Spectral analysis of the sleep onset period in primary insomnia

ObjectiveTo compare the EEG power spectra characteristics of the sleep onset period (SOP) in patients with sleep onset insomnia (SOI), sleep maintenance insomnia (SMI) and good sleepers (GS).MethodsThe time course of EEG power density (1–40 Hz) during the SOP was examined in thirty subjects (SOI patients: N = 10, SMI patients: N = 10, GS: N = 10).ResultsThe EEG power of the beta2 frequency band (18–29.75 Hz) was significantly lower in SOI than in SMI in the period preceding sleep onset. The alpha power was significantly higher for the SMI group compared to GS before sleep onset. Despite the lack of statistical significance, several differences in EEG dynamics were observed in SOI compared to two other groups: delta power increased slower after sleep onset; beta2 and 3 (18–29.75 and 30–39.75 Hz) power decrease less abruptly before sleep onset; beta1 (15–17.75 Hz) power increase through the whole SOP.ConclusionsThe lower level of beta2 frequency band in SOI and the differences in dynamics in delta and beta bands may suggest that a mechanism other than hyperarousal participates in etiology of SOI.SignificanceSOI and SMI patients have different spectral characteristics in SOP, thus future studies should avoid the inclusion of mixed insomnia samples.     

Longitudinal study of EEG frequency maturation and power changes in children on the Russian North

The aim of the study was to reveal longitudinal changes in electroencephalogram spectral power and frequency (percentage frequency composition of EEG and alpha peak frequency) patterns in normal children from northern Russia. Fifteen children (9 girls and 6 boys) participated in the study. The resting state (eyes closed) EEGs were recorded yearly (2005–2013) from age 8 to age 16–17 for each child. EEG frequency patterns were estimated as the percentages of waves with a 1 Hz step revealed by measuring the interval durations between points crossing zero (isoline) by a curve. EEG spectral power changes were analyzed for delta (1.5–4 Hz), theta (4–7.5 Hz), alpha-1 (7.5–9.5 Hz), alpha-2 (9.5–12.5 Hz), beta-1 (12.5–18 Hz) and beta-2 (18–30 Hz) bands. According to the frequency composition of the EEG signals fast synchronous, polymorphous synchronous, polymorphous desynchronous and slow synchronous types of children EEG were revealed. These EEG types were relatively stable during adolescence. In these EEG types, the frequency patterns and spectral power dynamics with age had several common and specific features. Slow wave percentage and spectral power in the delta band remarkably decreased with age in all groups. Starting from the theta band the EEG types were characterized by different EEG spectral power changes with age. In fast synchronous EEG type, the theta and alpha-1 EEG power decreased, and the alpha-2 power increased in the occipital and parietal areas. The polymorphous synchronous type was characterized by increased both the alpha-1 and alpha-2 power with regional peculiarities. In the polymorphous desynchronous type spectral power in all bands decreased with age, and in the slow synchronous type, the alpha-1 power massively increased with age. Obtained results suggest predictive strength of the spatial-frequency patterns in EEG for its following maturation through the years.     

Cortical sources of EEG rhythms are abnormal in down syndrome

ObjectivePrevious studies have been inconclusive whether dominant resting state alpha rhythms are greater or lower in amplitude in subjects with Down syndrome (DS) when compared to control subjects, ample resting alpha rhythms being considered as a reflection of good mechanisms of cortical neural synchronization. Here we tested the hypothesis that when the effects of head volume conduction are taken into account by the normalization of the cortical sources of resting alpha rhythms, these sources are lower in amplitude in DS subjects than in controls in line with typical findings in Alzheimer’s disease patients.MethodsEyes-closed resting electroencephalographic (EEG) data were recorded in 45 DS subjects (25 males; mean age of 22.8 years ± 0.7 standard error of mean (SEM)) and in 45 age-matched cognitively normal subjects (25 males; mean age of 22.4 years ± 0.5 SEM). EEG rhythms of interest were delta (2–4 Hz), theta (4–8 Hz), alpha 1 (8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), beta 2 (20–30 Hz), and gamma (30–40 Hz). Cortical EEG sources were estimated by low resolution electromagnetic tomography (LORETA) and normalized across all voxels and frequencies.ResultsCentral, parietal, occipital, and temporal cortical sources of resting alpha and beta rhythms were lower in amplitude in the DS than control subjects, whereas the opposite was true for occipital delta cortical sources. A control analysis on absolute source values showed that they were globally larger in amplitude across several frequency bands in DS than control subjects.ConclusionsThese results suggest that normalized cortical sources of alpha rhythms are lower in amplitude in DS than control subjects, as it is typically found in Alzheimer’s disease.SignificanceDS is accompanied by a functional impairment of cortical neuronal synchronization mechanisms in the resting state condition.     

Neuropeptide S reduces propofol- or ketamine-induced slow wave states through activation of cognate receptors in the rat

Intracerebroventricular injection of NPS reduces the duration of the ketamine- or thiopental-induced loss of the righting reflex in rats. But the specific EEG activities are unknown. We therefore sought to examine the effects of the NPS-NPSR system on anesthetic-induced characteristics of EEG power spectra and sleep-wake profiles. NPS alone or together with an NPSR antagonist was injected intracerebroventricularly, whereas the propofol (50 mg/kg) or ketamine (100 mg/kg) was administrated intraperitoneally. NPS (1 or 2 nmol) significantly reduced the amount of propofol-induced EEG delta activity and slow wave states (SWS). NPS (1 or 5 nmol) significantly reduced the amount of ketamine-induced SWS and EEG delta activity. Cortical EEG power spectral analysis showed that, in saline-pretreated rats, propofol induced a marked increase in delta (0.5–4 Hz) activity, decrease in theta (4.5–8.5 Hz) activity, and decrease in high frequency activity (14.5–60 Hz), while, in rats pretreated with 1 nmol of NPS, the duration of delta activity was reduced, while its spectral pattern was not changed. Whereas injection of ketamine into saline-pretreated rats induced a marked increase in delta (0.5–4 Hz) activity, a moderate increase in theta (4.5–8.5 Hz) activity, and a marked decrease in high frequency (14.5–60 Hz) activity. However, delta activity was reduced while theta activity increased under pretreatment with 1 nmol of NPS. The inhibitory effect of NPS on anesthetic-induced SWS was characterized by a reduced SWS episode duration with no significant change in either episode number or latency to SWS. [D-Val⁵]NPS, an NPSR antagonist (20 nmol), significantly attenuated the arousal-promoting effect of 1 nmol of NPS, but had no effect on SWS when injected alone. We speculate that NPS significantly reduces anesthetic-induced SWS and EEG slow activity by selective activation of the NPSR, which, in turn, would trigger subsequent arousal pathways.     

Hypercapnia affects the functional coupling of resting state electroencephalographic rhythms and cerebral haemodynamics in healthy elderly subjects and in patients with amnestic mild cognitive impairment

ObjectiveCerebral vasomotor reactivity (VMR) and coherence of resting state electroencephalographic (EEG) rhythms are impaired in Alzheimer’s disease (AD) patients. Here we tested the hypothesis that these two variables could be related.MethodsWe investigated VMR and coherence of resting state EEG rhythms in nine normal elderly (Nold) and in 10 amnesic mild cognitive impairment (MCI) subjects. Resting state eyes-closed EEG data were recorded at baseline pre-CO₂ (ambient air, 2 min), during 7% CO₂/air mixture inhalation (hypercapnia, 90 s) and post-CO₂ (ambient air, 2 min) conditions. Simultaneous frontal bilateral near-infrared spectroscopy (NIRS) was performed to assess VMR by cortical oxy- and deoxy-haemoglobin concentration changes. EEG coherence across all electrodes was computed at delta (2–4 Hz), theta (4–8 Hz), alpha 1 (8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), beta 2 (20–30 Hz) and gamma (30–40 Hz) bands.ResultsIn Nold subjects, ‘total coherence’ of EEG across all frequency bands and electrode pairs decreased during hypercapnia, with full recovery during post-CO₂. Total coherence resulted lower in pre-CO₂ and post-CO₂ and presented poor reactivity during CO₂ inhalation in MCI patients compared with Nold subjects. Hypercapnia increased oxy-haemoglobin and decreased deoxy-haemoglobin concentrations in both groups. Furthermore, the extent of changes in these variables during CO₂ challenge was correlated with the EEG coherence, as a reflection of neurovascular coupling.ConclusionsHypercapnia induced normal frontal VMR that was detected by NIRS in both Nold and amnesic MCI groups, while it produced a reactivity of global functional coupling of resting state EEG rhythms only in the Nold group.SignificanceIn amnesic MCI patients, global EEG functional coupling is basically low in amplitude and does not react to hypercapnia.     

Uppermost synchronized generators of spike–wave activity are localized in limbic cortical areas in late-onset absence status epilepticus

PurposeAbsence status (AS) epilepticus with generalized spike–wave pattern is frequently found in severely ill patients in whom several disease states co-exist. The cortical generators of the ictal EEG pattern and EEG functional connectivity (EEGfC) of this condition are unknown. The present study investigated the localization of the uppermost synchronized generators of spike–wave activity in AS.MethodSeven patients with late-onset AS were investigated by EEG spectral analysis, LORETA (Low Resolution Electromagnetic Tomography) source imaging, and LSC (LORETA Source Correlation) analysis, which estimates cortico-cortical EEGfC among 23 ROIs (regions of interest) in each hemisphere.ResultsAll the patients showed generalized ictal EEG activity. Maximum Z-scored spectral power was found in the 1–6 Hz and 12–14 Hz frequency bands. LORETA showed that the uppermost synchronized generators of 1–6 Hz band activity were localized in frontal and temporal cortical areas that are parts of the limbic system. For the 12–14 Hz band, abnormally synchronized generators were found in the antero-medial frontal cortex. Unlike the rather stereotyped spectral and LORETA findings, the individual EEGfC patterns were very dissimilar.ConclusionThe findings are discussed in the context of nonconvulsive seizure types and the role of the underlying cortical areas in late-onset AS. The diversity of the EEGfC patterns remains an enigma. Localizing the cortical generators of the EEG patterns contributes to understanding the neurophysiology of the condition.     

Reliability of early cortical auditory gamma-band responses

ObjectiveTo evaluate the test–retest reliability of event-related power changes in the 30–150 Hz gamma frequency range occurring in the first 150 ms after presentation of an auditory stimulus.MethodsRepeat intracranial electrocorticographic (ECoG) recordings were performed with 12 epilepsy patients, at ?1-day intervals, using a passive odd-ball paradigm with steady-state tones. Time–frequency matching pursuit analysis was used to quantify changes in gamma-band power relative to pre-stimulus baseline. Test–retest reliability was estimated based on within-subject comparisons (paired t-test, McNemar’s test) and correlations (Spearman rank correlations, intra-class correlations) across sessions, adjusting for within-session variability. Reliability estimates of gamma-band response robustness, spatial concordance, and reproducibility were compared with corresponding measurements from concurrent auditory evoked N1 responses.ResultsAll patients showed increases in gamma-band power, 50–120 ms post-stimulus onset, that were highly robust across recordings, comparable to the evoked N1 responses. Gamma-band responses occurred regardless of patients’ performance on behavioral tests of auditory processing, medication changes, seizure focus, or duration of test–retest interval. Test–retest reproducibility was greatest for the timing of peak power changes in the high-gamma range (65–150 Hz). Reliability of low-gamma responses and evoked N1 responses improved at higher signal-to-noise levels.ConclusionsEarly cortical auditory gamma-band responses are robust, spatially concordant, and reproducible over time.SignificanceThese test–retest ECoG results confirm the reliability of auditory gamma-band responses, supporting their utility as objective measures of cortical processing in clinical and research studies.     

Effect of levetiracetam monotherapy on background EEG activity and cognition in drug-naïve epilepsy patients

ObjectiveTo investigate the cognitive effect of levetiracetam (LEV) monotherapy with quantitative electroencephalogram (EEG) analysis and neuropsychological (NP) tests.MethodsTwenty-two drug-naïve epilepsy patients were enrolled. EEG recordings were performed before and after LEV therapy. Relative power of discrete frequency bands was computed, as well as alpha peak frequency (APF) at occipital electrodes. Eighteen patients performed a battery of NP tests twice across LEV treatment.ResultsLEV therapy decreased the power of delta (1–3 Hz, p < 0.01) and theta (3–7 Hz, p < 0.05) bands and increased that of alpha-2 (10–13 Hz, p < 0.05) and beta-2 (19–24 Hz, p < 0.05) bands. Region-specific spectral change was observed: delta power change was significant in fronto-polar region, theta in anterior region, alpha-2 in broad region, and beta-2 in left fronto-central region. APF change was not significant. Improvement in diverse NP tests requiring attention, working memory, language and executive function was observed. Change in theta, alpha-2, and beta-2 power was correlated with improvement in several NP tests.ConclusionsOur data suggest LEV is associated with acceleration of background EEG frequencies and improved cognitive function. Change in frequency band power could predict improvement in several cognitive domains across LEV therapy.SignificanceCombined study of quantitative EEG analysis and NP tests can be useful in identifying cognitive effect of antiepileptic drugs.     

Relationship between delta power and the electrocardiogram-derived cardiopulmonary spectrogram: possible implications for assessing the effectiveness of sleep

ObjectivesThe physiologic relationship between slow-wave activity (SWA) (0–4 Hz) on the electroencephalogram (EEG) and high-frequency (0.1–0.4 Hz) cardiopulmonary coupling (CPC) derived from electrocardiogram (ECG) sleep spectrograms is not known. Because high-frequency CPC appears to be a biomarker of stable sleep, we tested the hypothesis that that slow-wave EEG power would show a relatively fixed-time relationship to periods of high-frequency CPC. Furthermore, we speculated that this correlation would be independent of conventional nonrapid eye movement (NREM) sleep stages.MethodsWe analyzed selected datasets from an archived polysomnography (PSG) database, the Sleep Heart Health Study I (SHHS-I). We employed the cross-correlation technique to measure the degree of which 2 signals are correlated as a function of a time lag between them. Correlation analyses between high-frequency CPC and delta power (computed both as absolute and normalized values) from 3150 subjects with an apnea-hypopnea index (AHI) of ⩽5 events per hour of sleep were performed.ResultsThe overall correlation (r) between delta power and high-frequency coupling (HFC) power was 0.40 ± 0.18 (P = .001). Normalized delta power provided improved correlation relative to absolute delta power. Correlations were somewhat reduced in the second half relative to the first half of the night (r = 0.45 ± 0.20 vs r = 0.34 ± 0.23). Correlations were only affected by age in the eighth decade. There were no sex differences and only small racial or ethnic differences were noted.ConclusionsThese results support a tight temporal relationship between slow wave power, both within and outside conventional slow wave sleep periods, and high frequency cardiopulmonary coupling, an ECG-derived biomarker of “stable” sleep. These findings raise mechanistic questions regarding the cross-system integration of neural and cardiopulmonary control during sleep.     

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

ObjectiveBrain 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.MethodsTo 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).ResultsIn 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.ConclusionsThese 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.SignificanceDichotomical 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.     

The stability of spike counts in children with interictal epileptiform activity

PurposeLittle is known about the stability of serial measures of spike counts in children or whether spike counts are an inherently stable or unstable measure. We investigated the variation in first- and second-night spike counts in children undergoing 48-h ambulatory EEG recording.MethodsWe analyzed 40 consecutive 48-h ambulatory EEGs performed at Boston Children's Hospital that manifested spikes but no seizures. Distinct spike foci in the same child were counted separately. We visually counted all spikes in the first 20 min after the first sleep spindle during nighttime sleep, comparing the first and second nights.ResultsFifty-five unique spike foci were counted in 40 children (age range: 9 months to 19 years; median: 8.4 years). Considerable variation was seen when comparing Night 1 and Night 2 spike counts: for all foci, Night 1 mean and median spike counts were 304.5 and 126 and Night 2 counts were 309.5 and 148, respectively. For each focus, the mean change in spike frequency between Night 1 and Night 2 was 42.1% (median = 28.3%, IQR 19.0–50.0%). The coefficient of variation of 0.94 suggested a large amount of variation. The percentage change weighted according to high or low spike frequency was 25.1%.ConclusionIn 40 children with 55 unique spike foci, significant variability in spike frequency was seen between consecutive nights of sleep, suggesting significant natural variation in spike frequency. A quarter of spike foci varied by 50% or more. Spike counts separated by longer intervals may show even more dramatic natural variation.     

Pallidal low β-low γ phase-amplitude coupling inversely correlates with Parkinson disease symptoms

ObjectiveRecent discoveries suggest that it is most likely the coupling of β oscillations (13–30 Hz) and not merely their power that relates to Parkinson disease (PD) pathophysiology.MethodsWe analyzed power and phase amplitude coupling (PAC) in local field potentials (LFP) recorded from Pallidum after placement of deep brain stimulation (DBS) leads in nineteen PD patients and three patients with dystonia.ResultsWithin GPi, we identified PAC between phase of β and amplitude of high frequency oscillations (200–300 Hz) and distinct β-low γ (40–80 Hz) PAC both modulated by contralateral movement. Resting β-low γ PAC, also present in dystonia patients, inversely correlated with severity of rigidity and bradykinesia (R = −0.44, P = 0.028). These findings were specific to the low β band, suggesting a differential role for the two β sub-bands.ConclusionsPAC is present across distinct frequency bands within the GPi. Given the presence of low β-low γ PAC in dystonia and the inverse correlation with symptom severity, we propose that this PAC may be a normal pallidal signal.SignificanceThis study provides new evidence on the pathophysiological contribution of local pallidal coupling and suggests similar and distinct patterns of coupling within GPi and STN in PD.     

Watching object related movements modulates mirror-like activity in parietal brain regions

ObjectiveWe studied the activation of cortical motor and parietal areas during the observation of object related grasping movements. By manipulating the type of an object (realistic versus abstract) and the type of grasping (correct versus incorrect), we addressed the question how observing such object related movements influences cortical rhythmicity, especially the mu-rhythm, in the context of an “extended” human mirror neuron system (MNS).MethodsMultichannel electroencephalogram (EEG) was recorded during the observation of different object-related grasping actions in twenty healthy subjects. Different movies were presented, showing sequences of correct or incorrect hand grasping actions related to an abstract or realistic (daily life) object.ResultsEvent-related de/synchronization (ERD/ERS) analyses revealed a larger ERD in the upper alpha (10–12 Hz), beta (16–20 Hz) and gamma (36–40 Hz) frequency bands over parietal brain regions depending on the type of grasping. The type of object only influenced ERD patterns in the gamma band range (36–40 Hz) at parietal sites suggesting a strong relation of gamma band activity and cortical object representation. Abstract and realistic objects produced lower beta band synchronization at central sites only, whereas depending on the type of grasping an ERS in the upper alpha band (10–12 Hz) was observed.ConclusionDepending on the type of the grasped object and the type of grasping stronger parietal cortical activation occurred during movement observation.SignificanceDiscussing the results in terms of an “extended” human mirror neuron system (MNS), it could be concluded that beside sensorimotor areas a stronger involvement of parietal brain regions was found depending on the type of object and grasping movement observed.     

Ibuprofen treatment modifies cortical sources of EEG rhythms in mild Alzheimer’s disease

ObjectiveNon-steroidal anti-inflammatory drugs such as ibuprofen have a protective role on risk of Alzheimer’s disease (AD). Here we evaluated the hypothesis that long-term ibuprofen treatment affects cortical sources of resting electroencephalographic (EEG) rhythms in mild AD patients.MethodsTwenty-three AD patients (13 treated AD IBUPROFEN; 10 untreated AD PLACEBO) were enrolled. Resting EEG data were recorded before and 1 year after the ibuprofen/placebo treatment. EEG rhythms were delta (2–4 Hz), theta (4–8 Hz), alpha 1 (8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), and beta 2 (20–30 Hz). LORETA was used for EEG source analysis.ResultsIn the AD PLACEBO group, amplitude of delta sources was globally greater at follow-up than baseline. Instead, amplitude of delta sources remained stable or decreased in the majority of the AD IBUPROFEN patients. Clinical (CDR) but not global cognitive status (MMSE) reflected EEG results.ConclusionsThese results suggest that in mild AD patients, a long-term ibuprofen treatment slightly slows down the progressive increment of delta rhythms as a sign of contrast against the neurodegenerative processes.SignificanceThey motivate future investigations with larger population and extended neuropsychological testing, to study the relationships among ibuprofen treatment, delta cortical sources, and higher order functions.     

Age dependent electroencephalographic changes in attention-deficit/hyperactivity disorder (ADHD)

ObjectiveObjective biomarkers for attention-deficit/hyperactivity disorder (ADHD) could improve diagnostics or treatment monitoring of this psychiatric disorder. The resting electroencephalogram (EEG) provides non-invasive spectral markers of brain function and development. Their accuracy as ADHD markers is increasingly questioned but may improve with pattern classification.MethodsThis study provides an integrated analysis of ADHD and developmental effects in children and adults using regression analysis and support vector machine classification of spectral resting (eyes-closed) EEG biomarkers in order to clarify their diagnostic value.ResultsADHD effects on EEG strongly depend on age and frequency. We observed typical non-linear developmental decreases in delta and theta power for both ADHD and control groups. However, for ADHD adults we found a slowing in alpha frequency combined with a higher power in alpha-1 (8–10 Hz) and beta (13–30 Hz). Support vector machine classification of ADHD adults versus controls yielded a notable cross validated sensitivity of 67% and specificity of 83% using power and central frequency from all frequency bands. ADHD children were not classified convincingly with these markers.ConclusionsResting state electrophysiology is altered in ADHD, and these electrophysiological impairments persist into adulthood.SignificanceSpectral biomarkers may have both diagnostic and prognostic value.     

Classification of schizophrenia with spectro-temporo-spatial MEG patterns in working memory

ObjectiveTo investigate whether temporo-spatial patterns of brain oscillations extracted from multichannel magnetoencephalogram (MEG) recordings in a working memory task can be used successfully as a biometric marker to discriminate between healthy control subjects and patients with schizophrenia.MethodsFive letters appearing sequentially on a screen had to be memorized. The letters constituted a word in one condition and a pronounceable non-word in the other. Power changes of 248 channel MEG data were extracted in frequency sub-bands and a two-step filter and search algorithm was used to select informative features that discriminated patients and controls.ResultsThe discrimination between patients and controls was greater in the word condition than in the non-word condition. Furthermore, in the word condition, the most discriminant patterns were extracted in delta (1–4 Hz), alpha (12–16 Hz) and beta (16–24 Hz) frequency bands. These features were located in the left dorso-frontal, occipital and left fronto-temporal, respectively.ConclusionThe analysis of the oscillatory patterns of MEG recordings in the working memory task provided a high level of correct classification of patients and controls.SignificanceWe show, using a newly developed algorithm, that the temporo-spatial patterns of brain oscillations can be used as biometric marker that discriminate schizophrenia patients and healthy controls.     

Muscle temperature has a different effect on force fluctuations in young and older women

ObjectiveTo investigate the effect of muscle temperature on force fluctuations during isometric contractions in young and older females.MethodsFifteen young and 11 older subjects performed 3 × 30-s long submaximal isometric ankle dorsi-flexions (5%, 10%, and 15% of the maximal force). Tibialis anterior muscle temperature was monitored with an intramuscular probe and manipulated to obtain a cold, control, and warm condition. The coefficient of variation (CofV) and the relative power in the frequency bands 0–3 Hz (low), 4–6 Hz (middle), and 8–12 Hz (high) of the force signal were computed to characterise steadiness. Intramuscular EMG signals were recorded from the tibialis anterior muscle to assess motor unit discharge pattern.ResultsCofV was higher in the older than in the young subjects (P < 0.001) in all conditions. In the older group only, CofV increased with cooling with respect to control temperature (P < 0.001), whereas in the young group only, relative power of force fluctuations at high frequency decreased with cooling. Motor unit discharge rate and inter-pulse interval variability were not different between groups and across temperatures.ConclusionsThe findings indicate a different effect of temperature on the ability to maintain constant force in young and older subjects.SignificanceThese results highlight the risk of further impairment to the motor control of older individuals with varying temperature.     

High frequency oscillations in intra-operative electrocorticography before and after epilepsy surgery

ObjectiveRemoval of brain tissue showing high frequency oscillations (HFOs; ripples: 80–250 Hz and fast ripples: 250–500 Hz) in preresection electrocorticography (preECoG) in epilepsy patients seems a predictor of good surgical outcome. We analyzed occurrence and localization of HFOs in intra-operative preECoG and postresection electrocorticography (postECoG).MethodsHFOs were automatically detected in one-minute epochs of intra-operative ECoG sampled at 2048 Hz of fourteen patients. Ripple, fast ripple, spike, ripples on a spike (RoS) and not on a spike (RnoS) rates were analyzed in pre- and postECoG for resected and nonresected electrodes.ResultsRipple, spike and fast ripple rates decreased after resection. RnoS decreased less than RoS (74% vs. 83%; p = 0.01). Most fast ripples in preECoG were located in resected tissue. PostECoG fast ripples occurred in one patient with poor outcome. Patients with good outcome had relatively high postECoG RnoS rates, specifically in the sensorimotor cortex.ConclusionsOur observations show that fast ripples in intra-operative ECoG, compared to ripples, may be a better biomarker for epileptogenicity. Further studies have to determine the relation between resection of epileptogenic tissue and physiological ripples generated by the sensorimotor cortex.SignificanceFast ripples in intra-operative ECoG can help identify the epileptogenic zone, while ripples might also be physiological.     

Cortical sources of resting-state alpha rhythms are abnormal in persistent vegetative state patients

ObjectiveHigh power of pre-stimulus cortical alpha rhythms (about 8–12 Hz) underlies conscious perception in normal subjects. Here we tested the hypothesis that these rhythms are abnormal in persistent vegetative state (PVS) patients, who are awake but not aware of self and environment.MethodsClinical and resting-state, eyes-closed electroencephalographic (EEG) data were taken from a clinical archive. These data were recorded in 50 PVS subjects (level of cognitive functioning – LCF score: I–II) and in 30 cognitively normal subjects. Rhythms of interest were delta (2–4 Hz), theta (4–8 Hz), alpha 1 (8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), and beta 2 (20–30 Hz). Cortical sources were estimated by low-resolution electromagnetic tomography (LORETA). Based on LCF score at 3-months follow-up, PVS patients were retrospectively divided into three groups: 30 subjects who did not recover (NON-REC patients; follow-up LCF: I–II), 8 subjects classified as minimally conscious state patients (MCS patients; follow-up LCF: III–IV), and 12 subjects who recovered (REC patients; follow-up LCF: V–VIII).ResultsOccipital source power of alpha 1 and alpha 2 was high in normal subjects, low in REC patients, and practically null in NON-REC patients. A Cox regression analysis showed that the power of alpha source predicted the rate of the follow up recovery, namely the higher its power, the higher the chance to recover consciousness. Furthermore, the MCS patients showed intermediate values of occipital alpha source power between REC and NON-REC patients.ConclusionsThese results suggest that cortical sources of alpha rhythms are related to the chance of recovery at a 3-months follow-up in patients in persistent vegetative state.SignificanceCortical sources of resting alpha rhythms might predict recovery in PVS patients.     

Somatosensory-related gamma-, beta- and alpha-augmentation precedes alpha- and beta-attenuation in humans

ObjectiveSeveral human studies have demonstrated that the amplitudes of cortical oscillations are altered by various sensorimotor and cognitive tasks. Event-related augmentation of gamma oscillations and attenuation of alpha and beta oscillations have been often used as surrogate markers of cortical activation elicited by tasks especially in presurgical identification of eloquent cortices. In the present study, we addressed a question whether somatosensory-related gamma augmentation ‘precedes’ or ‘co-occurs with’ somatosensory-related attenuation of alpha–beta oscillations.MethodsWe studied 10 patients who underwent intracranial electrocorticography for epilepsy surgery, and determined the temporal and spatial characteristics of median-nerve somatosensory-related amplitude changes at gamma- (30–100 Hz), beta- (14–28 Hz) and alpha-band (8–12 Hz) oscillations.ResultsWe found that somatosensory-related gamma augmentation involving the post- and pre-central gyri evolved into beta and alpha augmentation, which was subsequently followed by beta and alpha attenuation involving the post- and pre-central gyri.ConclusionsThese observations support the hypothesis that somatosensory-related gamma augmentation but not alpha–beta attenuation represents the initial cortical processing for external somatosensory stimuli. Somatosensory-related alpha–beta attenuation appears to represent a temporally distinct stage of somatosensory processing.SignificanceThe present study has increased our understanding of event-related gamma augmentation and alpha–beta attenuation seen on electrocorticography.