Objective Recognised causes of transient amnesia include transient global amnesia, transient epileptic amnesia, psychogenic amnesia and posterior circulation TIAs. Here we describe a previously unrecognised cause in otherwise healthy individuals: transient amnesia induced by sleep deprivation. We report four cases and suggest an explanation in terms of Tononi's Sleep Homeostasis Hypothesis.
Method Four physicians reporting the phenomenon were interviewed using a semi-structured questionnaire. They were asked to describe the episode as they remember it now, explain how the event came to light, detail the background of fatigue and sleep deprivation and provide a history of any similar events, and of drug or alcohol use.
Results Three participants described episodes of successful, complex patient care, undertaken at night, at times of sleep deprivation, which they documented in medical notes but for which they had no recollection on the following day. The fourth reported memory loss for a complex decision. No participant reported any other similar episodes, use of alcohol or other medications or other cause of memory loss. Thus despite responding appropriately in complex situations, with evidence of short-term recollection from the medical notes, these doctors failed to form new lasting memories in the context of marked sleep-deprivation.
Conclusion Sleep deprivation can lead to a selective transient anterograde amnesia. This phenomenon may be explained by the SHY (Sleep Homeostasis Hypothesis) proposed by Tononi et al. This proposes that during sleep synaptic weights are renormalized with selective weakening of synapses that constitute “noise” and preservation of the synaptic weights corresponding to “signal”. This creates “space” in the brain to allow memorisation of new experiences during wakefulness. Exhaustionof synaptic plasticity by prolonged wakefulness might thus give rise to anterograde amnesia as exemplified by the cases we describe.