Image: iStockphoto/Samuel Chesterman
In the 1920s the behavioral psychologist Karl Lashley conducted a now famous series of experiments in an attempt to identify the part of the brain in which memories are stored. He trained rats to find their way through a maze, then made lesions in different parts of the cerebral cortex in an attempt to erase what he called the "engram," or the original memory trace. Lashley failed to find the engram—his experimental animals were still able to find their way through the maze, no matter where he put lesions on their brains. He therefore concluded that memories are not stored in any single area of the brain, but are instead distributed throughout it.
Subsequent work on amnesics—most notably the studies of the recently deceased patient known only as H.M. carried out by Brenda Milner—implicated a part of the brain called the hippocampus as being crucial for memory formation. More recently, it was established that the frontal cortex is also involved; current thinking holds that new memories are encoded in the hippocampus and then eventually transferred to the frontal lobes for long-term storage. A new study, led by Christine Smith and Larry Squire at the University of California at San Diego, now provides evidence that the age of a memory determines the extent to which we are dependent on the frontal cortex and hippocampus for recalling it. In other words, the location of a recollection in the brain varies based on how old that recollection is.
Smith and Squire assessed the brain activity associated with the recollection of old and new memories. They recruited 15 healthy male participants, and used functional magnetic resonance imaging (fMRI) to scan their brains while they answered 160 questions about news events that took place at different periods of time during the past 30 years. The study sounds simple, but the design of the experiments was actually somewhat complex, because the researchers had to overcome a number of confounding variables.
First, when one is asked to recall any given memory, the brain encodes not only the questions that were asked to cue the retrieval, but also the resulting recollection, so the associated activity could therefore interfere with that which is being assessed. Second, more recent memories are likely to be richer and more vivid than older ones, so the strength of the fMRI signal could be related not just to the time at which a recalled event occurred but also to the richness of the participants' recollection of it. Finally, recalled memories could be strongly associated with personal events in the participants' lives, which could make them easier to remember.
Testing Old Memories
Smith and Squire therefore designed their experiments so that they could assess the effects of the age of a memory independently of both the encoding of the test questions and richness of the recollection of the memory. At the beginning of the task, the researchers presented in random order blocks of questions about events in each time period, and they asked participants to indicate whether or not they knew the answer. About 10 minutes later, while still in the scanner, the participants were asked three questions about each news event. First, they were asked to recall the original question they had been asked about the event (to assess how well they had encoded the information). Then, they were asked the answer to that question (to assess the accuracy of recall) and, finally, how much they knew about each of the events (to assess the richness of each memory).
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8 Comments
Add CommentI think so
Reply | Report Abuse | Link to thisMy father had Glioblastoma Grade IV. primary brain tumor in his Left Medial Lobe. Based on the videos compared to the MRI scans of progression from month to month it supports the fact that the short term memories became almost absent as the lesion progressed. However, the long term memories were still there in most cases except word associations. This is common with the hipp/region medial. When the tumor was shrunk at times and the swelling was decreased the short term memory would appear for short periods of time only to leave as the symptoms occured of the swelling and tumor growth.
Reply | Report Abuse | Link to thisMemory is so mysterious!
Reply | Report Abuse | Link to thishow can the frontal areas operate without the hippocampus at all?
Reply | Report Abuse | Link to thisor is that the stem-
Does this show where memory is stored or where it is processed?
Reply | Report Abuse | Link to thisWhy has nobody come up with the idea that the biggest part of the memory is located in the body to which tge brain is connected? Tge skin has a perfect connection with the brain and every touch activates memory. Without this associated touch the memory does not work.
Reply | Report Abuse | Link to thisThe brain is a perfect connection maker. Not the memory itself.
So all this theories and research in the brain will never bring the solution. I suggest to start research on the theory that the body is one big memory with a huge capacity to store events and reproduce them via the brain connections.
Cees de Vrieze, Bloemendaal, The Netherlands.
I have found that the longer the period of time I am given to remember or retrieve an old memory, the more detail comes to me. If I think of an old memory for a week or two, details start filling in as time goes by. Eventually, I can recall much more detail than I originally thought I could. Why is that?
Reply | Report Abuse | Link to thisThis isn't really on topic with the article, but I'm hoping someone can point me in the right direction for something I have been thinking about.
Reply | Report Abuse | Link to thisDoes anyone know of any books or articles dealing with the development in humans of the ability to conceptualize the future? Animals, as far as I know, have no concept of the future, operating instinctually through hardwired fixed action patterns. Yet, somewhere in our evolutionary history humans developed the ability to imagine events in the future, and consequently to plan, dream, and hope.
I don't know if the ability to image the future is linked to our ability to remember the past and/or our general concept of time, but perhaps someone is familiar with this idea and might know of someone who has written about it.