Biomedical subjects

Luigi De Gennaro

Publications and source records attributed to Luigi De Gennaro.

At least 19 recordsLinked to original sources

PubMed2006

Directional information flows between brain hemispheres during presleep wake and early sleep stages.

Neuroscientists' efforts to better understand the underlying processes of human consciousness are growing in a variety of multidisciplinary approaches. Relevant within these are the studies aimed at exploring the physiological substratum of the propagation and reduction of cerebral-namely, corticocortical-communication flows. However, the preferential direction of the information flow between brain hemispheres is as yet largely unknown. It is the aim of the present research to study the communication flows between brain hemispheres, their directionality, and their regional variations across wake-sleep states. A second aim is to investigate the possibility of an association between different brain rhythms and different preferred directions of the information flow. Scalp electroencephalograms (EEGs) were recorded in 10 normal volunteers from wakefulness to early sleep stages (viz., resting wakefulness, sleep stages 2 and 4, and rapid eye movement [REM] of the first sleep cycle). EEG rhythms of interest were delta (1-4 Hz), theta (5-7 Hz), alpha (8-11 Hz), sigma (12-15 Hz), and beta (16-30 Hz). The direction of the interhemispheric information flow was evaluated by computing directed transformation function from these EEG rhythms. Interhemispheric directional flows varied as a function of the state of consciousness (wake and early sleep stages) and in relation to different cerebral areas. Across wake to sleep states, we found that delta and beta rhythms convey interhemispheric signals with opposite directions: preferred right to left hemisphere direction for delta and left to right for beta rhythms. A log correlation confirmed that the trend of low to high EEG frequencies-traditionally associated with an increasing state of vigilance-was significantly related to the direction of the communication flow from the left to right hemisphere. This evidence might open the way for a variety of research lines on different psychophysiological and pathological conditions.

Adult↗

PubMed2006

Modulation of corticospinal excitability by paired associative stimulation: reproducibility of effects and intraindividual reliability.

OBJECTIVE: Electrical stimulation of the median nerve followed by a magnetic pulse on the primary motor cortex (M1) is effective to cause an increase in the amplitude of motor evoked potential (MEP) registered in the target muscle with the interstimulus interval (ISI) at 25ms (paired associative stimulation, PAS). The aim of this study is to evaluate the reproducibility of PAS with ISI 25 (PAS25), assessed in two separate sessions. Intraindividual reliability of TMS measures was also evaluated. METHODS: Motor threshold of abductor pollicis brevis (APB), assessed at rest, and MEP amplitude of APB and abductor digiti minimi (ADM) were assessed before and after PAS25 in 18 healthy volunteers (nine males and nine females). RESULTS: Data showed a significant increase of MEP amplitude in the target muscle (APB) after PAS25 and a reproducibility of group effect in the two sessions, as assessed by ANOVA, but a lack of intraindividual reliability, as assessed by intraclass correlation coefficients (ICC). CONCLUSIONS: The results underline the reproducibility of mean effects and the need to be careful when comparing the same subject on different days. SIGNIFICANCE: Electrical stimulation of the median nerve followed by a magnetic pulse delivered on M1 after 25ms causes a reproducible increase in MEP amplitude, without showing an acceptable intraindividual reliability.

Abducens Nerve↗

PubMed2006

The role of sleep in the consolidation of route learning in humans: a behavioural study.

Considerable evidence support the role of sleep in learning and memory processes. In rodents, the relationships between sleep and memory consolidation have been extensively investigated by taking into account mainly spatial learning. On the contrary, in humans the relationship between sleep and spatial memory consolidation has so far been scarcely taken into account. Here, we investigated the importance of sleep in the consolidation of the spatial memory traces of a new route learned in a real-life unfamiliar environment. Fifty-one subjects followed a defined route in a neighbourhood they had never been to before. Then, they were tested in the laboratory in a sequence-recognition test requiring them to evaluate whether or not sequences of three views, taken along the route, represented a correct sequential order as seen while walking along the route. Participants were then assigned to one of three groups: the sleep group was retested after one night's sleep, the sleep-deprived group was retested after a night of sleep deprivation, and the day-control group was retested the same day after 8h of wakefulness. At retest, performance speed increased in all groups, whereas the accuracy in the sequence-recognition task was improved only in the sleep group: neither sleep deprivation nor the simple passage of time gave way to any performance improvement. These preliminary findings shed more light on the role of sleep in spatial memory consolidation by extending to humans the considerable evidence found in animals.

Adult↗

PubMed2006

Sleep loss, learning capacity and academic performance.

At a time when several studies have highlighted the relationship between sleep, learning and memory processes, an in-depth analysis of the effects of sleep deprivation on student learning ability and academic performance would appear to be essential. Most studies have been naturalistic correlative investigations, where sleep schedules were correlated with school and academic achievement. Nonetheless, some authors were able to actively manipulate sleep in order to observe neurocognitive and behavioral consequences, such as learning, memory capacity and school performance. The findings strongly suggest that: (a) students of different education levels (from school to university) are chronically sleep deprived or suffer from poor sleep quality and consequent daytime sleepiness; (b) sleep quality and quantity are closely related to student learning capacity and academic performance; (c) sleep loss is frequently associated with poor declarative and procedural learning in students; (d) studies in which sleep was actively restricted or optimized showed, respectively, a worsening and an improvement in neurocognitive and academic performance. These results may been related to the specific involvement of the prefrontal cortex (PFC) in vulnerability to sleep loss. Most methodological limitations are discussed and some future research goals are suggested.

Achievement↗

PubMed2006

Mobile phone emissions and human brain excitability.

OBJECTIVE: To test-via Transcranial Magnetic Stimulation (TMS)-the excitability of each brain hemisphere after 'real' or 'sham' exposure to the electromagnetic field (EMF) generated by a mobile phone operating in the Global System for Mobile Communication (GSM). METHODS: Fifteen male volunteers attended two experimental sessions, one week apart, in a cross-over, double-blind paradigm. In one session the signal was turned ON (EMF-on, real exposure), in the other it was turned OFF (EMF-off, sham exposure), for 45 minutes. Motor Evoked Potentials (MEPs) were recorded using a paired-pulse paradigm (testing intracortical excitability with 1 to 17 ms interstimulus intervals), both before and at different times after exposure to the EMF. Short Intracortical Inhibition (SICI) and Facilitation (ICF) curves were evaluated both on the exposed and non-exposed hemispheres. Tympanic temperature was collected during each session. RESULTS: The intracortical excitability curve becomes significantly modified during real exposure, with SICI being reduced and ICF enhanced in the acutely exposed brain hemisphere as compared to the contralateral, non-exposed hemisphere or to sham exposure. Tympanic temperature showed no significant main effect or interactions. INTERPRETATION: These results demonstrate that GSM-EMFs modify brain excitability. Possible implications and applications are discussed.

Adult↗

PubMed2005

The electroencephalographic substratum of the awakening.

The aim of the present study was to characterize the regional electroencephalographic substratum of the awakening process by means of a Hz-by-Hz EEG spectral power analysis. For this purpose, we recorded a group of 25 female subjects who slept for at least two consecutive nights in the laboratory. The post-sleep waking EEG was compared to the one recorded during the presleep wakefulness from four midline derivations (Fz-A1, Cz-A1, Pz-A1, Oz-A1). Results indicated that the first 10 min after awakening are characterized by an increase of EEG power in the low-frequency range (1-9 Hz) compared to the corresponding presleep waking period, and by a significant decrease of EEG power in the beta range (18-24 Hz). As regards topographic differences, the increase of EEG power upon awakening in the delta-theta range showed a parieto-occipital prevalence. Moreover, the occipital derivation showed a larger decrease of power in the beta range as compared to the other derivations. In conclusion, the EEG substratum of the sleep offset period is characterized by a pattern of increased EEG power in the delta-theta and low-alpha bands, and of decreased power in the beta range. This pattern could be considered as the spectral EEG signature of the sleep inertia phenomenon. The state of post-sleep EEG hypo-arousal does not subside in the first 10-min period after awakening considered in the present analysis. Finally, according to our results, the more posterior scalp locations show stronger EEG signs of sleep inertia, and could be the last ones to properly wake up.

Adult↗

PubMed2005

Can an inert sleeping pill affect sleep? Effects on polysomnographic, behavioral and subjective measures.

RATIONALE: Since two recent meta-analyses on sleep changes associated with placebo in clinical trials suggested a beneficial effect of placebo treatments, pointing to a dissociation between subjective and objective measures of sleep, the current experiment was directly aimed to assess the effects of an inert compound, administered with the suggestion that it was a hypnotic substance in subjects with mild sleep complaints. OBJECTIVES: The aim of this study was to compare subjective, behavioral, polysomnographic (PSG), and quantitative electroencephalographic (EEG) changes during a night preceded or not by the intake of two 50-mg lactose capsules. METHODS: Ten female students, selected by the Pittsburgh Sleep Quality Index, slept for three consecutive nights in a sleep laboratory, with the experimental (EXP) night defined by the administration of two 50-mg lactose pills. Self-ratings of sleep quality and performance were assessed upon morning awakening of baseline (BSL) and EXP nights. RESULTS: The EXP nights were self-rated as more restful and characterized by a decreased number of nocturnal awakenings than the BSL nights. PSG measures showed that wakefulness after sleep onset significantly decreased during the EXP night as compared to the BSL night. The EXP nights also showed an increase of 0.5-4.0 Hz power during nonrapid eye movement sleep and a decrease of EEG activity in the beta frequency range during rapid eye movement sleep only at central brain sites. A specific improvement of behavioral measures was also found upon morning awakening after the EXP night compared to the BSL night. CONCLUSIONS: The administration of an inert pill improves both the subjective and objective quality of sleep. The reduced sleep fragmentation and the effects on some quantitative EEG markers of sleep homeostasis suggest that the experimental manipulation induced coherent changes in the subsequent sleep, resembling an enhancement of sleep pressure. The regional differences of EEG activity suggest the involvement of a specific physiological mechanism distinct from that of effective treatments.

Adult↗

PubMed2005

An electroencephalographic fingerprint of human sleep.

Homeostatic and circadian processes are basic mechanisms of human sleep which challenge the common knowledge of large individual variations in sleep need or differences in circadian types. However, since sleep research has mostly focused on group measures, an approach which emphasizes the similarities between subjects, the biological foundations of the individual differences in normal sleep are still poorly understood. In the present work, we assessed individual differences in a range of EEG frequencies including sigma activity during non-REM sleep (8.0-15.5 Hz range) in a group of 10 subjects who had participated in a slow-wave sleep (SWS) deprivation study. We showed that, like a "fingerprint", a particular topographic distribution of the electroencephalogram (EEG) power along the antero-posterior cortical axis distinguishes each individual during non-REM sleep. This individual EEG-trait is substantially invariant across six consecutive nights characterized by large experimentally induced changes of sleep architecture. One possible hypothesis is that these EEG invariances can be related to individual differences in genetically determined functional brain anatomy, rather than to sleep-dependent mechanisms.

Adult↗

PubMed2005

Antero-posterior functional coupling at sleep onset: changes as a function of increased sleep pressure.

The use of the directed transfer function (DTF), an advanced computational analysis of electroencephalogaphic (EEG) data, which provides an estimation of the direction of the information flow underlying cortico-cortical functional coupling, has shown that the presleep period is characterized by posterior-to-anterior functional cortical coupling, while at sleep onset there is an inversion of that direction. This finding supported the idea that anterior cortical areas first synchronize sleep EEG activity. The aim of the present study was to assess the changes of functional coupling between anterior and posterior midline cortical areas during the sleep onset process when sleep pressure is heightened by a selective slow-wave sleep (SWS) deprivation. The hypothesis was that the anterior-to-posterior direction of the cortical functional coupling at sleep onset is enhanced by SWS deprivation. Ten normal right-handed male students slept for six consecutive nights in the laboratory (1: adaptation, 2: baseline, 3: baseline with awakenings, 4 and 5: SWS deprivations, 6: recovery), with standard polysomnographic recordings. The DTF was computed on data recorded during nights two and six from anterior (Fz(A1)) and posterior (Pz(A1), Oz(A1)) derivations. Results showed that, during the recovery night, the anterior-to-posterior direction of functional cortical coupling is already present in the presleep period, indicating that SWS deprivation advances the shift to an anterior-to-posterior directionality of functional cortical coupling, possibly as a consequence of heightened sleep pressure. These findings support the notion that a spread of synchronizing signals from associative prefrontal to posterior areas play a role in the wake-sleep transition.

Adult↗

PubMed2005

Oculomotor changes are associated to daytime sleepiness in the multiple sleep latency test.

Sleep onsets in the diurnal multiple sleep latency test (MSLT), following different sleep lengths of the preceding night sleep (8, 5, 4, 3, 2, 1 h) and following the corresponding recovery nights, were considered for a study on changes of oculomotor activity during sleep onset. The study aimed to assess the individual time course in spontaneous blinks (SBs) and slow eye movements (SEMs) during the sleep onset period and also the relationship with sleep latencies in the MSLT. Group analyses compared oculomotor changes between conditions characterized by a different level of daytime sleepiness. The results show a clear inverse relation between the two oculomotor measures, with a linear SB decrease and quadratic SEM increase across the wake-sleep transition. A 150 s sample of SB and SEM activity at the start of MSLT trials correlates with individual subsequent sleep latency. Finally, mean changes in daytime sleepiness as measured by the MSLT are paralleled by coherent oculomotor changes, with a significant linear decrease of SB as sleepiness increases as a consequence of previous sleep reduction. Both individual and group results show that endogenous blinking is associated with moderate changes in daytime sleepiness.

Adult↗

PubMed2004

The relationship between alexithymia, depression, and sleep complaints.

The study assessed in normal subjects the hypothesis of a specific association between alexithymia and poor sleep quality, taking into consideration the contribution of depression. Five hundred fifty-four university students (480 F and 74 M) filled out the Italian version of the 20-item Toronto Alexithymia Scale (TAS-20), the Center for Epidemiologic Studies Depression Scale (CES-D), and the Pittsburgh Sleep Quality Index (PSQI). TAS-20 scores were significantly correlated with many measures of self-rated poor sleep quality and also strongly correlated with depression scores. Any association between alexithymia and sleep complaints disappears when the contribution of depression is partialled out by multiple regressions, and only the well-known relationship between depression and impairment of sleep quality is confirmed.

Adult↗

PubMed2004

Reduction of transcallosal inhibition upon awakening from REM sleep in humans as assessed by transcranial magnetic stimulation.

STUDY OBJECTIVES: The aim of the study is to assess, in humans, transcallosal inhibition upon awakening from rapid eye movement (REM) and non-REM sleep, by paired-pulse transcranial magnetic stimulation (TMS). DESIGN: During the daytime, a baseline session of motor evoked potentials (MEPs) was recorded. During the nighttime, the TMS sessions were administered just before sleep onset and upon awakenings from REM and stage 2 sleep, both in the early and final part of night. SETTING: The sleep research laboratory at the University of Rome "La Sapienza." PARTICIPANTS: Ten right-handed subjects participated in the experiment for 4 consecutive sleep-recording nights. INTERVENTIONS: N/A. MEASUREMENTS AND RESULTS: During the daytime, a robust transcallosal inhibition was found; the MEP amplitude reduction ranged from 35% to 40%. During the nighttime, a decrease of transcallosal inhibition from right-to-left motor cortex, as compared to that from left-to-right motor cortex, was observed. The direct assessment of MEP changes, as a function of sleep stage and of the time of night, pointed to a drop of transcallosal inhibition after awakening from REM sleep. Therefore, the inhibitory activity of transcallosal fibers observed after non-REM awakening almost disappeared after REM sleep awakenings. CONCLUSIONS: The drastic drop of transcallosal inhibition after awakenings from REM sleep represents the first evidence in humans of a change of interhemispheric connectivity mediated by the corpus callosum during this sleep stage and may open new avenues for a better understanding of some aspects of sleep mechanisms (ie, dreaming function and dream mentation).

Adult↗

PubMed2004

Paradoxes of the first-night effect: a quantitative analysis of antero-posterior EEG topography.

OBJECTIVE: The first-night effect (FNE) is a common issue in sleep research. Being considered fragmented and poorly efficient, the adaptation night is discarded for data analysis. The present study aims to provide a quantitative and topographical EEG analysis of this phenomenon. METHODS: Eight healthy subjects slept for two consecutive nights (adaptation (AD) and baseline (BSL)), and their polysomnography was visually scored and then submitted to spectral power analysis. RESULTS: The results showed a decreased quality and quantity of first-night sleep as indicated by more stage 1 and intrasleep wake, paralleled by a reduced sleep efficiency and a longer sleep onset latency. On the other hand, EEG quantitative data showed a more complex and apparently paradoxical picture. An increase in delta power was observed, particularly over the central areas during the first night, paralleled by an increased power in beta bin frequencies solely at posterior scalp locations. CONCLUSIONS: These results have been interpreted as caused by, respectively, a reduced total sleep time during the adaptation night and a cortical hyperactivity, typical of psychophysiological insomnia. The present results confirm the need to exclude the laboratory sleep adaptation night from data analysis since it is not a reliable index of sleep on subsequent nights as regards both visual scoring and quantitative EEG analysis. Finally, regional differences between REM and NREM sleep have been confirmed. SIGNIFICANCE: This is the first attempt to evaluate the FNE with a quantitative approach to the antero-posterior EEG topography, providing both a Hz-by-Hz and a classical EEG band-based analysis.

Adaptation, Physiological↗

PubMed2004

Handedness is mainly associated with an asymmetry of corticospinal excitability and not of transcallosal inhibition.

OBJECTIVE: The study aims to compare transcallosal inhibition (TI), as assessed by the paired-pulse transcranial magnetic stimulation (TMS) technique, in a sample of right-handed subjects (RH) and left-handed subjects (LH). Motor thresholds (MTs) and motor evoked potential (MEP) amplitudes were also measured in the two groups, as an index of corticospinal activity. METHODS: Thirty-two normal subjects (16 RH and 16 LH) were recorded with a paired-pulse TMS paradigm (intensity of both pulses=120% of MT). The inter-stimulus intervals (ISIs) were 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20 ms for both motor cortices, and MEP responses were recorded from the abductor digiti minimi muscles. RESULTS: Both groups showed a clear TI centred around the 12 ms ISI, but no difference was found as a function of handedness or of hemisphere. On the other hand, the two groups differed in terms of corticospinal activity, since the hand motor dominant hemisphere had lower MTs than the non-dominant one in LH, and larger MEP amplitudes for the right hand were found in RH. CONCLUSIONS: Results point to a functional asymmetry of the motor cortex on the hand-dominant versus the non-dominant hemisphere, while handedness does not seem associated with functional differences in callosal inhibition, as measured by the inter-hemispheric paired-pulse TMS technique.

Adult↗

PubMed2004

Callosal effects of transcranial magnetic stimulation (TMS): the influence of gender and stimulus parameters.

Transcranial magnetic stimulation (TMS) of the motor cortex of one hemisphere (conditioning stimulus, CS) inhibits EMG responses evoked in distal hand muscles by a magnetic stimulus given at appropriate interval later over the opposite hemisphere (test stimulus, TS). The common interpretation attributes this effect to an inhibition produced at cortical level via a transcallosal route. The variability of cortical excitability as measured by the interhemispheric paired-pulse (PP) technique has been assessed in healthy subjects in order to compare sub- and supra-threshold intensity of CS (80% versus 120% of individual motor threshold, MT). Within- and between-subject variability relating, respectively, to interhemispheric and gender differences were also assessed. Results point to an efficacy of a magnetic CS on one hemisphere in inhibiting EMG responses of the abductor digiti minimi (ADM) stimulated by a TS delivered over the opposite hemisphere in a range of intervals centered at 12ms. These reductions were produced by the 120% suprathreshold CS, while the 80% subthreshold CS did not affect EMG responses. Females showed a higher transcallosal inhibition than males, suggesting gender differences in interhemispheric connectivity that concern the anterior half of the trunk of the corpus callosum.

Adult↗

PubMed2004

Corticospinal excitability and sleep: a motor threshold assessment by transcranial magnetic stimulation after awakenings from REM and NREM sleep.

Transcranial magnetic stimulation (TMS) is a recently established technique in the neurosciences that allows the non-invasive assessment, among other parameters, of the excitability of motor cortex. Up to now, its application to sleep research has been very scarce and because of technical problems it provided contrasting results. In fact delivering one single suprathreshold magnetic stimulus easily awakes subjects, or lightens their sleep. For this reason, in the present study we assessed motor thresholds (MTs) upon rapid eye movement (REM) and non-rapid eye movement (NREM) sleep awakenings, both in the first and in the last part of the night. Taking into account that a full re-establishment of wake regional brain activity patterns upon awakening from sleep needs up to 20-30 min, it is possible to make inferences about the neurophysiological characteristics of the different sleep stages by analyzing the variables of interest immediately after provoked awakenings. Ten female volunteers slept in the lab for four consecutive nights. During the first night the MTs were collected, following a standardized procedure: 5 min before lights off, upon stage 2 awakening (second NREM period), upon REM sleep awakening (second REM period), upon the final morning awakening (always from stage 2). Results showed that MTs increased linearly from presleep wakefulness to REM sleep awakenings, and from the latter to stage 2 awakenings. There was also a time-of-night effect on MTs upon awakening from stage 2, indicating that MTs decreased from the first to the second part of the night. The increase in corticospinal excitability across the night, which parallels the fulfillment of sleep need, is consistent with the linear decrease of auditory arousal thresholds during the night. The maximal reduction of corticospinal excitability during early NREM sleep can be related to the hyperpolarization of thalamocortical neurons, and is in line with the decreased metabolic activity of motor cortices during this sleep stage. On the contrary, the increase of MTs upon REM sleep awakenings should reflect peripheral factors. We conclude that our findings legitimate the introduction of the TMS technique as a new proper tool in sleep research.

Adult↗

PubMed2004

Intracortical inhibition and facilitation upon awakening from different sleep stages: a transcranial magnetic stimulation study.

Intracortical facilitation and inhibition, as assessed by the paired-pulse transcranial magnetic stimulation technique with a subthreshold conditioning pulse followed by a suprathreshold test pulse, was studied upon awakening from REM and slow-wave sleep (SWS). Ten normal subjects were studied for four consecutive nights. Intracortical facilitation and inhibition were assessed upon awakening from SWS and REM sleep, and during a presleep baseline. Independently of sleep stage at awakening, intracortical inhibition was found at 1-3-ms interstimulus intervals and facilitation at 7-15-ms interstimulus intervals. Motor thresholds were higher in SWS awakenings, with no differences between REM awakenings and wakefulness, while motor evoked potential amplitude to unconditioned stimuli decreased upon REM awakening as compared to the other conditions. REM sleep awakenings showed a significant increase of intracortical facilitation at 10 and 15 ms, while intracortical inhibition was not affected by sleep stage at awakening. While the dissociation between motor thresholds and motor evoked potential amplitudes could be explained by the different excitability of the corticospinal system during SWS and REM sleep, the heightened cortical facilitation upon awakening from REM sleep points to a cortical motor activation during this stage.

Adult↗

PubMed2004

Changes in fronto-posterior functional coupling at sleep onset in humans.

The aim of this study was to assess the functional coupling between anterior and posterior areas as induced by the sleep onset process. The functional coupling was indexed by an analysis of spectral coherence and directed transfer function (DTF) from electroencephalographic (EEG) data. As it has been reported that more anterior areas first synchronize sleep EEG activity, we hypothesized a fronto-posterior direction of the cortical functional coupling during the sleep onset process. Ten normal right-handed male students slept for two-nights (one adaptation, one baseline) in the laboratory, with standard polysomnographic recordings. Spectral coherence and DTF were computed on data recorded by anterior (FzA1) and posterior (PzA1, OzA1) derivations. EEG coherence at the delta/theta band was higher during the presleep period than the sleep onset period, while EEG coherence at the alpha band was higher during the sleep onset period than the presleep period. The DTF findings indicated a prevalence of the occipital-to-frontal information flow at delta/theta and alpha bands during the presleep period and a prevalence of the frontal-to-parieto-occipital information flow at all bands during the sleep onset period. The coherent pattern of changes in EEG coherence and in DTF values at sleep onset lends further support to the notion of sleep as a local process, showing that the sleep onset process is subserved by the functional coordination of a cortical fronto-posterior network. In this network, prefrontal areas may play a leading role in the propagation of synchronizing signals conveyed at frequencies spanning delta to beta rhythms.

Adult↗