Spectral features of electroencephalogram in characterizing various brain states under anesthesia

The administration of the anesthetic agents is known to alter the electroencephalogram (EEG) signal significantly with the brain being their primary target. In this study, we analyzed the EEG recorded from six ASA I/II patients undergoing a 1-2 hour surgery. The EEG was collected before and during induction, maintenance and recovery of anesthesia using the 10/20 lead-system. A combination of fentanyl and propofol (± rocuronium) was used for induction and a Sevoflurane in air/O(2) mixture was administered through an endotracheal tube to achieve the steady minimum alveolar concentration (MAC). This study showed that 0 to 4 Hz signal power was most sensitive to the changes associated with induction of anesthesia whereas the 4 to 12 Hz power was important in classifying states during maintenance of anesthesia. Anesthesia also promoted heightened phase coherence in 8 to 16 Hz and 16 to 30 Hz ranges during maintenance and induction of anesthesia, respectively. Additionally, strong cross-frequency coupling between 7 to 20 Hz and 10 to 40 Hz was observed during anesthesia suggesting alteration of neural coding.

Transmembrane potential generated by a magnetically induced transverse electric field in a cylindrical axonal model

During the electrical stimulation of a uniform, long, and straight nerve axon, the electric field oriented parallel to the axon has been widely accepted as the major field component that activates the axon. Recent experimental evidence has shown that the electric field oriented transverse to the axon is also sufficient to activate the axon, by inducing a transmembrane potential within the axon. The transverse field can be generated by a time-varying magnetic field via electromagnetic induction. The aim of this study was to investigate the factors that influence the transmembrane potential induced by a transverse field during magnetic stimulation. Using an unmyelinated axon model, we have provided an analytic expression for the transmembrane potential under spatially uniform, time-varying magnetic stimulation. Polarization of the axon was dependent on the properties of the magnetic field (i.e., orientation to the axon, magnitude, and frequency). Polarization of the axon was also dependent on its own geometrical (i.e., radius of the axon and thickness of the membrane) and electrical properties (i.e., conductivities and dielectric permittivities). Therefore, this article provides evidence that aside from optimal coil design, tissue properties may also play an important role in determining the efficacy of axonal activation under magnetic stimulation. The mathematical basis of this conclusion was discussed. The analytic solution can potentially be used to modify the activation function in current cable equations describing magnetic stimulation.

Anterior thalamus deep brain stimulation at high current impairs memory in rats

Deep brain stimulation (DBS) of the anterior thalamic nucleus (AN), an important relay in the circuitry of memory, is currently being proposed as a treatment for epilepsy. Despite the encouraging results with the use of this therapy, potential benefits and adverse effects are yet to be determined. We show that AN stimulation at relatively high current disrupted the acquisition of contextual fear conditioning and impaired performance on a spatial alternating task in rats. This has not been observed at parameters generating a charge density that approximated the one used in clinical practice. At settings that impaired behavior, AN stimulation induced a functional depolarization block nearby the electrode, increased c-Fos expression in cerebral regions projecting to and receiving projections from the AN, and influenced hippocampal activity. This suggests that complex mechanisms might be involved in the effects of AN DBS, including a local target inactivation and the modulation of structures at a distance. Though translating data from animals to humans has to be considered with caution, our study underscores the need for carefully monitoring memory function while selecting stimulation parameters during the clinical evaluation of AN DBS.

Transformation of neuronal modes associated with low-Mg2+/high-K+ conditions in an in vitro model of epilepsy

Nonparametric system modeling constitutes a robust method for the analysis of physiological systems as it can be used to identify nonlinear dynamic input-output relationships and facilitate their description. First- and second-order kernels of hippocampal CA3 pyramidal neurons in an in vitro slice preparation were computed using the Volterra-Wiener approach to investigate system changes associated with epileptogenic low-magnesium/high-potassium (low-Mg(2+)/high-K(+)) conditions. The principal dynamic modes (PDMs) of neurons were calculated from the first- and second-order kernel estimates in order to characterize changes in neural coding functionality. From our analysis, an increase in nonlinear properties was observed in kernels under low-Mg(2+)/high-K(+). Furthermore, the PDMs revealed that the sampled hippocampal CA3 neurons were primarily of integrating character and that the contribution of a differentiating mode component was enhanced under low-Mg(2+)/high-K(+).

The 128-channel fully differential digital integrated neural recording and stimulation interface

We present a fully differential 128-channel integrated neural interface. It consists of an array of 8 X 16 low-power low-noise signal-recording and generation circuits for electrical neural activity monitoring and stimulation, respectively. The recording channel has two stages of signal amplification and conditioning with and a fully differential 8-b column-parallel successive approximation (SAR) analog-to-digital converter (ADC). The total measured power consumption of each recording channel, including the SAR ADC, is 15.5 ¿W. The measured input-referred noise is 6.08 ¿ Vrms over a 5-kHz bandwidth, resulting in a noise efficiency factor of 5.6. The stimulation channel performs monophasic or biphasic voltage-mode stimulation, with a maximum stimulation current of 5 mA and a quiescent power dissipation of 51.5 ¿W. The design is implemented in 0.35-¿m complementary metal-oxide semiconductor technology with the channel pitch of 200 ¿m for a total die size of 3.4 mm × 2.5 mm and a total power consumption of 9.33 mW. The neural interface was validated in in vitro recording of a low-Mg(2+)/high-K(+) epileptic seizure model in an intact hippocampus of a mouse.

The remarkably high prevalence of epilepsy and seizure history in fetal alcohol spectrum disorders

BACKGROUND

Fetal alcohol spectrum disorder (FASD) is the umbrella term that describes the range of adverse developmental outcomes that may occur in the offspring of mothers who drink alcohol during pregnancy. FASD is associated with several comorbidities including epilepsy. The objective of the study was to evaluate the prevalence of epilepsy or a history of seizures in subjects with FASD and the contribution of relevant risk factors.

METHODS

A retrospective chart review was conducted on all active charts (N = 1063) at two FASD clinics. After exclusion of subjects without a confirmed diagnosis, a total of 425 subjects between the ages of 2-49 were included in the analysis. The relationships between FASD diagnosis and other risk factors for co-occurrence of epilepsy or a seizure disorder (e.g., extent of exposure to alcohol and other drugs, type of birth, and trauma) were examined using chi-square and multivariate multinomial logistic regression.

RESULTS

Twenty-five (5.9%) individuals in the study population had a confirmed diagnosis of epilepsy, and 50 (11.8%) had at least one documented seizure episode, yielding an overall prevalence of 17.7% in this population. Importantly, a history of epilepsy or seizures was not different across the three diagnostic subgroups. In those subjects with available maternal drinking histories, first trimester exposure or drinking throughout all three trimesters were the predominant forms of fetal exposure. None of the other risk factors were associated with a greater prevalence of epilepsy or seizures.

CONCLUSIONS

There is a remarkably high prevalence of epilepsy/seizures in the FASD population.

Transmembrane potential induced on the internal organelle by a time-varying magnetic field: a model study

BACKGROUND

When a cell is exposed to a time-varying magnetic field, this leads to an induced voltage on the cytoplasmic membrane, as well as on the membranes of the internal organelles, such as mitochondria. These potential changes in the organelles could have a significant impact on their functionality. However, a quantitative analysis on the magnetically-induced membrane potential on the internal organelles has not been performed.

METHODS

Using a two-shell model, we provided the first analytical solution for the transmembrane potential in the organelle membrane induced by a time-varying magnetic field. We then analyzed factors that impact on the polarization of the organelle, including the frequency of the magnetic field, the presence of the outer cytoplasmic membrane, and electrical and geometrical parameters of the cytoplasmic membrane and the organelle membrane.

RESULTS

The amount of polarization in the organelle was less than its counterpart in the cytoplasmic membrane. This was largely due to the presence of the cell membrane, which "shielded" the internal organelle from excessive polarization by the field. Organelle polarization was largely dependent on the frequency of the magnetic field, and its polarization was not significant under the low frequency band used for transcranial magnetic stimulation (TMS). Both the properties of the cytoplasmic and the organelle membranes affect the polarization of the internal organelle in a frequency-dependent manner.

CONCLUSIONS

The work provided a theoretical framework and insights into factors affecting mitochondrial function under time-varying magnetic stimulation, and provided evidence that TMS does not affect normal mitochondrial functionality by altering its membrane potential.

Reversibility of alcohol-related brain damage: clinical and experimental observations

Chronic alcoholics who maintain abstinence often demonstrate remarkable improvement of neurological and mental dysfunction. This paper presents an overview of the clinical and laboratory work of our group. Reversible clinical manifestations include psychometric scores, ataxia, tremor, Parkinsonism, dyskinesia, cerebral atrophy, EEG parameters, and a CSF acidosis. Electrophysiological investigations showed that in the in vitro hippocampus of rats fed ethanol for several months there was evidence for diminished long-term potentiation, impaired neuronal inhibitory mechanisms (diminished inhibitory post-synaptic potentials and post-spike after hyperpolarisations), decreased neuronal specific membrane capacitance and increased specific membrane resistance. Golgi stains showed attenuation of hippocampal CA1 neuronal dendrites in rats fed ethanol for five months, which reverted to control size in rats permitted two months of alcohol withdrawal.

Seizure-like activity in the hypoglycemic rat: lack of correlation with the electroencephalogram of free-moving animals

BACKGROUND

The neuropathology of hypoglycemia and its mechanisms have been well studied. However, the physiopathogenesis of hypoglycemia-related seizures has escaped elucidation. Various animal models reportedly show "seizures" when rendered hypoglycemic, however, correlation with the electroencephalogram (EEG) is inconsistent. In order to characterize the role of the hippocampus and frontal neocortex in the generation of hypoglycemic seizures, this study was undertaken.

METHODS

Adult rats were implanted stereotaxically with electrodes in the left hippocampus and right frontal cortex. After 1 week, they were fasted 18-24h, then injected intraperitoneally with insulin, 35 IU/kg. Simultaneous EEG/video monitoring was conducted.

RESULTS

Interpretable EEG recordings were obtained in 8/12 animals. Two showed poor association of seizure-like behaviour (neck extension, vocalizations, tonic extension of the tail, digging or running limb movements) with ictal EEG patterns. Four animals exhibited such behaviours during periods of high amplitude polymorphic slow wave activity, burst-suppression patterns or non-rhythmic spiking. Two others were encephalopathic (behaviourally and electroencephalographically) until death.

CONCLUSIONS

Not all animals develop seizure-like behaviour when hypoglycemic. If these are seizures, they may originate from subcortical structures, or the "convulsive" behaviours observed may simply be flight/fight reflexes released during profound encephalopathy. Spike activity in the EEG may be a manifestation of this state. Recording EEG from rat cortex and hippocampus during seizure-like activity brought on by hypoglycemia correlates poorly with seizure-like behaviours suggesting that the relevant electrophysiological correlates, if present, are generated from deeper brain structures.

Impaired presynaptic cytosolic and mitochondrial calcium dynamics in aged compared to young adult hippocampal CA1 synapses ameliorated by calcium chelation

Impaired regulation of presynaptic intracellular calcium is thought to adversely affect synaptic plasticity and cognition in the aged brain. We studied presynaptic cytosolic and mitochondrial calcium (Ca) dynamics using axonally loaded Calcium Green-AM and Rhod-2 AM fluorescence respectively in young (2-3 months) and aged (23-26 months) CA3 to CA1 Schaffer collateral excitatory synapses in hippocampal brain slices from Fisher 344 rats. After a tetanus (100 Hz, 200 ms), the presynaptic cytosolic Ca peaked at approximately 10 s in the young and approximately 12 s in the aged synapses. Administration of the membrane permeant Ca chelator, bis (O-aminophenoxy)-ethane-N,N,N,N-tetraacetic acid (BAPTA-AM), significantly attenuated the Ca response in the aged slices, but not in the young slices. The presynaptic mitochondrial Ca signal was much slower, peaking at approximately 90 s in both young and aged synapses, returning to baseline by 300 s. BAPTA-AM significantly attenuated the mitochondrial calcium signal only in the young synapses. Uncoupling mitochondrial respiration by carbonyl cyanide m-chlorophenylhydrazone (CCCP) application evoked a massive intracellular cytosolic Ca increase and a significant drop of mitochondrial Ca, especially in aged slices wherein the cytosolic Ca signal disappeared after approximately 150 s of washout and the mitochondrial Ca signal disappeared after 25 s of washout. These signals were preserved in aged slices by BAPTA-AM. Five minutes of oxygen glucose deprivation (OGD) was associated with a significant increase in cytosolic Ca in both young and aged synapses, which was irreversible in the aged synapses. These responses were significantly attenuated by BAPTA-AM in both the young and aged synapses. These results support the hypothesis that increasing intracellular calcium neuronal buffering in aged rats ameliorates age-related impaired presynaptic Ca regulation.

Patient awareness of seizures as documented in the epilepsy monitoring unit

Treatment for epilepsy depends largely on seizure frequency reported by patients through their seizure diaries. However, patients may be unaware of some of their seizures, which may lead to incomplete diary data, impacting on appropriate treatment plans. The purpose of this study was to quantify awareness of seizures in patients admitted to an epilepsy monitoring unit through post event assessments by registered nurses. Results indicated that only 44.5% of complex partial and secondarily generalized tonic-clonic seizures were recognized by patients with epilepsy. Incomplete data in seizure diaries are likely a widespread problem, which may have an important impact on treatment and, thereby, on the safety and quality of life of individuals with epilepsy.

Cellular mechanisms of cobalt-induced hippocampal epileptiform discharges

PURPOSE

To explore the cellular mechanisms of cobalt-induced epileptiform discharges in mouse hippocampal slices.

METHODS

Hippocampal slices were prepared from adult mice and briefly exposed to a CoCl(2)-containing external solution. Population and single cell activities were examined via extracellular and whole-cell patch recordings.

RESULTS

Brief cobalt exposure induced spontaneous, ictal-like discharges originating from the CA3 area. These discharges were suppressed by anticonvulsants, gap junction blockers, or by raising extracellular Ca(2+), but their generation was not associated with overall hyperexcitability or impairment in GABAergic inhibition in the CA3 circuit. Electroencephalographic ictal discharges of similar waveforms were observed in behaving rats following intrahippocampal cobalt infusion.

DISCUSSION

Mechanisms involving activity-dependent facilitation of gap junctional communication may play a major role in cobalt-induced epileptiform discharges.

Towards real-time in-implant epileptic seizure prediction

We present an architecture of an epileptic seizure prediction system suitable for an implantable implementation. The microsystem comprises a neural interface, a spectral analysis processor and an artificial neural network (ANN). The neural interface and the spectral analysis processor have been prototyped in a 0.35 microm CMOS technology with experimental results are presented. The wavelet-based artificial neural network predicts the onsets of seizure up to two minutes before their occurrence in an in-vitro epilepsy model using a mouse hippocampal brain slice with recurrent spontaneous seizures.

Enhanced Ih depresses rat entopeduncular nucleus neuronal activity from high-frequency stimulation or raised Ke+

High-frequency stimulation (HFS) is used to treat a variety of neurological diseases, yet its underlying therapeutic action is not fully elucidated. Previously, we reported that HFS-induced elevation in [K(+)](e) or bath perfusion of raised K(e)(+) depressed rat entopeduncular nucleus (EP) neuronal activity via an enhancement of an ionic conductance leading to marked depolarization. Herein, we show that the hyperpolarization-activated (I(h)) channel mediates the HFS- or K(+)-induced depression of EP neuronal activity. The perfusion of an I(h) channel inhibitor, 50 microM ZD7288 or 2 mM CsCl, increased input resistance by 23.5 +/- 7% (ZD7288) or 35 +/- 10% (CsCl), hyperpolarized cells by 3.4 +/- 1.7 mV (ZD7288) or 2.3 +/- 0.9 mV (CsCl), and decreased spontaneous action potential (AP) frequency by 51.5 +/- 12.5% (ZD7288) or 80 +/- 13.5% (CsCl). The I(h) sag was absent with either treatment, suggesting a block of I(h) channel activity. Inhibition of the I(h) channel prior to HFS or 6 mM K(+) perfusion not only prevented the previously observed decrease in AP frequency, but increased neuronal activity. Under voltage-clamp conditions, I(h) currents were enhanced in the presence of 6 mM K(+). Calcium is also involved in the depression of EP neuronal activity, since its removal during raised K(e)(+) application prevented this attenuation and blocked the I(h) sag. We conclude that the enhancement of I(h) channel activity initiates the HFS- and K(+)-induced depression of EP neuronal activity. This mechanism could underlie the inhibitory effects of HFS used in deep brain stimulation in output basal ganglia nuclei.