Neuroelectric Activity Research Articles

Healthy aging changes in conventional frequency bands of neuroelectric brain activity reconstructed from resting-state MEG.

Age-related dependencies of electric and spectral powers in conventional frequency bands were studied by the newly proposed method of detailed spectral analysis. The magnetic encephalograms (MEG) and magnetic resonance images (MRI) of the head were obtained from the open archive Cam-CAN. The spatial distributions of elementary spectral components (MEG-based functional tomograms) were reconstructed from MEG for 501 subjects (248 males and 253 females, ages 18-88 years, mean age 54.8 ±18.4). Physiological noise was eliminated by joint analysis of MEG-based functional tomogram and magnetic resonance image for each subject. Spectral and electric powers were calculated in six conventional frequency bands (1-4 Hz - delta; 4-8 Hz - theta; 8-13 Hz - alpha; 13-21 Hz - beta-1; 21-30 Hz - beta-2; 30-48 Hz - gamma), and age-related changes were examined. It was found that the spectral power of the delta band is significantly decreasing (p-value 0.002) and beta-1 and gamma are significantly increasing (p-values 0.001, 0.003). Electric power in the delta band is significantly decreasing (p-value 0.033), while electric power in the beta-1 band is significantly increasing (p-value 0.001). Also, the summary electric power of theta, alpha, beta-1, beta-2, and gamma bands is significantly increasing (p-value 0.024). Results represent general time dependence of the aging brain's electrical sources. The proposed method of joint MEG and MRI analysis can be used for a detailed study of sources location and connectivity.

Stimulus-induced rotary saturation imaging of visually evoked response: A pilot study.

Spin-lock (SL) pulses have been proposed to directly detect neuronal activity otherwise inaccessible through standard functional magnetic resonance imaging. However, the practical limits of this technique remain unexplored. Key challenges in SL-based detection include ultra-weak signal variations, sensitivity to magnetic field inhomogeneities, and potential contamination from blood oxygen level-dependent effects, all of which hinder the reliable isolation of neuronal signals. This pilot study evaluates the performance of the stimulus-induced rotary saturation (SIRS) technique to map visual stimulation response in the human cortex. A rotary echo spin-lock (RESL) preparation followed by a 2D echo planar imaging readout was used to investigate 12 healthy subjects at rest and during continuous exposure to 8Hz flickering light. The SL amplitude was fixed to the target neuroelectric oscillations at that frequency. The signal variance was used as contrast metric, and two alternative post-processing pipelines (regression-filtering-rectification and normalized subtraction) were statistically evaluated. Higher variance in the SL signal was detected in four of the 12 subjects. Although group-level analysis indicated activation in the occipital pole, analysis of variance revealed that this difference was not statistically significant, highlighting the need for comparable control measures and more robust preparations. Further optimization in sensitivity and robustness is required to noninvasively detect physiological neuroelectric activity in the human brain.

Modal Analysis of Cerebrovascular Effects for Digital Health Integration of Neurostimulation Therapies-A Review of Technology Concepts.

Transcranial electrical stimulation (tES) is increasingly recognized for its potential to modulate cerebral blood flow (CBF) and evoke cerebrovascular reactivity (CVR), which are crucial in conditions like mild cognitive impairment (MCI) and dementia. This study explores the impact of tES on the neurovascular unit (NVU), employing a physiological modeling approach to simulate the vascular response to electric fields generated by tES. Utilizing the FitzHugh-Nagumo model for neuroelectrical activity, we demonstrate how tES can initiate vascular responses such as vasoconstriction followed by delayed vasodilation in cerebral arterioles, potentially modulated by a combination of local metabolic demands and autonomic regulation (pivotal locus coeruleus). Here, four distinct pathways within the NVU were modeled to reflect the complex interplay between synaptic activity, astrocytic influences, perivascular potassium dynamics, and smooth muscle cell responses. Modal analysis revealed characteristic dynamics of these pathways, suggesting that oscillatory tES may finely tune the vascular tone by modulating the stiffness and elasticity of blood vessel walls, possibly by also impacting endothelial glycocalyx function. The findings underscore the therapeutic potential vis-à-vis blood-brain barrier safety of tES in modulating neurovascular coupling and cognitive function needing the precise modulation of NVU dynamics. This technology review supports the human-in-the-loop integration of tES leveraging digital health technologies for the personalized management of cerebral blood flow, offering new avenues for treating vascular cognitive disorders. Future studies should aim to optimize tES parameters using computational modeling and validate these models in clinical settings, enhancing the understanding of tES in neurovascular health.

The relationship between cardiorespiratory fitness and inhibitory control following acute stress: An ERP study.

Although the relationships among acute stress, cardiorespiratory fitness (CRF), and cognitive function have been examined, whether CRF is related to behavioral and neuroelectric indices of inhibitory control following acute stress remains unknown. The purpose of the current study was to investigate the combined influence of acute stress and CRF on inhibitory control. Participants, aged 20-30 years, were stratified into the Higher-Fit (n = 31) and the Lower-Fit (n = 32) groups, and completed a Stroop task following the modified Maastricht Acute Stress Test (MAST) in the stress condition and the sham-MAST in the non-stress condition, during which electroencephalography was recorded. Behavioral (i.e., response time and accuracy) and neuroelectric (N2 and P3b components of the event-related potential) outcomes of inhibitory control were obtained. While the Higher-Fit group demonstrated shorter response times and higher accuracy than the Lower-Fit group following both the MAST and the sham-MAST, they also exhibited selective benefits of acute stress on inhibitory control performance (i.e., decreased response times and diminished interference scores). CRF-dependent alterations in neuroelectric indices were also observed, with the Higher-Fit group displaying smaller N2 and greater P3b amplitudes than the Lower-Fit group following the sham-MAST, and increased N2 and attenuated P3b amplitudes following the MAST. Collectively, these findings not only confirm the positive relationship between CRF and inhibitory control but also provide novel insights into the potential influence of CRF on inhibitory control and associated neuroelectric activity following acute stress.

A Simple, Testable Mind–Body Solution?

Neuroelectrical panpsychism (NP) offers a clear, simple, testable mind–body solution. It says that everything is at least minimally conscious, and electrical activity across separate neurons creates a unified, intelligent mind. NP draws on recent experimental evidence to address the easy problem of specifying the mind's neural correlates. These correlates are neuroelectrical activities that, for example, generate our different qualia, unite them to form perceptions and emotions, and help guide brain operations. NP also addresses the hard problem of why minds accompany these neural correlates. Here, the real nature of matter-energy (beyond how it appears to sense organs) is consciousness that occupies space, exerts forces, and unites neuroelectrically to form minds. This doesn't reduce consciousness to observable neural activities, nor posit any radically different entities. NP also deals with panpsychism's combination problem by explaining how the mind's subject and experiences arise by electrically combining simple experiences in brains.

Changes in brain rhythms and connectivity tracking fear acquisition and reversal

Fear conditioning is used to investigate the neural bases of threat and anxiety, and to understand their flexible modifications when the environment changes. This study aims to examine the temporal evolution of brain rhythms using electroencephalographic signals recorded in healthy volunteers during a protocol of Pavlovian fear conditioning and reversal. Power changes and Granger connectivity in theta, alpha, and gamma bands are investigated from neuroelectrical activity reconstructed on the cortex. Results show a significant increase in theta power in the left (contralateral to electrical shock) portion of the midcingulate cortex during fear acquisition, and a significant decrease in alpha power in a broad network over the left posterior-frontal and parietal cortex. These changes occur since the initial trials for theta power, but require more trials (3/4) to develop for alpha, and are also present during reversal, despite being less pronounced. In both bands, relevant changes in connectivity are mainly evident in the last block of reversal, just when power differences attenuate. No significant changes in the gamma band were detected. We conclude that the increased theta rhythm in the cingulate cortex subserves fear acquisition and is transmitted to other cortical regions via increased functional connectivity allowing a fast theta synchronization, whereas the decrease in alpha power can represent a partial activation of motor and somatosensory areas contralateral to the shock side in the presence of a dangerous stimulus. In addition, connectivity changes at the end of reversal may reflect long-term alterations in synapses necessary to reverse the previously acquired contingencies.

Automatic attention to sexual stimuli: exploring the role of neuroticism and sexual excitation/inhibition through event-related potentials.

Previous findings have shown that neuroticism is a higher-order vulnerability factor in the development and maintenance of sexual dysfunctions and can have an impact on the attentional processing of sexual stimuli; however, the influence of psychosexual dimensions on the early automatic phases of such cognitive processes has not been established yet. To examine the mediating role of sexual inhibition/excitation propensity in the relationship between neuroticism and automatic attention to visual erotica and to identify the neuroelectric correlates of such a process. We analyzed the answers provided by 58 individuals on the Neuroticism subscale of the NEO Personality Inventory-Revised and the Sexual Inhibition/Excitation Scales. Event-related potentials (ERPs) were recorded during a modified oddball paradigm containing romantic and sexually explicit pictures. Parallel mediations were performed to simultaneously test the mediating role of sexual inhibition/excitation in the relationship between neuroticism and each ERP. Three early attention ERP components (P1, P2, and N2) were assessed. Findings revealed an indirect effect of neuroticism on automatic attention, via sexual inhibition due to threat of performance failure (SIS1), for romantic and sexually explicit stimuli. This effect was significant only for component N2, which showed increased amplitudes and earlier latencies in participants with high SIS1. Sexual stimuli, due to their emotional valence and arousal potential, might be perceived as virtually threatening by individuals with neuroticism, who may benefit from strategies that decrease hyperarousal and sympathetic activation. This was one of the first studies to analyze neuroelectric activity associated with automatic attention toward sexual stimuli in relation to personality and sexual excitation/inhibition propensity. Nevertheless, the limited number of participants demands caution in generalizing the results. These results provide a better understanding of the relationship between personality and sexual cognition and open new avenues of research in relation to other automatic cognitive phenomena related to human sexual behavior.

Acute effects of exercise engagement on neurocognitive function: a systematic review and meta-analysis on P3 amplitude and latency

ABSTRACT Although the acute effect of exercise on behavioral cognitive performance is well-documented in the exercise psychology field, a comprehensive evaluation on neuroelectric brain activity that determines healthy cognitive functioning following acute exercise is lacking. This systematic review included 39 studies examining acute exercise effects on P3 of event-related potential through its amplitude and latency, which reflect the amounts of attentional resources allocated to and the processing speed for categorizing a stimulus. Exercise has small effects on increasing amplitude and decreasing latency. The amplitude effect was moderated by age and the type, intensity, and duration of exercise, with a smaller effect being observed for individuals aged ≤18 and 19–35 than >60 years, for high-intensity than moderate-intensity exercise, for high-intensity interval training exercise than aerobic, resistance, and combined exercise, as well as for exercise lasting ≤10 and 11–20 than exercise lasting 21–30 min. The latency effect was moderated by exercise duration, with 11–20 min exercise showing a smaller effect than exercise lasting ≤10 min. These results demonstrated that acute exercise enhances allocation of attentional resources and processing speed needed to implement cognitive processes underlying goal-directed behavior. Further, these effects may be manipulated through targeting specific age groups and prescribing specific exercise parameters.

Utilizing artificial intelligence and electroencephalography to assess expertise on a simulated neurosurgical task

Virtual reality surgical simulators have facilitated surgical education by providing a safe training environment. Electroencephalography (EEG) has been employed to assess neuroelectric activity during surgical performance. Machine learning (ML) has been applied to analyze EEG data split into frequency bands. Although EEG is widely used in fields requiring expert performance, it has yet been used to classify surgical expertise. Thus, the goals of this study were to (a) develop an ML model to accurately differentiate skilled and less-skilled performance using EEG data recorded during a simulated surgery, (b) explore the relative importance of each EEG bandwidth to expertise, and (c) analyze differences in EEG band powers between skilled and less-skilled individuals. We hypothesized that EEG recordings during a virtual reality surgery task would accurately predict the expertise level of the participant. Twenty-one participants performed three simulated brain tumor resection procedures on the NeuroVR™ platform (CAE Healthcare, Montreal, Canada) while EEG data was recorded. Participants were divided into 2 groups. The skilled group was composed of five neurosurgeons and five senior neurosurgical residents (PGY4-6), and the less-skilled group was composed of six junior residents (PGY1-3) and five medical students. A total of 13 metrics from EEG frequency bands and ratios (e.g., alpha, theta/beta ratio) were generated. Seven ML model types were trained using EEG activity to differentiate between skilled and less-skilled groups. The artificial neural network achieved the highest testing accuracy of 100% (AUROC = 1.0). Model interpretation via Shapley analysis identified low alpha (8–10 Hz) as the most important metric for classifying expertise. Skilled surgeons displayed higher (p = 0.044) low-alpha than the less-skilled group. Furthermore, skilled surgeons displayed significantly lower TBR (p = 0.048) and significantly higher beta (13–30 Hz, p = 0.049), beta 1 (15–18 Hz, p = 0.014), and beta 2 (19–22 Hz, p = 0.015), thus establishing these metrics as important markers of expertise. ACGME Core CompetenciesPractice-Based Learning and Improvement.

Some Conceptual and Empirical Shortcomings of IIT

The Integrated Information Theory of consciousness (IIT) has generated much excitement inside and outside the scientific community, and seems to many the leading contender for a satisfactory theory grounded in systems neuroscience. It is a bold theory, one that provides plausible explanations for various recognized neuroscientific facts, makes surprising predictions that go beyond current scientific orthodoxy but are potentially testable, and has inspired development of what appears to be an effective technique for detecting the presence of consciousness in organisms incapable of verbal report, such as non-human animals, neonates, and severely brain-damaged adults. Despite these virtues, IIT appears fundamentally flawed: This paper first revisits some key conceptual and technical issues that have been raised previously but remain unresolved—in particular, issues concerning IIT’s concept of “information” and its approach to the “hard problem”—and then focuses on several empirical phenomena that IIT seems unable to handle satisfactorily. These include: 1. cases of multiple personality or dissociative identity disorder in which complex and overlapping centers of consciousness co-occur in single human organisms; 2. the failure of the intense phenomenology of psychedelic states to be straightforwardly reflected in accompanying neuroelectric activity; and, most critically; 3. the occurrence of profound and personally transformative near-death experiences (NDEs) under extreme physiological conditions such as cardiac arrest, in which IIT predicts that no conscious experience whatsoever should be possible. These empirical arguments show that IIT itself is untenable, and they apply also to its physicalist competitors. Scientifically and philosophically respectable alternatives, however, are available.

Role of microtubules in neuro-electrical transmission

Unlike man-made electronic devices such as computers, the nervous system never suffers from “overheating” due to its massive neuro-electrical activities. This paper proposes a new hypothesis that neuronal microtubules (neuro-MTs), which are major structural components of axons and dendrites, are vacuum cylindrical nanotubes that can mediate electrical transmission with a unique form of quasi-superconductivity. It is speculated that hydrolysis of guanosine triphosphate catalyzed by the a-/ß-tubulin subunits would supply cellular energy to relocate electrons to form the conduction electrons inside neuro-MTs. Owing to the consecutive dipole ring structures of neuro-MTs, the moving speed of the conduction electrons inside neuro-MTs is expected to be very slow, and this feature would enable physiological neuro-electrical transmission with super-high energy efficiency. Further, the dipole ring structures of a neuro-MT would help terminate the electron conduction with high efficiency. The proposed neuro-MT-mediated electrical transmission offers a new mechanistic explanation for the saltatory conduction of action potentials along the axons. Lastly, it is speculated that owing to its unique consecutive dipole sheet structures, the myelin sheath which wraps around large axons and some dendrites, may functionally serve as an effective shield for the electromagnetic fields generated by the conduction electrons inside the axonal neuro-MTs.

The unique contribution of motor ability to visuospatial working memory in school-age children: Evidence from event-related potentials.

This study investigated the unique contribution of motor ability to visuospatial working memory (VSWM) and neuroelectric activity in school-age children. Seventy-six children aged 8.7 ± 1.1 years participated in this cross-sectional study. We assessed aerobic fitness using the 20-m endurance shuttle run test, muscular fitness (endurance, power) using a standard test battery, and motor ability (manual dexterity, ball skills, and static and dynamic balance) using the Movement Assessment Battery for Children. A modified delayed match-to-sample test was used to assess VSWM and the P3 component of event-related potentials. Hierarchical regression analyses indicated that greater aerobic fitness was associated with smaller coefficient of variation of reaction time (p=.008), greater muscular fitness was associated with higher response accuracy (p=.022), greater motor ability was associated with higher response accuracy (p < .001) and increased P3 mean amplitude (p < .001) after controlling for age. Furthermore, the positive associations of motor ability with response accuracy (p=.001) were independent of muscular fitness. The findings from this study provide new insight into the differential associations between health-related fitness domains and VSWM, highlighting the influence of motor ability on brain health and cognitive development during childhood.

Facemask wearing does not impact neuro-electrical brain activity

Given the massive use of facemasks (FMs) during the covid-19 pandemic, concerns have been raised regarding the effect of FMs wearing on overall health. This study aimed at evaluating the effect of surgical FM on brain neuro-electrical activity. Electroencephalography (EEG) background frequency (BGF) and background amplitude (BGA) was performed on 30 volunteers before (baseline), during and after wearing a FM for 60 min. Measurements were done during normal ventilation, hyperventilation and post-hyperventilation (PHVR). Blood gas levels were assessed at baseline and after FM use. EEG analysis concerning baseline (without FM) (BGA), was 47.69 ± 18.60 µV, wearing FM, BGA was 48.45 ± 17.79 µV, post FM use BGA was 48.08 ± 18.30 µV. There were no statistically significant differences between baseline BGA and BGA under FM and post FM. BGF, Baseline data were 10.27 ± 0.79, FM use 10.30 ± 0.76 and post FM use was 10.33 ± 0.76. There were no statistically significant differences between baseline BGF and BGF under FM and post FM. Venous blood gases, and peripheral oxygen saturation were not significantly affected by FM use. Short-term use of FM in young healthy individuals has no significant alteration impact on brain's neuro-electrical activity

Effects of rTMS on working memory abilities and time-varying spectrum coherence of LFPS and spikes in rats

PurposeThe purpose of this study was to evaluate the effects of repetitive transcranial magnetic stimulation (rTMS) at different frequencies on working memory (WM) and neuroelectric activity in rats.Design/methodology/approachThree rTMS protocols involving different frequencies were applied to rats, and 16-channel local field potentials (LFPs) and spikes were recorded from the prefrontal cortex (PFC) of rats in each group during the WM task. First, the behavior of rats during the T-maze task was analyzed, and then, the firing rate of spikes and the energy of the θ-band and γ-band in LFPs when rats performed the WM tasks were calculated. Finally, the spectral coherence between LFPs and spikes was analyzed by wavelet transform.FindingsThe results showed that rats in the stimulation groups needed fewer days than those in the control group to reach the task correction standard during the WM experiment (p < 0.05). High-frequency rTMS increases the firing rate of spikes and the degree of synchronization of LFPs-spikes in the θ-band and γ-band in the WM process.Originality/valueThis study showed that high-frequency rTMS can improve the spatial learning ability of rats, which might be due to the increased neuronal excitability of the PFC and the enhancement of co-coding between different modes of neural signals. This study is helpful for understanding the neuroregulatory mechanism of rTMS and will provide a reference for the selection of a suitable frequency for TMS treatment.

Abnormal neural adaptation consequent to combined exposure to jet fuel and noise

ABSTRACT A fundamental property of first-order sensory neurons is the ability to alter their response properties as a function of change in the statistical parameters of an input signal. Such neural adaptation shapes the performance features of contiguous neural circuits that ultimately drive sensory discrimination. The current study focused on whether combined exposure to jet fuel and noise might alter the capacity of the auditory nerve to adapt to stimulus presentation speed. Young hooded Long-Evans 4–5 weeks old male rats were grouped and used in the current experiment. One group was exposed via inhalation to 1000 mg/m3 of jet propulsion fuel for 6 hr per day, 5 days per week for 4 weeks. Another group was exposed to a 5.5–11.3 kHz band-pass noise at 85 dB SPL for 6 hr per day, 5 days per week for 4 weeks. An additional group was simultaneously exposed to both jet fuel and noise. An age-matched group served as control and was not exposed to either jet fuel or noise. After experimental exposures, animals were given 4 weeks to recover and then assessed for neural adaptation. Both slow and fast rectangular voltage pulses were employed to elicit neuroelectric activity from the animals. Data demonstrated significant neural adaptation (1.46 μV shift) among controls, where neural activity decreased as the stimulus presentation speed rose from 10 to 100 per sec. This effect might also be observed in animals in the jet fuel treated and rats in the noise-exposed group. However, animals who were simultaneously exposed to both jet fuel and noise failed to exhibit neural adaptation. This abnormality appeared to be masked because independent slow and fast stimuli produced similar neural activity between controls and rats exposed to both jet fuel and noise. Therefore, neural adaptation assays may further be developed to unmask silent neurotoxicity consequent to physiochemical exposures.

The Effects of Circadian Rhythm in Adolescents on Optimal Performance in Cognitive Tasks

Introduction: The circadian rhythm is a sleep-wake cycle determined by differences in serum melatonin and cortisol levels, and affects cognition and behaviour. Past research suggests that young adults tend to perform better on cognitive tasks during the afternoon and evening, which may be the optimal time of day in this population. This research protocol seeks to determine whether cognitive performance is affected at times assumed to be optimal for both populations (evening) compared with suboptimal times (morning). Methods: Individuals would be recruited and divided into two groups: adolescents 13–17 and younger adults aged ages 18–25, with all participants of the afternoon/evening chronotype. Saliva is collected directly preceding test-taking. Each group completes a standard computerized test of simple math, logical reasoning, and executive function at both their optimal time of day (TOD) (3:00 to 6:00 PM) and at their non-optimal time of day (8:00 to 11:00 AM). Neuroelectric activity is recorded using electroencephalography (EEG). Results: We hypothesize that adolescents and younger adults will be at their optimal performance level (measured by EEG and behavioural measures) between 3 to 6 P.M. rather than from 8 to 11 AM, due to their circadian rhythm. We expect TOD to influence reaction times and accuracy during task completion. A difference will be seen across many neural indices such as event-related potentials (ERPs) and alpha and theta power demonstrating optimal performance in the evening. Discussion: Higher cortisol levels and changes in amplitude and latency of P3, N2Pc, N450, and PD ERP indices and differences in alpha and theta frequencies may be associated with optimal cognitive performance. This is related to faster response time, focus, and overall higher accuracy. Based on the anticipated results, one could alter the timing of task completion to fit different age groups’ peak mental ability. Conclusion: Continuously working at non-optimal times could lead to chronic circadian rhythm disruption, which could result in the deterioration of physical and mental health. Aspects of everyday life, such as student test-taking times, can be improved to benefit both individuals and institutions by catering to an individual’s optimal TOD.

Autonomic arousals contribute to brain fluid pulsations during sleep

During sleep, slow waves of neuro-electrical activity engulf the human brain and aid in the consolidation of memories. Recent research suggests that these slow waves may also promote brain health by facilitating the removal of metabolic waste, possibly by orchestrating the pulsatile flow of cerebrospinal fluid (CSF) through local neural control over vascular tone. To investigate the role of slow waves in the generation of CSF pulsations, we analyzed functional MRI data obtained across the full sleep-wake cycle and during a waking respiratory task. This revealed a novel generating mechanism that relies on the autonomic regulation of cerebral vascular tone without requiring slow electrocortical activity or even sleep. Therefore, the role of CSF pulsations in brain waste clearance may, in part, depend on proper autoregulatory control of cerebral blood flow.

Long latency auditory evoked potentials and object-related negativity based on harmonicity in hearing-impaired children

Hearing-impaired children (HIC) have difficulty understanding speech in noise, which may be due to difficulty parsing concurrent sound object based on harmonicity cues. Using long latency auditory evoked potentials (LLAEPs) and object-related negativity (ORN), a neural metric of concurrent sound segregation, this study investigated the sensitivity of HIC in processing harmonic relation. The participants were 14 normal-hearing children (NHC) with an average age of 7.82 ± 1.31 years and 17 HIC with an average age of 7.98 ± 1.25 years. They were presented with a sequence of 200 Hz harmonic complex tones that had either all harmonic in tune or the third harmonic mistuned by 2%, 4%, 8%, and 16% of its original value while neuroelectric brain activity was recorded. The analysis of scalp-recorded LLAEPs revealed lower N2 amplitudes elicited by the tuned stimuli in HIC than control. The ORN, isolated in difference wave between LLAEP elicited by tuned and mistuned stimuli, was delayed and smaller in HIC than NHC. This study showed that deficits in processing harmonic relation in HIC, which may contribute to their difficulty in understanding speech in noise. As a result, top-down and bottom-up rehabilitations aiming to improve processing of basic acoustic characteristics, including harmonics are recommended for children with hearing loss.

Aging Enhances Neural Activity in Auditory, Visual, and Somatosensory Cortices: The Common Cause Revisited.

In humans, age-related declines in vision, hearing, and touch coincide with changes in amplitude and latency of sensory-evoked potentials. These age-related differences in neural activity may be related to a common deterioration of supra-modal brain areas (e.g., PFC) that mediate activity in sensory cortices or reflect specific sensorineural impairments that may differ between sensory modalities. To distinguish between these two possibilities, we measured neuroelectric brain activity while 37 young adults (18-30 years, 18 males) and 35 older adults (60-88 years, 20 males) were presented with a rapid randomized sequence of lateralized auditory, visual, and somatosensory stimuli. Within each sensory domain, we compared amplitudes and latencies of sensory-evoked responses, source activity, and functional connectivity (via phase-locking value) between groups. We found that older adults' early sensory-evoked responses were greater in amplitude than those of young adults in all three modalities, which coincided with enhanced source activity in auditory, visual, and somatosensory cortices. Older adults also showed stronger neural synchrony than young adults between superior prefrontal and sensory cortices; and in older adults, the degree of phase synchrony was positively correlated with the magnitude of source activity in sensory areas. Critically, older adults who showed enhanced neural activity in one sensory domain also showed enhanced activity in other modalities. Together, these findings support the common cause hypothesis of aging and highlight the role of prefrontal regions in exerting top-down control over sensory cortices.SIGNIFICANCE STATEMENT A prominent theory of aging posits that age-related declines in sensory processing across domains are related to a single common neurobiological mechanism. However, the neural evidence supporting this common cause hypothesis has remained elusive. Our study revealed robust age-related changes in three sensory domains across a range of neural metrics. Importantly, older adults who showed increased neural activity within one sensory domain also showed enhanced neural activity in the other two sensory modalities. No such relation among activity in sensory cortices was observed in young adults. Age-related increases in neural activity in sensory cortices coincided with enhanced neural synchrony between the PFC and sensory cortices, underlining the importance of the PFC in regulating sensory processing.

Multi-layer analysis of multi-frequency brain networks as a new tool to study EEG topological organization.

Oscillatory activity rising from the interaction among neurons is widely observed in the brain at different scales and is thought to encode distinctive properties of the neural processing. Classical investigations of neuroelectrical activity and connectivity usually focus on specific frequency bands, considered as separate aspects of brain functioning. However, this might not paint the whole picture, preventing to see the brain activity as a whole, as the result of an integrated process. This study aims to provide a new framework for the analysis of the functional interaction between brain regions across frequencies and different subjects. We ground our work on the latest advances in graph theory, exploiting multi-layer community detection. In our multi-layer network model, layers keep track of single frequencies, including all the information in a unique graph. Community detection is then applied by means of a multilayer formulation of modularity. As a proof-of-concept of our approach, we provide here an application to multi-frequency functional brain networks derived from resting state EEG collected in a group of healthy subjects. Our results indicate that α-band selectively characterizes an inter-individual common organization of EEG brain networks during open eyes resting state. Future applications of this new approach may include the extraction of subject-specific features able to capture selected properties of the brain processes, related to physiological or pathological conditions.