Into the future with little past: exploring mental time travel in a patient with damage to the mammillary bodies/fornix

Abstract

Objective: Remembering the past and imaging the future are both manifestations of ‘mental time travel’. These processes have been found to be impaired in patients with bilateral hippocampal lesions. Here, we examined the question of whether future thinking is affected by other Papez circuit lesions, namely: damage to the mammillary bodies/fornix.

Method: Case (SL) was a 43-year-old woman who developed dense anterograde and retrograde amnesia suddenly, as a result of Wernicke–Korsakoff’s syndrome. A region of interest volumetric Magnetic resonance imaging (MRI) analysis was performed. We assessed past and future thinking in SL and 11 control subjects of similar age and education with the adapted Autobiographical Interview (AI). Participants also completed a battery of neuropsychological tests.

Results: Volumetric MRI analyses revealed severely reduced fornix and mammillary body volumes, but intact hippocampi. SL showed substantial, albeit temporally graded retrograde memory deficits on the adapted AI. Strikingly, whilst SL could not provide any specific details of events from the past two weeks or past two years and had impaired recall of events from her late 30s, her descriptions of potential future events were normal in number of event details and plausibility.

Conclusions: This dissociation of past and future events’ performance after mammillary body and fornix damage is at odds with the findings of the majority of patients with adult onset hippocampal amnesia. It suggests that these non-hippocampal regions of the Papez circuit are only critical for past event retrieval and not for the generation of possible future events.

Keywords:

• Thalamus
• Wernicke–Korsakoff’s
• diencephalic lesion
• cognition
• memory

Acknowledgments

We would like to thank Carly Black and Michael Gascoigne for rating of transcripts and Hayley Donohue for assistance in manuscript preparation.

Funding

MH was supported by Alzheimer Research UK, the Wellcome Trust, and the Newton Trust. Suncica Lah was in part supported by The University of Sydney Thompson Fellowship. ST is supported by Alzheimer’s Australia Dementia. Research Foundation and NHMRC of Australia awards. The research was also supported by an ARC Centre of Excellence grant into Cognition and Its Disorders.