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The dynamic brain : an exploration of neuronal variability and its functional significance
Neuronal responses to identically presented stimuli are extremely variable. This variability has in the past often been regarded as “noise.” At the single neuron level, interspike interval (ISI) histograms constructed during either spontaneous or stimulus-evoked activity reveal a Poisson type distribution. These observations have been taken as evidence that neurons are intrinsically “noisy” in their firing properties. More recent attempts to measure the information content of single neuron spike trains have revealed that a surprising amount of information can be coded in spike trains even in the presence of trial-to-trial variability. Multiple single unit recording experiments have suggested that variability formerly attributed to noise in single cell recordings may instead simply reflect system-wide changes in cellular response properties. These observations raise the possibility that, at least at the level of neuronal coding, the variability seen in single neuron responses may not simply reflect an underlying noisy process. They further raise the very distinct possibility that noise may in fact contain real, meaningful information which is available for the nervous system in information processing. To understand how neurons work in concert to bring about coherent behavior and its breakdown in disease, neuroscientists now routinely record simultaneously from hundreds of different neurons and from different brain areas, and then attempt to evaluate the network activities by computing various interdependence measures including cross correlation, phase synchronization, and spectral coherence. This book examines neuronal variability from theoretical, experimental, and clinical perspectives.
eBook
Effects of desflurane and sevoflurane on somatosensory-evoked and motor-evoked potential monitoring during neurosurgery: a randomized controlled trial
Background
Better protection can be provided during neurosurgery due to the establishment of somatosensory-evoked potential (SEP) and motor-evoked potential (MEP) monitoring technologies. However, some studies have showed that inhaled halogenated anesthetics have a significant impact on neurophysiological monitoring.
Methods
A total of 40 consecutive patients undergoing neurosurgery were randomly assigned to two groups receiving inhaled anesthetics, either desflurane or sevoflurane. Multiples levels (concentrations of 0.3, 0.6 and 0.9) of anesthetics were administered at minimum alveolar concentration (MAC), and then the latencies and amplitudes of SEPs and MEPs were recorded.
Results
SEP and MEP signals were well preserved in patients who underwent neurosurgery under general anesthesia supplemented with desflurane or sevoflurane at concentrations of 0.3, 0.6 and 0.9 MAC. In each desflurane or sevoflurane group, the amplitudes of SEPs and MEPs decreased and the latencies of SEPs were prolonged significantly as the MAC increased (
P
< 0.05). The SEP latencies of both the upper and lower limbs in the desflurane group were significantly longer, and the SEP amplitudes were significantly lower than those in the sevoflurane group (
P
< 0.05). The MEP amplitudes in the desflurane group were significantly lower than those in the sevoflurane group (
P
< 0.05), only the amplitudes of the upper limbs at 0.3 MAC did not vary significantly.
Conclusions
SEPs and MEPs were inhibited in a dose-dependent manner by both desflurane and sevoflurane. At the same MAC concentration, desflurane appeared to have a stronger inhibitory effect than sevoflurane. All patients studied had normal neurological examination findings, hence, these results may not be applicable to patients with preexisting deficits.
Trial registration
The study registered on the Chinese Clinical Trial Registry (
www.chictr.org.cn
), Clinical Trials identifier
ChiCTR2100045504
(18/04/2021).
Journal Article
Effects of daily listening to 6 Hz binaural beats over one month: an event-related potentials study
The aim of the present study was to identify cognitive alterations, as indicated by event-related potentials (ERPs), after one month of daily exposure to theta binaural beats (BBs) for 10 minutes. The recruited healthy subjects (n = 60) were equally divided into experimental and control groups. For a month, the experimental group was required to practice BBs listening daily, while the control group did not. ERPs were assessed at three separate visits over a span of one month, with a two-week interval between each visit. At each visit, ERPs were measured before and after listening. The auditory and visual ERPs significantly increased the auditory and visual P300 amplitudes consistently at each visit. BBs enhanced the auditory N200 amplitude consistently across all visits, but the visual N200 amplitude increased only at the second and third visits. Compared to the healthy controls, daily exposure to BBs for two weeks resulted in increased auditory P300 amplitude. Additionally, four weeks of BBs exposure not only increased auditory P300 amplitude but also reduced P300 latency. These preliminary findings suggest that listening to BBs at 6 Hz for 10 minutes daily may enhance certain aspects of cognitive function. However, further research is needed to confirm these effects and to understand the underlying mechanisms. Identifying the optimal duration and practice of listening to 6 Hz BBs could potentially contribute to cognitive enhancement strategies in healthy individuals.
Journal Article
Frequency-specific modulation of motor cortical excitability by transcranial alternating current stimulation
Background
Transcranial alternating current stimulation (tACS) is a non-invasive technique that modulates neural oscillations, yet its specific effects on cortical excitability are not well-understood. This study investigated the effects of tACS on neuroplasticity in the primary motor cortex (M1) across different frequencies.
Methods
In this randomized, sham-controlled, crossover study, 18 healthy young adults received β-tACS γ-tACS, and sham stimulation over the M1. Neurophysiological responses were assessed using motor evoked potentials (MEPs), electroencephalograms (EEG), and transcranial evoked potentials (TEPs) to determine the frequency-specific effects of tACS on cortical excitability and neuroplasticity.
Results
γ-tACS significantly enhanced cortical excitability, as reflected by larger MEP amplitudes compared to both β-tACS and sham stimulation. In addition, γ-tACS resulted in significantly smaller M1-P15 amplitudes in TEP than other stimulation conditions. In contrast, β-tACS did not produce significant changes in either MEPs or TEPs compared to sham stimulation.
Conclusion
These findings provide evidence that tACS induces frequency-dependent effects on cortical excitability and neuroplasticity within the M1. This selective modulation of cortical excitability with γ-tACS suggests its potential as a therapeutic intervention for optimizing motor function and rehabilitation.
Trial registration
This study was registered in the Chinese Clinical Trial Registry (ChiCTR2300074898, date of registration: 2023/08/18).
Journal Article
Experimental suppression of transcranial magnetic stimulation‐electroencephalography sensory potentials
The sensory experience of transcranial magnetic stimulation (TMS) evokes cortical responses measured in electroencephalography (EEG) that confound interpretation of TMS‐evoked potentials (TEPs). Methods for sensory masking have been proposed to minimize sensory contributions to the TEP, but the most effective combination for suprathreshold TMS to dorsolateral prefrontal cortex (dlPFC) is unknown. We applied sensory suppression techniques and quantified electrophysiology and perception from suprathreshold dlPFC TMS to identify the best combination to minimize the sensory TEP. In 21 healthy adults, we applied single pulse TMS at 120% resting motor threshold (rMT) to the left dlPFC and compared EEG vertex N100‐P200 and perception. Conditions included three protocols: No masking (no auditory masking, no foam, and jittered interstimulus interval [ISI]), Standard masking (auditory noise, foam, and jittered ISI), and our ATTENUATE protocol (auditory noise, foam, over‐the‐ear protection, and unjittered ISI). ATTENUATE reduced vertex N100‐P200 by 56%, “click” loudness perception by 50%, and scalp sensation by 36%. We show that sensory prediction, induced with predictable ISI, has a suppressive effect on vertex N100‐P200, and that combining standard suppression protocols with sensory prediction provides the best N100‐P200 suppression. ATTENUATE was more effective than Standard masking, which only reduced vertex N100‐P200 by 22%, loudness by 27%, and scalp sensation by 24%. We introduce a sensory suppression protocol superior to Standard masking and demonstrate that using an unjittered ISI can contribute to minimizing sensory confounds. ATTENUATE provides superior sensory suppression to increase TEP signal‐to‐noise and contributes to a growing understanding of TMS‐EEG sensory neuroscience. We introduce a sensory suppression protocol superior to Standard masking and demonstrate that using an unjittered interstimulus interval can contribute to minimizing sensory confounds. ATTENUATE provides superior sensory suppression to increase transcranial magnetic stimulation (TMS)‐evoked potential signal‐to‐noise and contributes to a growing understanding of TMS‐electroencephalography sensory neuroscience.
Journal Article
A Novel Paired Somatosensory-Cerebellar Stimulation Induces Plasticity on Cerebellar-Brain Connectivity
The cerebellum receives and integrates a large amount of sensory information that is important for motor coordination and learning. The aim of the present work was to investigate whether peripheral nerve and cerebellum paired associative stimulation (cPAS) could induce plasticity in both the cerebellum and the cortex. In a cross-over design, we delivered right median nerve electrical stimulation 25 or 10 ms before applying transcranial magnetic stimulation over the cerebellum. We assessed changes in motor evoked potentials (MEP), somatosensory evoked potentials (SEP), short-afferent inhibition (SAI), and cerebellum-brain inhibition (CBI) immediately, and 30 min after cPAS. Our results showed a significant reduction in CBI 30 minutes after cPAS, with no discernible changes in MEP, SEP, and SAI. Notably, cPAS10 did not produce any modulatory effects on these parameters. In summary, cPAS25 demonstrated the capacity to induce plasticity effects in the cerebellar cortex, leading to a reduction in CBI. This novel intervention may be used to modulate plasticity mechanisms and motor learning in healthy individuals and patients with neurological conditions.
Journal Article
ISCEV standard for clinical visual evoked potentials: (2016 update)
Visual evoked potentials (VEPs) can provide important diagnostic information regarding the functional integrity of the visual system. This document updates the ISCEV standard for clinical VEP testing and supersedes the 2009 standard. The main changes in this revision are the acknowledgment that pattern stimuli can be produced using a variety of technologies with an emphasis on the need for manufacturers to ensure that there is no luminance change during pattern reversal or pattern onset/offset. The document is also edited to bring the VEP standard into closer harmony with other ISCEV standards. The ISCEV standard VEP is based on a subset of stimulus and recording conditions that provide core clinical information and can be performed by most clinical electrophysiology laboratories throughout the world. These are: (1) Pattern-reversal VEPs elicited by checkerboard stimuli with large 1 degree (°) and small 0.25° checks. (2) Pattern onset/offset VEPs elicited by checkerboard stimuli with large 1° and small 0.25° checks. (3) Flash VEPs elicited by a flash (brief luminance increment) which subtends a visual field of at least 20°. The ISCEV standard VEP protocols are defined for a single recording channel with a midline occipital active electrode. These protocols are intended for assessment of the eye and/or optic nerves anterior to the optic chiasm. Extended, multi-channel protocols are required to evaluate postchiasmal lesions.
Journal Article
Preoperative pregabalin has no effect on intraoperative neurophysiological monitoring in adolescents undergoing posterior spinal fusion for spinal deformities: a double-blind, randomized, placebo-controlled clinical trial
PurposeThis study was designed to evaluate the effect of preoperative pregabalin on intraoperative neurophysiological monitoring in adolescents undergoing surgery for spinal deformities.MethodsThirty-one adolescents undergoing posterior spinal fusion were randomized to receive preoperatively either pregabalin 2 mg/kg twice daily or placebo. The ability to make reliable intraoperative neurophysiological measurements, transcranial motor (MEPs) and sensory evoked potentials (SSEP) was evaluated.ResultsTwo patients (pregabalin group) did not fulfil the inclusion criteria and one patient’s (placebo group) spinal monitoring was technically incomplete and these were excluded from the final data. In the rest, spinal cord monitoring was successful. Anaesthesia prolonged the latency of MEPs and increased the threshold current of MEP. The current required to elicit MEPs did not differ between the study groups. There were no statistically significant differences between the study groups regarding the latency of bilateral SSEP (N32 and P37) and MEP latencies at any time point.ConclusionsPreoperative pregabalin does not interfere spinal cord monitoring in adolescents undergoing posterior spinal fusion.Level of evidenceI.
Journal Article