Chapter 16: Neuropsychiatry and Neuropsychology

The field recognizes two primary categories of psychiatric conditions: organic states arising from identifiable cerebral pathology such as tumors, lesions, or traumatic injury, and functional states like schizophrenia and mood disorders traditionally viewed as lacking physical brain abnormalities. Patients with organic nervous system disease commonly experience disturbances in consciousness, sleep disruption, memory impairment, and emotional dysregulation. Specific conditions including postconcussional syndrome, temporal lobe epilepsy, and progressive dementia illustrate how localized or diffuse brain damage produces predictable psychiatric symptoms. The chapter presents rare but clinically significant syndromes such as Capgras syndrome, where patients believe loved ones have been replaced by imposters, and Cotard syndrome, characterized by the delusional conviction of being dead or lacking vital organs. Modern neuropsychological research has challenged the traditional organic-functional distinction by revealing that functional psychiatric disorders show measurable abnormalities in cerebral laterality and hemispheric function. Schizophrenia appears associated with left hemisphere dysfunction, while affective disorders correlate with right hemisphere abnormalities. Three theoretical frameworks attempt to explain these relationships: the lateralized dysfunction model attributing psychiatric conditions to hemisphere-specific pathology, the interhemispheric disconnection model viewing schizophrenia as impaired corpus callosum communication, and the valence model proposing that left hemisphere function supports positive emotional states while right hemisphere function supports negative emotional processing. Despite advances in neuroimaging technology including MRI, PET scanning, and electroencephalography, significant methodological challenges persist, including inconsistent diagnostic criteria, confounding effects of psychotropic medication, and retrospective data interpretation. The chapter concludes that establishing a neuropsychological basis for psychiatric disorders represents a frontier in understanding mental illness and human cognition.