Reactivation of an old memory during sleep and wakefulness

Abstract

In aseries of four experiments, the effects of the reactivation of an old memory in different states of vigilance were investigated. Rats were trained to run in a six-unit spatial discrimination maze for food reward with low-Ievel electrical stimulation delivered to the ear when they entered blind alleys. Twenty-five days after training, electrotactile stimulation was given to animals as a reactivating treatment just before a retention test. When the cuing treatment was given during wakefulness, retention performance was improved. When it was given in slow-wave sleep, it had no effect. When it was given in paradoxicalsleep, performance was poorer. The use of control groups permitted an assesament of the specificity of the cuing effect in each case: Pretest presentation ofthe same stimulus did not modify performance when it had no cue value. Together, these results show that the effect of the reactivation of an old memory depends upon the vigilance state in which reactivation takes place. They suggest that reorganization of an old memory could be accomplished during paradoxical sleep.

About Sleep's Role in Memory

“…The delivery of the mild ear-shock was ineffective when the food-shock had been associated with a tone (rather than a mild ear-shock) at training, excluding unspecific effects of stimulus presentation during sleep. Cueing during waking did not affect learning, whereas cueing during SWS and also cueing of old, remote memories during REM sleep acquired 25 days before reduced fear memories (517,518), indicating that cueing of fear memories during sleep strengthen these memories only when cueing is conducted during REM sleep and as long as these memories are fresh. The effects could be connected to cue-specific arousal responses mediated by the mesencephalic reticular formation (MRF) as later studies of this group showed that MRF stimulation during post training REM sleep, but not during waking or SWS, also enhanced memory though in a different task (6-unit spatial discrimination maze) (535).…”

Second-order conditioning during sleep

“…The intensities were varied and delivered in a random order. As in our previous experiments (Hars & Hennevin, 1990;Hars et al, 1985), the chosen intensity induced a slight but reproducible head movement.…”

“…In previous experiments, it has been shown that such stimulation can serve as CS in active avoidance conditioning (Hars & Hennevin, 1987;Hars et al, 1985). In a foodreinforced maze-learning task, during which ETS was used as an intratask cue, it has been demonstrated that delivery of ETS in the maze has no effect on learning performance (Hars & Hennevin, 1990). These results show that ETS by itself has no reinforcing power.…”

“…Further, we have shown that when a cue stimulus that has acquired significance through conditioning in wakefulness is given as a reminder in PS, subsequent retention performance is modified. Presentation of the same stimulus has no effect when the stimulus has not previously been associated with the learning task (Hars & Hennevin, 1990;Hars, Hennevin, & Pasques, 1985). To account for the efficacy of cuing during PS, we must assume that the cue stimulus is detected during PS.…”

Evocation in paradoxical sleep of a hippocampal conditioned cellular response acquired during waking

“…Introducing the cue during SWS impaired retention (Hars & Hennevin, 1987). Most recently, we showed that 1 month after learning, presentation of the cue during PS was still effective in modifying retention performance, but that it had no effect during SWS (Hars & Hennevin, 1990).…”