Monday, 1 June 2015
In light of the recent discovery that some people have an uncanny ability to recall their lives in extreme detail, known as hyperthymesia or "highly superior autobiographical memory", Daniela Palombo and her team suggest their syndrome is at the opposite extreme and they propose the label "severely deficient autobiographical memory".
The researchers describe three individuals with the postulated syndrome: AA is a 52-year-old married woman; BB is a 40-year-old single man; and CC is a 49-year-old man living with his partner. All three are high functioning in their everyday lives, they have jobs, yet they also claim a life-long inability to recollect and relive past events from a first-person perspective (a condition they became fully aware of in their late teens or early adulthood). Their memory for facts and skills is completely normal. Two of the individuals had experienced depression many years earlier, but there was no evidence of this persisting.
Through intense neuropsychological testing for intelligence, memory and mental performance, the three individuals mostly scored normally or higher than normal. One key exception was poor performance on the ability to draw a complex figure from memory. The researchers think this visual memory deficit could be key to understanding their lack of autobiographical memories.
To test their memories of their lives, the researchers interviewed AA, BB and CC about various incidents from their pasts – a mixture of questions about generic life events and also personal incidents the participants proposed themselves after looking at their calendars or consulting loved ones.
Compared to fifteen comparison participants (matched with the target participants for age and educational background), the impaired participants were able to provide significantly fewer autobiographical, first-person details from their teen and youth years. For more recent events, the impaired participants' recall appeared more normal, but the researchers think this is due to a combination of conservative scoring (when in doubt the researchers scored reminisces as autobiographical in nature), and the participants having learned compensation strategies such as studying diaries and photos and substituting their lack of autobiographical memory for memory of facts and semantic detail.
From a subjective perspective, the impaired participants described their own memories of past events from both distant and more recent times as almost completely lacking a first-person perspective or involving any sense of "re-experiencing". They also struggled to imagine future events, consistent with the idea that memory and future imagination involve shared mental processes.
Brain scans of the impaired participants uncovered no evidence of brain damage or illness, but when they attempted to recall autobiographical details from their pasts, there was less activity in key brain regions associated with autobiographical memory, compared with control participants. This included the medial prefrontal cortex and the precuneus and parts of the temporal lobes. The right-sided hippocampus (an important brain area for memory) was slightly smaller in the impaired participants compared with controls. Whether cause or consequence, this might be relevant to their deficits but it also argues against the new syndrome merely being an instance of "developmental amnesia", which in contrast is characterised by a drastic lack of brain volume in areas involved in memory.
The researchers urge caution given their small sample, and they admit that many questions remain. Yet they state "there is no evidence to support a neurological or psychiatric explanation for our findings". If this research generates enough interest, I wonder if other healthy people will come forward and describe their own absence of autobiographical memories. This is what's happened with some other neuropsychological syndromes recently, such as "developmental prosopagnosia", which is the term for otherwise healthy people who have a specific difficulty remembering and recognising faces.
Palombo and her team say "our goal was to describe the 'severely deficient autobiographical memory' cases' cognitive syndrome and associated neuroimaging findings in as much detail as possible in order to stimulate further research on the nature of individual differences in episodic autobiographical memory...". A crucial question they note, is "whether these findings reflect an extreme on a continuum of ability in episodic autobiographical recollection, or, they may be qualitatively set apart from the normal distribution of mnemonic capacities."
UPDATE: The researchers have a website www.deficientautobiographicalmemory.com providing information on this new syndrome; you can also take part in a survey there and join a forum to share your experiences.
Palombo, D., Alain, C., Söderlund, H., Khuu, W., & Levine, B. (2015). Severely deficient autobiographical memory (SDAM) in healthy adults: A new mnemonic syndrome Neuropsychologia, 72, 105-118 DOI: 10.1016/j.neuropsychologia.2015.04.012
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Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.