Patient HC with developmental amnesia can construct future scenarios

Deficits in recalling the past and imagining fictitious and future scenarios have been documented in patients with hippocampal damage and amnesia that was acquired in adulthood. By contrast patients with very early hippocampal damage and developmental amnesia are not impaired relative to control participants when imagining fictitious/future experiences. Recently, however, a patient (HC) with developmental amnesia, resulting from bilateral hippocampal atrophy, was reported to be impaired, thus raising a question about the true nature of event construction in the context of developmental amnesia. Here, we assessed HC on a test of imagination which explored her ability to construct fictitious events or personal plausible future events. Her scenario descriptions were analysed in detail along a range of parameters, using two different scoring methods. HC's performance was comparable to matched control participants on all measures relating to the imagination of fictitious and future scenarios. We then considered why she was reported as impaired in the previous study. We conclude that various features of the previous testing methodology may have contributed to the underestimation of HC's ability in that instance. Patients like HC with developmental amnesia may be successful at future-thinking tasks because their performance is not based on true visualisation or scene construction supported by the hippocampus, but rather on preserved world knowledge and semantic representations.