Orbitofrontal sulci of the human and macaque monkey brain

The present study investigated the orbitofrontal sulci in 100 normal adult human cerebral hemispheres by using magnetic resonance images that were transformed into the standardized proportional stereotaxic space most commonly used, that of Talairach and Tournoux (Talairach and Tournoux [1988]. Co-planar stereotaxic atlas of the human brain. New York: Thieme). The patterns formed by the individual sulci were then examined and compared with those of the less convoluted macaque monkey brain. Four sulci forming a similar sulcal pattern were identified in both species. The olfactory sulcus occupies the most medial position forming the lateral border of the gyrus rectus. Lateral to this, the medial, lateral, and transverse orbital sulci form a pattern often resembling an "H," "X," or "K." These sulci divide the orbitofrontal cortex into four major gyri: the medial, lateral, anterior, and posterior orbital gyri. Three major types of sulcal pattern were identified in both species based on the arrangement of these orbital sulci. Additional sulci were observed in the human brain, creating more complex patterns. Probability maps were constructed for the four main orbitofrontal sulci of the human brain. These maps provide a statistical description of the variability of the location of the orbitofrontal sulci within the three-dimensional coordinate system of Talairach and Tournoux (Talairach and Tournoux [1988]. Co-planar stereotaxic atlas of the human brain. New York: Thieme). Because these maps may be directly compared with any image transformed into the same standardized space, they provide a valuable tool for identifying and describing the location of functional or structural changes in the orbitofrontal region of the human brain.