Relating Semantic and Episodic Memory Systems
Episodic and semantic memory are two forms of declarative memory that function in distinct but interdependent ways.
Imaging studies have shown that medial temporal lobe (MTL) structures like the hippocampus are involved in episodic memory, the left lateral temporal lobe (LTL) is involved in semantic memory, and left inferior frontal cortex involve both.
To study relationship between these two systems, 12 healthy adults (5 M/7F, 18-48 years) performed word encoding and retrieval tasks during fMRI scanning.
Encoding: participants were asked to remember 40 unique words to a semantic category (living or nonliving). Retrieval: participants made old/new memory judgements of 48 words (32 previously seen, 16 new).
Encoding—L lateral temporal cortex (LTL), prefrontal cortex, hippocampus
Retrieval (accurate and inaccurate)— frontal cortex, parietal lobe
Retrieval (accurate only)—LTL,(BA 21/22
Green circles=BA 21/22
|Hippocampal activation during Encoding (1) and Retrieval (2): hippocampus activated during encoding, but not retrieval.|
The LTL is involved in semantic memory and accurate episodic memory performance. Functional interaction between lateral and medial temporal lobes contributes to improved episodic memory retrieval.