Adaptating test timing to the sleep-wake schedule: effects on diurnal neurobehavioral performance changes in young evening and older morning chronotypes

in Chronobiology International (2012), 29(4), 482-490

The synchrony effect refers to the beneficial impact of temporal matching between the timing of cognitive task administration and preferred time of day for diurnal activity. Aging is often associated with ... [more ▼]

The synchrony effect refers to the beneficial impact of temporal matching between the timing of cognitive task administration and preferred time of day for diurnal activity. Aging is often associated with an advance in sleep-wake timing and concomitant optimal performance levels in the morning. In contrast, young adults often perform better in the evening hours. So far, the synchrony effect has been tested at fixed clock times, neglecting the individual’s sleep-wake schedule and thus introducing confounds such as differences in accumulated sleep pressure or circadian phase that may exacerbate synchrony effects. To probe this hypothesis, we tested older morning and young evening chronotypes with a psychomotor vigilance and a Stroop paradigm once at fixed morning and evening hours and once adapting testing time to their preferred sleep-wake schedule in a within-subject design. We observe a persistence of synchrony effects for overall median reaction times during a psychomotor vigilance task even when testing time is adapted to the specific individual’s sleep-wake schedule. However, data analysis also indicates that time-of-day modulations are weakened under those conditions for incongruent trials on Stroop performance and the slowest reaction times on the psychomotor vigilance task. The latter result suggests that the classically observed synchrony effect may be partially mediated by a series of parameters, such as differences in socio-professional timing constraints, the amount of accumulated sleep need or circadian phase, all leading to differential arousal levels at testing. [less ▲]

Lateralized processing of false memories and pseudoneglect in aging.

in Cortex : A Journal Devoted to the Study of the Nervous System & Behavior (2012)

Aging is associated with higher propensity to false memories and decreased retrieval of previously studied items. When young adults perform on a lateralized version of the Deese-Roediger-McDermott (DRM ... [more ▼]

Aging is associated with higher propensity to false memories and decreased retrieval of previously studied items. When young adults perform on a lateralized version of the Deese-Roediger-McDermott (DRM) paradigm, the right cerebral hemisphere (RH) is more sensitive than the left (LH) to false memories, suggesting hemispheric imbalance in the cerebral mechanisms supporting semantic and episodic memory processes. Since cerebral asymmetries tend to be reduced with age, we surmised that behavioral asymmetries in the generation of false memories would be diminished with aging. To probe this hypothesis, a lateralized version of the DRM paradigm was administered to old (OA) and young (YA) healthy adults. During the encoding phase, lists of semantically associated words were memorized. During the retrieval session, targets (previously seen words), lures (never seen strongly semantically related words) and distracters (never seen, unrelated words) were briefly displayed either in the left or right visual fields, thus primarily stimulating the RH or LH, respectively. Participants had to decide whether the word was previously studied (Old/New), but also whether they had a strong episodic recollection (Remember) or a mere feeling of familiarity (Know) about Old words. In line with our predictions, false memories were globally higher in OA than YA, and vivid false recollections (i.e. Remember responses) were higher when lures were presented in the RH in YA, but not in OA. Additionally, we found significant correlations between YA participants’ familiarity scores and leftward attentional bias as previously evidenced using a visuospatial landmark task [Schmitz, R., and Peigneux, P. (2011). Age-related changes in visual pseudoneglect. Brain and Cognition, 76(3), 382-389], an effect not present in OA. This result is in line with the hypothesis of an interplay between attentional resources allocated to visuospatial and memory processes, suggesting a memory pseudoneglect phenomenon that would be altered with aging. [less ▲]

Faux souvenirs et traitement hémisphérique dans le vieillissement.

Poster (2010, September)

Response to Comment on “Homeostatic Sleep Pressure and Responses to Sustained Attention in the Suprachiasmatic Area”

in Science (2010)

Astafiev et al. question whether the blood oxygen level–dependent (BOLD) response that we reported in the brainstem was located in the locus coeruleus (LC). Using high-resolution T1-turbo spin echo images ... [more ▼]

Astafiev et al. question whether the blood oxygen level–dependent (BOLD) response that we reported in the brainstem was located in the locus coeruleus (LC). Using high-resolution T1-turbo spin echo images (T1-TSE) acquired in an independent group of subjects, we show that the reported task-related BOLD response in the brainstem is actually compatible with the anatomical location of the LC. [less ▲]

Working memory load modulates time-of-day and chronotype effects on task-related BOLD activity

in NeuroImage (2010), 51(Suppl. 1),

Neuroimaging in Sleep and Sleep Disorders

in Chokroverty, Sudhansu (Ed.) Sleep Disorders Medicine (2009)

Homeostatic sleep pressure and responses to sustained attention in the suprachiasmatic area.

in Science (2009), 324(5926), 516-9

Throughout the day, cognitive performance is under the combined influence of circadian processes and homeostatic sleep pressure. Some people perform best in the morning, whereas others are more alert in ... [more ▼]

Throughout the day, cognitive performance is under the combined influence of circadian processes and homeostatic sleep pressure. Some people perform best in the morning, whereas others are more alert in the evening. These chronotypes provide a unique way to study the effects of sleep-wake regulation on the cerebral mechanisms supporting cognition. Using functional magnetic resonance imaging in extreme chronotypes, we found that maintaining attention in the evening was associated with higher activity in evening than morning chronotypes in a region of the locus coeruleus and in a suprachiasmatic area (SCA) including the circadian master clock. Activity in the SCA decreased with increasing homeostatic sleep pressure. This result shows the direct influence of the homeostatic and circadian interaction on the neural activity underpinning human behavior. [less ▲]

Perception of pain in the minimally conscious state with PET activation: an observational study.

in Lancet Neurology (2008), 7(11), 1013-20

BACKGROUND: Patients in a minimally conscious state (MCS) show restricted self or environment awareness but are unable to communicate consistently and reliably. Therefore, better understanding of cerebral ... [more ▼]

BACKGROUND: Patients in a minimally conscious state (MCS) show restricted self or environment awareness but are unable to communicate consistently and reliably. Therefore, better understanding of cerebral noxious processing in these patients is of clinical, therapeutic, and ethical relevance. METHODS: We studied brain activation induced by bilateral electrical stimulation of the median nerve in five patients in MCS (aged 18-74 years) compared with 15 controls (19-64 years) and 15 patients (19-75 years) in a persistent vegetative state (PVS) with (15)O-radiolabelled water PET. By way of psychophysiological interaction analysis, we also investigated the functional connectivity of the primary somatosensory cortex (S1) in patients and controls. Patients in MCS were scanned 57 (SD 33) days after admission, and patients in PVS 36 (9) days after admission. Stimulation intensities were 8.6 (SD 6.7) mA in patients in MCS, 7.4 (5.9) mA in controls, and 14.2 (8.7) mA in patients in PVS. Significant results were thresholded at p values of less than 0.05 and corrected for multiple comparisons. FINDINGS: In patients in MCS and in controls, noxious stimulation activated the thalamus, S1, and the secondary somatosensory or insular, frontoparietal, and anterior cingulate cortices (known as the pain matrix). No area was less activated in the patients in MCS than in the controls. All areas of the cortical pain matrix showed greater activation in patients in MCS than in those in PVS. Finally, in contrast with patients in PVS, those in MCS had preserved functional connectivity between S1 and a widespread cortical network that includes the frontoparietal associative cortices. INTERPRETATION: Cerebral correlates of pain processing are found in a similar network in controls and patients in MCS but are much more widespread than in patients in PVS. These findings might be objective evidence of a potential pain perception capacity in patients in MCS, which supports the idea that these patients need analgesic treatment. [less ▲]

Partially Segregated Neural Networks for Spatial and Contextual Memory in Virtual Navigation

in Hippocampus (2008), 18(5), 503-518

Finding our way in a previously learned, ecologically valid environment concurrently involves spatial and contextual cognitive operations. The former process accesses a cognitive map representing the ... [more ▼]

Finding our way in a previously learned, ecologically valid environment concurrently involves spatial and contextual cognitive operations. The former process accesses a cognitive map representing the spatial interactions between all paths in the environment. The latter accesses stored associations between landmark objects and their milieu. Here, we aimed at dissociating their neural basis in the context of memory-based virtual navigation. To do so, subjects freely explored a virtual town for 1 h, then were scanned using fMRI while retrieving their way between two locations, under four navigation conditions designed to probe separately or jointly the spatial and contextual memory components. Besides prominent commonalities found in a large hippocampo-neocortical network classically involved in topographical navigation, results yield evidence for a partial dissociation between the brain areas supporting spatial and contextual components of memory-based navigation. Performance-related analyses indicate that hippocampal activity mostly supports the spatial component, whereas parahippocampal activity primarily supports the contextual component. Additionally, the recruitment of contextual memory during navigation was associated with higher frontal, posterior parietal and lateral temporal activity. These results provide evidence for a partial segregation of the neural substrates of two crucial memory components in human navigation, whose combined involvement eventually leads to efficient navigation behavior within a learned environment. (c) 2008 Wiley-Liss, Inc. [less ▲]

Chronotype-dependent performance modulation according to time of day : a functional neuroimaging approach

in NeuroImage (2008), 41(Suppl. 1),