Hippocampus-retrosplenial cortex interaction is increased during phasic REM and contributes to memory consolidation.

Hippocampal (HPC) theta oscillation during post-training rapid eye movement (REM) sleep supports spatial learning. Theta also modulates neuronal and oscillatory activity in the retrosplenial cortex (RSC) during REM sleep. To investigate the relevance of theta-driven interaction between these two regions to memory consolidation, we computed the Granger causality within theta range on electrophysiological data recorded in freely behaving rats during REM sleep, both before and after contextual fear conditioning. We found a training-induced modulation of causality between HPC and RSC that was correlated with memory retrieval 24 h later. Retrieval was proportional to the change in the relative influence RSC exerted upon HPC theta oscillation. Importantly, causality peaked during theta acceleration, in synchrony with phasic REM sleep. Altogether, these results support a role for phasic REM sleep in hippocampo-cortical memory consolidation and suggest that causality modulation between RSC and HPC during REM sleep plays a functional role in that phenomenon.

Electrophysiological Evidence That the Retrosplenial Cortex Displays a Strong and Specific Activation Phased with Hippocampal Theta during Paradoxical (REM) Sleep.

It is widely accepted that cortical neurons are similarly more activated during waking and paradoxical sleep (PS; aka REM) than during slow-wave sleep (SWS). However, we recently reported using Fos labeling that only a few limbic cortical structures including the retrosplenial cortex (RSC) and anterior cingulate cortex (ACA) contain a large number of neurons activated during PS hypersomnia. Our aim in the present study was to record local field potentials and unit activity from these two structures across all vigilance states in freely moving male rats to determine whether the RSC and the ACA are electrophysiologically specifically active during basal PS episodes. We found that theta power was significantly higher during PS than during active waking (aWK) similarly in the RSC and hippocampus (HPC) but not in ACA. Phase-amplitude coupling between HPC theta and gamma oscillations strongly and specifically increased in RSC during PS compared with aWK. It did not occur in ACA. Further, 68% and 43% of the units recorded in the RSC and ACA were significantly more active during PS than during aWK and SWS, respectively. In addition, neuronal discharge of RSC but not of ACA neurons increased just after the peak of hippocampal theta wave. Our results show for the first time that RSC neurons display enhanced spiking in synchrony with theta specifically during PS. We propose that activation of RSC neurons specifically during PS may play a role in the offline consolidation of spatial memories, and in the generation of vivid perceptual scenery during dreaming.SIGNIFICANCE STATEMENT Fifty years ago, Michel Jouvet used the term paradoxical to define REM sleep because of the simultaneous occurrence of a cortical activation similar to waking accompanied by muscle atonia. However, we recently demonstrated using functional neuroanatomy that only a few limbic structures including the retrosplenial cortex (RSC) and anterior cingulate cortex (ACA) are activated during PS. In the present study, we show for the first time that the RSC and ACA contain neurons firing more during PS than in any other state. Further, RSC neurons are firing in phase with the hippocampal theta rhythm. These data indicate that the RSC is very active during PS and could play a key role in memory consolidation taking place during this state.

Restless legs syndrome in institutionalized elderly.

Restless legs syndrome (RLS) is characterized by disturbing leg sensations associated to sleep complaints and excessive daytime somnolence. In the elderly, it affects 10 to 35%. Our objective was to determine the prevalence of RLS in institutionalized elderly, analyzing its relationship with clinical, laboratorial and neurophysiological features. We conducted a cross-sectional study of all the subjects under treatment on a chronic-care geriatric service by using face-to-face interviews, which include sleep complaints, the Epworth Sleepiness Scale and standardized questions addressing the four minimal criteria for RLS. The patients with RLS diagnosis received neurological examination, laboratorial tests and three of them, neurophysiological evaluation. The prevalence of RLS was 15.6%. Women were more affected and sleep complaints were frequent. There was no significance on other clinical, laboratorial or neurophysiological findings. We conclude that RLS is a prevalent condition in elderly, may lead to sleep complaints and is often underdiagnosed.

Restless legs syndrome in institutionalized elderly / Síndrome de pernas inquietas em idosos institucionalizados

Restless legs syndrome (RLS) is characterized by disturbing leg sensations associated to sleep complaints and excessive daytime somnolence. In the elderly, it affects 10 to 35 percent. Our objective was to determine the prevalence of RLS in institutionalized elderly, analyzing its relationship with clinical, laboratorial and neurophysiological features. We conducted a cross-sectional study of all the subjects under treatment on a chronic-care geriatric service by using face-to-face interviews, which include sleep complaints, the Epworth Sleepiness Scale and standardized questions addressing the four minimal criteria for RLS. The patients with RLS diagnosis received neurological examination, laboratorial tests and three of them, neurophysiological evaluation. The prevalence of RLS was 15.6 percent. Women were more affected and sleep complaints were frequent. There was no significance on other clinical, laboratorial or neurophysiological findings. We conclude that RLS is a prevalent condition in elderly, may lead to sleep complaints and is often underdiagnosed.

Síndrome de pernas inquietas (SPI) é um distúrbio caracterizado por sensações parestésicas nos membros, aliviadas à sua movimentação ativa. A patologia se associa freqüentemente a distúrbios do sono, sendo especialmente prevalente em idosos (10 a 35 por cento), e pode estar associada a outras condições clínicas. Nosso objetivo foi determinar a prevalência da SPI em idosos institucionalizados, analisando queixas do sono e outras condições clínicas, bioquímicas e neurofisiológicas. Nós entrevistamos os idosos em regime de internato no Instituto São Vicente de Paula (Campina Grande, PB), utilizando questionários específicos para o sono, escala de sonolência de Epworth e um questionário para critérios mínimos para o diagnóstico de SPI. Os pacientes com o diagnóstico de SPI submeteram-se a exame neurológico, laboratoriais, e três deles, a exame neurofisiológico. A prevalência de SPI foi 15,62 por cento, afetando especialmente o sexo feminino. Queixas de sono e patologias associadas foram freqüentes, embora os testes laboratoriais e neurofisiológicos não tenham acrescentado dados significativos. Nós concluímos que SPI é prevalente em idosos, relaciona-se a alterações do sono e é freqüentemente subdiagnosticada.