An engram is a proposed physical trace of memory: a biophysical or biochemical change in biological tissue that occurs in response to experience. This lesson introduces the idea’s history, the evidence for memory-related brain circuits, and why finding a single, universal location for memories is difficult.
The term engram, also called a mnemic trace, describes a hypothesized physical record of information in an organism. In this account, experiences leave lasting changes in cells or their connections, and later activity in those changed networks helps enable remembering.
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What is an engram?
A proposed physical trace of memory: biophysical or biochemical changes in biological tissue associated with experience and memory storage.
What did Lashley’s maze experiments contribute to ideas about memory?
Removing more cortical tissue generally worsened rats’ maze performance, while the particular location removed mattered less consistently. The findings helped support the view that memory is broadly distributed, though not that every region contributes equally.
What was the conditioned response studied by McCormick and Thompson?
Rabbits learned to blink when they heard a tone after the tone had been paired with a puff of air to the cornea.
What evidence connected the lateral interpositus nucleus to conditioned blinking?
Neural activity in the nucleus tracked learning, stimulation could elicit the learned response, and lesioning or chemically deactivating it disrupted the response. Reactivation after chemical deactivation restored the response.
Why is it difficult to identify a single location for every engram?
Different kinds of memory use different systems, memory-related processes can be distributed across regions, and neural connections change over time. Evidence that one group of cells contributes to a memory does not show that it stores the whole memory alone.
Quiz questions
What does the term engram refer to?Answer: Experience-related physical changes in tissue associated with memory.
What did Lashley’s rat maze experiments suggest about memory organization?Answer: The amount of cortex removed affected performance more consistently than the particular location removed.
What evidence supported the importance of the lateral interpositus nucleus in conditioned blinking?Answer: Its activity tracked learning, stimulation could elicit the response, and disruption of the region impaired it.
Which function is associated with the hippocampus?Answer: Contributing to spatial and declarative memory and memory consolidation.
If stimulating neurons associated with a learned fear prompts related behavior, what is the most careful conclusion?Answer: The neurons may contribute to expressing or recalling that memory, but need not store it alone.