Declarative memory and skill-related knowledge: Evidence from a case study of amnesia and implications for theories of memory

ABSTRACT

Theoretical and empirical studies of memory have long been framed by a distinction between declarative and non-declarative memory. We question the sharpness of the distinction by reporting evidence from amnesic L.S.J., who despite retrograde memory losses in declarative knowledge domains, shows sparing of declarative knowledge related to premorbid skill (e.g., playing an instrument). We previously showed that L.S.J. had severe losses of retrograde declarative knowledge across areas of premorbid expertise (e.g., artists of famous works) and everyday knowledge (e.g., company names for logos). Here we present evidence that L.S.J. has sparing of what we call skill-related declarative knowledge, in four domains in which she had premorbid skill (art, music, aviation, driving). L.S.J.’s pattern of loss and sparing raises questions about the strict separation between classically-defined memory types and aligns with a recent proposal by Stanley and Krakauer [2013. Motor skill depends on knowledge of facts. Frontiers in Human Neuroscience, 7,1-11].

KEYWORDS:

• Retrograde amnesia
• declarative memory
• non-declarative memory
• skill knowledge

Acknowledgements

We are grateful to L.S.J. for participating and for the enthusiasm she brought to testing sessions. We thank Maggi and Aline Johnson for making this study possible as well as for their help in generating ideas, especially for the art and music tests, and for providing us with details (including materials such as transcripts) about L.S.J.’s background. We thank the knowledge area experts who helped create and review tests: Emily Blumenthal (art), Cathleen Steele (aviation), Edgar Fiallos (music), and Eleanor Chodroff (music). We thank James Caracoglia and Paula Choi for their help developing tests, analysing results, and recruiting and testing control participants.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. Modern theories of memory such as the multiple trace theory (e.g., Moscovitch, Nadel, Winocur, Gilboa, & Rosenbaum, 2006) suggest that the hippocampus is required for the initial formation of both episodic and semantic memories. Over time, semantic memory can come to be supported by the neocortex alone, but episodic memory always requires hippocampal engagement. Specifically, whenever an episodic memory is retrieved, it is re-encoded, and with repeated retrievals over time, multiple traces are formed in both hippocampus and neocortex. The traces should be distributed more widely for older memories than for more recent ones, protecting older memories against hippocampal damage unless it is severe. Although this mechanism is meant to account for the nature and breakdown of episodic memory, one might ask whether the same mechanism could account for L.S.J.’s sparing of skill-related knowledge. Specifically, if she repeatedly practised the skills that we tested, then a distributed system of traces between hippocampus and neocortex might account for her pattern of spared knowledge, compared to the severe impairment we observed in our earlier study (Gregory et al., 2014). We think this explanation is unlikely. First, as noted, L.S.J. did not continue to practise the relevant skills after her illness. Second, she had documented severe hippocampal damage, and severe deficits in retrograde memory, supported by her failure to remember any life events prior to her illness (see Gregory et al., 2014, for further discussion). Third, the domains of knowledge we tested here – although related to skills she regularly practised throughout her late adolescent and early adult life – overlapped with the domains of knowledge we tested in Gregory et al. (2014), suggesting that even if the theory were extended to general world knowledge (or semantic memory), the pattern of sparing and deficit could not be explained by repeated activities in the relevant knowledge domain.

Additional information

Funding

This work was supported by a grant from the Brain Science Institute, Johns Hopkins University to B.L. and M.M.