Time-frequency analysis of short-lasting modulation of EEG induced by TMS during wake, sleep deprivation and sleep

Cortical excitability on sleep deprivation measured by transcranial magnetic stimulation: A systematic review and meta-analysis

Sleep deprivation is a common public problem, and researchers speculated its neurophysiological mechanisms related to cortical excitatory and inhibitory activity. Recently, transcranial magnetic stimulation combined with electromyography (TMS-EMG) and electroencephalography (TMS-EEG) have been used to assess cortical excitability in sleep-deprived individuals, but the results were inconsistent. Therefore, we conducted a meta-analysis to summarize relevant TMS-evoked indices of excitability and inhibition for exploring the cortical effects of sleep deprivation. In TMS-EMG studies, short-interval cortical inhibition (SICI) significantly decreased in sleep-deprived subjects; while the intracortical facilitation (ICF), resting motor threshold (RMT), and cortical silent period (CSP) were not significant compared to healthy controls. In TMS-EEG studies, the amplitude and slope of TMS-evoked potential (TEP) increased in sleep-deprived subjects. This study indicated that cortical inhibition decreased following sleep deprivation based on the TMS-EMG results and cortical excitability enhanced in the TMS-EEG results, supporting the disturbance of cortical excitability in sleep-deprived individuals.

The Use of Cognitive Paired Associative Stimulation (C-PAS) in Investigating and Remediating the Effects of Sleep Deprivation on Working Memory in Humans: The Importance of State-Dependency

Purpose of Review

Sleep deprivation is a global health issue, and the resultant cognitive deficits can be debilitating. A series of studies reported success with individually neuronavigated transcranial magnetic stimulation (TMS), coupled with online task performance, in substantially reducing performance deficits in working memory in healthy adults caused by 2 days of total sleep depression. This paradigm of coupling TMS with online task performance has been referred to as Cognitive Paired Associative Stimulation (C-PAS). This review describes those studies and the research since using various TMS paradigms to remediate working memory deficits in sleep deprivation.

Recent Findings

Three such studies were found, but none replicated the earlier findings. However, in each case, there were differences in study design that might explain the negative findings and inform future methodological choices and to underline the need to combine TMS with brain imaging guidance.

Summary

Online task performance during TMS, as done in the C-PAS paradigm, appears to be essential to demonstrating lasting remediation of working memory deficits induced by sleep deprivation. This observation highlights the importance of state-dependency in determining the effects of TMS. Further work needs to be done to clarify the potential role of C-PAS in alleviating the effects of sleep deprivation and studying cognitive processes affected by sleep.

Response to photic stimulation as a measure of cortical excitability in epilepsy patients

Studying states and state transitions in the brain is challenging due to nonlinear, complex dynamics. In this research, we analyze the brain's response to non-invasive perturbations. Perturbation techniques offer a powerful method for studying complex dynamics, though their translation to human brain data is under-explored. This method involves applying small inputs, in this case via photic stimulation, to a system and measuring its response. Sensitivity to perturbations can forewarn a state transition. Therefore, biomarkers of the brain's perturbation response or "cortical excitability" could be used to indicate seizure transitions. However, perturbing the brain often involves invasive intracranial surgeries or expensive equipment such as transcranial magnetic stimulation (TMS) which is only accessible to a minority of patient groups, or animal model studies. Photic stimulation is a widely used diagnostic technique in epilepsy that can be used as a non-invasive perturbation paradigm to probe brain dynamics during routine electroencephalography (EEG) studies in humans. This involves changing the frequency of strobing light, sometimes triggering a photo-paroxysmal response (PPR), which is an electrographic event that can be studied as a state transition to a seizure state. We investigate alterations in the response to these perturbations in patients with genetic generalized epilepsy (GGE), with (n = 10) and without (n = 10) PPR, and patients with psychogenic non-epileptic seizures (PNES; n = 10), compared to resting controls (n = 10). Metrics of EEG time-series data were evaluated as biomarkers of the perturbation response including variance, autocorrelation, and phase-based synchrony measures. We observed considerable differences in all group biomarker distributions during stimulation compared to controls. In particular, variance and autocorrelation demonstrated greater changes in epochs close to PPR transitions compared to earlier stimulation epochs. Comparison of PPR and spontaneous seizure morphology found them indistinguishable, suggesting PPR is a valid proxy for seizure dynamics. Also, as expected, posterior channels demonstrated the greatest change in synchrony measures, possibly reflecting underlying PPR pathophysiologic mechanisms. We clearly demonstrate observable changes at a group level in cortical excitability in epilepsy patients as a response to perturbation in EEG data. Our work re-frames photic stimulation as a non-invasive perturbation paradigm capable of inducing measurable changes to brain dynamics.

Effects of sleep deprivation on cortical excitability: A threshold-tracking TMS study and review of the literature

Objective

Insufficient sleep is linked to several health problems. Previous studies on the effects of sleep deprivation on cortical excitability using conventional transcranial magnetic stimulation (TMS) included a limited number of modalities, and few inter-stimulus intervals (ISIs) and showed conflicting results. This study aimed to investigate the effects of sleep deprivation on cortical excitability through threshold-tracking TMS, using a wide range of protocols at multiple ISIs.

Methods

Fifteen healthy subjects (mean age ± SD: 36 ± 3.34 years) were included. The following tests were performed before and after 24 h of sleep deprivation using semi-automated threshold-tacking TMS protocols: short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) at 11 ISIs between 1 and 30 ms, short interval intracortical facilitation (SICF) at 14 ISIs between 1 and 4.9 ms, long interval intracortical inhibition (LICI) at 6 ISIs between 50 and 300 ms, and short-latency afferent inhibition (SAI) at 12 ISIs between 16 and 30 ms.

Results

No significant differences were observed between pre- and post-sleep deprivation measurements for SICI, ICF, SICF, or LICI at any ISIs (p < 0.05). As for SAI, we found a difference at 28 ms (p = 0.007) and 30 ms (p = 0.04) but not at other ISIs.

Conclusions

Sleep deprivation does not affect cortical excitability except for SAI.

Significance

This study confirms some of the previous studies while contradicting others.

Graph Analysis of TMS-EEG Connectivity Reveals Hemispheric Differences following Occipital Stimulation

(1) Background: Transcranial magnetic stimulation combined with electroencephalography (TMS-EEG) provides a unique opportunity to investigate brain connectivity. However, possible hemispheric asymmetries in signal propagation dynamics following occipital TMS have not been investigated. (2) Methods: Eighteen healthy participants underwent occipital single-pulse TMS at two different EEG sites, corresponding to early visual areas. We used a state-of-the-art Bayesian estimation approach to accurately estimate TMS-evoked potentials (TEPs) from EEG data, which has not been previously used in this context. To capture the rapid dynamics of information flow patterns, we implemented a self-tuning optimized Kalman (STOK) filter in conjunction with the information partial directed coherence (iPDC) measure, enabling us to derive time-varying connectivity matrices. Subsequently, graph analysis was conducted to assess key network properties, providing insight into the overall network organization of the brain network. (3) Results: Our findings revealed distinct lateralized effects on effective brain connectivity and graph networks after TMS stimulation, with left stimulation facilitating enhanced communication between contralateral frontal regions and right stimulation promoting increased intra-hemispheric ipsilateral connectivity, as evidenced by statistical test (p < 0.001). (4) Conclusions: The identified hemispheric differences in terms of connectivity provide novel insights into brain networks involved in visual information processing, revealing the hemispheric specificity of neural responses to occipital stimulation.

Recovery of clinical, cognitive and cortical activity measures following mild traumatic brain injury (mTBI): A longitudinal investigation

The mechanisms that underpin recovery following mild traumatic brain injury (mTBI) remain poorly understood. Identifying neurophysiological markers and their functional significance is necessary to develop diagnostic and prognostic indicators of recovery. The current study assessed 30 participants in the subacute phase of mTBI (10-31 days post-injury) and 28 demographically matched controls. Participants also completed 3 month (mTBI: N = 21, control: N = 25) and 6 month (mTBI: N = 15, control: N = 25) follow up sessions to track recovery. At each time point, a battery of clinical, cognitive, and neurophysiological assessments was completed. Neurophysiological measures included resting-state electroencephalography (EEG) and transcranial magnetic stimulation combined with EEG (TMS-EEG). Outcome measures were analysed using mixed linear models (MLM). Group differences in mood, post-concussion symptoms and resting-state EEG resolved by 3 months, and recovery was maintained at 6 months. On TMS-EEG derived neurophysiological measures of cortical reactivity, group differences ameliorated at 3 months but re-emerged at 6 months, while on measures of fatigue, group differences persisted across all time points. Persistent neurophysiological changes and greater fatigue in the absence of measurable cognitive impairment may suggest the impact of mTBI on neuronal communication may leads to increased neural effort to maintain efficient function. Neurophysiological measures to track recovery may help identify both temporally optimal windows and therapeutic targets for the development of new treatments in mTBI.

Oscillatory EEG-TMS Reactivity in Parkinson Disease

PURPOSE

A dysfunction of beta oscillatory activity is the neurophysiological hallmark of Parkinson disease (PD). How cortical activity reacts to external perturbations may provide insight into pathophysiological mechanisms. This study aims at identifying modifications in EEG rhythms after transcranial magnetic stimulation (TMS) in PD. We hypothesize that single-pulse TMS can modulate brain intrinsic oscillatory properties (e.g., beta excess).

METHODS

EEG data were coregistered during single-pulse TMS (100 stimuli over the primary motor cortex [M1, hotspot for Abductor Pollicis Brevis], random intertrial interval from 8 to 13 seconds). We used a time-frequency analysis based on wavelet method to characterize modification of oscillatory rhythms (delta [1-4 Hz], theta [4-7 Hz], alpha [8-12 Hz], and beta [13-30 Hz] in 15 participants with PD compared with 10 healthy controls.

RESULTS

An increase in beta power over the sensorimotor areas was recorded at rest in the PD group ( P < 0.05). Brain oscillations in PD transiently reset after TMS: beta power over M1 becomes comparable to that recorded in aged-matched healthy subjects in the 2 seconds following TMS.

CONCLUSIONS

Transcranial magnetic stimulation over the dominant motor cortex transiently normalizes cortical oscillations. More user-friendly noninvasive brain stimulation needs to be trialed, based on this proof of concept, to provide practical, portable techniques to treat motor symptoms in PD.

Brain Stimulation for Improving Sleep and Memory

Over the past few decades, the importance of sleep has become increasingly recognized for many physiologic functions, including cognition. Many studies have reported the deleterious effect of sleep loss or sleep disruption on cognitive performance. Beyond ensuring adequate sleep quality and duration, discovering methods to enhance sleep to augment its restorative effects is important to improve learning in many populations, such as the military, students, age-related cognitive decline, and cognitive disorders.

Randomized trial of rTMS in traumatic brain injury: improved subjective neurobehavioral symptoms and increases in EEG delta activity

PRIMARY OBJECTIVE

While repetitive transcranial magnetic stimulation (rTMS) has shown efficacy for cognitive difficulties accompanying depression, it is unknown if it can improve cognition in persons with traumatic brain injury.

RESEARCH DESIGN

Using a sham-controlled crossover design, we tested the capacity of high frequency rTMS of the prefrontal cortex to improve neuropsychological performance in attention, learning and memory, and executive function.

METHODS

Twenty-six participants with cognitive complaints and a history of mild-to-moderate traumatic brain injury were randomly assigned to receive first either active or sham 10 Hz stimulation for 20 minutes (1200 pulses) per session for five consecutive days. After a one-week washout, the other condition (active or sham) was applied. Pre- and post-treatment measures included neuropsychological tests, cognitive and emotional symptoms, and EEG.

MAIN OUTCOMES AND RESULTS

Results indicated no effect of treatment on cognitive function. Subjective measures of depression, sleep dysfunction, post-concussive symptoms (PCS), and executive function showed significant improvement with stimulation, retaining improved levels at two-week follow-up. EEG delta power exhibited elevation one week after stimulation cessation.

CONCLUSIONS

While there is no indication that rTMS is beneficial for neuropsychological performance, it may improve PCS and subjective cognitive dysfunction. Long-term alterations in cortical oscillations may underlie the therapeutic effects of rTMS.

Shaping the slow waves of sleep: A systematic and integrative review of sleep slow wave modulation in humans using non-invasive brain stimulation

The experimental study of electroencephalographic slow wave sleep (SWS) stretches over more than half a century and has corroborated its importance for basic physiological processes, such as brain plasticity, metabolism and immune system functioning. Alterations of SWS in aging or pathological conditions suggest that modulating SWS might constitute a window for clinically relevant interventions. This work provides a systematic and integrative review of SWS modulation through non-invasive brain stimulation in humans. A literature search using PubMed, conducted in May 2020, identified 3220 studies, of which 82 fulfilled inclusion criteria. Three approaches have been adopted to modulate the macro- and microstructure of SWS, namely auditory, transcranial electrical and transcranial magnetic stimulation. Our current knowledge about the modulatory mechanisms, the space of stimulation parameters and the physiological and behavioral effects are reported and evaluated. The integration of findings suggests that sleep slow wave modulation bears the potential to promote our understanding of the functions of SWS and to develop new treatments for conditions of disrupted SWS.

Natural oscillation frequencies in the two lateral prefrontal cortices induced by Transcranial Magnetic Stimulation

Different cortical regions respond with distinct rhythmic patterns of neural oscillations to Transcranial Magnetic Stimulation (TMS). We investigated natural frequencies induced by TMS in left and right homologous dorsolateral prefrontal cortices (DLPFC) and related hemispheric differences. In 12 healthy young adults, single-pulse TMS was delivered in different blocks close to F3 and F4 channels to target left and right DLPFC. An occipital site near PO3 was stimulated as control. TMS-related spectral perturbation analyses were performed on recorded EEG data. A widespread unspecific increase in theta power was observed for all stimulation sites. However, occipital TMS induced greater alpha activity and a 10.58 Hz natural frequency, while TMS over the left and right DLPFC resulted in similar beta band modulations and a natural frequency of 18.77 and 18.5 Hz, respectively. In particular, TMS-related specific increase in beta activity was stronger for the right than the left DLPFC. The right DLPFC is more specifically tuned to its natural beta frequency when it is directly stimulated by TMS than with TMS over the left counterpart (or a posterior region), while the left DLPFC increases its beta activity more similarly irrespective of whether it is directly stimulated or through right homologous stimulation. These results yield important implications for both basic neuroscience research on inter-hemispheric prefrontal interactions and clinical applications.

Concussive head injury exacerbates neuropathology of sleep deprivation: Superior neuroprotection by co-administration of TiO2-nanowired cerebrolysin, alpha-melanocyte-stimulating hormone, and mesenchymal stem cells

Sleep deprivation (SD) is common in military personnel engaged in combat operations leading to brain dysfunction. Military personnel during acute or chronic SD often prone to traumatic brain injury (TBI) indicating the possibility of further exacerbating brain pathology. Several lines of evidence suggest that in both TBI and SD alpha-melanocyte-stimulating hormone (α-MSH) and brain-derived neurotrophic factor (BDNF) levels decreases in plasma and brain. Thus, a possibility exists that exogenous supplement of α-MSH and/or BDNF induces neuroprotection in SD compounded with TBI. In addition, mesenchymal stem cells (MSCs) are very portent in inducing neuroprotection in TBI. We examined the effects of concussive head injury (CHI) in SD on brain pathology. Furthermore, possible neuroprotective effects of α-MSH, MSCs and neurotrophic factors treatment were explored in a rat model of SD and CHI. Rats subjected to 48h SD with CHI exhibited higher leakage of BBB to Evans blue and radioiodine compared to identical SD or CHI alone. Brain pathology was also exacerbated in SD with CHI group as compared to SD or CHI alone together with a significant reduction in α-MSH and BDNF levels in plasma and brain and enhanced level of tumor necrosis factor-alpha (TNF-α). Exogenous administration of α-MSH (250μg/kg) together with MSCs (1×10⁶) and cerebrolysin (a balanced composition of several neurotrophic factors and active peptide fragments) (5mL/kg) significantly induced neuroprotection in SD with CHI. Interestingly, TiO₂ nanowired delivery of α-MSH (100μg), MSCs, and cerebrolysin (2.5mL/kg) induced enhanced neuroprotection with higher levels of α-MSH and BDNF and decreased the TNF-α in SD with CHI. These observations are the first to show that TiO₂ nanowired administration of α-MSH, MSCs and cerebrolysin induces superior neuroprotection following SD in CHI, not reported earlier. The clinical significance of our findings in light of the current literature is discussed.

Brain Stimulation for Improving Sleep and Memory

Given the critical role of sleep, particularly sleep slow oscillations, sleep spindles, and hippocampal sharp wave ripples, in memory consolidation, sleep enhancement represents a key opportunity to improve cognitive performance. Techniques such as transcranial electrical and magnetic stimulation and acoustic stimulation can enhance slow oscillations and sleep spindles and potentially improve memory. Targeted memory reactivation in sleep may enhance or stabilize memory consolidation. Each technique has technical considerations that may limit its broader clinical application. Therefore, neurostimulation to enhance sleep quality, in particular sleep slow oscillations, has the potential for improving sleep-related memory consolidation in healthy and clinical populations.

Personalized transcranial alternating current stimulation (tACS) and physical therapy to treat motor and cognitive symptoms in Parkinson's disease: A randomized cross-over trial

Abnormal cortical oscillations are markers of Parkinson's Disease (PD). Transcranial alternating current stimulation (tACS) can modulate brain oscillations and possibly impact on behaviour. Mapping of cortical activity (prevalent oscillatory frequency and topographic scalp distribution) may provide a personalized neurotherapeutic target and guide non-invasive brain stimulation. This is a cross-over, double blinded, randomized trial. Electroencephalogram (EEG) from participants with PD referred to Specialist Clinic, University Hospital, were recorded. TACS frequency and electrode position were individually defined based on statistical comparison of EEG power spectra maps with normative data from our laboratory. Stimulation frequency was set according to the EEG band displaying higher power spectra (with beta excess on EEG map, tACS was set at 4 Hz; with theta excess, tACS was set at 30 Hz). Participants were randomized to tACS or random noise stimulation (RNS), 5 days/week for 2-weeks followed by ad hoc physical therapy. EEG, motor (Unified Parkinson's Disease Rating Scale-motor: UPDRS III), neuropsychological (frontal, executive and memory tests) performance and mood were measured before (T0), after (T1) and 4-weeks after treatment (T2). A linear model with random effects and Wilcoxon test were used to detect differences. Main results include a reduction of beta rhythm in theta-tACS vs. RNS group at T1 over right sensorimotor area (p = .014) and left parietal area (p = .010) and at T2 over right sensorimotor area (p = .004) and left frontal area (p = .039). Bradykinesia items improved at T1 (p = .002) and T2 (p = .047) compared to T0 in the tACS group. In the tACS group the Montréal Cognitive Assessment (MoCA) improved at T2 compared with T1 (p = .049). Individualized tACS in PD improves motor and cognitive performance. These changes are associated with a reduction of excessive fast EEG oscillations.

Phenomenology of neurophysiologic changes during surgical treatment of carotid stenosis using signal analysis

Objective

To describe the changes in the shape and topology of the somatosensory evoked potential (SSEP) during carotid endarterectomy, with particular reference to the time of clamping.

Methods

Routine intraoperative monitoring was performed on 30 patients undergoing carotid endarterectomy (15) or undergoing stenting (15) using median nerve SSEPs. Post-operatively the first and second derivatives of the potential were examined. Separate analysis of the SSEP using wavelets was also performed.

Results

In no instances did changes in the SSEP reach clinical significance. The first derivative showed significant changes that were temporally related to the clamp period. After clamping the 'velocity' was higher than baseline. There were changes in the wavelets related to the clamp period with more marked spectral edges at the conclusion of the procedure than baseline. In all instances the patient had a good clinical outcome.

Conclusions

Wavelet and derivative analysis of evoked potentials show changes that are not apparent with measures of amplitude and latency. The clinical relevance of these changes remains uncertain and await larger studies.

Significance

Increased velocity and spectral edges may be markers of increased cerebral blood flow, at least in the setting of pre-existing carotid stenosis.

Oscillatory Activities in Neurological Disorders of Elderly: Biomarkers to Target for Neuromodulation

Non-invasive brain stimulation (NIBS) has been under investigation as adjunct treatment of various neurological disorders with variable success. One challenge is the limited knowledge on what would be effective neuronal targets for an intervention, combined with limited knowledge on the neuronal mechanisms of NIBS. Motivated on the one hand by recent evidence that oscillatory activities in neural systems play a role in orchestrating brain functions and dysfunctions, in particular those of neurological disorders specific of elderly patients, and on the other hand that NIBS techniques may be used to interact with these brain oscillations in a controlled way, we here explore the potential of modulating brain oscillations as an effective strategy for clinical NIBS interventions. We first review the evidence for abnormal oscillatory profiles to be associated with a range of neurological disorders of elderly (e.g., Parkinson's disease (PD), Alzheimer's disease (AD), stroke, epilepsy), and for these signals of abnormal network activity to normalize with treatment, and/or to be predictive of disease progression or recovery. We then ask the question to what extent existing NIBS protocols have been tailored to interact with these oscillations and possibly associated dysfunctions. Our review shows that, despite evidence for both reliable neurophysiological markers of specific oscillatory dis-functionalities in neurological disorders and NIBS protocols potentially able to interact with them, there are few applications of NIBS aiming to explore clinical outcomes of this interaction. Our review article aims to point out oscillatory markers of neurological, which are also suitable targets for modification by NIBS, in order to facilitate in future studies the matching of technical application to clinical targets.

Neurophysiological, psychological and behavioural correlates of rTMS treatment in alcohol dependence

BACKGROUND

Addiction is associated with dorso-lateral prefrontal cortex (DLPFC) dysfunction and altered brain-oscillations. High frequency repetitive transcranial magnetic stimulation (HFrTMS) over DLPFC reportedly reduces drug craving. Its effects on neuropsychological, behavioural and neurophysiological are unclear.

METHODS

We assessed psychological, behavioural and neurophysiological effects of 4 sessions of 10-min adjunctive HFrTMS over the left DLPFC during two weeks during a residential programme for alcohol detoxification. Participants were randomized to active HFrTMS (10 Hz, 100% motor threshold) or sham. Immediately before the first and after the last session, 32-channels EEG was recorded and alcohol craving Visual Analogue Scale, Symptom Check List-90-R, Numeric Stroop task and Go/No-go task administered. Tests were repeated at 1-month follow-up.

RESULTS

17 subjects (mean age 44.7 years, 4 F) were assessed. Active rTMS subjects performed better at Stroop test at end of treatment (p=0.036) and follow up (p=0.004) and at Go-NoGo at end of treatment (p=0.05) and follow up (p=0.015). Depressive symptoms decreased at end of active treatment (p=0.036). Active-TMS showed an overall decrease of fast EEG frequencies after treatment compared to sham (p=0.026). No significant modifications over time or group emerged for craving and number of drinks at follow up.

CONCLUSION

4 HFrTMS sessions over two weeks on the left DLPFC can improve inhibitory control task and selective attention and reduce depressive symptoms. An overall reduction of faster EEG frequencies was observed. Nonetheless, this schedule is ineffective in reducing craving and alcohol intake.

Sleep Deprivation-Induced Blood-Brain Barrier Breakdown and Brain Dysfunction are Exacerbated by Size-Related Exposure to Ag and Cu Nanoparticles. Neuroprotective Effects of a 5-HT3 Receptor Antagonist Ondansetron

Military personnel are often subjected to sleep deprivation (SD) during combat operations. Since SD is a severe stress and alters neurochemical metabolism in the brain, a possibility exists that acute or long-term SD will influence blood-brain barrier (BBB) function and brain pathology. This hypothesis was examined in young adult rats (age 12 to 14 weeks) using an inverted flowerpot model. Rats were placed over an inverted flowerpot platform (6.5 cm diameter) in a water pool where the water levels are just 3 cm below the surface. In this model, animals can go to sleep for brief periods but cannot achieve deep sleep as they would fall into water and thus experience sleep interruption. These animals showed leakage of Evans blue in the cerebellum, hippocampus, caudate nucleus, parietal, temporal, occipital, cingulate cerebral cortices, and brain stem. The ventricular walls of the lateral and fourth ventricles were also stained blue, indicating disruption of the BBB and the blood-cerebrospinal fluid barrier (BCSFB). Breakdown of the BBB or the BCSFB fluid barrier was progressive in nature from 12 to 48 h but no apparent differences in BBB leakage were seen between 48 and 72 h of SD. Interestingly, rats treated with metal nanoparticles, e.g., Cu or Ag, showed profound exacerbation of BBB disruption by 1.5- to 4-fold, depending on the duration of SD. Measurement of plasma and brain serotonin showed a close correlation between BBB disruption and the amine level. Repeated treatment with the serotonin 5-HT3 receptor antagonist ondansetron (1 mg/kg, s.c.) 4 and 8 h after SD markedly reduced BBB disruption and brain pathology after 12 to 24 h SD but not following 48 or 72 h after SD. However, TiO2-nanowired ondansetron (1 mg/kg, s.c) in an identical manner induced neuroprotection in rats following 48 or 72 h SD. However, plasma and serotonin levels were not affected by ondansetron treatment. Taken together, our observations are the first to show that (i) SD could induce BBB disruption and brain pathology, (ii) nanoparticles exacerbate SD-induced brain damage, and (iii) serotonin 5-HT3 receptor antagonist ondansetron is neuroprotective in SD that is further potentiated byTiO2-nanowired delivery, not reported earlier.

Sleep affects cortical source modularity in temporal lobe epilepsy: A high-density EEG study

OBJECTIVE

Interictal epileptiform discharges (IEDs) constitute a perturbation of ongoing cerebral rhythms, usually more frequent during sleep. The aim of the study was to determine whether sleep influences the spread of IEDs over the scalp and whether their distribution depends on vigilance-related modifications in cortical interactions.

METHODS

Wake and sleep 256-channel electroencephalography (EEG) data were recorded in 12 subjects with right temporal lobe epilepsy (TLE) differentiated by whether they had mesial or neocortical TLE. Spikes were selected during wake and sleep. The averaged waking signal was subtracted from the sleep signal and projected on a bidimensional scalp map; sleep and wake spike distributions were compared by using a t-test. The superimposed signal of sleep and wake traces was obtained; the rising phase of the spike, the peak, and the deflections following the spike were identified, and their cortical generator was calculated using low-resolution brain electromagnetic tomography (LORETA) for each group.

RESULTS

A mean of 21 IEDs in wake and 39 in sleep per subject were selected. As compared to wake, a larger IED scalp projection was detected during sleep in both mesial and neocortical TLE (p<0.05). A series of EEG deflections followed the spike, the cortical sources of which displayed alternating activations of different cortical areas in wake, substituted by isolated, stationary activations in sleep in mesial TLE and a silencing in neocortical TLE.

CONCLUSION

During sleep, the IED scalp region increases, while cortical interaction decreases.

SIGNIFICANCE

The interaction of cortical modules in sleep and wake in TLE may influence the appearance of IEDs on scalp EEG; in addition, IEDs could be proxies for cerebral oscillation perturbation.

Wakefulness delta waves increase after cortical plasticity induction

OBJECTIVE

Delta waves (DW) are present both during sleep and in wakefulness. In the first case, DW are considered effectors of synaptic plasticity, while in wakefulness, when they appear in the case of brain lesions, their functional meaning is not unanimously recognized. To throw light on the latter, we aimed to investigate the impact on DW exerted by the cortical plasticity-inducing protocol of intermittent theta burst stimulation (iTBS).

METHODS

Twenty healthy subjects underwent iTBS (11 real iTBS and nine sham iTBS) on the left primary motor cortex with the aim of inducing long-term potentiation (LTP)-like phenomena. Five-minute resting open-eye 32-channel EEG, right opponens pollicis motor-evoked potentials (MEPs), and alertness behavioral scales were collected before and up to 30 min after the iTBS. Power spectral density (PSD), interhemispheric coherence between homologous sensorimotor regions, and intrahemispheric coherence were calculated for the frequency bands ranging from delta to beta.

RESULTS

Real iTBS induced a significant increase of both MEP amplitude and DW PSD lasting up to 30 min after stimulation, while sham iTBS did not. The DW increase was evident over frontal areas ipsilateral and close to the stimulated cortex (electrode F3). Neither real nor sham iTBS induced significant modifications in the PSD of theta, alpha, and beta bands and in the interhemispheric coherence. Behavioral visuo-analogic scales score did not demonstrate changes in alertness after stimulations. No correlations were found between MEP amplitude and PSD changes in the delta band.

CONCLUSIONS

Our data showed that LTP induction in the motor cortex during wakefulness, by means of iTBS, is accompanied by a large and enduring increase of DW over the ipsilateral frontal cortex.

SIGNIFICANCE

The present results are strongly in favor of a prominent role of DW in the neural plasticity processes taking place during the awake state.