Forgetting
Older news items (pre-2010) brought over from the old website
Relearning a forgotten language is easier for those under 40
A small study involving 7 native English speakers who had learned either Hindi or Zulu as children when living abroad, but now had no memory of the neglected language, found that the three who were under 40 could relearn certain phonemes that are difficult for native English speakers to recognize, but those over 40, like those who had never been exposed to the language in childhood, could not. The amount of experience of exposure in childhood ranged from 4 to 10 years, and it’s especially notable that the 47-year old individual who had 10 years exposure, having become almost fluent, still could not recover the ability to distinguish these difficult sounds. It should also be noted that where the ability was recovered (and recovered almost to native ability), it took about 15-20 training sessions. The findings point to the value of early foreign language learning.
Bowers, J.S., Mattys, S.L. & Gage, S.H. 2009. Preserved Implicit Knowledge of a Forgotten Childhood Language. Psychological Science, 20 (9), 1064–1069.
http://www.eurekalert.org/pub_releases/2009-09/afps-uio092409.php
Forgotten memories still there
In an imaging study in which 16 college students were shown a list of words, asked to say each word backwards, think of how it could be used, and imagine how an artist would draw it, then shown the list again 20 minutes later and asked to remember what they could of each word, brain activity showed that recollection reinstated the original pattern of activity, and its strength correlated with the strength of the memory. Moreover, even when the student had no conscious memory, the pattern was still there, although weak. Follow-up studies will explore the degradation over time.
Johnson, J.D. et al. 2009. Recollection, Familiarity, and Cortical Reinstatement: A Multivoxel Pattern Analysis. Neuron, 63 (5), 697-708.
http://www.wired.com/wiredscience/2009/09/forgottenmemories/
http://www.eurekalert.org/pub_releases/2009-09/uoc--mee090809.php
New insights into memory without conscious awareness
An imaging study in which participants were shown a previously studied scene along with three previously studied faces and asked to identify the face that had been paired with that scene earlier has found that hippocampal activity was closely tied to participants' tendency to view the associated face, even when they failed to identify it. Activity in the lateral prefrontal cortex, an area required for decision making, was sensitive to whether or not participants had responded correctly and communication between the prefrontal cortex and the hippocampus was increased during correct, but not incorrect, trials. The findings suggest that conscious memory may depend on interactions between the hippocampus and the prefrontal cortex.
Hannula, D.E. & Ranganath, C. 2009. The Eyes Have It: Hippocampal Activity Predicts Expression of Memory in Eye Movements. Neuron, 63 (5), 592-599.
http://www.eurekalert.org/pub_releases/2009-09/cp-ycb090309.php
http://sciencenow.sciencemag.org/cgi/content/full/2009/910/4?etoc
How we forget over the short term
Information in short-term memory is rapidly forgotten once attention is diverted, but why? Is it because memory traces decay in the absence of attention? Or is it because older traces interfere with new traces? In a study in which volunteers were shown a string of 3 letters, then told to count backwards for 4, 8, 12, or 16 seconds, before recalling the letters, it was found that those who counted backwards for the longest time were better able to recall the letters than those who counted backwards for shorter times. This suggests that temporal confusability, not decay, is the main culprit in short-term forgetting. The finding is consistent with research indicating that interference is more important than decay in long-term forgetting as well.
Unsworth, N., Heitz, R.P. & Parks, N.A. 2008. The Importance of Temporal Distinctiveness for Forgetting Over the Short Term. Psychological Science, 19 (11), 1078-1081.
http://www.eurekalert.org/pub_releases/2008-12/afps-src121208.php
Forgotten but not gone
We all know it’s easier to re-learn something than learn it for the first time. But why? When we learn, as we know, a neuron makes new connections with other neurons, and these connections are made through synapses. If that connection breaks down, we forget. A new study sheds light on what happens when we re-learn something we thought was forgotten. It appears that in the case of information (synaptic connections) that isn’t needed any more, the synapses are disabled, not destroyed. When needed again, they just need to be reactivated.
Hofer, S.B. et al. 2008. Experience leaves a lasting structural trace in cortical circuits. Nature, Published online November 12, 2008
http://www.eurekalert.org/pub_releases/2008-11/m-fbn111708.php
A new perspective on forgetting
A new mathematical model may shed light on forgetting. The model has found that "free-lunch learning" (the way in which forgotten material is called back to mind when we relearn some part of it — as when a few words in a foreign language we learned at school brings back many other words) occurs when forgetting was induced by random fluctuations in the strength of synaptic connections (‘synaptic drift'). But when forgetting is induced by progressive decay in synaptic strength (which is how forgetting has traditionally been thought of), then "negative free-lunch learning" (where relearning parts of forgotten associations decreases the recall of associated knowledge) occurs. This suggests that forgetting occurs because of random drift rather than a decay in the strength of synaptic connections.
Stone, J.V. & Jupp P.E. 2008. Falling towards Forgetfulness: Synaptic Decay Prevents Spontaneous Recovery of Memory. PLoS Computational Biology, 4(8), e1000143. Full text available at http://dx.plos.org/10.1371/journal.pcbi.1000143
http://www.eurekalert.org/pub_releases/2008-08/plos-rpn082108.php
New research shows why too much memory may be a bad thing
People who are able to easily and accurately recall historical dates or long-ago events may have a harder time with word recall or remembering the day's current events. A mouse study reveals why. Neurogenesis has been thought of as a wholly good thing — having more neurons is surely a good thing — but now a mouse study has found that stopping neurogenesis in the hippocampus improved working memory. Working memory is highly sensitive to interference from information previously stored in memory, so it may be that having too much information may hinder performing everyday working memory tasks.
Saxe, M.D. et al. 2007. Paradoxical influence of hippocampal neurogenesis on working memory. Proceedings of the National Academy of Sciences, 104 (11), 4642-4646.
Full text is available at http://www.pnas.org/cgi/reprint/104/11/4642
http://www.physorg.com/news94384934.html
http://www.eurekalert.org/pub_releases/2007-03/cumc-nrs032807.htm
More insight into why we forget
Increasingly researchers have come to believe interference is far more important for forgetting than the traditional notion of decay over time. A technique called "transcranial magnetic stimulation" (TMS) has now revealed that an area within the prefrontal cortex called the left inferior frontal gyrus, known to be active when volunteers take memory tests while confronting interference, is essential for blocking interference.
Feredoes, E., Tononi, G. & Postle, B.R. 2006. Direct evidence for a prefrontal contribution to the control of proactive interference in verbal working memory. Proceedings of the National Academy of Sciences, 103 (51), 19530-19534.
http://www.eurekalert.org/pub_releases/2006-12/uow-ccr120406.php
Memories are harder to forget than recently thought
Previous rodent studies have shown that the process of encoding a memory can be blocked by the use of a protein synthesis inhibitor called anisomycin (http://www.eurekalert.org/pub_releases/2000-08/NYU-Nnfl-1508100.htm). Experiments with anisomycin helped lead to the acceptance of a theory in which a learned behavior is consolidated into a stored form and that then enters a 'labile' - or adaptable - state when it is recalled. According to these previous studies, the act of putting a labile memory back into storage involves a reconsolidation process identical to the one used to store the memory initially. Indeed, experiments showed that anisomycin could make a mouse forget a memory if it were given anisomycin directly after remembering an event. In a new study, however, researchers have showed that disruption of a "re-remembered" memory was not permanent. Mice demonstrated that they could remember the original learned behavior 21 days later. This research thus casts doubt on the concept of “reconsolidation”, or at least demonstrates that we still have much to learn about this process.
Lattal, K.M. & Abel, T. 2004. Behavioral impairments caused by injections of the protein synthesis inhibitor anisomycin after contextual retrieval reverse with time. PNAS, 101, 4667-4672.
http://www.eurekalert.org/pub_releases/2004-03/uop-mah031504.php
More evidence for active forgetting
In an imaging study involving 24 people aged 19 to 31, participants were given pairs of words and told to remember some of the matched pairs but forget others. Trying to shut out memory appeared more demanding than remembering, in that some areas of the brain were significantly more when trying to suppress memory. Both the prefrontal cortex and the hippocampus were active. Those whose prefrontal cortex and hippocampus were most active during this time were most successful at suppressing memory.
Anderson, M.C., Ochsner, K.N., Kuhl, B., Cooper, J., Robertson, E., Gabrieli, S.W., Glover, G.H. & Gabrieli, J.D.E. 2004. Neural Systems Underlying the Suppression of Unwanted Memories. Science, 303 (5655), 232-235.
http://www.eurekalert.org/pub_releases/2004-01/su-rrb010604.php
You may not be able to recall it, but it influences you anyway
“Forgetting” doesn’t mean the memory is erased from your brain. “Forgotten” information may in fact influence you more than it would if it hadn’t been forgotten — because you’re unaware of the influence. This somewhat alarming possibility has been raised by a recent study in which college students studied lists of nonfamous and famous names. Some participants were told to remember the nonfamous names, while the others were told to forget them. Later, both groups were asked to judge whether or not a name was famous from a mixed list of famous and nonfamous names. Those who were told to forget misidentified more nonfamous names as famous than those who had been told to remember.
Such a judgment is of course made on the basis of the familiarity of the name. It is exposure to an item that affects its familiarity – not whether or not you consciously remember it. By telling the participants to “forget” what they’d seen, the experimenters were removing the participants’ awareness of the source of the familiarity, not the familiarity itself.
Bjork, E.L. & Bjork, R.A. 2003. Intentional Forgetting Can Increase, Not Decrease, Residual Influences of To-Be-Forgotten Information. Journal of Experimental Psychology: Learning, Memory, and Cognition, 29 (4), 524–531.
Failing recall not an inevitable consequence of aging
New research suggests age-related cognitive decay may not be inevitable. Tests of 36 adults with an average age of 75 years found that about one out of four had managed to avoid memory decline. Those adults who still had high frontal lobe function had memory skills “every bit as sharp as a group of college students in their early 20s." (But note that most of those older adults who participated were highly educated – some were retired academics). The study also found that this frontal lobe decline so common in older adults is associated with an increased susceptibility to false memories – hence the difficulty often experienced by older people in recalling whether they took a scheduled dose of medication.
The research was presented on August 8 at the American Psychological Association meeting in Toronto.
http://www.eurekalert.org/pub_releases/2003-08/wuis-fmf080703.php
Selective erasure of memories one step closer
It is now believed that memories become “labile” (able to be changed) every time they are reactivated. If so, it would seem that we could, by re-activating a memory, “erase” it – even though the memory is very old. Researchers have, however, had mixed success in achieving this. A new report suggests why. Any memory is made up of a number of different associations, but only one association will be “dominant” (will determine our reaction). It is this dominant association that is susceptible to change, and thus, to erasure.
Eisenberg, M., Kobilo, T., Berman, D.E. & Dudai, Y. 2003. Stability of Retrieved Memory: Inverse Correlation with Trace Dominance. Science, 301 (5636), 1102-1104.
http://www.eurekalert.org/pub_releases/2003-08/wi-npg082003.php
Older adults better at forgetting negative images
It seems that this general tendency, to remember the good, and let the bad fade, gets stronger as we age. Following recent research suggesting that older people tend to regulate their emotions more effectively than younger people, by maintaining positive feelings and lowering negative feelings, researchers examined age differences in recall of positive, negative and neutral images of people, animals, nature scenes and inanimate objects. The first study tested 144 participants aged 18-29, 41-53 and 65-80. Older adults recalled fewer negative images relative to positive and neutral images. For the older adults, recognition memory also decreased for negative pictures. As a result, the younger adults remembered the negative pictures better. Preliminary brain research suggests that in older adults, the amygdala is activated equally to positive and negative images, whereas in younger adults, it is activated more to negative images. This suggests that older adults encode less information about negative images, which in turn would diminish recall.
Charles, S.T., Mather, M. & Carstensen, L.L. 2003. Aging and Emotional Memory: The Forgettable Nature of Negative Images for Older Adults. Journal of Experimental Psychology: General, 132(2), 310-24.
Memories may be hard to find when thalamus fails to synchronize rhythms
Memory codes - the representation of an object or experience in memory - are patterns of connected neurons. The neurons that are linked are not necessarily in the same region of the brain. Exciting new research has measured the electrical rhythms that parts of the brain use to communicate with each other and found that the thalamus regulates these rhythms. "Memory appears to be a constructive process in combining the features of the items to be remembered rather than simply remembering each object as a whole form. The thalamus seems to direct or modulate the brain's activity so that the regions needed for memory are connected." The authors suggest that tips of the tongue experiences (when only part of a memory is recalled) may occur when the rhythms don't synchronize with the regions properly.
Slotnick, S.D., Moo, L.R., Kraut, M.A., Lesser, R.P. & Hart, J. Jr. 2002. Interactions between thalamic and cortical rhythms during semantic memory recall in human. Proc. Natl. Acad. Sci. U.S.A., 99, 6440-6443.
http://www.eurekalert.org/pub_releases/2002-05/uoaf-mi050902.php