Stuart Fogel

• PhD
• Professor (Associate) at University of Ottawa

Sleep is thought to play a critical role in the retention of memory for past experiences (episodic memory), reducing the rate of forgetting compared with wakefulness. Yet it remains unclear whether and how sleep actively transforms the way we remember multidimensional real-world experiences, and how such memory transformation unfolds over the days,...

Sleep is essential for the optimal consolidation of newly acquired memories. This study examines the neurophysiological processes underlying memory consolidation during sleep, via reactivation. Here, we investigated the impact of slow wave - spindle (SW-SP) coupling on regionally-task-specific brain reactivations following motor sequence learning....

We examined how aging affects the role of sleep in the consolidation of newly learned cognitive strategies. Forty healthy young adults (20-35 years) and 30 healthy older adults (60-85 years) were included. Participants were trained on the Tower of Hanoi (ToH) task, then, half of each age group were assigned to either the 90-minute nap condition, or...

Understanding the complex relationship between sleep and memory consolidation is a major challenge in cognitive neuroscience and psychology. Many studies suggest that sleep triggers off-line memory processes, resulting in less forgetting of declarative memory and performance stabilization in non-declarative memory. However, the role of sleep in hum...

Sleep is thought to play a critical role in the retention of episodic memories. Yet it remains unclear whether and how sleep actively transforms memory for specific experiences. More generally, little is known about sleep’s effects on memory for multidimensional real-world experiences, both overnight and in the days to months that follow. In an exc...

Arousal and awareness are two components of consciousness whose neural mechanisms remain unclear. Spontaneous peaks of global (brain-wide) blood-oxygenation-level-dependent (BOLD) signal have been found to be sensitive to changes in arousal. By contrasting BOLD signals at different arousal levels, we find decreased activation of the ventral postero...

Functional magnetic resonance imaging (fMRI) studies have demonstrated that intrinsic neuronal timescales (INT) undergo modulation by external stimulation during consciousness. It remains unclear if INT keep the ability for significant stimulus-induced modulation during primary unconscious states, such as sleep. This fMRI analysis addresses this qu...

Complete locked-in syndrome (CLIS) resulting from late-stage amyotrophic lateral sclerosis (ALS) is characterised by loss of motor function and eye movements. The absence of behavioural indicators of consciousness makes the search for neuronal correlates as possible biomarkers clinically and ethically urgent. EEG-based measures of brain dynamics su...

Understanding the complex relationship between sleep and memory is a major challenge in neuroscience. Many studies on memory consolidation in humans suggest that sleep triggers offline memory processes, resulting in less forgetting of declarative memory and performance stabilization in non-declarative memory. However, issues related to non-optimal...

The hallmark eye movement (EM) bursts that occur during Rapid Eye Movement (REM) sleep are markers of consolidation for procedural memory involving novel cognitive strategies and problem-solving skills. Examination of the brain activity associated with EMs during REM sleep might elucidate the processes involved in memory consolidation, and may unco...

Dreams are one of the most bizarre and least understood states of consciousness. Bridging the gap between brain and phenomenology of (un)conscious experience, we propose the Topographic-dynamic Re-organization model of Dreams (TRoD). Topographically, dreams are characterized by a shift towards increased activity and connectivity in the default-mode...

Sleep consolidates procedural memory for motor skills, and this process is associated with strengthened functional connectivity in hippocampal–striatal–cortical areas. It is unknown whether similar processes occur for procedural memory that requires cognitive strategies needed for problem-solving. It is also unclear whether a full night of sleep is...

Spindles are often temporally coupled to slow waves (SW). These SW-spindle complexes have been implicated in memory consolidation that involves transfer of information from the hippocampus to the neocortex. However, spindles and SW, which are characteristic of NREM sleep, can occur as part of this complex, or in isolation. It is not clear whether d...

Understanding the complex relationship between sleep and memory is a major challenge in neuroscience. Many studies on memory consolidation in humans suggest that sleep triggers offline memory processes, resulting in less forgetting of declarative memory and performance stabilization in non-declarative memory. However, an increasing number of contra...

As we age, the added benefit of sleep for memory consolidation is lost. One of the hallmark age-related changes in sleep is the reduction of sleep spindles and slow waves. Gray matter neurodegeneration is related to both age-related changes in sleep and age-related changes in memory, including memory for problem-solving skills. Here, we investigate...

Arousal and awareness are two components of consciousness whose the neural mechanisms remain unclear. Spontaneous increases of global (brain-wide) blood-oxygenation-level-dependent (BOLD) signal has been found to be sensitive to changes in arousal. By contrasting BOLD datasets with altered arousal levels, we found that the activation of ventral pos...

Sleep spindles (SP) are one of the few known electrophysiological neuronal biomarkers of interindividual differences in cognitive abilities and aptitudes. Recent simultaneous electroencephalography with functional magnetic resonance imaging (EEG-fMRI) studies suggest that the magnitude of the activation of brain regions recruited during spontaneous...

Sleep spindles (SP) are some of the few known electrophysiological neuronal biomarkers of cognitive abilities. Spindles can occur as part of slow wave (SW) – spindle – hippocampal ripple complexes or in isolation. Spindle related activation in certain subset of regions has been correlated with reasoning abilities. However, whether this relationship...

Individuals in remission from depression (MDDR) tend to experience lingering cognitive and emotional processing alterations. However, little is known about the neural profiles underlying these features. Using simultaneous EEG-fMRI, we assessed neural profiles during the emotional word Stroop task (eStroop) in people with MDDR and healthy volunteers...

Objectives Chronotype impacts our state at a given time of day, however, chronotype is also heritable, trait-like, and varies systematically as a function of age and sex. However, only a handful of studies support a relationship between chronotype and trait-like cognitive abilities (i.e., intelligence), and the evidence is sparse and inconsistent b...

Sleep is necessary for memory consolidation, via reactivation. Memory consolidation involves transfer of information from the hippocampus to the neocortex. This hippocampal-neocortical dialog is supported by the co-occurrence of spindles and slow waves (SW). Spindles can occur as part of this complex, or in isolation. However, it is not clear wheth...

Objective: Here, we investigated the behavioral, cognitive, and electrophysiological impact of mild, acute sleep loss via simultaneously recorded behavioral and electrophysiological measures of vigilance during a "real-world", simulated driving task. Methods: Participants (N=34) visited the lab for two testing days where their brain activity and...

During sleep we lack conscious awareness of the external environment. Yet, our internal mental state suggests that high-level cognitive processes persist. The nature and extent to which the external environment is processed during sleep remain largely unexplored. Here, we used an fMRI synchronization-based approach to examine responses to a narrati...

We investigated the behavioural and neuronal functional consequences of age-related differences in sleep for gaining insight into novel cognitive strategies. Forty healthy young adults (20-35 years), and twenty-nine healthy older adults (60-85 years) were assigned to either nap or wake conditions. Participants were trained on the Tower of Hanoi in...

The sleep spindle, a waxing and waning oscillation in the sigma frequency range, has been shown to correlate with fluid intelligence; i.e. the ability to use logic, learn novel rules/patterns, and solve problems. Using simultaneous EEG and fMRI, we previously identified the neural correlates of this relationship, including activation of the thalamu...

The neural mechanism that enables the recovery of consciousness in patients with unresponsive wakefulness syndrome (UWS) remains unclear. The aim of the current study is to characterize the cortical hub regions related to the recovery of consciousness. In the current fMRI study, voxel-wise degree centrality analysis was adopted to identify the cort...

Understanding the complex relationship between sleep and memory is a major challenge in neuroscience. Thousands of studies on memory consolidation in humans suggest that sleep triggers offline memory processes, resulting in less forgetting of declarative memory and performance stabilization in non-declarative memory. However, an increasing number o...

In older adults, motor sequence learning (MSL) is largely intact. However, consolidation of newly learned motor sequences is impaired compared to younger adults, and there is evidence that brain areas supporting enhanced consolidation via sleep degrade with age. It is known that brain activity in hippocampal–cortical–striatal areas is important for...

Introduction Second-language learning (SLL) depends on distinct functional-neuroanatomical systems including procedural and declarative long-term memory. Characteristic features of rapid eye movement (REM) and non-REM sleep such as rapid eye movements and sleep spindles are electrophysiological markers of cognitively complex procedural and declarat...

Sleep consolidates memory for procedural motor skills, reflected by sleep-dependent changes in the hippocampal-striatal-cortical network. Other forms of procedural skills require the acquisition of a novel strategy to solve a problem, which recruit overlapping brain regions and specialized areas including the caudate and prefrontal cortex. Sleep pr...

Sleep resting state network (RSN) functional connectivity (FC) is poorly understood, particularly for rapid eye movement (REM), and in non-sleep deprived subjects. REM and non-REM (NREM) sleep involve competing drives; towards hypersynchronous cortical oscillations in NREM; and towards wake-like desynchronized oscillations in REM. This study employ...

Sleep fragmentation and reductions in sleep spindles have been observed in individuals with depression. Sleep spindles are known to play a protective role for sleep, and there are indications that melatonin agents can enhance spindles in healthy people. Whether agomelatine, a melatonin agonist indicated for the treatment of depression, may increase...

Orexins regulate a wide variety of biological functions, most notably the sleep-wake cycle, reward and stress processing, alertness, vigilance, and cognitive functioning. Alterations of central and peripheral orexin levels are linked to conditions such as narcolepsy, anorexia nervosa, age-related cognitive decline, and neurodegenerative disease. Pr...

Introduction Sleep consolidates memory, including newly acquired procedural skills. One putative systems-level mechanism for this function of sleep is via sleep-dependent strengthening of functional connectivity between the putamen and the cortico-hippocampal-striatal-cerebellar network, which supports procedural motor skills. For procedural motor...

Introduction Sleep is known to enhance the realization of novel solutions to problems. As we age, both the quantity and quality of sleep are reduced. Age-related deficits in sleep-dependent memory consolidation have been recently identified, however, the scope of these deficits is not. Here, we sought to investigate the behavioural and neuronal fun...

Introduction Older adults do not consolidate newly learned motor sequences with the same efficiency compared to younger adults, and there is evidence that enhanced consolidation by sleep is also impaired with age. It is known that brain activity in the hippocampal-cortical-striatal network is important for off-line consolidation of motor-sequences,...

Introduction Much is known about the behavioural and cognitive consequences of chronic sleep loss but relatively little is known about the changes in brain activity associated with reduced vigilance after mild and acute sleep loss. Mild and acute sleep loss is generally thought to be innocuous despite research showing emotional processing, visual a...

Background and Objectives: The neural mechanism that enables the recovery of consciousness in patients with unresponsive wakefulness syndrome (UWS) remains unclear. The aim of the current study is to characterize the cortical hub regions related to the recovery of consciousness in patients with UWS. Methods: Voxel-wise degree centrality analysis wa...

Objective. Nested into slow oscillations (SOs) and modulated by their up-states, spindles are electrophysiological hallmarks of N2 sleep stage that present a complex hierarchical architecture. However, most studies have only described spindles in basic statistical terms, which were limited to the spindle itself without analyzing the characteristics...

Highlights: • EEG resting-state shows a hierarchy of intrinsic neural timescales. • Sensory deficits as in disorders and alterations of consciousness lead to prolonged intrinsic neural timescales. • Clinical conditions with motor deficits do not show changes in intrinsic neural timescales. Abstract: The brain exhibits a complex temporal structur...

Consciousness is a mental characteristic of the human mind, whose exact neural features remain unclear. We aimed to identify the critical nodes within the brain's global functional network that support consciousness. To that end, we collected a large fMRI resting state dataset with subjects in at least one of the following three consciousness state...

Fourteen patients with severe brain injuries and chronic disorders of consciousness underwent polysomnographic recordings for a 24-h period. Their electrophysiological data were scored using a modified sleep staging system employed in a previous study of similar patients (J Head Trauma Rehabil 30:334–346, 2015). In addition to sleep scoring, the pa...

Supplementary Materials

Objective The current study investigated the behavioral, cognitive, and electrophysiological impact of mild (only a few hours) and acute (one night) sleep loss via simultaneously recorded behavioural and physiological measures of vigilance. Methods Participants (N = 23) came into the lab for two testing days where their brain activity and vigilanc...

When someone loses consciousness, one of the main things that happens is a loss of integrated activity across functionally separate brain networks. But there isn’t a single way of measuring this that tracks with the degree of consciousness. That could soon change given the findings of a new article in the journal Anesthesiology. A group of internat...

The neural correlates of consciousness, defined as the minimum neuronal mechanisms sufficient for any conscious percept, are usually subject to different interpretations depending on whether one uses measures of local or global brain activities. We argue that the local regions may support consciousness by serving as hubs within the brain’s global n...

The brain exhibits a complex temporal structure which translates into a hierarchy of distinct neural timescales. An open question is how these intrinsic timescales are related to sensory or motor information processing and whether these dynamics have common patterns in different behavioural states. We address these questions by investigating the br...

There is much evidence that sleep is important for maintaining optimal cognition in humans; however, the link between cognitive capabilities and specific brain activity during sleep is less clear. Recently, converging evidence suggests that brain activity during sleep is linked to interindividual differences in intellectual abilities. In particular...

Human sleep can be broadly categorized as rapid eye movement (REM) and non-REM (NREM) sleep according to the electrophysiological features and oscillations that characterize these distinct states. The most dramatic changes that occur to sleep are observed over the course of the life span. With aging, the neural oscillations of sleep may provide ins...

EEG studies have shown that interindividual differences in the electrophysiological properties of sleep spindles (e.g., density, amplitude, duration) are highly correlated with trait-like “reasoning” abilities (i.e., “fluid intelligence”; problem-solving skills; the ability to employ logic or identify complex patterns), but not interindividual diff...

Background: Consciousness is supported by integrated brain activity across widespread functionally segregated networks. The functional magnetic resonance imaging-derived global brain signal is a candidate marker for a conscious state, and thus the authors hypothesized that unconsciousness would be accompanied by a loss of global temporal coordinat...

Advances in neuroimaging open up the possibility for new powerful tools to be developed that potentially can be applied to clinical populations to improve the diagnosis of neurological disorders, including sleep disorders. At present, the diagnosis of narcolepsy and primary hypersomnias is largely limited to subjective assessments and objective mea...

The effects of aging on cognition are not uniform. Rather, certain aspects of attention and memory are adversely affected by aging, whereas other cognitive domains are relatively preserved, and others even show positive age-related changes. Several cognitive theories have been advanced to explain these aging-related patterns, but none has yet preva...

The transition from wakefulness to sleep is accompanied by widespread changes in brain functioning. Here we investigate the implications of this transition for interregional functional connectivity and their dynamic changes over time. Simultaneous EEG-fMRI was used to measure brain functional activity of 21 healthy participants as they transitioned...

Background: Abnormalities in heart rate during sleep linked to impaired neuro-cardiac modulation may provide new information about physiological sleep signatures of depression. This study assessed the validity of an algorithm using patterns of heart rate changes during sleep to discriminate between individuals with depression and healthy controls....

Sleep is known to be beneficial to the strengthening of two distinct forms of procedural memory: memory for novel, cognitively simple series of motor movements, and memory for novel, cognitively complex strategies required to solve problems. However, these two types of memory are intertwined, since learning a new cognitive procedural strategy occur...

Ample evidence suggests that consolidation of the memory trace associated with a newly acquired motor sequence is supported by thalamo-cortical spindle activity during subsequent sleep, as well as functional changes in a distributed cortico-striatal network. To date, however, no studies have investigated whether the structural white matter connecti...

Simultaneous electroencephalography and functional magnetic resonance imaging (EEG–fMRI) studies have revealed brain activations time-locked to spindles. Yet, the functional significance of these spindle-related brain activations is not understood. EEG studies have shown that inter-individual differences in the electrophysiological characteristics...

Reconsolidation theory posits that upon retrieval, consolidated memories are destabilized and need to be restabilized in order to persist. It has been suggested that experience with a competitive task immediately after memory retrieval may interrupt these restabilization processes leading to memory loss. Indeed, using a motor sequence learning para...

Resting state network (RSN) functional connectivity (FC) has been investigated under a wealth of different healthy and compromised conditions. However such investigations are often dependent on the defined spatial boundaries and nodes of so-called canonical RSNs, themselves the product of extensive deliberations over distinctions between functional...

Study Objectives The behavioural and cognitive consequences of severe sleep deprivation are well understood. Surprisingly, relatively little is known about the neural correlates of mild and acute sleep restriction on tasks that require sustained vigilance for prolonged periods of time during the day. Methods and Results Event-related potential (ER...

There is now ample evidence that sleep spindles play a critical role in the consolidation of newly acquired motor sequences. Previous studies have also revealed that the interplay between different types of sleep oscillations (e.g. spindles, slow waves, sharp-wave ripples) promotes the consolidation process of declarative memories. Yet the function...

Can dreams reveal insight into our cognitive abilities and aptitudes (i.e., “human intelligence”)? The relationship between dream production and trait-like cognitive abilities is the foundation of several long-standing theories on the neurocognitive and cognitive-psychological basis of dreaming. However, direct experimental evidence is sparse and r...

Introduction Sleep is beneficial for consolidation of both “cognitive procedural memory” (CPM) and “simple procedural memory” (SPM). CPM involves the acquisition of a novel cognitive strategy through the execution of a series of motor movements. By contrast, SPM involves motor skills learning of a cognitively simple sequence of movements. Sleep has...

Introduction Periodic limb movements (PLMs) during sleep increase with age and are associated with striatal neurodegeneration and dopamine deficiency. Limb movements are often associated with disruptions to non-rapid eye movement (NREM) sleep. Motor skill memory consolidation recruits the striatum and learning-dependent striatal activation is assoc...

Introduction Sleep abnormalities are highly prevalent among individuals with depression and these abnormalities are thought to contribute to the onset and maintenance of mood disorders. There are some indications that some people with sleep or mood problems self-medicate with cannabis in attempt to improve their sleep. While further work is require...

Introduction The behavioural and cognitive consequences of severe sleep deprivation are well understood. Surprisingly, relatively little is known about the EEG correlates of mild and acute sleep restriction during tasks demanding sustained vigilance for prolonged periods of time during the day. Event-related potential (ERP) paradigms can reveal ins...

Sleep facilitates the consolidation (i.e., enhancement) of simple, explicit (i.e., conscious) motor sequence learning (MSL). MSL can be dissociated into egocentric (i.e., motor) or allocentric (i.e., spatial) frames of reference. The consolidation of the allocentric memory representation is sleep-dependent, whereas the egocentric consolidation proc...

Animal models suggest that consolidated memories return to their labile state when reactivated and need to be restabilized through reconsolidation processes to persist. Consistent with this notion, post-reactivation pharmacological protein synthesis blockage results in mnemonic failure in hippocampus-dependent memories. It has been proposed that, i...

Sleep benefits motor memory consolidation. This mnemonic process is thought to be mediated by thalamo-cortical spindle activity during NREM-stage2 sleep episodes as well as changes in striatal and hippocampal activity. However, direct experimental evidence supporting the contribution of such sleep-dependent physiological mechanisms to motor memory...

Sleep is necessary for the optimal consolidation of newly acquired procedural memories. However, the mechanisms by which motor memory traces develop during sleep remain controversial in humans, as this process has been mainly investigated indirectly by comparing pre- and post-sleep conditions. Here, we used functional magnetic resonance imaging and...

Summary of activation peaks related to the learning pattern.The learning pattern represents all brain areas with greater activation in the MSL compared to the CTL condition during the learning practice session (S1). For each peak of activity, the anatomical label, MNI coordinates, the corrected cluster-level p value using GRF, and the associated Z-...

Summary of activation peaks related to the consolidated pattern.The consolidated pattern represents all brain areas with greater activation in the MSL compared to the CTL condition during the retest practice session (S2). Reporting conventions are as in Figure 1—source data 1.DOI: http://dx.doi.org/10.7554/eLife.24987.005

Regions of interest (ROI) used in the seed-based functional connectivity analysis.Each ROI is selected based on the location of activation peaks in the learning pattern (Le), the consolidated pattern (Co), or both (Le/Co). The table shows seeds’ coordinates in MNI space (given in mm) and their anatomical labels.DOI: http://dx.doi.org/10.7554/eLife....

Average duration and number of epochs used in the temporal dynamics analysis (Figure 5).Table reports the average epoch duration and the number of epochs which were used in data analysis during the sleep scanning session in the MSL or CTL condition nights. Mean and SEM duration values are reported in minutes. p values are calculated based on paired...

Periodic limb movements (PLMs) during sleep increase with age and are associated with striatal neurodegeneration and dopamine deficiency. Limb movements are often associated with disruptions to non-rapid eye movement (NREM) sleep. Motor skill memory consolidation recruits the striatum, and learning-dependent striatal activation is associated with N...

Inter-individual differences in sleep spindles are highly correlated with “Reasoning” abilities (problem solving skills; i.e., the ability to employ logic, identify complex patterns), but not Short Term Memory or Verbal abilities. Simultaneous electroencephalography and functional magnetic resonance imaging (EEG-fMRI) have revealed brain activation...

Motor memory consolidation is thought to depend on sleep-dependent reactivation of brain areas recruited during learning. However, up to this point, there has been no direct evidence to support this assertion in humans, and the physiological processes supporting such reactivation are unknown. Here, simultaneous electroencephalographic and functiona...

Sleep spindles—short, phasic, oscillatory bursts of activity that characterize non-rapid eye movement sleep—are one of the only electrophysiological oscillations identified as a biological marker of human intelligence (e.g., cognitive abilities commonly assessed using intelligence quotient tests). However, spindles are also important for sleep main...

Sleep is necessary for the optimal consolidation of procedural learning, and in particular, for motor sequential skills. Motor sequence learning (MSL) remains intact with age, but sleep-dependent consolidation is impaired, suggesting that memory deficits for procedural skills are specifically impacted by age-related changes in sleep. Age-related ch...

Older adults show impaired consolidation in motor sequence learning (MSL) tasks, failing to demonstrate the sleep-dependant performance gains usually seen in young individuals. To date, few studies have investigated the white matter substrates of MSL in healthy aging, and none have addressed how fiber pathways differences may contribute to the age-...