Episodic memory refers to the memory of events, times, places, associated emotions, and other conception-based knowledge in relation to an experience. Semantic and episodic memory together make up the category of declarative memory, which is one of the two major divisions in memory. The counterpart to declarative, or explicit memory, is procedural memory, or implicit memory.
The formation of new episodic memories requires the medial temporal lobe, a structure that includes the hippocampus. Without the medial temporal lobe, one is able to form new procedural memories (such as playing the piano) but cannot remember the events during which they happened.
The prefrontal cortex (and in particular the left hemisphere) is also involved in the formation of new episodic memories (also known as episodic encoding). Patients with damage to the prefrontal cortex can learn new information, but tend to do so in a disordered fashion. For example, they might show normal recognition of an object they had seen in the past, but fail to recollect when or where it had been viewed (Janowsky et al., 1989). Some researchers believe that the prefrontal cortex helps organize information for more efficient storage, drawing upon its role in executive function. Others believe that the prefrontal cortex underlies semantic strategies which enhance encoding, such as thinking about the meaning the study material or rehearsing it in working memory (Gabrieli et al., 1998).
Researchers do not agree about how long episodic memories are stored in the hippocampus. Some researchers believe that episodic memories always rely on the hippocampus. Others believe the hippocampus only stores episodic memories for a short time, after which the memories are consolidated to the neocortex. The latter view is strengthened by recent evidence that neurogenesis in the adult hippocampus may ease the removal of old memories and increase the efficiency of forming new memories (Deisseroth et al 2004).
According to Brain activation during episodic memory retrieval: sex differences, women tend to outperform men on episodic memory tasks.
Activation of specific brain areas (mostly the hippocampus) seems to be different between young and older people upon episodic memory retrieval, as shown by Maguire and Frith 2003. Older people tend to activate both left and right hippocampus, while young people activate only the left one.
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