Riccardo Cristiani

Antero-posterior EEG changes during the wakefulness-sleep transition

OBJECTIVES To investigate the brain topography of the human sleep EEG along the antero-posterior axis during the wakefulness-sleep transition, by means of both a single Hz analysis and a grouped-frequency analysis of EEG changes. METHODS EEG power values were calculated across a 1-28 Hz frequency range in a 1 Hz resolution during the wakefulness-sleep transition of 7 normal subjects. Topographical changes were assessed from C3-A2, C4-A1, Fpz-A1, Fz-A1, Cz-A1, Pz-A1, Oz-A1 recordings, after averaging individual time series, aligned with respect to the onset of stage 2. RESULTS The single Hz analysis showed that before sleep onset (SO), the <7 Hz slow frequencies were more prominent at the more anterior scalp locations; this anterior prominence was counterbalanced by a reciprocal prevalence across the >8 Hz frequencies of EEG activity from the occipital areas; while the >13 Hz fast frequencies were not characterized by significant antero-posterior differences. After SO, more EEG power was found in the range of slow frequencies at the centro-frontal scalp locations and a second peak of EEG activity was also revealed within the range of the sigma frequency, higher at the centro-parietal scalp locations. No consistent topographical changes were observed within the range of faster EEG frequencies. Grouped-frequency analysis confirmed these results, also pointing to different changes in the alpha frequency as a function of the SO point. CONCLUSIONS The results suggest that: (a) the alpha rhythm spreads anteriorly as the transition progresses; (b) several anterior areas first synchronize EEG activity; (c) the functional meaning of the EEG bands during the SO period should be partially revised with regard at least to alpha rhythm; (d) SO coincides with the start of stage 2.

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.

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.

Time-course of electromagnetic field effects on human performance and tympanic temperature.

The study aimed to investigate the time-course of electromagnetic field (EMF)-induced effects on human cognitive and behavioral performance and on tympanic temperature. Subjects were randomly assigned to two groups, exposed to a 902.40 MHz EMF before the testing session, or to the same signal during the data collecting session. Following a double-blind paradigm, subjects were tested on four performance tasks: an acoustic simple-reaction time task, a visual search task, an arithmetic descending subtraction task and an acoustic choice-reaction time task. Moreover, tympanic temperature was collected five times during each session. Results indicated an improvement of both simple- and choice-reaction times and an increase of local temperature on the exposed region under the active exposure. There was a clear time-course of the reaction time and temperature data, indicating that performance and physiological measures need a minimum of 25 min of EMF exposure to show appreciable changes.

The Cyclic Alternating Pattern Decreases as a Consequence of Total Sleep Deprivation and Correlates with EEG Arousals

The aim of this study was to assess the sensitivity of the cyclic alternating pattern (CAP) parameters to the increased need for recuperation that follows one night of sleep deprivation. Nine normal male subjects were recorded for 3 nights [adaptation, baseline (BSL) and recovery (REC)]. BSL and REC nights were separated by a 40-hour sleep deprivation. Recovery after sleep deprivation was characterized by a decrease in stage 1, stage 2 and sleep latency, and an increase in slow wave sleep (SWS) and the sleep efficiency index, while rapid eye movement (REM) and non-REM (NREM) time did not differ as compared to BSL sleep. CAP parameters were significantly affected by sleep deprivation, and the main results were the following: (1) the CAP rate (time spent in CAP phases/NREM time) significantly decreased from 38.85 to 31.47%, and (2) within phase A subtypes, there was a significant decrease in A3 subtypes (from 38.11 to 19.57). Furthermore, the number of arousals scored according to American Sleep Disorders Association rules strongly correlated with A3 subtypes during both the BSL (r = 0.79) and REC nights (r = 0.95). These results indicate that recuperative processes after sleep deprivation are also associated with a lesser arousal instability as defined by the reduction of the CAP rate, which is strongly correlated with EEG arousals.

Alexithymia and Dream Recall Upon Spontaneous Morning Awakening

Objective The issue of a quantitative and qualitative impoverishment of dream activity in alexithymic subjects was assessed by analysis of the 14-day dream reports of two groups of accurately selected alexithymic and nonalexithymic subjects. Methods Ten alexithymic and 10 nonalexithymic women were selected from a larger sample of 160 undergraduate students. The transcriptions of their audio-recorded dream reports on 14 consecutive morning awakenings were compared with regard to their length and emotional content. Self-ratings obtained from sleep and dream diaries were further considered to assess between-groups differences in dream recall frequency and in the emotional valence, vividness, and bizarreness of dreams. Results Dream recall frequency and mean length of dream reports were lower in alexithymic than in nonalexithymic subjects. There were no significant between-groups differences in emotional valence, vividness, bizarreness, and emotions scored according to the Hall and Van de Castle coding system. Conclusions The results suggest a general difficulty of alexithymics in accessing (recalling) their dreams.

Reproducibility of callosal effects of transcranial magnetic stimulation (TMS) with interhemispheric paired pulses

Transcranial magnetic stimulation (TMS) of the motor cortex of one hemisphere (conditioning stimulus (CS)) inhibits EMG responses evoked in distal hand muscles by a later magnetic stimulus given at an appropriate interval, over the opposite hemisphere (test stimulus (TS)). This effect is commonly attributed to an inhibition produced at cortical level via a transcallosal route. The present study assessed the reproducibility of the transcallosal inhibition effects in different sessions in healthy subjects. Within- and between-subject variability, relating to interhemispheric differences was also evaluated. A magnetic CS on one hemisphere effectively inhibited EMG responses of the abductor digiti minimi stimulated by a TS delivered over the opposite hemisphere in a range of intervals centered at 12 ms. Even though group effects were reproduced in separate sessions, the high between- and within-subject variability yielded low test-retest correlations. This differentiation forces the definition of reproducibility (or repeatability), as the replication of the same mean curves of EMG reduction, and of reliability, as the between- or within-subject correlations between values of specific EMG measures.

Regional differences of the temporal EEG dynamics during the first 30 min of human sleep.

The analysis of the time-course of different EEG bands during the first sleep cycle has up to now taken into account mostly central derivations. In the present study, we assessed the topographical differences of the time-course of different EEG bands during the first 30 min of sleep, by analysing the EEG power from four different scalp locations along the antero-posterior axis. Correlation of EEG bands time courses within and between each derivation has also been evaluated. Delta-theta (1-6.75 Hz) and alpha (7-10.75 Hz) activities exhibited an antero-posterior gradient with maximal power on the frontal lead and increased at all derivations in the first 15 min and 5 min periods, respectively. Then alpha power decreased at all derivations, but the frontal. Sigma EEG power (11-15.75 Hz) showed a coherent behavior over the four derivations, characterized by a steep increase in the first 3-5 min of sleep, followed by a stable decreasing trend. Beta power (16-25.75 Hz) linearly decreased only on the more posterior derivations, abruptly increasing on the frontal lead after a 15 min interval. Correlations between delta-theta and alpha band were higher on the frontal derivation. Moreover, frontal alpha was strongly related to delta-theta activity on all the four derivations, while occipital alpha was not. The negative correlations between delta-theta and beta time courses were very high on all derivations but the frontal one. This study shows the existence of topographical differences in the time-course of different EEG bands during the first 30 min of sleep. The peculiar behavior of the alpha and beta EEG bands over the frontal derivation indicates the need to re-consider the functional role of traditional EEG bands during sleep.

Cortical EEG topography of REM onset: the posterior dominance of middle and high frequencies

OBJECTIVES To investigate the brain topography of human sleep electroencephalography (EEG) along the antero-posterior axis during rapid eye movement sleep (REM) onset and REM offset, by means of a quantitative analysis of EEG changes. METHODS EEG power values were calculated across a 1.00-25.75 Hz frequency range during time intervals preceding and following REM onset of the first 4 sleep cycles of 10 normal subjects. Topographical changes were assessed through Fpz-A1, Fz-A1, Cz-A1, Pz-A1, Oz-A1 recordings during NREM-REM-NREM transitions. RESULTS The temporal dynamics of REM onset is characterized by a specific topographical pattern of EEG changes with a relatively higher EEG activity at posterior sites: Oz does not show any clear change within the alpha and beta frequencies, at variance with the marked reductions of the other sites, while it shows reductions of power in the delta/theta and sigma frequency ranges of smaller size as compared to the other sites. REM offset does not appear as a mirror-image of REM onset, since the pattern of regional differences characterizing the NREM sleep preceding REM onset is not fully reached. CONCLUSIONS REM onset is characterized by a general change of EEG activity toward a relative occipital diffusion of power, specifically distinguished by a posterior dominance of middle and high frequencies.

Interhemispheric asymmetry of human sleep EEG in response to selective slow-wave sleep deprivation

Recent evidence suggests that the human sleep electroencephalogram (EEG) shows regional differences over both the sagittal and coronal planes. In the present study, in a group of 10 right-handers, the authors investigated the presence of hemispheric asymmetries in the homeostatic regulation of human sleep EEG power during and after selective slow-wave sleep (SWS) deprivation. The SWS deprivation was slightly more effective over the right hemisphere, but the left hemisphere showed a markedly larger increase of EEG power in the 1.00-24.75 Hz range during recovery-night non-REM sleep, and a larger increase of EEG power during both deprivation-night and recovery-night REM sleep. These results support the greater need for sleep recuperative processes of the left hemisphere, suggesting that local sleep regulation processes may also act during REM sleep.