Papers by Gilles Vandewalle
Proceedings of the National Academy of Sciences of the United States of America, Jan 9, 2010
Light therapy can be an effective treatment for mood disorders, suggesting that light is able to ... more Light therapy can be an effective treatment for mood disorders, suggesting that light is able to affect mood state in the long term. As a first step to understand this effect, we hypothesized that light might also acutely influence emotion and tested whether short exposures to light modulate emotional brain responses. During functional magnetic resonance imaging, 17 healthy volunteers listened to emotional and neutral vocal stimuli while being exposed to alternating 40-s periods of blue or green ambient light. Blue (relative to green) light increased responses to emotional stimuli in the voice area of the temporal cortex and in the hippocampus. During emotional processing, the functional connectivity between the voice area, the amygdala, and the hypothalamus was selectively enhanced in the context of blue illumination, which shows that responses to emotional stimulation in the hypothalamus and amygdala are influenced by both the decoding of vocal information in the voice area and th...
Abstract Slow wave sleep (SWS) is associated with spontaneous brain oscillations that are thought... more Abstract Slow wave sleep (SWS) is associated with spontaneous brain oscillations that are thought to participate in sleep homeostasis and to support the processing of information related to the experiences of the previous awake period. At the cellular level, during SWS, a slow oscillation (< 1 Hz) synchronizes firing patterns in large neuronal populations and is reflected on electroencephalography (EEG) recordings as large-amplitude, low-frequency waves.
Journal of Neuroscience, 2009
Sleep promotes memory consolidation, a process by which fresh and labile memories are reorganized... more Sleep promotes memory consolidation, a process by which fresh and labile memories are reorganized into stable memories. Emotional memories are usually better remembered than neutral ones, even at long retention delays. In this study, we assessed the influence of sleep during the night after encoding onto the neural correlates of recollection of emotional memories 6 months later. After incidental encoding of emotional and neutral pictures, one-half of the subjects were allowed to sleep, whereas the others were totally sleep deprived, on the first postencoding night. During subsequent retest, functional magnetic resonance imaging sessions taking place 3 d and 6 months later, subjects made recognition memory judgments about the previously studied and new pictures. Between these retest sessions, all participants slept as usual at home. At 6 month retest, recollection was associated with significantly larger responses in subjects allowed to sleep than in sleep-deprived subjects, in the ventral medial prefrontal cortex (vMPFC) and the precuneus, two areas involved in memory retrieval, as well as in the extended amygdala and the occipital cortex, two regions the response of which was modulated by emotion at encoding. Moreover, the functional connectivity was enhanced between the vMPFC and the precuneus, as well as between the extended amygdala, the vMPFC, and the occipital cortex in the sleep group relative to the sleep-deprived group. These results suggest that sleep during the first postencoding night profoundly influences the long-term systems-level consolidation of emotional memory and modifies the functional segregation and integration associated with recollection in the long term.
Science, 2009
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Proceedings of the National Academy of Sciences, 2007
After encoding, memory traces are initially fragile and have to be reinforced to become permanent... more After encoding, memory traces are initially fragile and have to be reinforced to become permanent. The initial steps of this process occur at a cellular level within minutes or hours. Besides this rapid synaptic consolidation, systems consolidation occurs within a time frame of days to years. For declarative memory, the latter is presumed to rely on an interaction between different brain regions, in particular the hippocampus and the medial prefrontal cortex (mPFC). Specifically, sleep has been proposed to provide a setting that supports such systems consolidation processes, leading to a transfer and perhaps transformation of memories. Using functional MRI, we show that postlearning sleep enhances hippocampal responses during recall of word pairs 48 h after learning, indicating intrahippocampal memory processing during sleep. At the same time, sleep induces a memory-related functional connectivity between the hippocampus and the mPFC. Six months after learning, memories activated the mPFC more strongly when they were encoded before sleep, showing that sleep leads to longlasting changes in the representation of memories on a systems level.
Proceedings of the National Academy of Sciences, 2007
In humans, some evidence suggests that there are two different types of spindles during sleep, wh... more In humans, some evidence suggests that there are two different types of spindles during sleep, which differ by their scalp topography and possibly some aspects of their regulation. To test for the existence of two different spindle types, we characterized the activity associated with slow (11-13 Hz) and fast (13-15 Hz) spindles, identified as discrete events during non-rapid eye movement sleep, in non-sleepdeprived human volunteers, using simultaneous electroencephalography and functional MRI. An activation pattern common to both spindle types involved the thalami, paralimbic areas (anterior cingulate and insular cortices), and superior temporal gyri. No thalamic difference was detected in the direct comparison between slow and fast spindles although some thalamic areas were preferentially activated in relation to either spindle type. Beyond the common activation pattern, the increases in cortical activity differed significantly between the two spindle types. Slow spindles were associated with increased activity in the superior frontal gyrus. In contrast, fast spindles recruited a set of cortical regions involved in sensorimotor processing, as well as the mesial frontal cortex and hippocampus. The recruitment of partially segregated cortical networks for slow and fast spindles further supports the existence of two spindle types during human non-rapid eye movement sleep, with potentially different functional significance. electroencephalography (EEG)/functional MRI (fMRI) ͉ light sleep ͉ neuroimaging ͉ sleep physiology Author contributions: M.S., T.T.D.-V., and P.M. designed research; M.S., T.T.D.-V., G.A., M.B., J.C., A.D., M.D., S.G., G.R., C.S., V.S., G.V., and P.M. performed research; E.B., C.D., C.P., A.L., and P.M. contributed new reagents/analytic tools; M.S. and T.T.D.-V. analyzed data; and M.S. and P.M. wrote the paper. The authors declare no conflict of interest.
PLoS ONE, 2007
Background. Relatively long duration retinal light exposure elicits nonvisual responses in humans... more Background. Relatively long duration retinal light exposure elicits nonvisual responses in humans, including modulation of alertness and cognition. These responses are thought to be mediated in part by melanopsin-expressing retinal ganglion cells which are more sensitive to blue light than violet or green light. The contribution of the melanopsin system and the brain mechanisms involved in the establishment of such responses to light remain to be established. Methodology/Principal Findings. We exposed 15 participants to short duration (50 s) monochromatic violet (430 nm), blue (473 nm), and green (527 nm) light exposures of equal photon flux (10 13 ph/cm 2 /s) while they were performing a working memory task in fMRI. At light onset, blue light, as compared to green light, increased activity in the left hippocampus, left thalamus, and right amygdala. During the task, blue light, as compared to violet light, increased activity in the left middle frontal gyrus, left thalamus and a bilateral area of the brainstem consistent with activation of the locus coeruleus. Conclusion/Significance. These results support a prominent contribution of melanopsin-expressing retinal ganglion cells to brain responses to light within the very first seconds of an exposure. The results also demonstrate the implication of the brainstem in mediating these responses in humans and speak for a broad involvement of light in the regulation of brain function. Citation: Vandewalle G, Schmidt C, Albouy G, Sterpenich V, Darsaud A, et al (2007) Brain Responses to Violet, Blue, and Green Monochromatic Light Exposures in Humans: Prominent Role of Blue Light and the Brainstem. PLoS ONE 2(11): e1247.
PLoS Biology, 2007
Emotional events are usually better remembered than neutral ones. This effect is mediated in part... more Emotional events are usually better remembered than neutral ones. This effect is mediated in part by a modulation of the hippocampus by the amygdala. Sleep plays a role in the consolidation of declarative memory. We examined the impact of sleep and lack of sleep on the consolidation of emotional (negative and positive) memories at the macroscopic systems level. Using functional MRI (fMRI), we compared the neural correlates of successful recollection by humans of emotional and neutral stimuli, 72 h after encoding, with or without total sleep deprivation during the first post-encoding night. In contrast to recollection of neutral and positive stimuli, which was deteriorated by sleep deprivation, similar recollection levels were achieved for negative stimuli in both groups. Successful recollection of emotional stimuli elicited larger responses in the hippocampus and various cortical areas, including the medial prefrontal cortex, in the sleep group than in the sleep deprived group. This effect was consistent across subjects for negative items but depended linearly on individual memory performance for positive items. In addition, the hippocampus and medial prefrontal cortex were functionally more connected during recollection of either negative or positive than neutral items, and more so in sleeping than in sleep-deprived subjects. In the sleep-deprived group, recollection of negative items elicited larger responses in the amygdala and an occipital area than in the sleep group. In contrast, no such difference in brain responses between groups was associated with recollection of positive stimuli. The results suggest that the emotional significance of memories influences their sleep-dependent systems-level consolidation. The recruitment of hippocampo-neocortical networks during recollection is enhanced after sleep and is hindered by sleep deprivation. After sleep deprivation, recollection of negative, potentially dangerous, memories recruits an alternate amygdalo-cortical network, which would keep track of emotional information despite sleep deprivation. Citation: Sterpenich V, Albouy G, Boly M, Vandewalle G, Darsaud A, et al. (2007) Sleep-related hippocampo-cortical interplay during emotional memory recollection. PLoS Biol 5(11): e282.
NeuroImage, 2009
313 SA-AM Brain activity associated with a lexical decision task in Spanish speakers, 329 SA-AM C... more 313 SA-AM Brain activity associated with a lexical decision task in Spanish speakers, 329 SA-AM Connectivity in the mesolimbic reward system is modulated by personality and reward bias, A McNamara, A Sterr, University of Surrey, Guildford, United Kingdom 331 SA-AM Emotional charge of encoding context modulates recognition memory for neutral visual stimuli, M Tapia, S López-Martín,
Journal of Neurology, Neurosurgery & Psychiatry, 2008
Journal of Biological Rhythms, 2012
Many nonvisual functions are regulated by light through a photoreceptive system involving melanop... more Many nonvisual functions are regulated by light through a photoreceptive system involving melanopsin-expressing retinal ganglion cells that are maximally sensitive to blue light. Several studies have suggested that the ability of light to modulate circadian entrainment and to induce acute effects on melatonin secretion, subjective alertness, and gene expression decreases during aging, particularly for blue light. This could contribute to the documented changes in sleep and circadian regulatory processes with aging. However, age-related modification in the impact of light on steady-state pupil constriction, which regulates the amount of light reaching the retina, is not demonstrated. We measured pupil size in 16 young (22.8±4 years) and 14 older (61±4.4 years) healthy subjects during 45-second exposures to blue (480 nm) and green (550 nm) monochromatic lights at low (7×10(12) photons/cm2/s), medium (3×10(13) photons/cm2/s), and high (10(14) photons/cm2/s) irradiance levels. Results showed that young subjects had consistently larger pupils than older subjects for dark adaptation and during all light exposures. Steady-state pupil constriction was greater under blue than green light exposure in both age groups and increased with increasing irradiance. Surprisingly, when expressed in relation to baseline pupil size, no significant age-related differences were observed in pupil constriction. The observed reduction in pupil size in older individuals, both in darkness and during light exposure, may reduce retinal illumination and consequently affect nonvisual responses to light. The absence of a significant difference between age groups for relative steady-state pupil constriction suggests that other factors such as tonic, sympathetic control of pupil dilation, rather than light sensitivity per se, account for the observed age difference in pupil size regulation. Compared to other nonvisual functions, the light sensitivity of steady-state pupil constriction appears to remain relatively intact and is not profoundly altered by age.
Journal of sleep research, 2007
Heart rate (HR) and heart rate variability (HRV) undergo marked fluctuations over the 24-h day. A... more Heart rate (HR) and heart rate variability (HRV) undergo marked fluctuations over the 24-h day. Although controversial, this 24-h rhythm is thought to be driven by the sleep-wake/rest-activity cycle as well as by endogenous circadian rhythmicity. We quantified the endogenous circadian rhythm of HR and HRV and investigated whether this rhythm can be shifted by repeated melatonin administration while exposed to an altered photoperiod. Eight healthy males (age 24.4 +/- 4.4 years) participated in a double-blind cross-over design study. In both conditions, volunteers were scheduled to 16 h-8 h rest : wake and dark : light cycles for nine consecutive days preceded and followed by 29-h constant routines (CR) for assessment of endogenous circadian rhythmicity. Melatonin (1.5 mg) or placebo was administered at the beginning of the extended sleep opportunities. For all polysomnographically verified wakefulness periods of the CR, we calculated the high- (HF) and low- (LF) frequency bands of th...
Frontiers in Neurology, 2012
The present study aimed at identifying the neurophysiological responses associated with auditory ... more The present study aimed at identifying the neurophysiological responses associated with auditory stimulation during non-rapid eye movement (NREM) sleep using simultaneous electroencephalography (EEG)/functional magnetic resonance imaging (fMRI) recordings. It was reported earlier that auditory stimuli produce bilateral activation in auditory cortex, thalamus, and caudate during both wakefulness and NREM sleep. However, due to the spontaneous membrane potential fluctuations cortical responses may be highly variable during NREM. Here we now examine the modulation of cerebral responses to tones depending on the presence or absence of sleep spindles and the phase of the slow oscillation. Thirteen healthy young subjects were scanned successfully during stage 2-4 NREM sleep in the first half of the night in a 3T scanner. Subjects were not sleep-deprived and sounds were post hoc classified according to (i) the presence of sleep spindles or (ii) the phase of the slow oscillation during (±300 ms) tone delivery. These detected sounds were then entered as regressors of interest in fMRI analyses. Interestingly wake-like responsesalthough somewhat altered in size and location -persisted during NREM sleep, except during present spindles (as previously published in and the negative going phase of the slow oscillation during which responses became less consistent or even absent. While the phase of the slow oscillation did not alter brain responses in primary sensory cortex, it did modulate responses at higher cortical levels. In addition EEG analyses show a distinct N550 response to tones during the presence of light sleep spindles and suggest that in deep NREM sleep the brain is more responsive during the positive going slope of the slow oscillation. The presence of short temporal windows during which the brain is open to external stimuli is consistent with the fact that even during deep sleep meaningful events can be detected. Altogether, our results emphasize the notion that spontaneous fluctuations of brain activity profoundly modify brain responses to external information across all behavioral states, including deep NREM sleep.
European Neuropsychopharmacology, 2006
Current Biology, 2004
1 Centre de Recherches du Cyclotron (B30) Université de Liè ge Although alerting effects of light... more 1 Centre de Recherches du Cyclotron (B30) Université de Liè ge Although alerting effects of light have been observed Sart Tilman during the biological day, they have been most exten-4000 Liè ge sively documented during the biological night [8, 9]. Belgium We therefore assessed the regional cerebral blood flow 2 Neurosciences et Systè mes Sensoriels (rCBF) by Positron Emission Tomography (PET) 12 times Unité Mixte de Recherche 5020 at 20 min intervals between 12:30 and 4:30 am in a group Université Claude Bernard Lyon 1 -CNRS of 13 right-handed [10] male subjects. During the scans, 69007 Lyon the attention set was kept constant by asking the sub-France jects to count deviant sounds in an auditory oddball 3 Surrey Sleep Research Centre paradigm [11] and fixate a red diode. The latter light University of Surrey stimulus is unlikely to elicit any non-image-forming (NIF) Guildford GU2 7XP response because the red light does not fall within the United Kingdom known NIF action spectra and the illuminance level gen-4 Dé partement de Neurologie (B35) erated by the source is well below the threshold for any Centre Hospitalier Universitaire known NIF response. All scans were otherwise obtained Sart Tilman in darkness. During the scans, the electroencephalo-4000 Liè ge gram (EEG) was recorded (at Fz, Cz, and Pz) continu-Belgium ously to compute the P300 wave, a positive potential 5 Dé partement de Physique (B5) occurring when the expected but unpredictable deviant Université de Liè ge auditory stimulus is detected [11]. A block of four scans Sart Tilman was repeated three times during the night. In each block, 4000 Liè ge scans differed only by the duration (respectively 0.5, 17, Belgium 16.5, and 0 min, see ) of immediately preceding exposure to bright broadband polychromatic white light, which activates all photoreceptors known to be involved Summary in NIF responses. Our aim was to demonstrate the presence of NIF responses in humans. The identification The brain processes light information to visually repreof the photoreceptors involved in these responses will sent the environment but also to detect changes in require further experiments using monochromatic light. ambient light level. The latter information induces non-
Current Biology, 2006
In humans, light enhances both alertness and performance during nighttime and daytime and influen... more In humans, light enhances both alertness and performance during nighttime and daytime and influences regional brain function . These effects do not correspond to classical visual responses but involve a non-image forming (NIF) system, which elicits greater endocrine, physiological, neurophysiological, and behavioral responses to shorter light wavelengths than to wavelengths geared toward the visual system . During daytime, the neural changes induced by light exposure, and their time courses, are largely unknown. With functional magnetic resonance imaging (fMRI), we characterized the neural correlates of the alerting effect of daytime light by assessing the responses to an auditory oddball task , before and after a short exposure to a bright white light. Light-induced improvement in subjective alertness was linearly related to responses in the posterior thalamus. In addition, light enhanced responses in a set of cortical areas supporting attentional oddball effects, and it prevented decreases of activity otherwise observed during continuous darkness. Responses to light were remarkably dynamic. They declined within minutes after the end of the light stimulus, following various region-specific time courses. These findings suggest that light can modulate activity of subcortical structures involved in alertness, thereby dynamically promoting cortical activity in networks involved in ongoing nonvisual cognitive processes.
Behavioural Brain Research, 2011
This study aimed to determine the distinct contribution of slow (11-13 Hz) and fast (13-15 Hz) sp... more This study aimed to determine the distinct contribution of slow (11-13 Hz) and fast (13-15 Hz) spindles in the consolidation process of a motor sequence learning task (MSL). Young subjects (n = 12) were trained on both a finger MSL task and a control (CTRL) condition, which were administered one week apart in a counterbalanced order. Subjects were asked to practice the MSL or CTRL task in the evening (approximately 9:00 p.m.) and their performance was retested on the same task 12h later (approximately 9:00 a.m.). Polysomnographic (PSG) recordings were performed during the night following training on either task, and an automatic algorithm was used to detect fast and slow spindles and to quantify their characteristics (i.e., density, amplitude, and duration). Statistical analyses revealed higher fast (but not slow) spindle density after training on the MSL than after practice of the CTRL task. The increase in fast spindle density on the MSL task correlated positively with overnight performance gains on the MSL task and with difference in performance gain between the MSL and CTRL tasks. Together, these results suggest that fast sleep spindles help activate the cerebral network involved in overnight MSL consolidation, while slow spindles do not appear to play a role in this mnemonic process.
Abstract Light therapy can be an effective treatment for mood disorders, suggesting that light is... more Abstract Light therapy can be an effective treatment for mood disorders, suggesting that light is able to affect mood state in the long term. As a first step to understand this effect, we hypothesized that light might also acutely influence emotion and tested whether short exposures to light modulate emotional brain responses. During functional magnetic resonance imaging, 17 healthy volunteers listened to emotional and neutral vocal stimuli while being exposed to alternating 40-s periods of blue or green ambient light.
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Papers by Gilles Vandewalle