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SDAM: severely deficient autobiographical memory

What the term means, what research shows and how SDAM relates to aphantasia

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SDAM stands for “severely deficient autobiographical memory”. It describes people who, throughout their lives, can hardly relive personally experienced events vividly from their own point of view, even though the rest of their thinking is unremarkable. SDAM was first described in three healthy adults (Palombo et al. 2015).

What is SDAM?

Autobiographical memory is memory for your own life: for events you have experienced yourself. In 2015, Palombo and colleagues described three healthy adults who functioned well in everyday life but had a lifelong, severely deficient autobiographical memory. They could hardly recall personally experienced events vividly from a first-person perspective. Their other mental abilities were preserved.

So the limitation is selective: it affects vividly re-experiencing your own past, not thinking, learning or recognising in general. The researchers confirmed the self-descriptions with brain measurements and with memory tasks in which retrieving visual details in particular was weaker.

  • First description: Palombo et al. 2015
  • 3 cases in the first description
  • Prevalence: unknown

What research shows

The first description is based on three people, one woman and two men, who had contacted the research team on their own to learn more about their memory. Depending on the measurement, they were compared with 15, 21 or 9 comparison participants (Palombo et al. 2015).

Vividness of recall
2.03 vs 5.99
self-rating during MRI: SDAM cases vs 21 comparison participants
Recognition
64% vs 70%
corrected hits: SDAM cases vs comparison participants, i.e. similar
Right hippocampus
approx. 10%
smaller, on one side only; in developmental amnesia usually approx. 30–50% on both sides
  • Tests of thinking and memory:With one exception, results were in the normal range or higher. Only on the Rey Complex Figure test, a task involving a complex drawing, did all three perform consistently worse.
  • Brain signals:During recognition, comparison participants showed a typical late signal in the EEG (late positivity). It was absent in the SDAM cases, even though they recognised items about as well. The activation patterns that normally occur during remembering were also absent in the MRI.

Interpret with caution

The authors themselves write that because of the small sample and the large number of statistical comparisons, the findings should be interpreted cautiously. (Palombo et al. 2015)

SDAM and aphantasia: how are they related?

Aphantasia describes the absence of voluntary images in the mind’s eye; SDAM describes a severely limited ability to relive your own memories. The word aphantasia does not appear in the first description of SDAM. The researchers explicitly left open whether the memory deficit stems from a more basic weakness in visual imagery or from how self-related information is processed.

Later, the link became clearer. Zeman writes in a 2024 review: in some people with aphantasia, autobiographical memory is so severely reduced that coexisting SDAM seems likely. At least one of the three people from the first description is also aphantasic. This person, Watkins, has written about both himself. He observes that some, but not all, aphantasic people have memory deficits, and concludes that aphantasia and SDAM are not exactly the same (Watkins 2018).

First aphantasia study

14 of 21 participants reported difficulties with autobiographical memory. (Zeman et al. 2015)

Large questionnaire study

People with aphantasia more often reported difficulties with face recognition and autobiographical memory. (Zeman et al. 2020)

Fewer details when remembering

Participants with aphantasia generated significantly fewer episodic details than comparison participants, for past events as well as for imagined future events. (Dawes et al. 2022)

Hardly any sensory impressions when remembering

In a memory questionnaire, people with aphantasia reported almost no ability to generate visual sensory details when remembering. (Dawes et al. 2020)

These studies show an overlap. But they did not diagnose SDAM. Having aphantasia does not automatically mean having SDAM.

What research does not know yet

  • How common SDAM is remains unknown. We found no reliable figures, either for the general population or for people with aphantasia.
  • There is no established cut-off for when to speak of SDAM.
  • The first description is based on three people who came forward themselves.
  • How aphantasia and SDAM are related is an open question. According to Zeman (2024), current evidence suggests overlapping phenomena, but this still needs clarification.

Not a disease, not a diagnosis

SDAM was described in healthy adults who functioned well in everyday life. Lifelong aphantasia is not considered a disorder either (Zeman et al. 2020). A self-test can give you pointers but does not replace a professional assessment. If your memory or imagery has changed suddenly, have it checked by a doctor.

Frequently asked questions about SDAM

What is SDAM?

SDAM (severely deficient autobiographical memory) is a lifelong, severely limited autobiographical memory: personally experienced events can hardly be relived vividly from one’s own perspective, while other thinking is preserved. It was first described in 2015 in three healthy adults. (Palombo et al. 2015)

Do all people with aphantasia have SDAM?

No. Many people with aphantasia report difficulties with autobiographical memory, 14 of 21 in the first study. But not all have memory problems, and these studies did not diagnose SDAM. Exactly how the two are related has not been clarified. (Zeman et al. 2015; Watkins 2018; Zeman 2024)

Is SDAM brain damage or amnesia?

In the first description, other test results were in the normal range or higher. The right hippocampus was about 10% smaller in each case, on one side only. In developmental amnesia, by contrast, it is usually reduced by about 30–50% on both sides. The people described were healthy adults. (Palombo et al. 2015)

How was SDAM demonstrated?

In the MRI scanner, the three people rated the vividness of their memories much lower than comparison participants (on average 2.03 versus 5.99). In the EEG, a late signal seen in comparison participants during recognition was absent, although the hit rate was similar (64% versus 70%). (Palombo et al. 2015)

Can people with SDAM live and learn normally?

The three people described were healthy and functioned well in everyday life, and with one exception their test results were in the normal range or higher. The small sample does not allow broader conclusions. (Palombo et al. 2015)

Can I test whether I have SDAM?

Our SDAM self-test asks how you remember your own experiences and gives you an initial orientation. It is not a diagnosis, because there is no established cut-off for SDAM yet.

Scientific Sources

  1. Palombo, D. J., 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
  2. Watkins, N. W. (2018). (A)phantasia and severely deficient autobiographical memory: Scientific and personal perspectives. Cortex, 105, 41–52. doi:10.1016/j.cortex.2017.10.010
  3. Zeman, A. (2024). Aphantasia and hyperphantasia: exploring imagery vividness extremes. Trends in Cognitive Sciences, 28(5), 467–480. doi:10.1016/j.tics.2024.02.007
  4. Zeman, A., Dewar, M. & Della Sala, S. (2015). Lives without imagery – Congenital aphantasia. Cortex, 73, 378–380. doi:10.1016/j.cortex.2015.05.019
  5. Zeman, A., Milton, F., Della Sala, S. et al. (2020). Phantasia – The psychological significance of lifelong visual imagery vividness extremes. Cortex, 130, 426–440. doi:10.1016/j.cortex.2020.04.003
  6. Dawes, A. J., Keogh, R., Andrillon, T. & Pearson, J. (2020). A cognitive profile of multi-sensory imagery, memory and dreaming in aphantasia. Scientific Reports, 10, 10022. doi:10.1038/s41598-020-65705-7
  7. Dawes, A. J., Keogh, R., Robuck, S. & Pearson, J. (2022). Memories with a blind mind: Remembering the past and imagining the future with aphantasia. Cognition, 227, 105192. doi:10.1016/j.cognition.2022.105192

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