Time Course Of Consolidation Research Articles

Performance-Dependent Consolidation of Learned Vocal Changes in Adult Songbirds.

Motor skills learned through practice are consolidated at later time, which can include nighttime, but the time course of motor memory consolidation and its underlying mechanisms remain poorly understood. We investigated neural substrates underlying motor memory consolidation of learned changes in birdsong, a tractable model system for studying neural basis of motor skill learning. Previous studies in male zebra finches and Bengalese finches have demonstrated that adaptive changes in adult song structure learned through a reinforcement paradigm are initially driven by a cortical-basal ganglia circuit, and subsequently consolidated into downstream cortical motor circuitry. However, the time course of the consolidation process, including whether it occurs offline during nighttime or online during daytime, remains unclear and even controversial. Here, we provide in both species experimental evidence of virtually no consolidation of learned vocal changes during nighttime. We demonstrate instead that the consolidation occurs during daytime and the amount of consolidation is strongly correlated with the amount of learning, suggesting online, performance-dependent mechanisms of consolidation of learned vocal changes. Moreover, by using computer simulations based on our experimental results, we demonstrate that such online, performance-dependent consolidation can account for the contradicting conclusions concerning the time course of consolidation process reached by previous studies. These results thus reconcile a controversy in the study of vocal motor consolidation in songbirds, and illustrate the neural substrates through which newly learned motor skills initially implemented by cortical-basal ganglia circuits become encoded in the cortical motor circuitry.SIGNIFICANCE STATEMENT Motor skills learned through repetitive practice become stable and are consolidated into cortical motor circuits. We investigate neural substrates of this "motor memory consolidation" in adult songbirds, which produce songs that are complex motor skills learned and maintained through repetitive vocal practice. We demonstrate that learned changes in song acoustic structure are consolidated into the cortical motor circuits predominantly during daytime, but not during nighttime, depending on ongoing song performance. These consolidation mechanisms reconcile seemingly contradicting results of previous studies regarding the time course of vocal learning consolidation, and provide fundamental insights into the process through which learned performance of complex motor skills is consolidated and encoded in in motor circuits.

Synaptic consolidation as a temporally variable process: Uncovering the parameters modulating its time-course.

Memories are not instantly created in the brain, requiring a gradual stabilization process called consolidation to be stored and persist in a long-lasting manner. However, little is known whether this time-dependent process is dynamic or static, and the factors that might modulate it. Here, we hypothesized that the time-course of consolidation could be affected by specific learning parameters, changing the time window where memory is susceptible to retroactive interference. In the rodent contextual fear conditioning paradigm, we compared weak and strong training protocols and found that in the latter memory is susceptible to post-training hippocampal inactivation for a shorter period of time. The accelerated consolidation process triggered by the strong training was mediated by glucocorticoids, since this effect was blocked by pre-training administration of metyrapone. In addition, we found that pre-exposure to the training context also accelerates fear memory consolidation. Hence, our results demonstrate that the time window in which memory is susceptible to post-training interferences varies depending on fear conditioning intensity and contextual familiarity. We propose that the time-course of memory consolidation is dynamic, being directly affected by attributes of the learning experiences.

Age-related differences in sleep-dependent consolidation of motor skills in patients with narcolepsy type 1

ObjectiveThe influence of post-training sleep on the consolidation process of procedural (ie, visual and motor) knowledge has shown to be less effective in patients with chronic sleep disorders compared with healthy subjects. To ascertain whether the influence of the altered architecture of sleep in patients with narcolepsy type 1 (ie, with cataplexy: NT1) also varies with age, we compared the performance values of 16 children (aged from nine to 14 years) and 16 adults (aged from 24 to 51 years) on finger tapping task (FTT) after daytime and nighttime periods of sleep in the 24 hours following training. MethodsAll patients, who were drug-free and underwent continuous polysomnographic recordings, could take one or more naps after the training session (at 10 a.m.) until one hour before the first retrieval session (at 6 p.m.) and had an undisturbed period of nighttime sleep from about 10 p.m. to two hours before the second retrieval session (again at 10 a.m.). ResultsThe pattern of sleep-dependent consolidation was significantly different in the two groups of patients: while performance accuracy was higher in adults compared with children at each session, performance speed improved after daytime sleep in children and after nighttime sleep in adults. The improvement in performance speed, although not related with any sleep parameters in both groups, was positively correlated with the daytime and nighttime total sleep time (TST) in children with greater consolidation gain. ConclusionThe interaction between time of day and age in the time course of consolidation of new motor skills discloses a different role of daytime sleep (active in children, simply protective from interferences in adults) in NT1 patients and suggests a flexible use of napping in the educational context.

Time- but Not Sleep-Dependent Consolidation of tDCS-Enhanced Visuomotor Skills

Consolidation of motor skills after training can occur in a time- or sleep-dependent fashion. Recent studies revealed time-dependent consolidation as a common feature of visuomotor tasks. We have previously shown that anodal transcranial direct current stimulation (tDCS) in combination with repeated motor training benefits consolidation by the induction of offline skill gains in a complex visuomotor task, preventing the regular occurrence of skill loss between days. Here, we asked 2 questions: What is the time course of consolidation between days for this task and do exogenously induced offline gains develop as a function of time or overnight sleep? We found that both the development of offline skill loss in sham-stimulated subjects and offline skill gains induced by anodal tDCS critically depend on the passage of time after training, but not on overnight sleep. These findings support the view that tDCS interacts directly with the physiological consolidation process. However, in a control experiment, anodal tDCS applied after the training did not induce skill gains, implying that coapplication of tDCS and training is required to induce offline skill gains, pointing to the initiation of consolidation already during training.

The time course of consolidation of ensemble feature in visual working memory

The time course of consolidation of ensemble feature in visual working memory

Sleep and time course of consolidation of visual discrimination skills in patients with narcolepsy–cataplexy

The level of procedural skills improves in normal individuals when the acquisition is followed by a period of sleep rather than wake. If sleep plays an important role in the consolidation process the advantage it provides should be reduced or delayed when its organization is altered, as in patients with chronic sleep disorders. To test this prediction in patients with narcolepsy-cataplexy (NC), who usually have a more fragmented organization of sleep than normals, we compared the initial, intermediate and delayed level of consolidation of visual skills. Twenty-two drug-naive NC patients and 22 individually-matched controls underwent training at a texture discrimination task (TDT) and were re-tested on the next morning (after a night spent in laboratory with polysomnography) and after another six nights (spent at home). TDT performance was worse in patients than controls at training and at both retrieval sessions and the time course of consolidation was different in NC patients (who improved mainly from next-day to 7th-day retrieval session) compared with controls. Moreover, the less-improving patients at next-day retrieval had a wider disorganization of sleep, probably because of an episode of rapid eye movement (REM) sleep at sleep onset REM, on post-training night more frequently than more-improving patients. These findings suggest that the time course of the consolidation process of procedural skills may be widely influenced by the characteristics of sleep organization (varying night-by-night much more in NC patients than controls) during post-training night.

The time course of consolidation in visual working memory.

How long does it take to form a durable representation in visual working memory? Several theorists have proposed that this consolidation process is very slow. Here, we measured the time course of consolidation. Observers performed a change-detection task for colored squares, and shortly after the presentation of the first array, pattern masks were presented at the locations of each of the colored squares to disrupt representations that had not yet been consolidated. Performance on the memory task was impaired when the delay between the colored squares and the masks was short, and this effect became larger when the number of colored squares was increased. The rate of consolidation was approximately 50 ms per item, which is considerably faster than previous proposals.

Factors regulating the reversibility of long-term potentiation

Theta burst stimulation (TBS) produces an extremely stable form of long-term potentiation (LTP). In contrast, a brief episode of single-pulse stimulation at theta frequency [theta pulse stimulation (TPS)] has been demonstrated to reverse LTP in area CA1 of slices and freely moving animals without causing depression when administered to nonpotentiated pathways. The present in vitro studies confirm these results and establish that the susceptibility of LTP to reversal and the degree of depotentiation are time-dependent. Specifically, a 1 min train of TPS delivered 30 sec after LTP induction produced an almost complete and lasting depotentiation but had increasingly less impact at longer delays and virtually no effect at 30 min. Increasing the duration of TPS did not cause more depotentiation. However, pharmacological facilitation of AMPA receptor-mediated currents significantly enhanced the strength of the reversal process and allowed TPS to produce robust depotentiation up to 30 min after LTP induction. The reversal effect was selective to potentiated synapses receiving TPS, was reversible, and was not blocked by NMDA receptor antagonism. Additional experiments indicated that AMPA receptor facilitation promotes depotentiation by enhancing an active process triggered by TPS that reverses expression without extending the time course of consolidation. These results suggest that the mechanisms responsible for LTP reversal are linked to the amplitude and/or duration of fast excitatory currents mediated by synaptic AMPA receptors and are effective up to the completion of LTP stabilization.

Hippocampal stimulation disrupts spatial working memory even 8 h after acquisition

The present experiment used hippocampal stimulation to determine the temporal gradient of consolidation of spatial working memory. Rats were trained to perform a spatial working memory task on a radial maze with 12 arms. Each rat went to the ends of 6 arms to obtain a food reward. After 8 h, the rat chose among all the arms to find the ones not previously chosen (and consequently still having food). During some test sessions, the hippocampus was stimulated electrically either at a current level just high enough to produce an electrophysiological seizure, or at a current level below this seizure threshold. Stimulation occurred at one of five intervals (0 to 8 h) following the completion of the first six choices. During other test sessions, the hippocampus was not stimulated. After seizure stimulation, the number of retroactive errors (returning to arms chosen prior to stimulation) increased at all delay intervals; the number of proactive errors (returning to arms chosen after stimulation) increased only with the delay of 8 h. Subthreshold stimulation had no influence on either type of error. These results indicate that normal hippocampal function is required for the maintenance of spatial information in working memory, and that the time course of consolidation of this information is significantly greater than that seen in other types of memory, or consolidation may not take place at all.

Shrinking retrograde amnesia.

Frank Benson and I decided to publish this case not because the phenomenon was new — Ritchie Russell and Peter Nathan had described it in 1946 — but because it had been neglected. Thus many animal experimenters had attempted to study the time course of consolidation of memory traces by such experiments as teaching the animal a task and after a variable interval using chemical or physiological methods to ‘erase’ the unconsolidated memory. The presumption in these experiments was that a failure of performance was equivalent to loss of the unconsolidated memory. This presumption failed, however, to take into account the possibility that such an experiment might merely reflect the production of a transient difficulty in retrieval. Only in recent years have animal experimenters come to be aware of this phenomenon and to study it.