degeneration which followed cingulate and uncinate routes to the hippocampal region. Degenerating fibers were observed primarily in the alvear, but also in the perforant, bundle. Preterminal and terminal debris was seen on basket cells of the stratum oriens and pyramidal cells within the sratum pyramidalis of CA1-3. Since the prefrontal cortex has been shown to receive convergent sensory inputs from both external and internal milieu, this projection may represent the anatomical substrate for the essential influence of this information on the hippocampus proper, and also explain data which show the prefrontal cortex and hippocampus to be integrally related to mechanisms of learning and memory behavior.