Early neurodevelopment of the social brain may play an important role in a wide range of psychiatric disorders, including schizophrenia spectrum and autism spectrum disorders. The acquired social deficit consequences induced by a penetrating injury through the orbitofrontal cortex (OFC) have long been known, ¹ although the connection between anatomical variations of the OFC development with social disabilities have not been well documented. Moreover, and dating back to the seminal work of Bleuler, ² social disturbances in schizophrenia have often been described, but the extent to which they may reflect disease-related neuropathology of the OFC has yet to be established.

OFC, a major part of the social brain, is important for sensory-visceromotor multimodal integration, ³ for emotional processing, and for hedonic experience, ⁴ as well as for the evaluation of reinforcers, expectation, motivation, decision making, and goal-directed behavior.^{5bibr6-1550059420904180-7} Of particular note, human OFC is characterized by marked interindividual variability in its cytoarchitecture ³ and sulcogyral morphology.^{8bibr9-1550059420904180-10} The neurodevelopmental formation of the convolutional sulcogyral morphology, which is termed gyrogenesis or gyrification, could reflect neuronal migration, local neuronal connection, synaptic development, and/or lamination of the cortical cytoarchitecture.^11,12 In social neuroscience, OFC figures significantly in emotions, decision making, and social behavior, and individual variability in OFC development may therefore be associated with individual variabilities in personality traits, emotional processing, and social behavior.

In order to estimate the degree of cortical folding, a number of the previous studies have employed the gyrification index (GI), ¹³ which is the ratio of the inner and outer cortical surface contours, or more recently the local gyrification index (LGI), ¹⁴ which considers the 3-dimensional nature of the cortical surface. However, neither GI nor LGI are independent of brain tissue volume, and thus they are potentially unstable longitudinally and susceptible to confounds affecting brain tissue volume. Given that the sulcogyral morphology is genetically determined, ¹⁵ and is formed during early neurodevelopment and then stable over time, the sulcogyral pattern classification may provide a morphological trait marker, which could reflect neurodevelopmental variability independent of brain tissue volumes, their longitudinal changes, and possibly confounding factors, including psychotropic medications and chronic illness. Accordingly, the categorical sulcogyral pattern could reflect a totally different aspect of cortical folding from cortical surface geometry such as gyrification indices.

Our group previously reported sulcogyral pattern anomalies in the temporal lobe in schizophrenia using magnetic resonance 3-dimensional surface rendering. ¹⁶ To investigate the presence of sulcogyral morphological alterations of OFC in schizophrenia, we further focused on the sulcogyral pattern of the “H-shaped” sulcus, which forms the boundary of 4 major orbitofrontal gyri, including medial, anterior, posterior, and lateral orbital gyri.^9,17 In the earlier study on OFC comparative neuroanatomy, Chiavaras and Petrides ⁹ classified the OFC sulcogyral pattern into 3 types (type I, type II, type III in order of frequency) in each hemisphere, based on the continuity of the medial and lateral orbital sulci (MOS and LOS, respectively). In type I, rostral and caudal portions of the LOS were connected, while the MOS were clearly interrupted between rostral and caudal portions of MOS. In type II, rostral and caudal portions of both the MOS and LOS were connected, and continuous MOS and LOS were connected by the horizontally oriented transverse orbital sulcus (TOS). In type III, rostral and caudal portions of both MOS and LOS were interrupted. Neighboring orbitofrontal sulci were also identified including the olfactory sulcus (Olf), intermediate orbital sulcus (IOS), posterior orbital sulcus (POS), and sulcus fragmentosus (Fr) (see Figure 1).

We compared the sulcogyral pattern distribution between schizophrenic patients and matched healthy control subjects. We found that the most common Type I expression was decreased and the least common type III expression was increased in schizophrenia, as compared with healthy controls. ⁸ Furthermore, there was a contrasting association of type III expression with poorer outcome, and that of type I expression with better outcome, suggesting clinical heterogeneity based on early neurodevelopment in schizophrenia. In the data set (n = 100), subjects with type III expression in the right hemisphere showed a 2.84-fold risk for being diagnosed schizophrenia, as compared with subjects without type III expression in the right hemisphere. Following this study, there have been more than 25 studies on OFC sulcogyral morphology reported in several neuropsychiatric disorders. Some of the subsequent studies ¹⁸ have proposed an additional sulcogyral pattern of type IV, which was the rarest expression (3% to 6 %) in healthy controls, or even an unclassified case in neurodevelopmental disorder. ¹⁹

As described above, OFC has been regarded as a part of the social brain and associated with several different neuropsychiatric disorders. Also, it has been reported that sulcogyral pattern is formed during early neurodevelopment and stable over time. However, there is yet to be a systematic and integrative review addressing the potential utility of OFC sulcogyral patterns as a potential transdiagnostic trait marker of early neurodevelopment in the social brain. Accordingly, the principal aim guiding this review is to examine and evaluate the current body of empirical evidence bearing on the question of the reliability and validity of abnormalities in OFC sulcogyral patterns as an early neurodevelopmental marker that is shared across different psychiatric disorders or conditions.