altered patterns can reflect ApoE genetic status (a risk factor associated with the disease). It has been found that neurodegenerative diseases spread 'prion-like' through the brain. For example, when the proteins amyloid-b and TDP-43 are in their abnormal form, they spread across synapses and are associated with neurodegeneration. This transmission of abnormal protein would be constrained by the organization of white matter connections and could potentially explain the spatial distribution of pathology within the DMN, in Alzheimer's . In Alzheimer's disease, the topology of white matter connectivity helps in predicting atrophic patterns, possibly explaining why the PCC is affected in the early stages of the disease. Autism spectrum disorder Autism spectrum disorders (ASDs) are associated with metabolic and functional abnormalities of the PCC. Individuals with ASDs show reduction in metabolism, exhibit abnormal functional responses and demonstrate reductions in functional connectivity. One study showed these reductions are prominent in the PCC. Studies have shown that the abnormalities in cingulate responses during interpersonal interaction correlate with the severity of symptoms in ASD, and the failure to show task dependent deactivation in the PCC correlates with overall social function. Finally, post-mortem studies show that the PCC in patients with ASD have cytoarchitectonic abnormalities, including reduced levels of GABA A receptors and benzodiazepine binding sites. Attention deficit hyperactivity disorder It has been suggested that ADHD is a disorder of the DMN, where neural systems are disrupted by uncontrolled activity that leads to attentional lapses. In a meta-analysis of structural MRI studies, Nakao et al. (2011) found that patients with ADHD exhibit an increased left PCC, suggesting that developmental abnormalities affect the PCC. In fact, PCC function is abnormal in ADHD. Within the DMN, functional connectivity is reduced and resting state activity is used to diagnose ADHD in children. Treatment for ADHD, includes psychostimulant medication that directly affects PCC activity. Other studies addressing medication for PCC abnormalities, report that the PCC may only respond to stimulant treatments and the effectiveness of medication can be dependent on motivation levels. Furthermore, ADHD has been associated with the gene SNAP25. In healthy children, SNAP25 polymorphism is linked to working memory capacity, altered PCC structure, and task-dependent PCC deactivation patterns on working memory task. Depression Abnormal PCC functional connectivity has been linked to major depression, with variable results. One study reports increased PCC functional connectivity, while another shows that untreated patients had decreased functional connectivity from the PCC to