What is SDAM?
Severely Deficient Autobiographical Memory (SDAM) refers to a lifelong inability to vividly recollect or re-experience personal past events from a first-person perspective. Our research on this topic emerged from studies of autobiographical episodic memory in healthy adults and individuals with brain disease. We are currently applying these same behavioral and neuroimaging methods to better understand individual differences in autobiographical memory capacities - or why some people remember events better than others.
One approach to this research is to study people with extremely high or low abilities. For instance, people with Highly Superior Autobiographical Memory (HSAM, also known as hyperthymnesia) can effortlessly retrieve detailed events from almost any time in their past at will. In SDAM, autobiographical recollection of events is absent, but other forms of learning are intact. Thus the cases of SDAM we have studied have no functional complaints; they are successful healthy people.
In 2014, Greenberg and Knowlton described two healthy individuals with impaired visual imagery who also lacked a sense of reliving past episodic memories. Although these individuals presented with visual imagery impairment, they share many characteristics of SDAM. Zeman and colleagues (2015) report a similar syndrome in a questionnaire study.
Our description and labeling of the SDAM syndrome
In our 2015 study, three healthy, high functioning individuals with SDAM and matched controls were intensively studied in our laboratory. We found that these individuals had reduced visual memory on laboratory tasks, reduced right hippocampal volume, and reduced activation of the canonical autobiographical memory network during fMRI scanning. They also showed a greatly reduced late positivity Event Related Potential (ERP) component of recognition memory for pictures presented in a laboratory experiment, in spite of the fact that their recognition memory performance was intact. The late positivity ERP component indicates conscious recollection or re-experiencing of the test item. This latter finding suggests that intact memory performance (and day-to-day memory function) in SDAM is may be supported by non-episodic processes (e.g., semantic memory, familiarity).
In a followup study, Fuentemilla, Palombo, and Levine (2018) played recordings of prospectively collected autobiographical events during monitoring of brain activity with magnetoencephalography (MEG), which directly measures brain activity. Healthy adults showed robust synchronized oscillations in the gamma frequency (27-45 Hz) when listening to these recordings, whereas an individual with SDAM did not, although normal activity was observed in relation to stimulation with semantic information.
Sheldon et al (2016) recently demonstrated that individual differences in "memory style" (not as extreme as SDAM and HSAM) are related to intrinsic functional connectivity as measured by resting state functional MRI (i.e., brain activity in the absence of overt task demands). Endorsement of strongly vivid episodic memory was associated with increased connectivity between the medial temporal lobes and posterior regions. That is, individuals who report high episodic autobiographical memory in their day-to-day lives show increased connectivity in memory networks involved in accessing images and other perceptual information. Endorsement of high factual or semantic memory showed a different pattern: enhanced connectivity between the medial temporal lobes and prefrontal regions involved in organization and integrating conceptual information (see also Petrican and Levine, 2020). These findings suggest that individual differences in how people remember the past correspond to functional brain organization at rest.
Many people interested in learning more about SDAM have contacted us and participated in our ongoing research.
For more information and to participate in our online memory survey, click here.
.
To read more about individual differences in autobiographical memory, click here.
For more information about SDAM, see our FAQs.
One approach to this research is to study people with extremely high or low abilities. For instance, people with Highly Superior Autobiographical Memory (HSAM, also known as hyperthymnesia) can effortlessly retrieve detailed events from almost any time in their past at will. In SDAM, autobiographical recollection of events is absent, but other forms of learning are intact. Thus the cases of SDAM we have studied have no functional complaints; they are successful healthy people.
In 2014, Greenberg and Knowlton described two healthy individuals with impaired visual imagery who also lacked a sense of reliving past episodic memories. Although these individuals presented with visual imagery impairment, they share many characteristics of SDAM. Zeman and colleagues (2015) report a similar syndrome in a questionnaire study.
Our description and labeling of the SDAM syndrome
In our 2015 study, three healthy, high functioning individuals with SDAM and matched controls were intensively studied in our laboratory. We found that these individuals had reduced visual memory on laboratory tasks, reduced right hippocampal volume, and reduced activation of the canonical autobiographical memory network during fMRI scanning. They also showed a greatly reduced late positivity Event Related Potential (ERP) component of recognition memory for pictures presented in a laboratory experiment, in spite of the fact that their recognition memory performance was intact. The late positivity ERP component indicates conscious recollection or re-experiencing of the test item. This latter finding suggests that intact memory performance (and day-to-day memory function) in SDAM is may be supported by non-episodic processes (e.g., semantic memory, familiarity).
In a followup study, Fuentemilla, Palombo, and Levine (2018) played recordings of prospectively collected autobiographical events during monitoring of brain activity with magnetoencephalography (MEG), which directly measures brain activity. Healthy adults showed robust synchronized oscillations in the gamma frequency (27-45 Hz) when listening to these recordings, whereas an individual with SDAM did not, although normal activity was observed in relation to stimulation with semantic information.
Sheldon et al (2016) recently demonstrated that individual differences in "memory style" (not as extreme as SDAM and HSAM) are related to intrinsic functional connectivity as measured by resting state functional MRI (i.e., brain activity in the absence of overt task demands). Endorsement of strongly vivid episodic memory was associated with increased connectivity between the medial temporal lobes and posterior regions. That is, individuals who report high episodic autobiographical memory in their day-to-day lives show increased connectivity in memory networks involved in accessing images and other perceptual information. Endorsement of high factual or semantic memory showed a different pattern: enhanced connectivity between the medial temporal lobes and prefrontal regions involved in organization and integrating conceptual information (see also Petrican and Levine, 2020). These findings suggest that individual differences in how people remember the past correspond to functional brain organization at rest.
Many people interested in learning more about SDAM have contacted us and participated in our ongoing research.
For more information and to participate in our online memory survey, click here.
.
To read more about individual differences in autobiographical memory, click here.
For more information about SDAM, see our FAQs.
ERP and Recognition Memory in SDAM Participants
Further reading
For overall review this topic, see: Palombo, D., Sheldon, S., & Levine, B. (2018). Individual differences in autobiographical memory. Trends in Cognitive Sciences.
SDAM/Imagery deficit
For overall review this topic, see: Palombo, D., Sheldon, S., & Levine, B. (2018). Individual differences in autobiographical memory. Trends in Cognitive Sciences.
SDAM/Imagery deficit
- Watkins, N.W. (2017) (A)phantasia and severely deficient autobiographical memory: Scientific and personal perspectives. Cortex.
- Fuentemilla, L. Palombo, D.J., & Levine, B. (2018). Gamma phase-synchrony in autobiographical memory: evidence from magnetoencephalography and Severely Deficient Autobiographical Memory. Neuropsychologia. 110:7-13
- Palombo, D.J., Alain, C., Södurland, H., Khuu, W., & Levine, B. (2015). Severely deficient autobiographical memory (SDAM) in healthy adults: A new mnemonic syndrome. Neuropsychologia, 72, 105-118
- Greenberg, D.L. & Knowlton, B.J. (2014). The role of visual memory in autobiographical memory. Memory and Cognition, 42(6), 922-934.
- Zeman, A., Dewarb, M., Della Sala, S. (2015) Lives without imagery – Congenital aphantasia. Cortex. doi:10.1016/j.cortex.2015.05.019
HSAM
- McGaugh, J.L. (2017). Highly superior autobiographical memory.In Learning and Memory: A Comprehensive Reference (2nd edn). Byrne, J.H., ed. pp137-145, Academic Press
- Brandt, J. and Bakker, A. (2018). Neuropsychological investigation of "the amazing memory man". Neuropsychology. 32:304-316.
- LePort, A.K. et al. (2015). Highly superior autobiographical memory: quality and quantity of retention over time. Front. Psychol. 6, 2017
- Patihis, L. (2016) Individual differences and correlates of highly superior autobiographical memory. Memory. 24:961-978.
- Patihis, L., Frenda, S.J., LePort, A.K., Petersen, N., Nichols, R.M., Stark, C.E., McGaugh, J.L., & Loftus, E.F. (2013). False memories in highly superior autobiographical memory individuals. Proceedings of the National Academy of Sciences of the United States of America, 110(52), 20947-20952.
- McGaugh J.L. (2013). Making lasting memories: Remembering the significant. Proceedings of the National Academy of Sciences of the United States of America, 110, 10402-10407.
- LePort, A.K., Mattfield, A.T., Dickinson- Anson, H., Fallon, J.H., Stark, C.E., Kruggel, F., Cahill, L., & McGaugh, J.L. (2012). Behavioral and neuroanatomical investigation of Highly Superior Autobiographical Memory (HSAM). Neurobiology of Learning and Memory, 98(1), 78-92.
- Parker, E.S., Cahill, L., & McGaugh, J.L. (2006). A case of unusual autobiographical remembering. Neurocase, 12(1), 35-49.