Memory System, Processing Stages and Neural Mechanisms: A Review of Normal Function and Disorder Patterns

Human memory is a collection of interacting systems that differ in the type of information they store, the timescale over which they operate, and the brain structures that support them. Despite decades of research, questions remain about how cleanly memory systems and processing stages map onto specific neural substrates, and about what memory disorders can reveal about the healthy architecture of memory. This review synthesizes literature on memory classification (sensory, short-term, and long-term memory), on the sequential processes of encoding, consolidation, and storage/retrieval, and on the neural mechanisms that underline these systems, including the medial temporal lobe, prefrontal cortex, basal ganglia, cerebellum, and amygdala. It then examines four common patterns of memory disorder—anterograde and retrograde amnesia, Alzheimer's disease, working-memory impairment as seen in attention-deficit/hyperactivity disorder (ADHD), and emotional-memory disturbance as seen in post-traumatic stress disorder (PTSD)—as case studies of how damage to specific circuits produces selective, rather than global, memory impairment. The review is organized as a narrative synthesis of experimental, clinical, and neuroimaging findings rather than a new empirical study. Its central question is whether distinct memory systems and processing stages correspond to dissociable brain regions, and whether disorders of memory are best understood as exaggerations or breakdowns of these normal mechanisms.