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Links to a list of papers on the trauma-memory argument.


Imaging the Suppression 

of Emotional Memory

Comment on "Prefrontal Regions Orchestrate Suppression of emotional memories via a Two-Phase Process" by B.E. Depue, T. Curran, & M.T. Banich (Science, July 12, 2007).

In this paper, the authors report that suppressing emotional memories (i.e., an emotional picture paired with a face) is accomplished by one of two processes: (1)  suppression of sensory components of a memory representation by deactivation of the right inferior frontal gyrus, followed by (2) suppression of multimodal and emotional components of the representation by deactivation of the right medial frontal gyrussuppression of the emotional component.  The authors conclude that it is possible to suppress emotional memories, and suggest that they have identified one of the neural mechanisms involved in traumatic amnesia and the memory problems displayed by patieents with post-traumatic stress disorder.

The authors start off on the wrong foot by claiming that there's a debate about whether emotional memories can be suppressed. There is no such debate. Of course memories can be suppressed, and emotional memories are no exception (although their emotional nature makes them stand out in memory, and thus probably harder to suppress than nonemotional ones).

The actual debate is somewhat different. The question is whether trauma victims ever become amnesic for their trauma by virtue of such pathological defense mechanisms as repression or dissociation, and Freud and his ilk claimed. The fact is that there is no evidence from any systematic study of trauma victims for anything like psychogenic amnesia. No evidence of forgetting of the traumatic event that can't be accounted for by such "normal" mechanisms as the passage of time, head injury, infantile and childhood amnesia, and the like. All the "evidence" comes in the form of anecdotal case studies in which either the trauma, or the amnesia, or both lack independent corroboration; or where there is some other ambiguity of the sort that plagues case-study evidence.

There are people who believe that traumatic memories can be repressed or dissociated, including Mike Anderson, whose papers are cited as references #2 and #3 in the embargoed paper, and who have suggested, based on psychological and neuroscientific evidence how this might take place. But since there's no evidence that it *does* take place -- that is, no evidence that trauma victims repress or dissociate anything, period, the search for mechanisms that would enable it to take place seems somewhat pointless. I lay all this out in the following paper: http://socrates.berkeley.edu/~kihlstrm/Tsukuba05.htm.

The authors also talk about the relevance of memory suppression to PTSD. But the problem in PTSD isn't amnesia. Amnesia is a hallmark of the dissociative disorders, but it's not a hallmark of PTSD. The problem in PTSD is that people can't forget their traumas -- which is why PTSD patients complain of intrusive, unbidden memories.

So, the paper has nothing to do with traumatic amnesia, because traumatic amnesia apparently doesn't actually occur. It's a piece of clinical folklore, a myth that has its origins with Freud and other 19th-century romantics, and has been passed down across generations of mental health workers as if it were true.

And it has nothing to do with PTSD, because PTSD is a problem of remembering, not forgetting.

So that's the big issue.

Turning to smaller issues, setting aside the question of whether repression actually occurs (apparently it doesn't), one has to ask whether the experiment reported is an adequate laboratory model of the suppression of traumatic memories. It isn't, anymore than the studies by Mike Anderson, on which this one is based, are. See my critique of one of Anderson's studies in the paper above, also at http://socrates.berkeley.edu/~kihlstrm/Anderson&Green.pdf. In the first place, the stimuli may be unpleasant, but they are hardly traumatic (I know the Lang stimulus set referenced in #10). In the second place, there's not too much forgetting even with the "Think-No Think" paradigm. Look at Figure 1B: against a baseline of 62.5%, items in the Think condition were recalled 71.1% of the time, and items in the No Think condition were recalled 53.2% of the time. That's a significant difference, but it's not amnesia, and it's not even very successful suppression. The to-be-forgotten targets are still being recalled on 50% of the trials.

There is another detail, which is whether the subjects in this experiment actually suppressed their memories of the targets, or simply suppressed verbal recall of them. There's a big difference between the two. The authors provide no evidence that their subjects are suppressing memories, as opposed to suppressing memory reports.

A third detail is that a critical comparison is missing. The authors contrast brain activity in successful Think and No Think trials, and show that certain brain areas are activated when the No Think trial is successful at suppressing memory (you should get an expert neuroscientist, which I'm not, to tell you whether these authors found activation in the same areas revealed by the prior Anderson et al. study, Science 2004). Try my colleague Art Shimamura (who will probably like this study more than I do). But they also should have contrasted brain activity in successful and unsuccessful Think trials (to see what brain areas are activated when attempts to remember succeed or fail, as well as successful and unsuccessful No Think trials (to see what brain areas are activated when attempts to suppress succeed or fail).

This is not to say that the study is pointless, or methodologically inadequate, or anything else negative. We do have a capacity to regulate our memories, and to set some memories aside, as it were, so that they're difficult if not impossible to retrieve. Assuming for a second that you're no longer in contact with your high-school boyfriend, tell me: What was his phone number? You can't remember it? How come? You called him almost every night for months. You had it in your memory once. Why can't you remember it now? You don't remember it because once you dumped him, you had no longer any need for that information. You didn't think about it, and so you forgot about it. But it's a perfectly normal process of updating memory, and needn't be tarted up with references to Freudian repression.

The experiment reported is an interesting contribution to our understanding of the neural mechanisms by which we regulate our own memories -- as was the earlier study by Anderson et al. (Science 2004) which formed the basis for this one. But neither one has anything to do with repression and traumatic amnesia (because repression of trauma apparently doesn't occur). And it's got nothing to do with PTSD (because the problem in PTSD is that people can't forget, not that they can't remember).


This page last revised 04/08/2010 02:58:39 PM .