While there may not be such a clearly identifiable structural difference in DID patients, functional imaging studies (those that measure the amount of brain activity) have produced some valuable results. Two studies of interest measured regional cerebral blood flow (rCBF) as a way of inferring relative activity in different areas of the brain. One study compared rCBF of DID patients while they were in their host personality with normal controls and observed lower rCBF in the orbitofrontal cortex (OFC) of the DID subjects (Sar, et al. 219–20). The orbitofrontal cortex is thought to be involved in decision-making. Thus, Sar hypothesizes that the decreased functioning of the OFC results in impulsivity and that the switch to an alter personality may represent a drastic expression of impulsive behavior caused by cognitive and emotional conflicts (222).
The second study, conducted by Reinders, et al., measured rCBF of DID subjects in a neutral personality state (NPS) compared with a traumatic personality state (TPS) while they listened to a memory script. The procedure is described: “Subjects listened to two autobiographical audiotaped memory scripts involving a neutral and a trauma-related experience. The neutral memory script was regarded as a personal experience by both personality states. However, only the TPS experienced the trauma-related script as personally relevant” (2120). The study discovered no difference between the NPS and TPS when listening to the neutral script, as well as no difference between the neutral and traumatic scripts for the NPS. Comparing the NPS and TPS rCBF when listening to the traumatic script, though, the study found a deactivation pattern of brain areas in the NPS. This pattern matches the deactivation pattern found in studies of normal subjects when recalling non-autobiographical memories as opposed to autobiographical memories. Thus, one conclusion of the study is that, on a neurobiological level, the alters