Validating the boundary element method for forward and inverse EEG computations in the presence of a hole in the skull

Holes in the skull may have a large influence on the EEG and ERP. Inverse source modeling techniques such as dipole fitting require an accurate volume conductor model. This model should incorporate holes if present, especially when either a neuronal generator or the electrodes are close to the hole, e.g., in case of a trephine hole in the upper part of the skull. The boundary element method (BEM) is at present the preferred method for inverse computations using a realistic head model, because of its efficiency and availability. Using a simulation approach, we have studied the accuracy of the BEM by comparing it to the analytical solution for a volume conductor without a hole, and to the finite difference method (FDM) for one with a hole. Furthermore, we have evaluated the influence of holes on the results of forward and inverse computations using the BEM. Without a hole and compared to the analytical model, a three-sphere BEM model was accurate up to 5-10%, while the corresponding FDM model had an error <0.5%. In the presence of a hole, the difference between the BEM and the FDM was, on average, 4% (1.3-11.4%). The FDM turned out to be very accurate if no hole is present. We believe that the difference between the BEM and the FDM represents the inaccuracy of the BEM. This inaccuracy in the BEM is very small compared to the effect that holes can have on the scalp potential (up to 450%). In regard to the large influence of holes on forward and inverse computations, we conclude that holes in the skull can be treated reliably by means of the BEM and should be incorporated in forward and inverse modeling.     

Modeling of the human skull in EEG source analysis

We used computer simulations to investigate finite element models of the layered structure of the human skull in EEG source analysis. Local models, where each skull location was modeled differently, and global models, where the skull was assumed to be homogeneous, were compared to a reference model, in which spongy and compact bone were explicitly accounted for. In both cases, isotropic and anisotropic conductivity assumptions were taken into account. We considered sources in the entire brain and determined errors both in the forward calculation and the reconstructed dipole position. Our results show that accounting for the local variations over the skull surface is important, whereas assuming isotropic or anisotropic skull conductivity has little influence. Moreover, we showed that, if using an isotropic and homogeneous skull model, the ratio between skin/brain and skull conductivities should be considerably lower than the commonly used 80:1. For skull modeling, we recommend (1) Local models: if compact and spongy bone can be identified with sufficient accuracy (e.g., from MRI) and their conductivities can be assumed to be known (e.g., from measurements), one should model these explicitly by assigning each voxel to one of the two conductivities, (2) Global models: if the conditions of (1) are not met, one should model the skull as either homogeneous and isotropic, but with considerably higher skull conductivity than the usual 0.0042 S/m, or as homogeneous and anisotropic, but with higher radial skull conductivity than the usual 0.0042 S/m and a considerably lower radial:tangential conductivity anisotropy than the usual 1:10. Hum Brain Mapp, 2010. © 2010 Wiley‐Liss, Inc.     

以螺旋CT数据建立的颅底三维有限元模型

背景：近年来国内外学者进行了大量生物力学实验研究,试图解释颅脑损伤的发生过程和受力大小与损伤部位的相关性。但是目前针对颅底骨折原因的研究主要是直接暴力,对于间接暴力作用于颅底后颅底的应力分布情况尚无报道。 目的：利用螺旋CT数据、三维重建软件及有限元分析软件,在普通PC机建立颅底三维有限元模型。 方法：选择正常成年女性作为建模对象,无头颈部损伤、手术及其他病史,CT扫描前进行X射线常规检查排除器质性疾病。头部螺旋CT薄层扫描后,将图像数据输入医用图像与三维重建软件MIMICS中,建立颅底的三维可视化模型。将该模型简化优化后,导入有限元分析软件ANSYS 10.0中,建立颅底的三维有限元模型。 结果与结论：建立了由额骨、蝶骨、筛骨、颞骨、枕骨等共同组成的颅底实体模型,由于成年人骨缝闭合,所以将其视为一个整体。对实体模型划分网格,得到颅底的三维有限元模型,共有51 053个单元,80 273个节点。提示所建立的颅底有限元模型外形逼真,几何相似性好,可以用来进行颅底骨折的生物力学研究。     

自体骨瓣、普通钛网、预塑二维钛网修补颅骨缺损比较

目的 比较自体骨瓣、普通钛网和预塑二维钛网修补颅骨缺损的临床效果.方法 回顾性分析2005年7月至2011年3月行颅骨修补术340例患者的临床资料,其中使用自体骨瓣修补168例、普通钛网122例和预塑二维钛网45例.结果 普通钛网组单侧颅骨缺损修补时间(92.5 min)和预塑二维钛网组(85 min)较自体骨瓣组(65 min)明显延长(P<0.05).三组之间术后并发症如头皮下感染、材料外露、再手术取出材料、癫痫、颅内血肿和皮下积液等发生率均无明显差异(P>0.05);而自体骨瓣组术后外观缺陷率最高,普通钛网组次之,预塑二维钛网组最低,三组之间差异均明显(P<0.05).结论 自体骨瓣、普通钛网和预塑二维钛网等材料与颅骨成形术后感染、癫痫、颅内出血等无明显相关性;额颞颅骨缺损首选预塑二维钛网,非额颞颅骨缺损修补应首选自体骨瓣;普通钛网逐渐淘汰,但可使用于颅骨缺损急诊一期修补.     

Effects of holes on EEG forward solutions using a realistic geometry head model

Holes in the skull and the scalp are associated with intracranial monitoring procedures. The purpose of the present study is to evaluate the effects of holes on extracranial electroencephalogram (EEG) and intracranial electrocorticogram (ECoG) recordings. The finite difference method (FDM) was used to model the head volume conductor with a hole of varying size. A current dipole was used to simulate the brain electrical activity with varying locations within the brain. The effects of the holes were assessed by comparing the forward potential distributions with and without a hole. The present computer simulation results indicate that the effect of a hole on the scalp EEG and ECoG recordings strongly depends on the dipole location and orientation. For a superficial radial dipole located under a hole of radius ranging from 5 mm to 40 mm, the relative error (RE) varies from 0.99% to 93.07% for the EEG and from 0.025% to 16.72% for the ECoG. The correlation coefficient (CC) varies from 99.99% to 21.1% and from 100% to 99.75% for the EEG and EcoG, respectively. For radial dipoles, the strongest effect on the EEG and ECoG occurs when the dipole is located below the center of the hole, while for tangential dipoles, the strongest effect occurs when the dipole is located below the border of the hole. The effect of a hole on the EEG is much larger than upon the ECoG.     

Effects of uncertainty in head tissue conductivity and complexity on EEG forward modeling in neonates

In this study, we investigated the impact of uncertainty in head tissue conductivities and inherent geometrical complexities including fontanels in neonates. Based on MR and CT coregistered images, we created a realistic neonatal head model consisting of scalp, skull, fontanels, cerebrospinal fluid (CSF), gray matter (GM), and white matter (WM). Using computer simulations, we investigated the effects of exclusion of CSF and fontanels, discrimination between GM and WM, and uncertainty in conductivity of neonatal head tissues on EEG forward modeling. We found that exclusion of CSF from the head model induced the strongest widespread effect on the EEG forward solution. Discrimination between GM and white matter also induced a strong widespread effect, but which was less intense than that of CSF exclusion. The results also showed that exclusion of the fontanels from the neonatal head model locally affected areas beneath the fontanels, but this effect was much less pronounced than those of exclusion of CSF and GM/WM discrimination. Changes in GM/WM conductivities by 25% with respect to reference values induced considerable effects in EEG forward solution, but this effect was more pronounced for GM conductivity. Similarly, changes in skull conductivity induced effects in the EEG forward modeling in areas covered by the cranial bones. The least intense effect on EEG was caused by changes in conductivity of the fontanels. Our findings clearly emphasize the impact of uncertainty in conductivity and deficiencies in head tissue compartments on modeling research and localization of brain electrical activity in neonates. Hum Brain Mapp 37:3604–3622, 2016. © 2016 Wiley Periodicals, Inc .     

Improved EEG source analysis using low‐resolution conductivity estimation in a four‐compartment finite element head model

Bioelectric source analysis in the human brain from scalp electroencephalography (EEG) signals is sensitive to geometry and conductivity properties of the different head tissues. We propose a low‐resolution conductivity estimation (LRCE) method using simulated annealing optimization on high‐resolution finite element models that individually optimizes a realistically shaped four‐layer volume conductor with regard to the brain and skull compartment conductivities. As input data, the method needs T1‐ and PD‐weighted magnetic resonance images for an improved modeling of the skull and the cerebrospinal fluid compartment and evoked potential data with high signal‐to‐noise ratio (SNR). Our simulation studies showed that for EEG data with realistic SNR, the LRCE method was able to simultaneously reconstruct both the brain and the skull conductivity together with the underlying dipole source and provided an improved source analysis result. We have also demonstrated the feasibility and applicability of the new method to simultaneously estimate brain and skull conductivity and a somatosensory source from measured tactile somatosensory‐evoked potentials of a human subject. Our results show the viability of an approach that computes its own conductivity values and thus reduces the dependence on assigning values from the literature and likely produces a more robust estimate of current sources. Using the LRCE method, the individually optimized four‐compartment volume conductor model can, in a second step, be used for the analysis of clinical or cognitive data acquired from the same subject. Hum Brain Mapp, 2009. © 2008 Wiley‐Liss, Inc.     

EEG/ERP as a pragmatic method to expand the reach of infant-toddler neuroimaging in HBCD: Promises and challenges

Though electrophysiological measures (EEG and ERP) offer complementary information to MRI and a variety of advantages for studying infants and young children, these measures have not yet been included in large cohort studies of neurodevelopment. This review summarizes the types of EEG and ERP measures that could be used in the HEALthy Brain and Cognitive Development (HBCD) study, and the promises and challenges in doing so. First, we provide brief overview of the use of EEG/ERP for studying the developing brain and discuss exemplar findings, using resting or baseline EEG measures as well as the ERP mismatch negativity (MMN) as exemplars. We then discuss the promises of EEG/ERP such as feasibility, while balancing challenges such as ensuring good signal quality in diverse children with different hair types. We then describe an ongoing multi-site EEG data harmonization from our groups. We discuss the process of alignment and provide preliminary usability data for both resting state EEG data and auditory ERP MMN in diverse samples including over 300 infants and toddlers. Finally, we provide recommendations and considerations for the HBCD study and other studies of neurodevelopment.     

Effects of carnosine on olfactory bulb EEG, evoked potentials and DC potentials

Carnosine is a dipeptide found in great quantities in the primary olfactory nerve and has been suggested to be the neurotransmitter of the olfactory receptor axons. The aim of the present study was to describe some of its electrophysiological actions in the olfactory bulb (OB) of rabbits under anesthesia. Carnosine as a 10% solution in amounts of 2-5 microliter was injected to the OB at the level of the glomerular layer by means of a pipette attached to a Hamilton syringe. Average evoked potentials (AEPs) on the stimulation of the lateral olfactory tract (LOT-AEP), electroencephalographic (EEG) activity and slow potential (DC) recordings were obtained. The LOT-AEPs were analyzed by fitting damped sine waves to them. The parameters of amplitude, frequency, decay rate, phase and rise rate were measured and statistically compared to the values obtained prior to the carnosine injection. An increase in frequency and decreases in the phase and the decay rate of the AEP were found. Carnosine also produced a sustained oscillation in the EEG and a surface negative, deep positive shift in the DC recording. The changes were maximal within the first minute after injection and lasted 2-7 min. Tyrodes' solution, which was used as the carnosine vehicle, did not produce any changes, nor did beta-alanine, which is one of the constituents of carnosine, at equivalent osmotic concentrations. It is concluded that carnosine has an excitatory action on the mitral/tufted cells, and that this effect is obscured by a secondary increase in granule cell (inhibitory) activity.     

低频脉冲磁场对全脑缺血再灌注大鼠脑电图及海马神经细胞的作用

目的探讨经颅低频脉冲磁场对全脑缺血再灌注大鼠海马神经细胞的作用。方法将24只SD大鼠随机分成对照组和磁辐射组，每组各12只，应用改良的Pulsineli4-VO法制做大鼠全脑缺血再灌注模型，磁辐射组在脑缺血模型完成后立即将其头颈部置磁场（20mT、10Hz）中轴中央，身体顺磁场方向放置，辐射45min，每天1次，作用4次后将大鼠记录脑电图后断头取脑，对照组同时处死断头取脑，应用Nissl染色及免疫组织化学方法进行海马神经细胞计数及凋亡相关基因caspase-3蛋白表达检测。结果磁疗组较对照组神经元数量多（P〈0．05），脑电图频率和波幅增高（P〈0．05），caspase-3蛋白表达低（P〈0．05）。结论低频脉冲磁场（20mT、10Hz）可以抑制大鼠脑缺血再灌注海马神经元的凋亡，对脑缺血再灌注损伤有保护作用。     

Effects of serial lateral hypothalamic destruction on feeding behavior, body weight, and neocortical and hippocampal EEG activity

A comparison was made of effects of simultaneous vs. serial lateral hypothalamic lesions on (i) feeding behavior, (ii) body weight, (iii) hippocampal rhythmical slow activity, (iv) neocortical low voltage fast activity, and (v) atropine-resistant patterns of neocortical and hippocampal EEG in rats. Serial lesions separated by 30 days produced no significant sparing of function on the first three variables but produced significant sparing on the last two. The results suggest the effects may be related to anatomic and/or pharmacologic differences in the way neural systems subserving the different functions are organized.     

Effects of a novel NMDA receptor antagonist on experimental stroke quantitatively assessed by spectral EEG and infarct volume

Abstract

We used spectral electroencephalographic (EEC) analysis to demonstrate the physiological effect of focal brain ischaemia induced by permanent occlusion of the right middle cerebral artery in rats. A significant shift to lower frequency EEC activity occurred relative to the baseline power spectrum within one hour following the occlusion. Spectral EEG analysis also revealed a cerebroprotective effect of a noncompetitive N-methyl-D-aspartate receptor antagonist, CNS 1102, administered 15 min post-occlusion. Animals treated with this NMDA antagonist exhibited only 26.5% of the slowing in the ischaemic hemisphere compared to aminals given a placebo. Post-mortem analysis conducted 24 h later also revealed reduced infarction volumes for the treated animals, there was a highly significant correlation between the extent of spectral EEG slowing during the initial development of the infarction and subsequent lesion size. These results suggest that spectral EEG analysis may be useful in the early evaluation of experimental and perhaps human stroke and for monitoring the effects of cerebroprotective therapies. [Neurol Res 1994; 16: 443-448]     

Rett syndrome, EEG and the motor cortex as a model for better understanding of attention deficit hyperactivity disorder (ADHD)

EEG data in Rett syndrome (RS) are quite often characterized by spikes over the central region (especially in sleep). Furthermore, there has been a recent observation of a prominent and peculiar theta (4–6/s) rhythm over the central region and vicinity. In view of the clinical phenomena of RS, it is pointed out that clinical and electrical findings are based upon hyperexcitability of the motor cortex (or a state of motor cortex dyscontrol). States of dyscontrol (disinhibition) are caused by deficits in higher cortical functions. It is reasonable to assume a primary dysfunction for the frontal lobe which is also smaller in size than other cerebral regions. The behavioral (motor) disturbance in RS can be easily explained as the expression of disturbed prefrontal/premotor function with special effect on the „syntax of action”. It is further theorized that such a state of fronto-motor cortex uncoupling may also exist in attention deficit hyperkinetic disorder (ADHD) even though there is hardly any structural CNS impairment in that condition. A presumed „lazy frontal lobe” is likely to react favorably to the stimulation provided by methylphenidate (a therapeutic effect which should not be viewed as paradoxical). Accepted: 27 June 1997     

Effects of sleep deprivation on cortical excitability in patients affected by juvenile myoclonic epilepsy: a combined transcranial magnetic stimulation and EEG study

OBJECTIVE: To investigate the effect of sleep deprivation on corticospinal excitability in patients affected by juvenile myoclonic epilepsy (JME) using different transcranial magnetic stimulation (TMS) parameters. METHODS: Ten patients with JME and 10 normal subjects underwent partial sleep deprivation. Motor threshold (MT), motor evoked potential amplitude (MEP), and silent period (SP) were recorded from the thenar eminence (TE) muscles. Short latency intracortical inhibition (SICI) and short latency intracortical facilitation (SICF) were studied using paired magnetic stimulation. TMS was performed before and after sleep deprivation; EEG and TMS were performed simultaneously. RESULTS: In patients with JME, sleep deprivation induced a significant decrease in SICI and an increase in SICF, which was associated with increased paroxysmal activity. A significant decrease in the MT was observed. No significant changes in any TMS parameters were noted in normal subjects after sleep deprivation. The F wave was unchanged by sleep deprivation in both control subjects and in patients with JME. CONCLUSIONS: In patients with JME, sleep deprivation produces increases in corticospinal excitability in motor areas as measured by different TMS parameters.     

Detecting dopaminergic neuronal degeneration using diffusion tensor imaging in a rotenone-induced rat model of Parkinson's disease: fractional anisotropy and mean diffusivity values

Dopamine content in the basal ganglia is strongly associated with the degree of dopaminergic neuron loss in the substantia nigra pars com-pacta. Symptoms of Parkinson's disease might not arise until more than 50% of the substantia nigra pars compacta is lost and the dopamine content in the basal ganglia is reduced by more than 80%. Greater diagnostic sensitivity and specificity would allow earlier detection of Parkinson's disease. Diffusion tensor imaging is a recently developed magnetic resonance imaging technique that measures mean diffusiv-ity and fractional anisotropy, and responds to changes in brain microstructure. When the microscopic barrier (including cell membranes, microtubules and other structures that interfere with the free diffusion of water) is destroyed and extracellular fluid volume accumulates, the mean diffusivity value increases; when the integrity of the microstructure (such as myelin) is destroyed, fractional anisotropy value decreases. However, there is no consensus as to whether these changes can reflect the early pathological alterations in Parkinson's disease. Here, we established a rat model of Parkinson's disease by injecting rotenone (or sunflower oil in controls) into the right substantia nigra. Diffusion tensor imaging results revealed that in the stages of disease, at 1, 2, 4, and 6 weeks after rotenone injection, fractional anisotropy value decreased, but mean diffusivity values increased in the right substantia nigra in the experimental group. Fractional anisotropy values were lower at 4 weeks than at 6 weeks in the right substantia nigra of rats from the experimental group. Mean diffusivity values were mark-edly greater at 1 week than at 6 weeks in the right corpus striatum of rats from the experimental group. These findings suggest that mean diffusivity and fractional anisotropy values in the brain of rat models of Parkinson's disease 4 weeks after model establishment can reflect early degeneration of dopaminergic neurons. The change in fractional anisotropy values after destruction of myelin integrity is likely to be of greater early diagnostic significance than the change in mean diffusivity values.     

The effect of stimulation type,head modeling,and combined EEG and MEG on the source reconstruction of the somatosensory P20/N20 component

Modeling and experimental parameters influence the Electro‐ (EEG) and Magnetoencephalography (MEG) source analysis of the somatosensory P20/N20 component. In a sensitivity group study, we compare P20/N20 source analysis due to different stimulation type (Electric‐Wrist [EW], Braille‐Tactile [BT], or Pneumato‐Tactile [PT]), measurement modality (combined EEG/MEG – EMEG, EEG, or MEG) and head model (standard or individually skull‐conductivity calibrated including brain anisotropic conductivity). Considerable differences between pairs of stimulation types occurred (EW‐BT: 8.7 ± 3.3 mm/27.1° ± 16.4°, BT‐PT: 9 ± 5 mm/29.9° ± 17.3°, and EW‐PT: 9.8 ± 7.4 mm/15.9° ± 16.5° and 75% strength reduction of BT or PT when compared to EW) regardless of the head model used. EMEG has nearly no localization differences to MEG, but large ones to EEG (16.1 ± 4.9 mm), while source orientation differences are non‐negligible to both EEG (14° ± 3.7°) and MEG (12.5° ± 10.9°). Our calibration results show a considerable inter‐subject variability (3.1–14 mS/m) for skull conductivity. The comparison due to different head model show localization differences smaller for EMEG (EW: 3.4 ± 2.4 mm, BT: 3.7 ± 3.4 mm, and PT: 5.9 ± 6.8 mm) than for EEG (EW: 8.6 ± 8.3 mm, BT: 11.8 ± 6.2 mm, and PT: 10.5 ± 5.3 mm), while source orientation differences for EMEG (EW: 15.4° ± 6.3°, BT: 25.7° ± 15.2° and PT: 14° ± 11.5°) and EEG (EW: 14.6° ± 9.5°, BT: 16.3° ± 11.1° and PT: 12.9° ± 8.9°) are in the same range. Our results show that stimulation type, modality and head modeling all have a non‐negligible influence on the source reconstruction of the P20/N20 component. The complementary information of both modalities in EMEG can be exploited on the basis of detailed and individualized head models.     

Effects of gabapentin on brain hyperactivity related to pain and sleep disturbance under a neuropathic pain-like state using fMRI and brain wave analysis

Neuropathic pain is the most difficult pain to manage in the pain clinic, and sleep problems are common among patients with chronic pain including neuropathic pain. In the present study, we tried to visualize the intensity of pain by assessing neuronal activity and investigated sleep disturbance under a neuropathic pain-like state in mice using functional magnetic resonance imaging (fMRI) and electroencephalogram (EEG)/electromyogram (EMG), respectively. Furthermore, we investigated the effect of gabapentin (GBP) on these phenomena. In a model of neuropathic pain, sciatic nerve ligation caused a marked decrease in the latency of paw withdrawal in response to a thermal stimulus only on the ipsilateral side. Under this condition, fMRI showed that sciatic nerve ligation produced a significant increase in the blood oxygenation level-dependent (BOLD) signal intensity in the pain matrix, which was significantly decreased 2 h after the i.p. injection of GBP. Based on the results of an EEG/EMG analysis, sciatic nerve-ligated animals showed a statistically significant increase in wakefulness and a decrease in non-rapid eye movement (NREM) sleep during the light phase, and the sleep disturbance was almost completely alleviated by a higher dose of GBP in nerve-ligated mice. These findings suggest that neuropathic pain associated with sleep disturbance can be objectively assessed by fMRI and EEG/EMG analysis in animal models. Furthermore, GBP may improve the quality of sleep as well as control pain in patients with neuropathic pain.     

Effects of sleep disruption on stress,nigrostriatal markers,and behavior in a chronic/progressive MPTP male mouse model of parkinsonism

Sleep complaints are an early clinical symptom of neurodegenerative disorders. Patients with Parkinson's disease (PD) experience sleep disruption (SD). The objective of this study was to determine if preexisting, chronic SD leads to a greater loss of tyrosine hydroxylase (TH) within the striatum and the substantia nigra following chronic/progressive exposure with the neurotoxin, 1-methyl-2-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Male mice underwent chronic SD for 4 weeks, then injected with vehicle (VEH) or increasing doses of MPTP for 4 weeks. There was a significant decrease in the plasma corticosterone levels in the MPTP group, an increase in the SD group, and a return to the VEH levels in the SD+MPTP group. Protein expression levels for TH in the striatum (terminals) and substantia nigra pars compacta (dopamine [DA] cell counts) revealed up to a 78% and 38% decrease, respectively, in the MPTP and SD+MPTP groups compared to their relevant VEH and SD groups. DA transporter protein expression increased in the striatum in the MPTP versus VEH group and in the SN/midbrain between the SD+MPTP and the VEH group. There was a main effect of MPTP on various gait measures (e.g., braking) relative to the SD or VEH groups. In the SD+MPTP group, there were no differences compared to the VEH group. Thus, SD, prior to administration of MPTP, has effects on serum corticosterone and gait but more importantly does not potentiate greater loss of TH within the nigrostriatal pathway compared to the MPTP group, suggesting that in PD patients with SD, there is no exacerbation of the DA cell loss.     

Effects of AlCl3 on toad skin, human erythrocytes, and model cell membranes

Aluminum, a very abundant metal, could play a toxic role in several pathological processes, including neurodegeneration. Although the effects of Al(III) on biological membranes have been extensively described, direct information concerning the molecular basis of its biological activity is rather scanty. To examine aluminum challenges on cell membranes, various concentrations of AlCl₃ in aqueous solutions were incubated with human erythrocytes, isolated toad skin, and molecular models of biomembranes. The latter consisted of multilayers of dimyristoylphosphatidylcholine and dimyristoylphosphatidylethanolamine, representing phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane. These specimens were studied by scanning electron microscopy, electrophysiological measurements, and x-ray diffraction. The results indicate that Al(III) in the concentration range of 10–100 μM induced the following structural and functional effects: (i) change in the normal discoid shape of human eryhrocytes to echinocytes due to the accumulation of Al(III) ions in the outer moiety of the red cell membrane; (ii) perturbation of dimyristoylphosphatidylcholine, and to a lesser extent of dimyristoylphosphatidylethanolamine bilayers, and (iii) decrease in the short-circuit current and in the potential difference of the isolated toad skin, effects that are in accordance with a time-dependent modulation of ion transport in response to changes in the molecular structure of the lipid bilayer.