The callosal sulcus separates the corpus callosum from the cingulate gyrus. The uncus is an anterior extremity of the parahippocampal gyrus. Lexical agraphia is associated with damage to the left angular gyrus and/or posterior temporal cortex. The EC, is located in the parahippocampal gyrus, a cortical region adjacent to the hippocampus. Upper motor neurons originate in the motor cortex located in the precentral gyrus. The CA3 is a portion of the hippocampal formation adjacent to the dentate gyrus. Working memory manipulation involves the DLPFC, inferior frontal gyrus, and areas of the parietal cortex. Associative prosopagnosia is thought to be due to impaired functioning of the parahippocampal gyrus. Pattern separation begins in the dentate gyrus. This process of neurogenesis is confined to the dentate gyrus. Sources could also include the inferior frontal gyrus, and the insular cortex. Sometimes the hippocampus is said to include the dentate gyrus and the subiculum. The OFA is located in the inferior occipital gyrus. Positive symptoms have been linked to reduced cortical thickness in the superior temporal gyrus. Apperceptive prosopagnosia is believed to be associated with impaired fusiform gyrus.