High-frequency oscillations, known as sharp-wave/ripple (SPW-R) complexes occurring in hippocampus during slow-wave sleep (SWS), have been proposed to promote synaptic plasticity necessary for memory consolidation. We recorded sleep for 3 h after rats were trained on an odor-reward association task. Learning resulted in an increased number SPW-Rs during the first hour of post-learning SWS. The magnitude of ripple events and their duration were also elevated for up to 2 h after the newly formed memory. Rats that did not learn the discrimination during the training session did not show any change in SPW-Rs. Successful retrieval from remote memory was likewise accompanied by an increase in SPW-R density and magnitude, relative to the previously recorded baseline, but the effects were much shorter lasting and did not include increases in ripple duration and amplitude. A short-lasting increase of ripple activity was also observed when rats were rewarded for performing a motor component of the task only. There were no increases in ripple activity after habituation to the experimental environment. These experiments show that the characteristics of hippocampal high-frequency oscillations during SWS are affected by prior behavioral experience. Associative learning induces robust and sustained (up to 2 h) changes in several SPW-R characteristics, while after retrieval from remote memory or performance of a well-trained procedural aspect of the task, only transient changes in ripple density were induced.Hippocampal neural activity during sleep has been hypothesized to play a critical role in memory consolidation (Buzsaki 1989(Buzsaki , 1996Pennartz et al. 2002;Born et al. 2006). Sharp-wave/ripple complexes (SPW-Rs), first described a quarter of a century ago (Buzsaki et al. 1983), are associated with a synchronous discharge of a large neuronal population in multiple hippocampal sites (Buzsaki et al. 1983;Suzuki and Smith 1985;Buzsaki 1986). Buzsaki (1989) suggested that the SPW-R bursts are initiated by neurons whose recurrent connectivity had been transiently potentiated during the preceding awake experience. The fact that only a small and select subpopulation of pyramidal cells fire during successive SPW-Rs indicates experience-specific modulation of neuronal connectivity during the SPW-R (Buzsaki 1996). SPW-Rs are present mainly during SWS but also occur during behaviors not associated with theta rhythm like eating, drinking, grooming, and drowsiness (Buzsaki et al. 1983;Suzuki and Smith 1985;Buzsaki 1986). This supports the notion that SPW-R activity provides a substrate for off-line memory consolidation during behavioral states not associated with new information processing. Slow-wave sleep (SWS) is of particular interest because learning-associated changes in cortical spindle activity during SWS are well documented both in humans (Meier-Koll et al. 1999;Fogel et al. 2002;Gais et al. 2002;Clemens et al. 2005) and recently in rats (Eschenko et al. 2006). Moreover, hippocampal ripples and cortical spindles tend to group...
The beneficial effect of sleep on memory has been well-established by extensive research on humans, but the neurophysiological mechanisms remain a matter of speculation. This study addresses the hypothesis that the fast oscillations known as ripples recorded in the CA1 region of the hippocampus during slow wave sleep (SWS) may provide a physiological substrate for long term memory consolidation. We trained rats in a spatial discrimination task to retrieve palatable reward in three fixed locations. Hippocampal local field potentials and cortical EEG were recorded for 2 h after each daily training session. There was an increase in ripple density during SWS after early training sessions, in both trained rats and in rats randomly rewarded for exploring the maze. In rats learning the place -reward association, there was a striking further significant increase in ripple density correlated with subsequent improvements in behavioral performance as the rat learned the spatial discrimination aspect of the task. The results corroborate others showing an experience-dependent increase in ripple activity and associated ensemble replay after exploratory activity, but in addition, for the first time, reveal a clear further increase in ripple activity related to associative learning based on spatial discrimination.
Objectives The objective of this study was to evaluate the effects of inspiratory muscle training on inspiratory muscle strength, functional capacity and dyspnoea for patients with chronic heart failure, by summarising the published research on the effects of inspiratory muscle training. To identify the best mode of intervention in terms of: the load of maximal inspiratory pressure; the frequency of sessions; and the total duration of intervention. Methods A relevant literature research using the PubMed database, Cochrane and references of published studies, from 1998 to 2016, was conducted. Out of 65 randomised controlled trials, seven were considered as potentially relevant and were retrieved for detailed analysis. The methodological quality of each randomised controlled trial was rated using the physiotherapy evidence database scale. Results The included seven studies contained data on 203 patients. Typical training protocols involved training three, six or seven times per week with intensity ranging from 30% to 60% and for a duration ranging from 6 to 12 weeks. Maximal inspiratory pressure, walking distance and dyspnoea were improved in all studies and especially in those who set a load of 60% in their maximal inspiratory pressure, and have trained patients six times per week for 12 weeks. Conclusion In chronic heart failure patients, inspiratory muscle training results in a marked improvement in inspiratory muscle strength, walking distance and dyspnoea, notably when training patients at 60% of maximal inspiratory pressure, six times per week and for 12 weeks. A small number of studies and heterogeneity among studies may limit the findings of the present study.
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