Inter-hemispherical functional coupling of EEG rhythms during the perception of facial emotional expressions.

OBJECTIVE: Brain rhythms of both hemispheres are involved in the processing of emotional stimuli but their interdependence between the two hemispheres is poorly known. Here we tested the hypothesis that passive visual perception of facial emotional expressions is related to a coordination of the two hemispheres as revealed by the inter-hemispherical functional coupling of brain electroencephalographic (EEG) rhythms. METHODS: To this aim, EEG data were recorded in 14 subjects observing emotional faces with neutral, happy or sad facial expressions (about 33% for each class). The EEG data were analyzed by directed transfer function (DTF), which estimates directional functional coupling of EEG rhythms. The EEG rhythms of interest were theta (about 4-6 Hz), alpha 1 (about 6-8 Hz), alpha 2 (about 8-10 Hz), alpha 3 (about 10-12 Hz), beta 1 (13-20 Hz), beta 2 (21-30 Hz), and gamma (31-44 Hz). RESULTS: In the frontal regions, inter-hemispherical DTF values were bidirectionally higher in amplitude across all frequency bands, during the perception of faces with sad compared to neutral or happy expressions. CONCLUSIONS: These results suggest that the processing of emotional negative facial expressions is related to an enhancement of a reciprocal inter-hemispherical flux of information in frontal cortex, possibly optimizing executive functions and motor control. SIGNIFICANCE: Dichotomical view of hemispherical functional specializations does not take into account remarkable reciprocal interactions between frontal areas of the two hemispheres during the processing of negative facial expressions.

Clowns benefit children hospitalized for respiratory pathologies.

The study aims at evaluating health-generating function of humor therapy in a hospital ward hosting children suffering from respiratory pathologies. The main scope of this study is to investigate possible positive effects of the presence of a clown on both the clinical evolution of the on-going disease, and on some physiological and pain parameters. Forty-three children with respiratory pathologies participated in the study: 21 of them belonged to the experimental group (EG) and 22 children to the control group (CG). During their hospitalization, the children of the EG interacted with two clowns who were experienced in the field of pediatric intervention. All participants were evaluated with respect to clinical progress and to a series of physiological and pain measures both before and after the clown interaction. When compared with the CG, EG children showed an earlier disappearance of the pathological symptoms. Moreover, the interaction of the clown with the children led to a statistically significant lowering of diastolic blood pressure, respiratory frequency and temperature in the EG as compared with the control group. The other two parameters of systolic pressure and heart frequency yielded results in the same direction, without reaching statistical significance. A similar health-inducing effect of clown presence was observed on pain parameters, both by self evaluation and assessment by nurses. Taken together, our data indicate that the presence of clowns in the ward has a possible health-inducing effect. Thus, humor can be seen as an easy-to-use, inexpensive and natural therapeutic modality to be used within different therapeutic settings.

Job characteristics, organizational conditions, and distress/well-being among Italian and Dutch nurses: a cross-national comparison.

BACKGROUND: Among health care workers, nursing has been identified as particularly stressful. Several studies have shown cross-national differences in nurses' levels of occupational stress and burnout. OBJECTIVES: The purpose of the study was to compare job characteristics, organizational conditions, and strain reactions in Italian (N = 609) and Dutch (N = 873) nurses. It was also examined how and to what extent various job characteristics and organizational conditions explain occupational and general strain. DESIGN: The study was a cross-sectional questionnaire survey. METHOD: Based on the Job Demand-Control-Support Model and the Tripod accident causation model, respectively job characteristics and organizational conditions were assessed as independent variables. Strain was operationalized in terms of job satisfaction, burnout, and psychosomatic complaints. RESULTS: Italian nurses perceived their job characteristics, organizational conditions, and well-being as more unfavourable than their Dutch colleagues. Hierarchical regression analyses showed that high job demands, low skill discretion, and low social support from supervisor were the most consistent predictors of occupational and general strain across samples. Organizational conditions added significantly to the prediction of job satisfaction and burnout. Furthermore, lack of personnel was a stronger predictor of burnout in the Italian nurses than in the Dutch nurses. CONCLUSIONS: The study provides cross-national confirmation of the impact of job characteristics and organizational conditions on nurses' well-being. Differences in job characteristics partially explain the observed cross-national differences in distress/well-being. Furthermore, some evidence for crossnational differential effects of job characteristics and organizational conditions on well-being was found.

Directional information flows between brain hemispheres across waking, non-REM and REM sleep states: an EEG study.

The present electroencephalographic (EEG) study evaluated the hypothesis of a preferred directionality of communication flows between brain hemispheres across 24 h (i.e., during the whole daytime and nighttime), as an extension of a recent report showing changes in preferred directionality from pre-sleep wake to early sleep stages. Scalp EEGs were recorded in 10 normal volunteers during daytime wakefulness (eyes closed; first period: from 10:00 to 13:00 h; second period: from 14:00 to 18:00 h; third period: from 19:00 to 22:00 h) and nighttime sleep (four NREM-REM cycles). EEG rhythms of interest were delta (1-4 Hz), theta (5-7 Hz), alpha (8-11 Hz), sigma (12-15 Hz) and beta (16-28 Hz). The direction of the inter-hemispheric information flow was evaluated by computing the directed transfer function (DTF) from these EEG rhythms. Inter-hemispheric directional flows varied as a function of the state of consciousness (wake, NREM sleep, REM sleep) and in relation to different cerebral areas. During the daytime, alpha and beta rhythms conveyed inter-hemispheric signals with preferred Left-to-Right hemisphere direction in parietal and central areas, respectively. During the NREM sleep periods of nighttime, the direction of inter-hemispheric DTF information flows conveyed by central beta rhythms was again preponderant from Left-to-Right hemisphere in the stage 2, independent of cortical areas. No preferred direction emerged across the REM periods. These results support the hypothesis that specific directionality of communication flows between brain hemispheres is associated with wakefulness, NREM (particularly stage 2) and REM states during daytime and nighttime. They also reinforce the suggestive hypothesis of a relationship between inter-hemispheric directionality of EEG functional coupling and frequency of the EEG rhythms.

The electroencephalographic fingerprint of sleep is genetically determined: a twin study.

Humans have an individual profile of the electroencephalographic power spectra at the 8 to 16 Hz frequency during non-rapid eye movement sleep that is stable over time and resistant to experimental perturbations. We tested the hypothesis that this electroencephalographic "fingerprint" is genetically determined, by recording 40 monozygotic and dizygotic twins during baseline and recovery sleep after prolonged wakefulness. We show a largely greater similarity within monozygotic than dizygotic pairs, resulting in a heritability estimate of 96%, not influenced by sleep need and intensity. If replicated, these results will establish the electroencephalographic profile during sleep as one of the most heritable traits of humans.

Development and validation of a brief Occupational Coping Self-Efficacy Questionnaire for Nurses.

AIM: This paper is a report of a study to develop and test the psychometric properties of the Occupational Coping Self-Efficacy for Nurses Scale. BACKGROUND: Coping self-efficacy beliefs are defined as self-appraisals of capabilities to cope with environmental demands. People with higher levels of coping self-efficacy beliefs tend to approach challenging situations in an active and persistent way, whereas those with lower levels of coping self-efficacy beliefs tend to direct greater energy to managing increasing emotional distress. METHOD: In 2006, 1383 nurses completed the following measures: Occupational Coping Self-Efficacy Questionnaire for Nurses, Coping Inventory for Stressful Situations Short Form and Maslach Burnout Inventory. Based on a randomized split of the data, we conducted exploratory factor analysis on group 1 data (n = 691) and confirmatory factor analysis within the framework of structural equation modelling on group 2 data (n = 692). FINDINGS: The exploratory results revealed two factors: Coping Self-Efficacy to cope with the occupational burden (Cronbach alpha = 0.77) and Coping Self-Efficacy to cope with the relational burden (alpha = 0.79). In the confirmatory group, the two-factor structure was tested against an alternative one-factor structure and confirmed as the best solution. Correlation patterns between the Occupational Coping Self-Efficacy for Nurses Scales, and both coping and burnout variables, supported the criterion-related validity of the Occupational Coping Self-Efficacy for Nurses dimensions. CONCLUSION: Nurses can have two basic and distinct coping self-efficacy beliefs: beliefs about occupational burden and beliefs about relational difficulties in the workplace. Research is needed into how efficacy evaluations shift as a result of specific stress management interventions.

Interhemispheric transfer deficit in alexithymia: a transcranial magnetic stimulation study.

BACKGROUND: A deficit in interhemispheric transfer was hypothesized in alexithymia more than 30 years ago, following the observation that split-brain patients manifest certain alexithymic characteristics. However, direct evidence of interhemispheric transfer deficit has never been provided. This study investigated the hypothesis of a transcallosal interhemispheric transfer deficit in alexithymia by means of paired-pulse transcranial magnetic stimulation. METHODS: A random sample of 300 students was screened for alexithymia using the Italian version of the 20-item Toronto Alexithymia Scale. Eight right-handed males and eight females with high alexithymic scores and an age- and gender-matched group with low alexithymic scores were selected. A first (conditioning) magnetic stimulus was delivered to one motor cortex followed by a second (test) stimulus to the opposite hemisphere at different interstimulus intervals for both motor cortices. Motor evoked responses were recorded from the abductor digit minimi muscles. RESULTS: High alexithymic subjects showed reduced transcallosal inhibition as compared to low alexithymic subjects at interstimulus intervals of 10, 12 and 14 ms in the left-to-right and right-to-left interhemispheric transfer directions. CONCLUSIONS: Results point to functional differences in transcallosal interactions in high alexithymic as compared to low alexithymic subjects, supporting the hypothesis of an interhemispheric transfer deficit in alexithymia.

Night-time right hemisphere superiority and daytime left hemisphere superiority: a repatterning of laterality across wake-sleep-wake states.

During the sleep onset period (SOP), there is a state-specific relative advantage of the right hemisphere (RH). This superiority could either be due to the ability of the RH when operating at levels of reduced arousal, as suggested by its superiority in sustaining vigilance, or it could depend on a more pronounced homeostatic deactivation of the left hemisphere (LH). To evaluate whether variations of lateralization from wake to sleep are consistent with one of these two hypotheses, we considered a finger tapping task (FTT) bimanually performed during two wakeful conditions, during the SOP, upon experimental awakenings from stage 2 and REM sleep in the first and in the second part of the night, and upon morning awakening. The RH advantage in sustaining vigilance would be supported if the relative RH advantage was present throughout the sleep period. Finding that the repatterning of hemispheric asymmetry is present and/or prominent in the first part of the night would support the homeostatic hypothesis, i.e. when the homeostatic process is more pronounced. Results from 16 subjects revealed a significant superiority of the LH during the two wakeful conditions. At sleep onset, a clear reversal of dominance was observed and it was followed by a steady RH superiority upon both REM and NREM sleep awakenings, and upon the morning sleep-wake transition. Therefore, performance in a FTT reveals a repatterning of laterality across wake-sleep-wake states. These results are interpreted as consistent with the hypothesis concerning an advantage of the RH in sustaining vigilance.

Laterality of the sleep onset process: which hemisphere goes to sleep first?

This study aims to assess whether the hemispheric asymmetry inversion observed in the wake-sleep transition can also be revealed by the latency of inter tapping intervals >or= 2.5s for each hand and the latency of theta burst >or= 2.5s in symmetrical loci of the two hemispheres during the sleep onset process. Data collected from 16 right-handed subjects showed a hemispheric asymmetry in the sleep onset latency with both behavioural and EEG indices. For the first time, a hemispheric asymmetry in the sleep onset latency was found considering a visual analysis of EEG. Results suggest that the hemispheric pattern found during sleep onset can be considered a steady characteristic of the transition from wake to sleep, relatively independent of homeostatic and time of night effects. These results are interpreted as being consistent with the hypothesis concerning an advantage of the right hemisphere in sustaining vigilance.

Sleep in the human hippocampus: a stereo-EEG study.

BACKGROUND: There is compelling evidence indicating that sleep plays a crucial role in the consolidation of new declarative, hippocampus-dependent memories. Given the increasing interest in the spatiotemporal relationships between cortical and hippocampal activity during sleep, this study aimed to shed more light on the basic features of human sleep in the hippocampus. METHODOLOGY/PRINCIPAL FINDINGS: We recorded intracerebral stereo-EEG directly from the hippocampus and neocortical sites in five epileptic patients undergoing presurgical evaluations. The time course of classical EEG frequency bands during the first three NREM-REM sleep cycles of the night was evaluated. We found that delta power shows, also in the hippocampus, the progressive decrease across sleep cycles, indicating that a form of homeostatic regulation of delta activity is present also in this subcortical structure. Hippocampal sleep was also characterized by: i) a lower relative power in the slow oscillation range during NREM sleep compared to the scalp EEG; ii) a flattening of the time course of the very low frequencies (up to 1 Hz) across sleep cycles, with relatively high levels of power even during REM sleep; iii) a decrease of power in the beta band during REM sleep, at odds with the typical increase of power in the cortical recordings. CONCLUSIONS/SIGNIFICANCE: Our data imply that cortical slow oscillation is attenuated in the hippocampal structures during NREM sleep. The most peculiar feature of hippocampal sleep is the increased synchronization of the EEG rhythms during REM periods. This state of resonance may have a supportive role for the processing/consolidation of memory.

Neurophysiological correlates of sleepiness: a combined TMS and EEG study.

Changes of cortical and corticospinal excitability as a function of sleep deprivation have been studied, using EEG power maps and several TMS measures in 33 normal subjects before and after a 40-h sleep deprivation (SD). The effects of SD were independently assessed by subjective and EEG measures of sleepiness, the latter being represented in terms of cortical maps for different frequency bands. Short intracortical facilitation (SICF) and inhibition (SICI) were measured by the paired-pulse TMS technique with different inter-stimulus intervals. Besides standardized motor threshold (MT), lower threshold (LT) and upper threshold (UT) were also determined. Subjective sleepiness severely increased as a consequence of SD, paralleled by a drastic decrease of alertness. EEG topography showed large increases in delta and theta activity, mainly evident at fronto-central areas. Standard MTs, as well as LTs and UTs, all increased as a consequence of SD. SICF also showed a significant increase as compared to pre-deprivation values, but only in females. The increase of theta activity was strongly associated in the left frontal and prefrontal cortex to a smaller decrease of corticospinal excitability, expressed by MTs, and a larger increase of intracortical facilitation, expressed by SICF. TMS and EEG measures converge in indicating that SD has severe effects on both cortical and corticospinal excitability, as shown respectively by the increases of slow-frequency EEG power and MTs. The SICF enhancement in females and the results of the combined topographical analysis of EEG and TMS changes are coherent with the hypothesis that cortical TMS-evoked responses are higher as a consequence of a longer wakefulness. However, the lack of an increase in cortical excitability after prolonged wakefulness in males suggests some caution in the generalization of these effects, that deserve further investigation.

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.

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.

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.

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.

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.

Beneficial effects of enriched environment on adolescent rats from stressed pregnancies.

The capacity of an early environmental intervention to normalize the behavioural and immunological dysfunctions produced by a stressed pregnancy was investigated. Pregnant Sprague-Dawley rats underwent three 45-min sessions per day of prenatal restraint stress (PS) on gestation days 11-21, and their offspring were assigned to either an enriched-environment or standard living cages throughout adolescence [postnatal days (pnd) 22-43]. Juvenile rats from stressed pregnancies had a prominent depression of affiliative/playful behaviour and of basal circulating CD4 T lymphocytes, CD8 T lymphocytes and T4/T8 ratio. They also showed increased emotionality and spleen and brain frontal cortex levels of pro-inflammatory interleoukin-1beta (IL-1beta) cytokine. A more marked response to cyclophosphamide (CPA: two 2 mg/kg IP injections) induced immunosuppression was also found in prenatal stressed rats. Enriched housing increased the amount of time adolescent PS rats spent in positive species-typical behaviours (i.e. play behaviour), reduced emotionality and reverted most of immunological alterations. In addition to its effects in PS rats, enriched housing increased anti-inflammatory IL-2 and reduced pro-inflammatory IL-1beta production by activated splenocytes, also producing a marked alleviation of CPA-induced immune depression. In the brain, enriched housing increased IL-1beta values in hypothalamus, while slightly normalizing these values in the frontal cortex from PS rats. This is a first indication that an environmental intervention, such as enriched housing, during adolescence can beneficially affect basal immune parameters and rats response to both early stress and drug-induced immunosuppression.

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).

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.

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.