EVANSTON – Leading theories propose that sleep presents an opportune time for important, new memories to become stabilized. And it’s long been known which brain waves are produced during sleep. But in a new study, researchers set out to better understand the brain mechanisms that secure memory storage.
The team from Northwestern and Princeton universities set out to find more direct and precisely timed evidence for the involvement of one particular sleep wave — known as the “sleep spindle.”
In the study, sleep spindles, described as bursts of brain activity typically lasting around one second, were linked to memory reactivation. The paper, “Sleep spindle refractoriness segregates periods of memory reactivation,” published today in the journal Current Biology.
“The most novel aspect of our study is that we found these spindles occur rhythmically — about every three to six seconds — and this rhythm is related to memory,” said James W. Antony, first author of the study and a postdoctoral fellow in Princeton’s Computational Memory Lab.
Three experiments explored how recent memories are reactivated during sleep. While volunteers took an afternoon nap, sound cues were surreptitiously played. Each was linked to a specific memory. The researchers’ final experiment showed that if cues were presented at opportune times such that spindles could follow them, the linked memories were more likely to be retained. If they were presented when a spindle was unlikely to follow, the linked memories were more likely to be forgotten.
Background: Epileptic patients sometimes report experiential phenomena related to a previous dream they had during seizures or electrical brain stimulation (EBS). This has been alluded to in the literature as “deja-reve” (“already dreamed”). However, there is no neuroscientific evidence to support its existence and this concept is commonly mixed up with deja-vu. We hypothesized that deja-reve would be a specific entity, i.e., different from other experiential phenomena reported in epileptic patients, induced by EBS of specific brain areas.
Methods: We collected all experiential phenomena related to dreams induced by electrical brain stimulations (EBS) in our epileptic patients (2003e2015) and in a review of the literature. The content of these deja-reve and the location of EBS were analyzed.
Results: We collected 7 deja-reve in our database and 35 from the literature, which corresponds to an estimated prevalence of 0.3‰ of all EBS-inducing deja-reve. Deja-reve is a generic term for three distinct entities: it can be the recollection of a specific dream (“episodic-like”), reminiscence of a vague dream (“familiarity-like”) or experiences in which the subject feels like they are dreaming (literally “a dreamy state”). EBS-inducing “episodic-like” and “familiarity-like” deja-reve were mostly located in the medial temporal lobes. “Dreamy states” were induced by less specific EBS areas although still related to the temporal lobes.
Conclusions: This study demonstrates that deja-reve is a heterogeneous entity that is different from deja-vu, the historical “dreamy state” definition and other experiential phenomena. This may be relevant for clinical practice as it points to temporal lobe dysfunction and could be valuable for studying the neural substrates of dreams.
Restless Sleep Disorder in Children: A Pilot Study on a Tentative New Diagnostic Category | Sleep | Oxford AcademicPosted: May 20, 2018
Restless Sleep Disorder in Children: A Pilot Study on a Tentative New Diagnostic Category.
A group of children with “restless sleep” who do not fit the criteria for any other sleep disorder but with daytime impairment are studied to identify restless sleep disorder (RSD) clinically and polysomnographically and to differentiate it from other sleep disorders of childhood.
A pilot study of 15 school aged children with restless sleep and 15 sex and age matched children with restless leg syndrome (RLS) and 37 normal controls were included. Data obtained included nocturnal and diurnal parental concerns, iron and ferritin levels and polysomnography (PSG).
15 children with RLS (12 males; 3 females), with a mean age of 11.9 (standard deviation 3.52), 15 subjects with RSD (11 males, 4 females) with a mean age of 9.5 (standard deviation 3.18), the control subjects were 30 males and 7 females; mean age was 10.6 with a standard deviation of 3.8. Age and sex did not differ between groups. Parental concerns in RSD included frequent nocturnal large body movements involving limbs, head and trunk, and restless sleep and perception of sleep disruption without nocturnal awakening. Daytime impairment included daytime sleepiness. All children with RSD had low ferritin levels (mean 20, SD 8.87). PSG data showed decreased sleep efficiency similar to RLS group but not prolonged sleep latency.
We have characterized clinically and polysomnographically children with RSD and attempted a new diagnostic category. We also have identified an association between RDS and iron deficiency. Future larger studies are needed to confirm these findings and evaluate the natural progression of restless sleepers.