Definition of the Orbital Cortex in Relation to Specific Connections with Limbic and Visceral Structures and Other Cortical Regions

The orbitofrontal cortex is often defined topographically as the cortex on the ventral surface of the frontal lobe. Unfortunately, this definition is not consistently used, and it obscures distinct connectional and functional systems within the orbital cortex. It is difficult to interpret data on the orbital cortex that do not take these different systems into account. Analysis of cortico-cortical connections between areas in the orbital and medial prefrontal cortex indicate two distinct networks in this region. One system, called the orbital network, involves most of the areas in the central orbital cortex. The other system, has been called the medial prefrontal network, though it is actually more complex, since it includes areas on the medial wall, in the medial orbital cortex, and in the posterolateral orbital cortex. Some areas in the medial orbital cortex are involved in both networks. Connections to other brain areas support the distinction between the networks. The orbital network receives several sensory inputs, from olfactory cortex, taste cortex, somatic sensory association cortex, and visual association cortex, and is connected with multisensory areas in the ventrolateral prefrontal cortex and perirhinal cortex. The medial network has outputs to the hypothalamus and brain stem and connects to a cortical circuit that includes the rostral part of the superior temporal gyrus and dorsal bank of the superior temporal sulcus, the cingulate and retrosplenial cortex, the entorhinal and posterior parahippocampal cortex, and the dorsomedial prefrontal cortex.