Memories

Memories are the mental representations of past experiences stored in the brain and retrieved when needed. They arise from encoding sensory input, consolidation of that information, and subsequent retrieval or reconstruction. Memory is often discussed in terms of duration and content.

In terms of duration, sensory memory lasts under a second, short-term or working memory holds information for seconds to minutes, and long-term memory can persist for days to decades. In terms of content, memory includes explicit (declarative) memory—episodic memory for personal events and semantic memory for facts—and implicit (nondeclarative) memory such as procedural skills, conditioning, and priming.

The formation and use of memory involve various brain regions. The hippocampus and surrounding medial temporal structures support the formation and consolidation of new memories, especially episodic and semantic memory. The prefrontal cortex contributes to working memory and the organization of information. The neocortex stores distributed representations, while the amygdala modulates memories with emotional significance, and the basal ganglia and cerebellum support procedural and motor memories.

Forgetting can occur through decay, interference, or retrieval failure, and memories are often reconstructive, subject to biases and distortions. Memory performance tends to change with age, with some decline in certain domains while other types remain stable or improve.

Memory can be affected by disorders such as amnesia, dementia (including Alzheimer's disease), or PTSD, and is frequently studied with behavioral tasks and neuroimaging. Strategies to support memory include adequate sleep, focused attention during encoding, repetition and elaboration, retrieval practice, and mnemonic techniques.