Friday, September 08, 2006
The September issue of Hippocampus is a special on Hippocampal Place Fields and Episodic Memory. Episodic memory is the type of memory that you immediately think of if you are not a memory researcher. It is what Proust is doing while Remembrancing (which is part of why he is such a favorite quotee among the memory community). EM is supposed to have key elements that distinguish it from other memory types, one of which is this experience of "mental time travel". This is an idea almost entirely based in introspection. It is not clear how to ascertain if a patient is replaying the experience subjectively or merely retrieving facts without the VR-like aspect. The subjective nature of this type of memory retrieval makes it well-nigh impossible to study in rodents. But it may be that people who are mostly concerned with the mental time travel issue are hardly interested in memory, per se, but are rather interested in our ability to "fill in the gaps" and create continuous narratives. From the second article of the issue by Ferbinteanu et al.:
Furthermore, though intuition also suggests that our memories are veridical-an accurate reproduction of past events-empirical data indicate that autobiographical memories are in fact reconstructed by active processes sensitive to systematic errors based upon inattention, suggestion, expectancy, and familiar cognitive scripts (Schacter, 1999; e.g., Conway, 2001b). Even completely false memories are acquired easily (Loftus, 1997, 2004) and activate the same neural network involved in true memories (Okado and Stark, 2005). These memory distortions show that rather than "traveling down the memory lane" to re-experience past events, memories for episodes are reconstructed representations based on fragmentary data fit together using heuristics (Schacter, 1999; Conway and Pleydell-Pearce, 2000).So, you don't really remember. You confabulate based on the information you have at hand, the "fragmentary data". I have gotten so paranoid about confabulation that I will hardly ever state one of my memories of a past event as fact. I would be a horrible murder-trial witness. I notice errors all the time among friends of mine that are better story-tellers. We will be reminiscing about some event 4 or 5 years ago and place some individual there that we didn't even know yet. Everyone knows we have memory errors. I wonder if better story-tellers are better at "smoothing the curve". We have a bunch of data points stored up, but it may take our narrative-building ability (which may be uniquely human) to experience "mental time travel". This habit humans have of telling ourselves stories seems pervasive. I am reminded of the hyperactive agency detection device, proposed as an explanation for our need to make gods. Also, Gazzaniga's experiments with split-brain patients: Studies on split-brain patients have dominated Dr. Gazzaniga's work ever since. In the 1970's, he and his colleagues reported that the left hemisphere acts as an interpreter, creating theories to makes sense of a person's experiences.The point of the Hippocampus article is that we can ignore this business for now, while we study how the hippocampus brings together the information that we actually have remembered rather than confabluated. This process is amenable to animal studies, which is great because we are getting really good at multi-electrode recording in the rat hippocampus and gaining lots of insight into place cells, which may provide the spatial context for remembered events to happen in. Which brings up an interesting question: Do you ever remember an event without remembering where you were during that event? Or does the term "event" imply a spatial setting? |