Behavioral and neuroanatomical investigation of Highly Superior Autobiographical Memory (HSAM)

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Abstract

A single case study recently documented one woman’s ability to recall accurately vast amounts of autobiographical information, spanning most of her lifetime, without the use of practiced mnemonics (Parker, Cahill, & McGaugh, 2006). The current study reports findings based on eleven participants expressing this same memory ability, now referred to as Highly Superior Autobiographical Memory (HSAM). Participants were identified and subsequently characterized based on screening for memory of public events. They were then tested for personal autobiographical memories as well as for memory assessed by laboratory memory tests. Additionally, whole-brain structural MRI scans were obtained. Results indicated that HSAM participants performed significantly better at recalling public as well as personal autobiographical events as well as the days and dates on which these events occurred. However, their performance was comparable to age- and sex-matched controls on most standard laboratory memory tests. Neuroanatomical results identified nine structures as being morphologically different from those of control participants. The study of HSAM may provide new insights into the neurobiology of autobiographical memory.

Highlights

► Eleven Highly Superior Autobiographical Memory (HSAM) participants were identified. ► HSAM participants were significantly better at recalling public/autobiographical events. ► HSAM participants’ performance on standard laboratory memory tests was comparable to controls. ► Whole-brain analyses identified 9 structures as being morphologically different from controls.

Introduction

Highly Superior Autobiographical Memory (HSAM) is a newly described ability in which individuals are able to recall events from their personal past, including the days and dates on which they occurred, with very high accuracy. Previously termed “hyperthymestic syndrome,” it was first studied in an individual referred to as A.J. (Parker, Cahill, & McGaugh, 2006). HSAM is distinct from other types of superior memory as participants with this ability perform autobiographical remembering without the apparent use of mnemonic skills. Typically, individuals with superior memory encode and retrieve domain-specific and/or relatively meaningless information utilizing strategies acquired through practice (e.g., street maps of entire cities, pi out to 22,514 decimal places, and long displays of words or digits; Ericsson et al., 2004, Hunt and Love, 1972, Gordon et al., 1984, Wilding and Valentine, 1997). Even the extreme memory abilities of one of the most famous mnemonists, patient S., described by Luria (1968), did not entail autobiographical remembering. Patient S. described living his personal life “as in a haze” (p. 159).

Since the publication of Parker et al. (2006) numerous individuals have contacted our research group professing either to have HSAM, or to know someone who does. We have identified ten new HSAM participants (in addition to A.J.) utilizing a screening process developed to identify HSAM characteristics.

Here we report a detailed analysis of both cognitive function and brain structure of the eleven HSAM participants (including A.J.). Cognitive assessment involved a battery of memory tests both general in nature and specific to autobiographical memory. We examined potential differences in the neuroanatomy of the HSAM participants, as compared to that of age- and sex-matched controls, using structural magnetic resonance imaging (MRI). A substantial literature indicates that changes in human brain structure can be associated with changes in behavior, including memory (Golestani et al., 2002, Bohbot et al., 2007, Boyke et al., 2008, Draganski et al., 2006, Fujie et al., 2008, Scholz et al., 2009). For the present project, four neuroanatomical methods were used. The first two, Voxel Based Morphometry Grey-Matter (VBM-GM) and Voxel Based Morphometry White-Matter (VBM-WM) allowed for the comparison, between groups, of the local concentration of grey and white matter found in any given voxel throughout the brain (Ashburner & Friston, 2000). The third, Tensor Based Morphometry (TBM) was used to detect group-related differences in the shape of regions of the brain (Chung et al., 2001). The fourth, Diffusion Tensor Imaging-Fractional Anisotropy (DTI-FA) allowed for a means of quantifying and comparing differences in white-matter structure (Beaulieu, 2009, Moseley et al., 1990). We present here the results of these cognitive and neuroanatomical analyses.

Section snippets

Materials and methods

A multi-step, Institutional Review Board (IRB) approved process was developed to identify and test HSAM participants. Individuals, who contacted us proclaiming to have HSAM, were screened over the telephone and if they met criteria, were formally consented. One hundred and fifteen adults, claiming to have HSAM, were screened with the Public Event Quiz (the first screening quiz, described below). Forty-one of those adults scored well enough to advance to the 10 Dates Quiz (the second screening

Public Events Quiz and 10 Dates Quiz results

A histogram of the percentage scored on the Public Events Quiz by individuals claiming to have HSAM (n = 115, white bars) and screening controls (n = 30, grey bars) is presented in Fig. 1. A bimodal distribution resulted suggesting the presence of two separate populations within those individuals claiming to have HSAM. A notable number of these individuals performed at a level indistinguishable from that of controls, falsely self-identifying their autobiographical memory as superior. Forty, of the

Background and behavioral observations

This investigation identified and studied, both behaviorally and neuroanatomically, a group of individuals who have HSAM. Our findings have revealed commonalities among HSAM participants in both behavioral and neuroanatomical domains. Additionally, some light has been shed on what may and may not enable HSAM participants to achieve such remarkable levels of autobiographical and public event recall.

Our testing procedures, as well as the formal AMT, have verified that all HSAM participants not

Acknowledgments

This research was supported by NIH 1RO1 AG034613 (C.E.LS.), the Gerard Family Trust (J.L.M), Unither Neurosciences, Inc. (J.L.M) NIH 5RO1 MH12526 (J.L.M).

We wish to give a very special thank you to Nancy Collett and our team of undergraduate researchers whose ideas, dedication and support greatly facilitated the progress of this research project. We are also incredibly appreciative of the HSAM as well as control participants who opened their lives to us and devoted themselves so

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