Chapter 18: Disorders of Thought, Emotion and Memory

Mental illnesses are highly prevalent, often coexisting with physical or substance use disorders. Understanding these conditions relies on the stress-diathesis theory, which posits that a genetic predisposition interacts with environmental stressors, such as adverse childhood experiences (ACE), leading to chronic biological and metabolic changes, particularly through the dysregulation of the HPA axis. The foundation of psychopathology involves dysregulation in information processing neural networks and plasticity, mediated by numerous neurochemicals, including dopamine (DA), serotonin (5-HT), norepinephrine (NE), and GABA. Specific disorders explored include Schizophrenia, a chronic psychotic disorder marked by both positive symptoms (hallucinations, delusions) and negative symptoms (apathy, alogia), linked to dysfunctions in DA, serotonin, and glutamate systems, as well as structural changes like cortical gray matter loss. Mood disorders encompass depressive disorders (like MDD) and Bipolar disorder (featuring manic episodes); depression involves HPA axis hyperactivity and neurotransmitter imbalances (serotonin/NE), while bipolar disorder involves impaired neuroplasticity and abnormalities in the prefrontal cortex. Anxiety disorders (the most prevalent group), such as GAD and Panic Disorder, relate to the overactivation of the adrenergic system and hyperactive amygdala. The chapter also covers Obsessive-Compulsive and Related Disorders (OCRDs) and Substance Use Disorders (SUDs), the latter being closely tied to the activation of the brain's DA reward system. Finally, the text details Neurocognitive Disorders (NCDs), distinguishing them from normal cognitive aging. The most common NCD, Alzheimer Disease (AD), follows a progressive course characterized by short-term memory loss and hallmark neuropathologic findings: neurofibrillary tangles (hyperphosphorylated tau protein) and neuritic amyloid plaques (Aβ accumulation). Other NCDs discussed include Delirium, Vascular NCD, Frontotemporal Degeneration (FTD), Parkinson Disease, Lewy Body Disease, Huntington Disease (HD), and substance-induced disorders like Wernicke-Korsakoff syndrome.