Accelerated long-term forgetting can become apparent within 3 - 8 hours of wakefulness in patients with Transient Epileptic Amnesia

Objective: Accelerated Long-term Forgetting (ALF) is typically defined as a memory disorder in which information that is learned and retained normally over standard intervals (~30 minutes) is forgotten at an abnormally rapid rate thereafter. ALF has been reported, in particular, among patients with Transient Epileptic Amnesia (TEA). Previous work in TEA has revealed ALF 24 hours – 1 week after initial memory acquisition. It is unclear, however, if ALF observed 24 hours after acquisition reflects (i) an impairment of sleep consolidation processes taking place during the first night’s sleep, or (ii) an impairment of daytime consolidation processes taking place during the day of acquisition. Here we focus on the ‘daytime forgetting’ hypothesis of ALF in TEA by tracking in detail the time course of ALF over the day of acquisition, as well as over 24 hours and 1 week.
Method: 11 TEA patients who showed ALF at one week, and 16 matched controls learned four categorical word lists on the morning of the day of acquisition. We subsequently probed word list retention 30-min, 3-hours and 8-hours post-acquisition (i.e. over the day of acquisition), as well as 24-hours and 1-week post acquisition.
Results: ALF became apparent in the TEA group over the course of the day of acquisition, 3-8 hours after learning. No further forgetting was observed over the first night in either group.
Conclusions: This study shows that ALF in TEA can result from a deficit in memory consolidation occurring within hours of learning, without a requirement for intervening sleep.