A population approach to cortical dynamics with an application to orientation tuning

A typical functional region in cortex contains thousands of neurons, therefore direct neuronal simulation of the dynamics of such a region necessarily involves massive computation. A recent efficient alternative formulation is in terms of kinetic equations that describe the collective activity of the whole population of similar neurons. A previous paper has shown that these equations produce results that agree well with detailed direct simulations. Here we illustrate the power of this new technique by applying it to the investigation of the effect of recurrent connections upon the dynamics of orientation tuning in the visual cortex. Our equations express the kinetic counterpart of the hypercolumn model from which Somers et al (Somers D, Nelson S and Sur M 1995 J. Neurosci. 15 5448-65) computed steady-state cortical responses to static stimuli by direct simulation. We confirm their static results. Our method presents the opportunity to simulate the data-intensive dynamical experiments of Ringach et al (Ringach D, Hawken M and Shapley R 1997 Nature 387 281-4), in which 60 randomly oriented stimuli were presented each second for 15 min, to gather adequate statistics of responses to multiple presentations. Without readjustment of the previously defined parameters. our simulations yield substantial agreement with the experimental results. Our calculations suggest that differences in the experimental dynamical responses of cells in different cortical layers originate from differences in their recurrent connections with other cells. Thus our method of efficient simulation furnishes a variety of information that is not available from experiment alone.

Common pulmonary vein atresia: a diagnostic and therapeutic challenge

Following Doppler echocardiographic evaluation, a 16 hour-old infant underwent successful surgical repair of common pulmonary vein atresia. Investigations for prolonged postoperative ventilatory assistance, including cardiac catheterization and computerized tomography, led to a clinical diagnosis of associated pulmonary lymphangiectasia. Although this has caused continuing tachypnoea, at 16 months of age, he remains otherwise well but with an uncertain prognosis.

An autonomy supportive model of geriatric team function

Interdisciplinary teams play a critical role in the delivery of geriatric health care. Health care professionals are commonly left to develop teamwork skills by chance. Medical team function differs from traditional group theory in that all members are caregivers. A non-competitive supportive atmosphere is appropriate for patient care. We propose a participatory (autonomy supportive) model fostering self-realization and positive reinforcement as an organizing philosophy. The primary group task is to maximize patient functional independence and personal goals. Leadership is task-dependent.

Visualizing muscle cell migration in situ

BACKGROUND

Cell migration has been studied extensively by manipulating and observing cells bathed in putative chemotactic or chemokinetic agents on planar substrates. This environment differs from that in vivo and, consequently, the cells can behave abnormally. Embryo slices provide an optically accessible system for studying cellular navigation pathways during development. We extended this system to observe the migration of muscle precursors from the somite into the forelimb, their cellular morphology, and the localization of green fluorescent protein (GFP)-tagged adhesion-related molecules under normal and perturbed conditions.

RESULTS

Muscle precursors initiated migration synchronously and migrated in broad, rather than highly defined, regions. Bursts of directed migration were followed by periods of meandering or extension and retraction of cell protrusions. Although paxillin did not localize to discernible intracellular structures, we found that alpha-actinin localized to linear, punctate structures, and the alpha5 integrin to some focal complexes and/or vesicle-like concentrations. Alterations in the expression of adhesion molecules inhibited migration. The muscle precursors migrating in situ formed unusually large, long-lived protrusions that were polarized in the direction of migration. Unlike wild-type Rac, a constitutively active Rac localized continuously around the cell surface and promoted random protrusive activity and migration.

CONCLUSIONS

The observation of cellular migration and the dynamics of molecular organization at high temporal and spatial resolution in situ is feasible. Migration from the somite to the wing bud is discontinuous and not highly stereotyped. In situ, local activation of Rac appears to produce large protrusions, which in turn, leads to directed migration. Adhesion can also regulate migration.

Post-mortem analysis of apoptotic changes associated with human skin bruises

The estimation of the age of skin bruises is of importance in forensic medicine, especially in child abuse cases. Time-dependent changes in bruise colour and/or associated histological features have been used with a limited degree of success. An increased rate of apoptosis in the injured tissue has been considered as a novel time-dependent marker of cell death, by injury inflicted in a rat model. The object of the present study was to apply the TUNEL method of DNA end labelling to identify and enumerate apoptotic cells in bruised and normal skin in order to study the relationship of apoptotic cell density with the age of the bruise. A commercially available DNA end labelling kit, TUNEL method, was standardised, validated and used for this purpose. Twenty unselected post-mortem cases with bruises due to a variety of causes were studied. The apoptotic cells stained with TUNEL reaction were counted in 10 high power fields in the epidermis, as well as in the dermis of formaldehyde-fixed paraffin-embedded skin specimens. The mean positive cell densities (+/- 1 S.E.) were compared with respect to the age of the bruise. In the epidermis, the mean apoptotic cell count was statistically significantly greater in the bruised skin compared to normal skin in 2- to 6-day-old bruises; whilst in the dermis the same was true in 3- to 8-day-old bruises. The overall findings suggest that there is a quiescent period prior to the increase in the apoptotic cell activity that is seen following skin bruising. This is so provided the post-mortem skin samples were collected within a lapse of 6 days or less between the time of death and formalin fixation and paraffin embedding to avoid the bias made by the difference of length of post-mortem interval.

Vacuum deposition of chiral sculptured thin films with high optical activity

We present the technique of bideposition to realize thin-film helicoidal bianisotropic mediums (TFHBM's) that exhibit high optical activity. We show, by experiment as well as by simulation, that the optical rotation produced by these chiral sculptured thin films is roughly proportional to the square of the local linear birefringence. Experimental measurements on bideposited TFHBM's of titanium oxide yield a typical value of 5 degrees /mum for the effective specific rotation in the short-wavelength regime; the corresponding value determined for the standard unideposited TFHBM's is 1 degrees /mum. Both types of TFHBM's are highly optically active in comparison with quartz, fluorite films, and cholesteric liquid crystals. Bideposited TFHBM's will lend themselves to many different types of optical devices.

Radiofrequency catheter ablation of inappropriate sinus tachycardia guided by activation mapping

OBJECTIVE

The purpose of this study was to evaluate the value of activation mapping for radiofrequency modification of the sinus node and the long-term success rate of the procedure in a series of patients with inappropriate sinus tachycardia.

BACKGROUND

The results of radiofrequency ablation of inappropriate sinus tachycardia have been reported in only a small number of patients.

METHODS

The subjects of this study were 29 consecutive drug-refractory patients who underwent catheter ablation of inappropriate sinus tachycardia. Target sites were selected by activation mapping during sinus tachycardia.

RESULTS

The ablation procedure was successful acutely in reducing the baseline sinus rate to <90/min and the sinus rate during isoproterenol infusion by >20% in 22 of 29 patients (76%). In 13 of 22 patients (59%) with a successful acute outcome, successive applications of radiofrequency energy at the site of earliest endocardial activation resulted in a cranial-caudal migration of earliest endocardial activation from the high lateral right atrium, along with a step-wise reduction in heart rate. In the other nine patients (41%) with a successful acute outcome, the reduction in sinus rate occurred abruptly, unaccompanied by migration of the site of earliest activation. Symptoms due to inappropriate sinus tachycardia recurred at a mean of 4.4+/-; 3 months after the ablation procedure in 6 of 22 patients (27%). After additional procedures in three patients, symptoms of inappropriate sinus tachycardia ultimately were successfully eliminated over the long-term in 19 of 29 patients (66%).

CONCLUSIONS

In conclusion, radiofrequency ablation is at best only modestly effective for managing patients with inappropriate sinus tachycardia. The two different responses of heart rate to radiofrequency ablation may reflect differences in the number and/or multicentricity of subsidiary sites of impulse generation within the sinus node and/or atrium in patients with inappropriate sinus tachycardia.

Voluntary and reflex control of human back muscles during induced pain

1. Back pain is known to change motor patterns of the trunk. The purpose of this study was to examine the motor output of the erector spinae (ES) muscles during pain in the lumbar region. First, their voluntary activation was assessed during flexion and re-extension of the trunk. Second, effects of cutaneous and muscle pain on the ES stretch reflex were measured, since increased stretch reflex gain has been suggested to underlie increased muscle tone in painful muscles. 2. The trunk movement and electromyographical (EMG) signals from the right and left ES during pain were compared with values before pain. Controlled muscle pain was induced by infusion of 5 % saline into the right lumbar ES. Cutaneous pain was elicited by mechanical or electrical stimulation of the dorsal lumbar skin. The stretch reflex was evoked by rapidly indenting the right lumbar ES with a servo-motor prodder. 3. The results from the voluntary task show that muscle pain decreased the modulation depth of ES EMG activity. This pattern was associated with a decreased range and velocity of motion of the painful body segment, which would normally serve to avoid further injury. Interestingly, when subjects overcame this guarding tendency and made exactly the same movements during pain as before pain, the EMG modulation depth was still reduced. The results seem to reconcile the controversy of previous studies, in which both hyper- and hypoactivity of back muscles in pain have been reported. 4. In the tapped muscle, the EMG response consisted of two peaks (latency 19.3 +/- 2.1 and 44.6 +/- 2.5 ms, respectively) followed by a trough. On the contralateral side the first response was a trough (26.2 +/- 3.2 ms) while the second (46.4 +/- 4.3 ms) was a peak, similar to the second peak on the tapped side. Cutaneous pain had no effect on the short-latency response but significantly increased the second response on the tapped side. Surprisingly, deep muscle pain had no effect on the stretch reflex. A short-latency reciprocal inhibition exists between the right and left human ES. 5. It is concluded that deep back pain does not influence the stretch reflexes in the back muscles but modulates the voluntary activation of these muscles.

Automated identification of tubercle bacilli in sputum. A preliminary investigation

OBJECTIVE

To use an automated method to detect tubercle bacilli in sputum specimens.

STUDY DESIGN

Using fluorescence microscopy, tubercle bacilli were identified on auramine-stained sputum specimens. Images were then captured with a digital camera and enhanced through imaging processing techniques. The bacilli were recognized using neural network classifiers.

RESULTS

This preliminary investigation demonstrated a sensitivity of 94.1% for the identification of individual bacilli. As there are usually fairly numerous tubercle bacilli in the sputum of patients with active pulmonary tuberculosis, the overall diagnostic accuracy of sputum smear-positive patients can be expected to be very high.

CONCLUSION

Potential benefits of automated screening for TB bacilli are: rapid, accurate, inexpensive diagnosis; the ability to screen larger numbers of people; increased resources to monitor patients; and reduction in health risks to staff.

Assuring professional pastoral care for every nursing home resident

Ministry to persons in nursing homes is built on two mandates: "... He has sent me to bring good news to the oppressed, to bind up the brokenhearted, to proclaim liberty to the captives, and release to the prisoners; ... to comfort all who mourn ..." (Isaiah 61:1-3). The federal government provides the second: "Quality of Life. A facility must care for its residents in a manner and in an environment that promotes maintenance or enhancement of each resident's quality of life" (OBRA '87, Guidance to Surveyors in Long Term Care Facilities, Code of Federal Regulations, Health Care Financing Administration, 1995, section 483.15, F240). This article discusses both the religious and the U.S. political history of caring for the old and frail. It concludes by describing political efforts in one state to increase the quality of that care and pastoral efforts to support the nursing assistants in long-term care facilities.

Contact-evoked changes in EMG activity during human grasp

Contact-evoked changes in EMG activity during human grasp. 2215 Cutaneous receptors in the digits discharge bursts of activity on contact with an object during human grasp. In this study, we investigated the contribution of this sensory activity to the responses of muscles involved in the task. Twelve subjects performed a standardized precision grasp task without the aid of vision. Electromyographic (EMG) responses in trials when the object was present were compared with those in which the object, and hence the associated afferent responses, were unexpectedly absent. Significant differences in EMG amplitude occurred in the interval 50-100 ms after contact in all subjects and in 33/46 of the muscles sampled. The differences emerged as early as 34 ms after contact and comprised as much as a fourfold change in EMG from 50 to 100 ms after contact with the object. Typically, EMG responses were larger when the object was present (OP), though there were cases, particularly in the thenar muscles, in which the responses increased when the object was absent (OA). Local anesthesia of the thumb and index finger attenuated contact-evoked EMG activity in at least one muscle in all four subjects tested. In one subject, contact-evoked responses were abolished completely during the anesthesia in all four muscles sampled. The results indicate that the sensory activity signaling contact plays a key role in regulating EMG activity during human grasp. Much of this feedback action is attributable to cutaneous receptors in the digits and probably involves both spinal and supraspinal pathways.

Comparison of the core size distribution in iron dextran complexes using Mössbauer spectroscopy and X-ray diffraction

Mössbauer spectra of a series of iron dextran complexes in the intermediate temperature range where both sextet and doublet coexist may be used to obtain a qualitative description of the distribution of core sizes in these samples. Eight samples from five suppliers have been examined at 100 and 77 K. These differ markedly in the relative doublet contribution to the total spectral area and also in the hyperfine fields characterizing the sextets. The results indicate three distinct types of distribution. One sample from each type has also been examined at 4 K, where the doublet component has vanished and the hyperfine field distribution has become narrow and symmetric. These data are compared with estimates of average core diameters from X-ray line broadening.

Discrete systolic potentials during ventricular tachycardia in patients with prior myocardial infarction

INTRODUCTION

Isolated diastolic potentials have been found to be helpful in identifying critical sites for ablation of ventricular tachycardia (VT) in patients with coronary artery disease. However, discrete potentials that occur during systole have not been previously described. The purpose of this study was to determine the significance of discrete systolic potentials during VT in patients with coronary artery disease.

METHODS AND RESULTS

Twenty-seven patients with a mean age of 66 +/- 12 years ( +/- standard deviation) who had coronary artery disease underwent radiofrequency catheter ablation of 42 VTs that had a mean cycle length of 486 +/- 78 msec. The only criterion used to select target sites for ablation was concealed entrainment, which was present at 92 sites. Thirty-five of the 42 VTs (83%) were successfully ablated. A discrete systolic potential was recorded during 7 of the 42 VTs (17%). In all cases, the interval between the discrete systolic potential and the next QRS complex was equal to the stimulus-QRS interval during concealed entrainment. At all seven sites where a discrete systolic potential was recorded, delivery of radiofrequency energy resulted in successful ablation of the VT.

CONCLUSION

Discrete systolic potentials may be present in patients with coronary artery disease in approximately 17% of VTs in which there is concealed entrainment. If the interval between the discrete systolic potential and the next QRS complex matches the stimulus-QRS interval during concealed entrainment, delivery of radiofrequency energy is likely to result in successful ablation of the VT.

Dietary and genetic interactions in the regulation of plasma lipoprotein(a)

Lipoprotein(a) is a plasma particle which is considered to be a risk factor for the development of coronary heart disease. Plasma levels of lipoprotein(a) are affected by different types of dietary fat and steroid hormones. Two regions upstream of the apolipoprotein(a) promoter have been isolated which could be the site of regulation of apolipoprotein(a) gene transcription.

Clinical value of the postpacing interval for mapping of ventricular tachycardia in patients with prior myocardial infarction

INTRODUCTION

The postpacing interval (PPI) has been used to discriminate bystander sites from critical sites within a ventricular tachycardia (VT) reentry circuit, with a PPI that is similar to the VT cycle length (CL) being indicative of a site within the reentry circuit. The purpose of this study was to assess the clinical value of the PPI for identifying effective target sites for ablation of VT at sites of concealed entrainment in patients with prior myocardial infarction.

METHODS AND RESULTS

In 24 patients with coronary artery disease and a past history of myocardial infarction, 36 VTs with a mean CL of 483+/-80 msec (+/- SD) were mapped and targeted for radiofrequency (RF) ablation. The only criterion used to select target sites for ablation was concealed entrainment. In a post hoc analysis, the PPI was measured at 47 ineffective and 26 effective ablation sites. The mean PPI-VTCL difference at the 26 effective sites (114+/-137 msec) did not differ significantly from the mean at the 47 ineffective sites (177+/-161 msec; P = 0.1). The sensitivity of a PPI-VTCL difference < or = 30 msec for identifying an effective ablation site was 46%, the specificity 64%, the positive predictive value 41%, and the negative predictive value 68%.

CONCLUSION

The PPI-VTCL difference is not useful for discriminating between sites of concealed entrainment that are within or outside of a VT reentry circuit in patients with prior infarction. Therefore, in patients with prior infarction, the PPI is not clinically useful for identifying sites of concealed entrainment at which RF ablation should or should not be attempted.

Is the incidence of SIDS increasing in Asia?

The incidence of SIDS in western countries has decreased since the late 1980s after active SIDS prevention campaigns. By contrast, both Taiwan and Japan have reported an increase in incidences. In this report data from England, Wales, Scotland, Northern Ireland, Japan and Hong Kong are analysed. Regression coefficient and linearity of regression tests were used to determine if there was any significant increase or decrease in post-neonatal mortality (PNNM), SIDS mortality and mortality among infants 1-5 months old. A statistically significant decrease in SIDS was recognized in England, Wales, Scotland and Northern Ireland, whereas statistically significant increases were noted for Japan and Hong Kong. However in Japan and Hong Kong both the PNNM and mortality of infants between 1-5 months in age fell significantly, suggesting that the increased SIDS rates could be due to a change in diagnostic labelling. Further study will be required to determine whether this increase in the incidence of SIDS is genuine or only an artifact.

A controlled trial of venlafaxine in trichotillomania: interim phase I results

This article reports the preliminary findings of a two-phase trial examining the efficacy of venlafaxine in trichotillomania. Phase 1 is a 12-week, open-label, prospective trial of venlafaxine in trichotillomania. Venlafaxine was effective in significantly reducing the symptoms of trichotillomania; 8 of 12 patients were considered responders. The implications of the efficacy of venlafaxine in trichotillomania are discussed, including its important advantages over other available antidepressant and anxiolytic medications.

Screening systems for detecting inhibitors of cell wall transglycosylation in Enterococcus. Cell wall transglycosylation inhibitors in Enterococcus

We devised two screening systems to detect cell wall transglycosylation inhibitors. One screen utilizes a mutant of Enterococcus faecalis strain A256 that is dependent on vancomycin or moenomycin for growth. In the absence of transglycosylation inhibitors the strain fails to grow, while in the presence of inhibitors, cells are rescued. A second screening organism E. faecalis strain MDD212 utilizes a translational fusion of the lacZ gene to the vanH promoter in a derivative of E. faecalis that contains a vancomycin resistance determinant. Induction of beta-galactosidase occurs when cells are exposed to inhibitors of transglycosylation. Our natural products drug source of fungal fermentations was tested with these screens. Several cultures that produced the same family of compounds, called the thielavins, were detected. Thielavin B inhibited the formation of peptidoglycan in an in vitro assay, suggesting that these screening systems can detect compounds that interfere with cell wall transglycosylation.

Accessing Prior Knowledge to Remember Text: A Comparison of Advance Organizers and Maps

Two theories, schema and dual coding, and the conjoint retention model were contrasted to explain the role of geographic familiarity and prior knowledge in map-passage retention. One hundred, eighty-six college students listened to a passage taking place in either a familiar or unfamiliar geographic domain and viewed either a map or no map of either of the two geographic areas. One-third of each group received either a general or specific advance organizer of the passage topic, or no organizer at all. Results revealed that maps function to bridge what learners already know about an area and what they need to remember from a passage. However, prior knowledge of geography is activated by the geographic propositions contained in a passage, with or without a map. Thus, maps serve a mnemonic function of imagery, but learners' prior knowledge of the geography of the map's space mediates the value of the map. Learners are able to generate an image of the map themselves if there are locational markers in the passage, and the geography of those markers are familiar. Copyright 1998 Academic Press.

Clomipramine challenge responses covary with Tridimensional Personality Questionnaire scores in healthy subjects

Cloninger's Unified Biosocial Theory of Personality postulates a relationship between the relative functional activity of central serotonergic, dopaminergic, and noradrenergic neurotransmitter systems, and the strength of three elemental dimensions of personality. These dimensions are Harm Avoidance, Novelty Seeking, and Reward Dependence, respectively. Accordingly, we predicted that neuroendocrine responses to serotonergic challenge would correlate with Harm Avoidance scores, but not with Novelty Seeking or Reward Dependence scores. We examined the relationship between the prolactin and cortisol responses to a 12.5-mg intravenous clomipramine challenge and these personality dimensions as measured by Cloninger's Tridimensional Personality Questionnaire in 32 healthy subjects. The cortisol response correlated only with Harm Avoidance scores, as predicted; however, prolactin response did not correlate with Harm Avoidance scores. Instead, it demonstrated an inverse relationship with Novelty Seeking scores. There was a positive relationship of baseline prolactin with Harm Avoidance in a post hoc analysis. Cortisol response to serotonergic challenge may be a better indicator for responsivity of serotonergic systems as they relate to the personality dimension of Harm Avoidance than is prolactin. Prolactin responses may be overly affected by dopaminergic influences; however, baseline prolactin may still be a valid indicator of serotonergic tone.