the caudate. Other studies have looked at interactions between the PCC and the sub-genual cingulate region (Brodmann area 25), a region of the brain that potentially causes depression. The anterior node of the DMN is formed, in part, by the highly connected PCC and Brodmann area 25. These two regions are metabolically overactive in treatment resistant major depression. The link between the activity in the PCC and Brodmann area 25 correlates with rumination, a feature of depression. This link between the two regions could influence medication responses in patients. Already, it has been found that both regions show alterations in metabolism after antidepressant treatment. Furthermore, patients who undergo deep brain stimulation, have increased glucose metabolism and cerebral flow in the PCC, while also showing an altered Brodmann area 25. Schizophrenia Abnormal activity in the PCC has been linked to schizophrenia, a mental disorder with common symptoms such as hallucinations, delusions, disorganized thinking, and a lack of emotional intelligence. What is common between symptoms is that they have to do with an inability to distinguish between internal and external events. Two PET studies on patients with schizophrenia showed abnormal metabolism in the PCC. One study reports that glucose metabolism was decreased in people with schizophrenia, while another shows abnormal glucose metabolism that was highly correlated in the pulvinar and the PCC. In the latter study, thalamic interactions with the frontal lobes were reduced, which could mean that schizophrenia affects thalamocortical connections. Further abnormalities in the PCC, abnormal NMDA, cannabinoid, and GABAergic receptor binding have been found with post-mortem autoradiography of people with schizophrenia. Abnormalities in the structure and white matter connections of the PCC have also been recorded in patients with schizophrenia. Those with a poor outcome often have reduced PCC volume. Furthermore, white matter abnormalities in the cingulum bundle, a structure that connects the PCC to other limbic structures, are found in some patients with schizophrenia. In functional MRI studies, abnormal PCC function., has been linked to increases and decreases in functional connectivity. There are also abnormal PCC responses during task performance. These abnormalities may contribute to psychotic symptoms of some persons with schizophrenia. Research on the effect of the psychedelic drug psilocybin shows that the altered state of consciousness induced by this drug can be correlated with abnormal metabolism and functional connectivity of the PCC, as well as a reduction in the strength of anti-correlations between the DMN and