Simulated electrocortical activity at microscopic, mesoscopic, and global scales

Simulation of electrocortical activity requires (a) determination of the most crucial features to be modelled, (b) specification of state equations with parameters that can be determined against independent measurements, and (c) explanation of electrical events in the brain at several scales. We report our attempts to address these problems, and show that mutually consistent explanations, and simulation of experimental data can be achieved for cortical gamma activity, synchronous oscillation, and the main features of the EEG power spectrum including the cerebral rhythms and evoked potentials. These simulations include consideration of dendritic and synaptic dynamics, AMPA, NMDA, and GABA receptors, and intracortical and cortical/subcortical interactions. We speculate on the way in which Hebbian learning and intrinsic reinforcement processes might complement the brain dynamics thus explained, to produce elementary cognitive operations.

FHL3 is an actin-binding protein that regulates alpha-actinin-mediated actin bundling: FHL3 localizes to actin stress fibers and enhances cell spreading and stress fiber disassembly

Four and a half LIM domain (FHL) proteins are members of the LIM protein superfamily. Several FHL proteins function as co-activators of CREM/CREB transcription factors and the androgen receptor. FHL3 is highly expressed in skeletal muscle, but its function is unknown. FHL3 localized to the nucleus in C2C12 myoblasts and, following integrin engagement, exited the nucleus and localized to actin stress fibers and focal adhesions. In mature skeletal muscle FHL3 was found at the Z-line. Actin was identified as a potential FHL3 binding partner in yeast two-hybrid screening of a skeletal muscle library. FHL3 complexed with actin both in vitro and in vivo as shown by glutathione S-transferase pull-down assays and co-immunoprecipitation of recombinant and endogenous proteins. FHL3 promoted cell spreading and when overexpressed in spread C2C12 cells disrupted actin stress fibers. Increased FHL3 expression was detected in highly motile cells migrating into an artificial wound, compared with non-motile cells. The molecular mechanism by which FHL3 induced actin stress fiber disassembly was demonstrated by low speed actin co-sedimentation assays and electron microscopy. FHL3 inhibited alpha-actinin-mediated actin bundling. These studies reveal FHL3 as a significant regulator of actin cytoskeletal dynamics in skeletal myoblasts.

Increased zinc finger protein zFOC1 transcripts in gastric cancer compared with normal gastric tissue

BACKGROUND

Screening of cDNA arrays of the IMAGE library identified human zFOC1 as a differentially expressed cDNA that was upregulated in KATO III gastric cancer cells following stimulation with the gastric pathogen Helicobacter pylori.

AIMS

To determine the expression of zFOC1 in gastric mucosa with and without H pylori infection and in patients with gastric cancer.

RESULTS

zFOC1 is localised on chromosome 12q24.3 and encodes a zinc finger protein. Expression studies in human H pylori infected and uninfected gastric biopsies, gastric tumours, and gastric cancer cell lines revealed that zFOCI gene transcripts are significantly higher in gastric cancer than in non-cancerous gastric tissues.

CONCLUSIONS

The zFOC1 gene appears to be a tumour marker associated with gastric cancer.

Neurophysical theory of coherence and correlations of electroencephalographic and electrocorticographic signals

Correlation and coherence functions of electroencephalographic signals are calculated using a recent continuum theory that has previously yielded excellent agreement with observations of electroencephalographic spectra. The predicted properties of these functions are found to be in semiquantitative agreement with observations for parameters consistent with those used in previous studies of spectra. The corresponding results for electrocorticographic signals point to an additional contribution at characteristic scales of around 6mm, as has been previously inferred, and are consistent with a crossover to the long-range behavior seen in scalp data. Analysis within the framework of the model enables constraints on the relative strengths of the two contributions to be inferred, and makes it plausible that the short-range component reflects the point-spread function of external stimuli and corticothalamic feedback reaching the cortex.

Wave-number spectrum of electrocorticographic signals

A physiologically based continuum model of corticothalamic electrodynamics is generalized and used to derive the theoretical form of the electrocorticographic (ECoG) wave-number spectrum. A one-dimensional projection of the spectrum is derived, as is the azimuthally averaged two-dimensional spectrum for isotropic and anisotropic cortices. The predicted spectra are found to consist of a low-k plateau followed by three regions of power-law decrease, which result from filtering of the electrical activity through physical structures at different scales in the cortex. The magnitude of the maximum theoretical power-law exponent is larger for the two-dimensional (2D) spectrum than for its 1D counterpart. The predicted spectra agree well with experimental data obtained from 1D and 2D recording arrays on the cortical surface, enabling the structures in the brain that are important in determining spatial cortical dynamics to be identified. The cortical dispersion relation predicted by our model is also investigated, providing insight into the relationships between temporal and spatial brain dynamics.

Self-organized criticality in ant brood tending

A new stochastic lattice gas model of ant brood tending is formulated to examine the role played by repulsive ant-ant interactions in the even distribution of care among brood members. The deterministic limit of the model is known to be self-organized critical. Numerical simulations of the model show that the ant-ant repulsion facilitates an even distribution of brood care in the middle of the brood. This provides a possible explanation for the fact that ants sort their brood so that the youngest brood (which are most in need of care) are placed in the middle. Simulations show that the uniformity of brood care distribution is optimal when ants operate in a regime intermediate between completely random and completely deterministic. A certain degree of randomness helps ants to avoid becoming trapped in suboptimal configurations but does not destroy the long-range correlations that are inherent to self-organized critical systems.

Self-organized criticality and emergent oscillations in models of termite architecture with crowding

The termite architecture model of O'Toole et'al. (1999) is extended to incorporate arbitrary halting time-scales. It is shown that this also means that the assumption of synchronous building must be relaxed. Numerical simulations show that ordered nest architecture emerges under a wide range of time-scales but also that there is an optimal region of halting times. This optimal region is explained by the emergence of synchronized periods of termite activity. The correlation length of the building distribution is shown to diverge providing strong evidence that the model is self-organized critical.

Interpretation of scaling properties of electroencephalographic fluctuations via spectral analysis and underlying physiology

Detrended fluctuation analysis has recently demonstrated the existence of two approximate temporal scaling regimes in locally detrended human electroencephalographic (EEG) fluctuations, and has suggested a connection between the location of the breakpoint between regimes and the alpha resonance near 10 Hz. It is shown here that these scalings can be explained in terms of the filtering of the underlying power spectrum implied by the detrending process. Using a recent physiologically based model of EEG generation, the main features of the scalings, and deviations from them, are related to the underlying physiology of dendritic propagation and muscle electrical activity, and it is concluded that the effects of such physiological features are usually clearer in spectra.

Diffusion and anomalous diffusion of light in two-dimensional photonic crystals

The transport properties of electromagnetic waves in disordered, finite, two-dimensional photonic crystals composed of circular cylinders are considered. Transport parameters such as the transport and scattering mean free paths and the transport velocity are calculated, for the case where the electromagnetic radiation has its electric field along the cylinder axes. The range of the parameters in which the diffusion process can take place is specified. It is shown that the transport velocity upsilon(E) can be as much as 10(8) times less than its free space value, while just outside the cluster upsilon(E) can be 0.3c. The effects of weak and strong disorders on the transport velocity are investigated. Different regimes of the wave transport-ordered propagation, diffusion, and anomalous diffusion-are demonstrated, and it is inferred that Anderson localization is incipient in the latter regime. Exact numerical calculations from the Helmholtz equation are shown to be in good agreement with the diffusion approximation.

Skeletal muscle LIM protein 1 regulates integrin-mediated myoblast adhesion, spreading, and migration

The skeletal muscle LIM protein 1 (SLIM1) is highly expressed in skeletal and cardiac muscle, and its expression is downregulated significantly in dilated human cardiomyopathy. However, the function of SLIM1 is unknown. In this study, we investigated the intracellular localization of SLIM1. Endogenous and recombinant SLIM1 localized to the nucleus, stress fibers, and focal adhesions in skeletal myoblasts plated on fibronectin, collagen, or laminin. However, after inhibition of integrin signaling either by plating on poly-l-lysine or by soluble RGD peptide, SLIM1 localized diffusely in the cytosol, with decreased nuclear expression. Disruption of the actin cytoskeleton by cytochalasin D did not inhibit nuclear localization of SLIM1 in integrin-activated cells. Green fluorescent protein-tagged SLIM1 shuttled in the nucleus of untransfected NIH 3T3 cells, in a heterokaryon fusion assay. Overexpression of SLIM1 in Sol8 myoblasts inhibited cell adhesion and promoted cell spreading and migration. These studies show SLIM1 localizes in an integrin-dependent manner to the nucleus and focal adhesions where it functions downstream of integrin activation to promote cell spreading and migration.

Field statistics of two vectorially superposed wave populations

Field statistics of observed waves and radiation constrain the physics of the emission process and source region. However, data often contain two or more superposed signals or a signal superposed on a noise background, creating difficulties for interpretation. Here, the combined probability distribution of the field formed by vector superposition of two signals, each with specified statistics, is written as a double integral with integrable singularities. The analytic result and its numerical solutions for combinations of Gaussian and lognormally distributed signals show that these predictions differ from those for field or intensity convolution and from the individual wave distributions. At high fields, the combined distribution takes the qualitative form of the dominant individual distribution (which is localized or otherwise extends to larger fields) but develops a significant tail at low fields due to vector superposition of almost antiparallel fields with similar magnitudes. It is shown that very nearly power-law distributions can develop in significant field domains, despite neither component distribution being power law. This is relevant to alternative interpretations in terms of self-organized criticality and certain modulational wave instabilities. The formalism is then applied to observations of the Vela pulsar, resulting in greatly improved fits to data and different interpretations. Specifically, the results are strong evidence that stochastic growth theory (SGT) is relevant and that the approximate power-law statistics found at some phases are not intrinsic but rather due to vector convolution of a Gaussian background with a lognormal; the latter is interpretable in terms of SGT. The field statistics are consistent with the emission mechanism being a direct linear instability or indirect generation via linear mode conversion of nonescaping waves driven by a linear instability. They are inconsistent with nonlinear self-focusing instabilities generating the observed pulsar radiation. This formalism and its results should also be widely applicable to other types of wave growth in inhomogeneous media.

Wave-number spectrum of electroencephalographic signals

A recently developed, physiologically based continuum model of corticothalamic electrodynamics is used to derive the theoretical form of the electroencephalographic wave-number spectrum and its projection onto a one-dimensional recording array. The projected spectrum is found to consist of a plateau followed by regions of power-law decrease with various exponents, which are dependent on both model parameters and temporal frequency. The theoretical spectrum is compared with experimental results obtained in other studies, showing good agreement. The model provides a framework for understanding the nature of the spatial power spectrum by linking the underlying physiology with the large-scale dynamics of the brain.

Helicobacter pylori-stimulated EGF receptor transactivation requires metalloprotease cleavage of HB-EGF

Helicobacter pylori has a major aetiological role in human gastric carcinogenesis but the cellular and molecular pathways by which infection promotes transformation remain to be resolved. This study demonstrates that H. pylori exposure to MKN-1, ST42, and MKN-28 gastric epithelial tumour cells results in the activation of HB-EGF gene expression and EGFR tyrosine phosphorylation. These cell responses are induced by both cagPAI positive and cagPAI negative H. pylori strains and are dependent on cell surface expression of the HB-EGF precursor. The induction of HB-EGF gene transcription by H. pylori requires metalloprotease-, EGFR-, and Mek1-activities, indicating the involvement of the "triple membrane passing signal" (TMPS) for EGFR transactivation. Moreover, the release of the inflammatory cytokine IL-8 by cells exposed to H. pylori is significantly impaired by inhibitors of TMPS pathway elements. Our findings support a model in which H. pylori triggers constitutive EGFR signal activation, which enhances IL-8 production, and initiates neoplastic transformation of gastric epithelial cells.

Unified neurophysical model of EEG spectra and evoked potentials

Evoked potentials -- the brain's transient electrical responses to discrete stimuli -- are modeled as impulse responses using a continuum model of brain electrical activity. Previous models of ongoing brain activity are refined by adding an improved model of thalamic connectivity and modulation, and by allowing for two populations of excitatory cortical neurons distinguished by their axonal ranges. Evoked potentials are shown to be modelable as an impulse response that is a sum of component responses. The component occurring about 100 ms poststimulus is attributed to sensory activation, and this, together with positive and negative feedback pathways between the cortex and thalamus, results in subsequent peaks and troughs that semiquantitatively reproduce those of observed evoked potentials. Modulation of the strengths of positive and negative feedback, in ways consistent with psychological theories of attentional focus, results in distinct responses resembling those seen in experiments involving attentional changes. The modeled impulse responses reproduce key features of typical experimental evoked response potentials: timing, relative amplitude, and number of peaks. The same model, with further modulation of feedback, also reproduces experimental spectra. Together, these results mean that a broad range of ongoing and transient electrocortical activity can be understood within a common framework, which is parameterized by values that are directly related to physiological and anatomical quantities.

Dynamics of large-scale brain activity in normal arousal states and epileptic seizures

Links between electroencephalograms (EEGs) and underlying aspects of neurophysiology and anatomy are poorly understood. Here a nonlinear continuum model of large-scale brain electrical activity is used to analyze arousal states and their stability and nonlinear dynamics for physiologically realistic parameters. A simple ordered arousal sequence in a reduced parameter space is inferred and found to be consistent with experimentally determined parameters of waking states. Instabilities arise at spectral peaks of the major clinically observed EEG rhythms-mainly slow wave, delta, theta, alpha, and sleep spindle-with each instability zone lying near its most common experimental precursor arousal states in the reduced space. Theta, alpha, and spindle instabilities evolve toward low-dimensional nonlinear limit cycles that correspond closely to EEGs of petit mal seizures for theta instability, and grand mal seizures for the other types. Nonlinear stimulus-induced entrainment and seizures are also seen, EEG spectra and potentials evoked by stimuli are reproduced, and numerous other points of experimental agreement are found. Inverse modeling enables physiological parameters underlying observed EEGs to be determined by a new, noninvasive route. This model thus provides a single, powerful framework for quantitative understanding of a wide variety of brain phenomena.

Unexpected benefit of sorbitol placebo in Mg intervention study of premenstrual symptoms: implications for choice of placebo in RCTs

We carried out a randomized, double-blind, crossover study of 85 women, designed to investigate the dose-response of daily Mg supplementation on premenstrual symptoms. Each woman took one of four treatments: Mg (200, 350 or 500 mg/day) or sorbitol (placebo) for 2 months. This was followed by a washout of 1 month, and then each woman received one of the three remaining treatments for a further 2 months. Unexpectedly, sorbitol (1305 mg) reduced anxiety-related and total premenstrual symptoms after 2 months compared with Mg treatments (P<0.001 and P<0.001, respectively). We conclude that low-dose sorbitol reduces premenstrual symptoms beyond that expected of a placebo. After 2 months of treatment, sorbitol also reduced urinary Mg excretion compared to baseline (no intervention) and Mg treatments (P=0.005). A follow-up study on 17 healthy volunteers confirmed lack of effect on urinary Mg output of a similar sorbitol intervention regime compared with either baseline or cellulose placebo. It appears that sorbitol may influence Mg homeostasis in women suffering premenstrual symptoms, but not in healthy individuals. Implications for placebo choice in RCTs are discussed.

Promising hypotensive effect of hawthorn extract: a randomized double-blind pilot study of mild, essential hypertension

This pilot study was aimed at investigating the hypotensive potential of hawthorn extract and magnesium dietary supplements individually and in combination, compared with a placebo. Thirty-six mildly hypertensive subjects completed the study. At baseline, anthropometric and dietary assessment, as well as blood pressure measurements were taken at rest, after exercise and after a computer 'stress' test. Volunteers were then randomly assigned to a daily supplement for 10 weeks of either: (a) 600 mg Mg, (b) 500 mg hawthorn extract, (c) a combination of (a) and (b), (d) placebo. Measurements were repeated at 5 and 10 weeks of intervention. There was a decline in both systolic and diastolic blood pressure in all treatment groups, including placebo, but ANOVA provided no evidence of difference between treatments. However, factorial contrast analysis in ANOVA showed a promising reduction (p = 0.081) in the resting diastolic blood pressure at week 10 in the 19 subjects who were assigned to the hawthorn extract, compared with the other groups. Furthermore, a trend towards a reduction in anxiety (p = 0.094) was also observed in those taking hawthorn compared with the other groups. These findings warrant further study, particularly in view of the low dose of hawthorn extract used.

Redo carotid endarterectomy versus primary carotid endarterectomy

BACKGROUND AND PURPOSE

Several authorities have recently advocated carotid stenting for recurrent carotid stenosis because of the perception that redo surgery has a higher complication rate than primary carotid endarterectomy (CEA). This study compares the early and late results of reoperations versus primary CEA.

METHODS

All reoperations for recurrent carotid stenosis performed during a recent 7-year period by a single vascular surgeon were compared with primary CEA. Because all redo CEAs were done with polytetrafluoroethylene (PTFE) or vein patch closure, we only analyzed those primary CEAs that used the same patch closures. A Kaplan-Meier life-table analysis was used to estimate stroke-free survival rates and freedom from >/=50% recurrent stenosis.

RESULTS

Of 547 primary CEAs, 265 had PTFE or saphenous vein patch closure, and 124 reoperations had PTFE or vein patch closure during the same period. Both groups had similar demographic characteristics. The indications for reoperation and primary CEA were symptomatic stenosis in 78% and 58% of cases and asymptomatic >/=80% stenosis in 22% and 42% of cases, respectively (P<0.001). The 30-day perioperative stroke and transient ischemic attack rates for reoperation and primary CEA were 4.8% versus 0.8% (P=0.015) and 4% versus 1.1%, respectively, with no perioperative deaths in either group. Cranial nerve injury was noted in 17% of reoperation patients versus 5.3% of primary CEA patients; however, most of these injuries were transient (P<0.001). Mean hospital stay was 1.8 days for reoperation versus 1.6 days for primary CEA. Cumulative rates of stroke-free survival and freedom from >/=50% recurrent stenosis for reoperation and primary CEA at 1, 3, and 5 years were 96%, 91%, and 82% and 98%, 96%, and 95% versus 94%, 92%, and 91% and 98%, 96%, and 96%, respectively (no significant differences).

CONCLUSIONS

Reoperation carries higher perioperative stroke and cranial nerve injury rates than primary CEA. However, reoperations are durable and have stroke-free survival rates that are similar to primary CEA. These considerations should be kept in mind when carotid stenting is recommended instead of reoperation.

Toward an integrated continuum model of cerebral dynamics: the cerebral rhythms, synchronous oscillation and cortical stability

Continuum models of cerebral cortex with parameters derived from physiological data, provide explanations of the cerebral rhythms, synchronous oscillation, and autonomous cortical activity in the gamma frequency range, and suggest possible mechanisms for dynamic self-organization in the brain. Dispersion relations and derivations of power spectral response for the models, show that a low frequency resonant mode and associated travelling wave solutions of the models' equations of state can account for the predominant 1/f spectral content of the electroencephalogram (EEG). Large scale activity in the alpha, beta, and gamma bands, is accounted for by thalamocortical interaction, under regulation by diffuse cortical excitation. System impulse responses can be used to model Event-Related Potentials. Further classes of local resonance may be generated by rapid negative feedbacks at active synapses. Activity in the gamma band around 40 Hz, associated with large amplitude oscillations of pulse density, appears at higher levels of cortical activation, and is unstable unless compensated by synaptic feedbacks. Control of cortical stability by synaptic feedbacks offers a partial account of the regulation of autonomous activity within the cortex. Synchronous oscillation occurs between concurrently excited cortical sites, and can be explained by analysis of wave motion radiating from each of the co-active sites. These models are suitable for the introduction of learning rules-most notably the coherent infomax rule.

cDNA array analysis of cag pathogenicity island-associated Helicobacter pylori epithelial cell response genes

Helicobacter pylori strains containing the cag pathogenicity island (PAI) induce NF-kappaB activation and interleukin-8 secretion in gastric epithelial cells. The aim of this study was to investigate changes in epithelial gene expression induced by cag PAI-positive and -negative strains of H. pylori using high-density cDNA array hybridization technology. Radio-labeled cDNA prepared from H. pylori-infected Kato 3 gastric epithelial cells was hybridized to high-density cDNA arrays to identify changes in epithelial gene expression compared to noninfected controls. In vivo expression of selected, differentially expressed genes was examined by reverse transcription-PCR analysis of H. pylori-positive and -negative gastric mucosa. Screening of ca. 57,800 cDNAs identified 208 known genes and 48 novel genes and/or expressed sequence tags of unknown function to be differentially expressed in Kato 3 cells following H. pylori infection. Marked differences in gene expression profiles were observed following cag PAI-positive and cag PAI-negative infection with 15 novel cDNAs and 92 known genes being differentially expressed. H. pylori was found to change the expression of genes encoding growth factors and cytokine/chemokines and their receptors, apoptosis proteins, transcription factors and metalloprotease-disintegrin proteins (ADAMs), and tissue inhibitors of metalloproteinases. Gastric differential expression of selected known genes (amphiregulin and ADAM 10) and a novel gene (HPYR1) was confirmed in vivo in patients with H. pylori infection. Confirmation of the in vivo expression of selected genes demonstrates the usefulness of this approach for investigating pathogen-induced changes in host gene expression.

Expression of the Sonic Hedgehog receptor "PATCHED" in basal cell carcinomas and odontogenic keratocysts

Basal cell carcinoma (BCC) is a common invasive skin lesion in Caucasians. Odontogenic keratocysts (OKs) are developmental, non-inflammatory oral cysts. They can be sporadic and/or multiple and are locally destructive. Basal cell naevus syndrome (BCNS) comprises both multiple BCCs and multiple OKs, in addition to several other systemic manifestations. The genetic defect underlying this autosomal dominant syndrome is a germ line mutation in the Sonic Hedgehog receptor PATCHED (PTCH) gene. For this study, a rabbit anti-peptide PTCH antiserum was produced. Immunohistochemistry procedures were performed using PTCH antibody and commercially produced GLI-1 antibody (downstream member in the hedgehog pathway) to stain 11 BCNS-OKs, eight sporadic OKs, two BCNS-BCCs, and six sporadic BCCs. Most of these lesions had been previously screened for PTCH mutation. Most BCCs (n=7) demonstrated moderate staining, with the heaviest staining in the outer palisading cell layer, except a BCNS-BCC which had mutation proximal to the sequence used for production of immunogenic peptide; this demonstrated only weak staining. Although moderate to heavy staining with PTCH antibody was demonstrated in the epithelium of both types of OK (n=19), a quite different pattern of staining of the basal cell layer was observed in the two patient groups. In BCNS, OK staining was heaviest in basal epithelial layers. In contrast, staining in non-BCNS odontogenic keratocysts was exclusively located in the superficial epithelial layers. Up-regulation of PTCH and GLI-1 protein was demonstrated in both BCCs and OKs. The pattern of PTCH expression matched the PTCH transcript pattern previously reported in BCCs and appeared sufficiently characteristic in OKs to allow differentiation between syndromic and non-syndromic cysts.

Features of the parkin/ariadne-like ubiquitin ligase, HHARI, that regulate its interaction with the ubiquitin-conjugating enzyme, Ubch7

We recently reported the identification of a RING finger-containing protein, HHARI (human homologue of Drosophila ariadne), which binds to the human ubiquitin-conjugating enzyme UbcH7 in vitro. We now demonstrate that HHARI interacts and co-localizes with UbcH7 in mammalian cells, particularly in the perinuclear region. We have further defined a minimal interaction region of HHARI comprising residues 186-254, identified individual amino acid residues essential for the interaction, and determined that the distance between the RING1 finger and IBR (in between RING fingers) domains is critical to maintaining binding. We have also established that the RING1 finger of HHARI cannot be substituted for by the highly homologous RING finger domains of either of the ubiquitin-protein ligase components c-CBL or Parkin, despite their similarity in structure and their independent capabilities to bind UbcH7. Furthermore, mutation of the RING1 finger domain of HHARI from a RING-HC to a RING-H2 type abolishes interaction with UbcH7. These studies demonstrate that very subtle changes to the domains that regulate recognition between highly conserved components of the ubiquitin pathway can dramatically affect their ability to interact.

Role of LIM domains in mediating signaling protein interactions

LIM domains are double zinc-finger motifs that mediate protein interactions between transcription factors, cytoskeletal and signaling proteins. This review outlines the protein interactions mediated by LIM domains with signaling proteins including tyrosine and serine/threonine kinases and phosphatases.

Prospective controlled study of carotid endarterectomy with hemashield patch: is it thrombogenic?

The use of patch angioplasty after carotid endarterectomy (CEA) has been shown to have superior results to CEA with primary closure. Polytetrafluoroethylene (PTFE) patches have been shown to have comparable results to autogenous vein patching; however, PTFE has the disadvantage of prolonged hemostasis time. Therefore, many surgeons are using collagen-impregnated Dacron patches (Hemashield[HP]). We believe this is the first prospective controlled study of the use of HP in carotid endarterectomy. This study included 144 consecutive patients who had 151 CEAs with HP. Postoperative duplex ultrasounds were done at 1 month and every 6 months thereafter. The mean follow-up was 12 months (range: 1-30 months). Indications for CEA included symptomatic (64%) and asymptomatic (36%) stenoses. The overall incidence of ipsilateral stroke was 5% (4% perioperative), with a combined TIA and stroke rate of 12%. Incidence of > or =50% recurrent stenosis was 21% (7% symptomatic TIA/stroke) and > or =80% recurrent stenosis was 9%. Kaplan-Meier analysis showed that at 1 year and 2.5 years freedom from > or =50% recurrent stenosis was 78% and 57%, respectively, freedom from > or =80% recurrent stenosis was 92% and 77%, respectively, and a stroke-free survival rate of 94% and 72%, respectively. Women had a 22% and men a 14% recurrent stenosis rate (p=0.04). There was no correlation between other specific risk factors and recurrent stenosis except for hypertension (33% vs 12%, p=0.003). The authors concluded that CEA with HP had a higher incidence of recurrent stenosis (21%), and a higher perioperative stroke rate (4%) after a mean follow-up of 12 months than previously reported using PTFE or saphenous vein patching (2% and 9% recurrent stenosis rates, respectively, and 1% and 0% perioperative stroke rates, respectively after a mean follow-up of 30 months). This raises the question as to whether this patch is thrombogenic in this location. Therefore, a randomized controlled trial comparing this patch with other patches (PTFE or vein) is warranted.

Modal analysis of corticothalamic dynamics, electroencephalographic spectra, and evoked potentials

The effects of cortical boundary conditions and resulting modal aspects of continuum corticothalamic electrodynamics are explored, including feedbacks. Dispersion relations, electroencephalographic spectra, and stimulus response functions are calculated from the underlying physiology, and the effects of discrete mode structure are determined. Conditions under which modal effects are important are obtained, along with estimates of the point at which modal series can be truncated, and the limit in which only a single globally uniform mode need be retained. It is found that for physiologically plausible parameters only the lowest cortical spatial eigenmode together with the set of next-lowest modes can produce distinct modal structure in spectra and response functions, and then only at frequencies where corticothalamic resonances reduce dissipation to the point where the spatial eigenmodes are weakly damped. The continuum limit is found to be a good approximation, except at very low frequencies and, under some circumstances, near the alpha resonance. It is argued that the major electroencephalographic rhythms result from corticothalamic feedback resonances, but that cortical modal effects can contribute to weak substructure in the alpha resonance. This mechanism is compared and contrasted with purely cortical and pacemaker-based alternatives and testable predictions are formulated to enable experimental discrimination between these possibilities.