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PubMed1990

Influence of reflow ventricular fibrillation and electrical defibrillation on infarct size in a canine preparation of myocardial infarction.

STUDY OBJECTIVE - The aim of the study was to investigate the influence of reflow ventricular fibrillation and electrical defibrillation on infarct size in a model of myocardial ischaemia. DESIGN - Myocardial ischaemia was induced in an open chest canine model by occluding the left coronary artery for 2 h. This was followed by 6 h reperfusion. The influence of reflow fibrillation and internal electric defibrillation on infarct size was investigated and compared to dogs which did not develop fibrillation. Infarct size and its major determinants, rate-pressure product (RPP), area at risk (AR), and collateral flow (MBF), were measured and their relationships studied in the two situations, using uni- and multilinear regression analysis. SUBJECTS - 21 adult mongrel dogs of either sex were used in the studies, which were done under pentobarbitone anaesthesia. Two were excluded because they developed ventricular fibrillation soon after coronary occlusion, and one did not survive reflow ventricular fibrillation. Of the remaining 18 dogs, six developed reflow ventricular fibrillation and were compared to the control group of 12 which did not develop fibrillation. MEASUREMENTS and RESULTS - A mean of 70.8(SEM 18.7) joules was required to revive the six dogs with reflow ventricular fibrillation. Difference in mean infarct size in the two groups did not reach significance [49.1(4.4) in fibrillation group v 38(6.2) in the controls]. The multiple linear regression model in the control group accounted for 91% of the variation in infarct size (IS): IS = -3.4 + 0.49 (AR) -21.8 (MBF) + 0.025 (RPP). The equation was not modified by including the reflow fibrillation dogs: IS = -3.1 + 0.52 (AR) - 19 (MBF) + 0.02 (RPP). Ischaemic determinants of infarct size in the reflow fibrillation dogs were computed in the control group equation to compare the infarct size predicted by the model to the measured infarct size in each individual dog in the reflow fibrillation group. There was no significant difference between the means: 12.9(2.9)% (predicted) v 14.9(2.5)% (measured). CONCLUSIONS - In this model of myocardial infarction, reflow ventricular fibrillation and low energy internal electric shocks do not damage the myocardium at risk significantly.

Animals↗

PubMed1981

Assessment of fox control in areas of wildlife rabies.

This paper describes a technique for the analysis of the interaction between rabies control measures and the annual turnover of a fox population. The basic conditions are deduced from data on the turnover of a steady fox population, which have been found to be representative for large parts of central Europe. These conditions, together with field data on the critical density for rabies transmission and the recovery of reduced fox populations, provide a model for the prediction and evaluation of various measures of rabies control. The method is simplified by the introduction of a semigraphical procedure using the relative density of a reduced fox population, defined as the ratio of the actual population density to that of a non-reduced population.Simulation of epidemics and control measures over consecutive population cycles shows the limited effect of population control in a rabies-free area and demonstrates the questionable impact of measures that reduce a regular fox population by less than 40%, even when such reduction is effected annually.The method is easy to apply in the field and helps in assessing a number of disease and service indicators, as well as ecological factors in the planning and evaluation of comprehensive rabies control programmes.

Animals↗

PubMed1993

[Projections of the impact of the smoking habit on the health of the Spanish population and on the potential benefits from its control].

BACKGROUND: Smoking continues to be an important public health problem in Spain. With the aim to know some of the health care consequences derived from the evolution of this habit in the Spanish population and to anticipate the health care benefits which would be a result of intervention on the same the estimations of mortality related with smoking and its control in the next few decades were predicted. METHODS: Mathematic models of simulation of the effects derived from changes in the prevalence of smoking based on the techniques of attributable risk, the multiplicity of the diseases involved and the time of reversal of the risk of death following health care intervention were used. RESULTS: In absence of intervention on smoking the number of total deaths by the causes under consideration will, in general, increase, from 1987 to 2020. The reduction of 40% in the prevalence of smoking in adult Spanish smokers over a period of 8 years (1992-2000) would potentially decrease the number of cardiovascular deaths by 6,035, deaths by COPD by 394 and the deaths by malignant tumors studied in the year 2020 by 5,237. By the year 2020 the effects of intervention would, in general, be completely manifest. A part of this reduction of mortality would translate in a gaining of 57,323 real years of life in the year 2020. These benefits are also appreciable, although lesser, in the previous years from the beginning of intervention. CONCLUSIONS: Smoking will continue to be an important public health problem in Spain in the future. The health care benefits which may be derived from correct application of effective control programs of the same would be appreciable.

Adult↗

PubMed2006

The Physical Performance Test as a predictor of frequent fallers: a prospective community-based cohort study.

OBJECTIVE: To construct a risk model in order to identify elderly individuals at risk of frequent falling. DESIGN: Prospective community-based cohort study over 12 months. SETTING: Baseline measures were performed at a local community centre. SUBJECTS: Two hundred and sixty-three community-dwelling elderly people (mean age 72 years). MEASUREMENTS: A variety of variables were evaluated, including medical, psychological, sensory, physical and postural control measurements. Fall incidence was monitored retrospectively and during one-year follow-up. RESULTS: Logistic regression analysis showed that polypharmacia was the most prominent medical fall predictor with an odds ratio (OR) of 1.29 (P= 0.005), poor visual acuity the best sensory predictor (OR = 0.84; P= 0.009) and general fear of falling the most crucial psychological predictor (OR = 3.25; P< 0.001). Increased postural sway in near-tandem stance with eyes open was selected as the best balance predictor for falls (OR = 5.60; P= 0.010), followed by delayed anteroposterior movement velocity during rhythmic weight shifts (OR = 0.42; P= 0.004). The best physical predictor was a low score on the Physical Performance Test (OR =4.16; P< 0.001), followed by decreased maximal handgrip strength (OR = 0.87; P< 0.001) and increased timed chair-stands (OR = 1.13; P= 0.003). Step-by-step regression analysis revealed a risk model for the prediction of future falls, as a combination of the Physical Performance Test and maximal handgrip strength. CONCLUSION: This study confirms the multicausality of falls, since medical, psychological, sensory, postural control as well as physical variables provides a predictive value. The composed fall risk model was mainly physically oriented.

Accidental Falls↗

PubMed2003

Short-term heart rate variability strongly predicts sudden cardiac death in chronic heart failure patients.

BACKGROUND: The predictive value of heart rate variability (HRV) in chronic heart failure (CHF) has never been tested in a comprehensive multivariate model using short-term laboratory recordings designed to avoid the confounding effects of respiration and behavioral factors. METHODS AND RESULTS: A multivariate survival model for the identification of sudden (presumably arrhythmic) death was developed with data from 202 consecutive patients referred between 1991 and 1995 with moderate to severe CHF (age 52+/-9 years, left ventricular ejection fraction 24+/-7%, New York Heart Association class 2.3+/-0.7; the derivation sample). Time- and frequency-domain HRV parameters obtained from an 8' recording of ECG at baseline and during controlled breathing (12 to 15 breaths/min) were challenged against clinical and functional parameters. This model was then validated in 242 consecutive patients referred between 1996 and 2001 (validation sample). In the derivation sample, sudden death was independently predicted by a model that included low-frequency power (LFP) of HRV during controlled breathing < or =13 ms2 and left ventricular end-diastolic diameter > or =77 mm (relative risk [RR] 3.7, 95% CI 1.5 to 9.3, and RR 2.6, 95% CI 1.0 to 6.3, respectively). The derivation model was also a significant predictor in the validation sample (P=0.04). In the validation sample, LFP < or =11 ms2 during controlled breathing and > or =83 ventricular premature contractions per hour on Holter monitoring were both independent predictors of sudden death (RR 3.0, 95% CI 1.2 to 7.6, and RR 3.7, 95% CI 1.5 to 9.0, respectively). CONCLUSIONS: Reduced short-term LFP during controlled breathing is a powerful predictor of sudden death in patients with CHF that is independent of many other variables. These results refine the identification of patients who may benefit from prophylactic implantation of a cardiac defibrillator.

Death, Sudden, Cardiac↗

PubMed1991

Behavioral and demographic predictors of suicide after traumatic spinal cord injury.

Among people with spinal cord injuries, death from suicide is two to six times more prevalent than in the general population. To determine if individual characteristics and behaviors present during rehabilitation can identify high-risk individuals, records of 5,200 spinal cord injured patients admitted to the Rocky Mountain Regional Spinal Injury System were reviewed. Of 489 deaths, 9% were due to suicide. They were compared with a control group of equal size, matched on age, gender, and injury level. The two groups differed significantly on postinjury despondency; expressions of shame, apathy, and hopelessness; and preinjury family disruption (p less than .01). They also differed on alcohol abuse, active involvement in the injury, preinjury depression or despondency, destructive behavior, and one aspect of etiology (p less than .05). Discriminant analysis yielded a predictive model that correctly classified 81% of the suicide group and 79% of the control group. Many of the demographic predictors identified in this study are similar to those reported in the scientific literature. However, when combined with specific behavioral characteristics manifested during rehabilitation, they comprise an array of variables that permits development of a clinical model for predicting suicide among persons with spinal cord injuries.

Adolescent↗

PubMed2006

Acceptance and relationship context: a model of substance use disorder treatment outcome.

AIMS: This study presented and tested a model of behavior change in long-term substance use disorder recovery, the acceptance and relationship context (ARC) model. The model specifies that acceptance-based behavior and constructive social relationships lead to recovery, and that treatment programs with supportive, involved relationships facilitate the development of these factors. DESIGN: This study used a prospective longitudinal naturalistic design and controlled for baseline levels of study variables. SETTING AND PARTICIPANTS: The model was tested on a sample of 2549 patients in 15 residential substance use disorder treatment programs. MEASUREMENTS: Acceptance-based responding (ABR), social relationship quality (SRQ), treatment program alliance (TPA) and substance use-related impairment were assessed using interviews and self-report questionnaires. FINDINGS: TPA predicted ABR and SRQ and, in turn, ABR predicted better 2-year and 5-year treatment outcomes. The baseline-controlled model accounted for 41% of the variance in outcome at 2-year follow-up and 28% of the variance in outcome at 5-year follow-up. CONCLUSIONS Patients from treatment programs with an affiliative relationship network are more likely to respond adaptively to internal states associated previously with substance use, develop constructive social relationships and achieve long-term treatment benefits.

Adaptation, Physiological↗

PubMed2000

Theoretical simulation of oxygen transport to brain by networks of microvessels: effects of oxygen supply and demand on tissue hypoxia.

OBJECTIVE: Simulations of oxygen delivery by a three-dimensional network of microvessels in rat cerebral cortex were used to examine how the distribution of partial pressure of oxygen (PO2) in tissue depends on blood flow and oxygen consumption rates. METHODS: Network geometry was deduced from previously published scanning electron micrographs of corrosion casts. A nonlinear least-squares method, using images obtained at three different angles, was used to estimate vessel locations. The network consisted of 50 segments in a region 140 microm x 150 microm x 160 microm. A Green's function method was used to predict the PO2 distribution. Effects of varying perfusion and consumption were examined, relative to a control state with consumption 10 cm3O2/100 g per min and perfusion 160 cm3/100 g per min. RESULTS: In the control state, minimum tissue PO2, was 7 mm Hg. A Krogh-type model with the same density of vessels, but with uniform spacing, predicted a minimum tissue PO2 of 23 mm Hg. For perfusion below 60% of control, tissue hypoxia (PO2 <1 mm Hg) was predicted. When perfusion was reduced by 75%, the resulting hypoxia could be eliminated by a 31% reduction in oxygen consumption rate. CONCLUSIONS: The simulations suggest that tissue hypoxia resulting from a severe decrease in brain perfusion, as can occur in stroke, may be avoided by a moderate decrease in oxygen consumption rate.

Animals↗

PubMed2006

Trends in the incidence of tuberculosis in possums and livestock, associated with differing control intensities applied to possum populations.

AIM: To determine the trap-catch index (an estimate of abundance) of brushtail possum (Trichosurus vulpecula) populations infected with bovine tuberculosis (Tb; Mycobacterium bovis) that must be achieved, and the length of time such an index must be maintained, for Tb to be eliminated from possum populations and adjacent livestock. METHODS: Between 1997-1998 and 2000-2001, trap-catch surveys of possum populations naturally infected with Tb and subjected to population-control measures were undertaken at four forest sites and two farmland sites. At the same time, possum carcasses were collected at these sites and their Tb status determined, and all contiguous cattle and deer herds were Tb tested and abattoir slaughter data for these herds were interrogated. RESULTS: Trap-catch surveys indicated that numbers of possums on the farmland sites surveyed were usually very low and well below the control targets set (i.e. a 5% trap catch or approximately 0.5-1 possum/ha) for the study. In contrast, trap-catch surveys undertaken in forest sites indicated possum numbers were more variable, and often recovered rapidly from control operations to exceed control targets within 1-3 years. The annual rate of recovery of possum populations in half of the forest population surveys undertaken exceeded published intrinsic rates of increase for possums. The overall prevalence of Tb in possum populations was < or =1.9% at 5/6 sites, and was 6.5% at the sixth site. Juvenile possums infected with Tb were trapped within but near the edge of control zones and appeared to represent an immigrant source of infection. Mature infected possums survived control operations apparently by having home ranges in uncontrolled patches within control areas. Infection in possums appeared to be eliminated from one study site by the intensive control undertaken, but elimination at other sites appeared less likely. Levels of Tb in livestock on or adjacent to the study sites fell by at least 50% during the study, and cattle in one area tested clear for the first time in 20 years. CONCLUSIONS: Initial control of possums in forest appeared to achieve national control targets set by the Animal Health Board (AHB), despite trap-catch data often providing misleading population estimates. Such targets were often exceeded within 1-3 years. By comparison, possum control on farmland appeared to maintain populations at very low levels, while control on forest margins maintained populations at intermediate levels. Control was least effective in deep forest where human access was most difficult. Intensive population control measures appeared to have led to a reduced incidence of Tb in livestock at 3/4 sites, and elimination of Tb in livestock at one site. This result supports modelling studies that predict the eradication of Tb from possums through ongoing intensive control and may explain the lower success achieved with earlier less-intensive possum control.

Animals↗

PubMed1999

A Bayesian hierarchical approach for combining case-control and prospective studies.

Motivated by the absolute risk predictions required in medical decision making and patient counseling, we propose an approach for the combined analysis of case-control and prospective studies of disease risk factors. The approach is hierarchical to account for parameter heterogeneity among studies and among sampling units of the same study. It is based on modeling the retrospective distribution of the covariates given the disease outcome, a strategy that greatly simplifies both the combination of prospective and retrospective studies and the computation of Bayesian predictions in the hierarchical case-control context. Retrospective modeling differentiates our approach from most current strategies for inference on risk factors, which are based on the assumption of a specific prospective model. To ensure modeling flexibility, we propose using a mixture model for the retrospective distributions of the covariates. This leads to a general nonlinear regression family for the implied prospective likelihood. After introducing and motivating our proposal, we present simple results that highlight its relationship with existing approaches, develop Markov chain Monte Carlo methods for inference and prediction, and present an illustration using ovarian cancer data.

Bayes Theorem↗

PubMed2006

Advances and challenges in predicting the impact of lymphatic filariasis elimination programmes by mathematical modelling.

Mathematical simulation models for transmission and control of lymphatic filariasis are useful tools for studying the prospects of lymphatic filariasis elimination. Two simulation models are currently being used. The first, EPIFIL, is a population-based, deterministic model that simulates average trends in infection intensity over time. The second, LYMFASIM, is an individual-based, stochastic model that simulates acquisition and loss of infection for each individual in the simulated population, taking account of individual characteristics. For settings like Pondicherry (India), where Wuchereria bancrofti infection is transmitted by Culex quinquefasciatus, the models give similar predictions of the coverage and number of treatment rounds required to bring microfilaraemia prevalence below a level of 0.5%. Nevertheless, published estimates of the duration of mass treatment required for elimination differed, due to the use of different indicators for elimination (EPIFIL: microfilaraemia prevalence < 0.5% after the last treatment; LYMFASIM: reduction of microfilaraemia prevalence to zero, within 40 years after the start of mass treatment). The two main challenges for future modelling work are: 1) quantification and validation of the models for other regions, for investigation of elimination prospects in situations with other vector-parasite combinations and endemicity levels than in Pondicherry; 2) application of the models to address a range of programmatic issues related to the monitoring and evaluation of ongoing control programmes. The models' usefulness could be enhanced by several extensions; inclusion of different diagnostic tests and natural history of disease in the models is of particular relevance.

Journal Article↗

PubMed1995

Movement-related potentials in Parkinson's disease. Presence and predictability of temporal and spatial cues.

Activity of the supplementary motor area may be inferred from movement-related potentials (MRPs) which are associated with the preparation and execution of voluntary, or internally determined movements. Supplementary motor area activity may be abnormal in Parkinson's disease since its major input from the basal ganglia is disrupted. Investigation of the abnormalities in supplementary motor area activity associated with movement deficits in Parkinson's disease may therefore reveal functions of the basal ganglia and the supplementary motor area. Movement-related potentials associated with sequential movements were investigated under various cueing conditions in Parkinson's disease subjects and age-matched controls. In controls, MRPs revealed involvement of the supplementary motor area in movements which can be internally determined (non-cued and externally cued, predictable movements, but not unpredictable movements). In Parkinson's disease, however, the supplementary motor area was only involved in movements which must be internally determined (non-cued movements, but not externally cued movements); therefore impaired internal control mechanisms, operating via the supplementary motor area, are bypassed when external cues are given. As a result, Parkinson's disease patients are more reliant on external cues and are unable to use predictive models to internally guide movement. Supplementary motor area involvement also relied on the predictability (in controls) or presence (in Parkinson's disease) of timing cues and not spatial cues, indicating a role of the supplementary motor area and basal ganglia in the temporal organizations of sequential movement rather than the programming of specific movements. For non-cued movements, abnormalities in MRPs for Parkinson's disease subjects consisted of delayed MRP onset and peak times, and prolonged cortical activity following movement. These observations led to a proposed model of the interaction between the basal ganglia and the supplementary motor area, involving the temporal organization of voluntary and internally determined sequential movements.

Aged↗

PubMedDate not supplied

Application of uncertainty reasoning based on cloud model in time series prediction.

Time series prediction has been successfully used in several application areas, such as meteorological forecasting, market prediction, network traffic forecasting, etc., and a number of techniques have been developed for modeling and predicting time series. In the traditional exponential smoothing method, a fixed weight is assigned to data history, and the trend changes of time series are ignored. In this paper, an uncertainty reasoning method, based on cloud model, is employed in time series prediction, which uses cloud logic controller to adjust the smoothing coefficient of the simple exponential smoothing method dynamically to fit the current trend of the time series. The validity of this solution was proved by experiments on various data sets.

Information Systems↗

PubMed1992

On the application of mathematical models of schistosome transmission dynamics. II. Control.

Mathematical models have considerable potential as aids to the design of schistosome control programmes. This is because of the complex nature of the schistosome transmission cycle and the variety of control measures available, which make the comparative effectiveness of different control options extremely difficult to predict. This review aims to demonstrate how control can be incorporated in models of schistosome transmission dynamics, and to make explicit the assumptions and limitations of the models and their relationships with field data. A basic model is described which considers changes in the mean number of schistosomes per person. The criteria for the eradication of endemic infection and the potential for reducing levels of infection are discussed. The treatment of various control measures within this framework is reviewed. These include: chemotherapy (mass, selective and targeted), molluscicide application (blanket and focal) and other snail control measures, larval stage control, improved water supplies and sanitation, and health education. The incorporation of economic variables is also discussed. The choice between different control options depends on the relationships between schistosome epidemiology and the costs and effects of control. The evaluation of cost-effectiveness is a dynamic problem, and the outcome will depend on local conditions and constraints. Very general recommendations for the design of schistosome control programmes are unlikely to prove useful.

Animals↗

PubMed1988

CO2 control of the respiratory system: plant dynamics and stability analysis.

A stability analysis of respiratory chemical control is developed using a mathematical model of CO2 mass transport dynamics. Starting with a 3-compartment model of CO2 stores that distinguishes alveolar, muscle, and other tissue, model reduction techniques are applied to obtain a first-order representation of the respiratory plant. This model contains an effective tissue volume for CO2, whose derived value is much smaller than previously predicted. To investigate oscillatory instabilities, a controller which incorporates only peripheral chemoreceptor responses was added to the first-order plant model. An explicit stability index (SI) is obtained analytically from a linearized version of this model. SI varies directly with the controller gain and circulation delay time and inversely with the effective tissue volume and inspired CO2 concentration. Numerical simulations using the first-order nonlinear model show that SI is a good predictor of system stability. According to the linearized model, the system is stable for SI less than 1; from the nonlinear model, the system is stable for SI less than 1.1. For typical normal adults, the SI value is well within the stable region.

Adult↗

PubMed1997

Prostate-specific antigen cancer volume: a significant prognostic factor in prostate cancer patients at intermediate risk of failing radiotherapy.

PURPOSE: Although the pretreatment serum prostate-specific antigen level (PSAL) is the single-most significant predictor of local and biochemical control in prostate cancer patients treated with radiotherapy, it is relatively insensitive for patients with a PSAL in the intermediate range (4-20 ng/ml). PSA density (PSAD) has been shown to be slightly more predictive of outcome than PSAL for this intermediate risk group; however, this improvement is small and of little use clinically. PSA cancer volume (PSACV), an estimate of cancer volume based on PSA, has recently been described and has been purported to be more significant than PSAL in predicting early biochemical failure after radiotherapy. We report a detailed comparison between this new prognostic factor, PSAL, and PSAD. METHODS AND MATERIALS: The records of 356 patients treated with definitive external beam radiotherapy for regionally localized (T1-4,Nx,M0) adenocarcinoma of the prostate were reviewed. Each patient had a PSAL, biopsy Gleason score, and pretreatment prostate volume by transrectal ultrasonography. The median PSAL was 9.3 ng/ml and 66% had Gleason scores in the 2-6 range. The median radiation dose was 66.0 Gy and the median follow-up for those living was 27 months. PSACV was calculated using a formula which takes into account PSAL, pretreatment prostate ultrasound volume, and Gleason score. The median PSACV was 1.43 cc. Biochemical failure was defined as increases in two consecutive follow-up PSA levels, one increase by a factor > 1.5, or an absolute increase of > 1 ng/ml. Local failure was defined as a cancer-positive prostate biopsy, obtained for evidence of tumor progression. RESULTS: The distributions of PSACV and PSAL were similar and, when normalized by log transformation, were highly correlated (p < 0.0001, linear regression). There was a statistically significant relationship between PSACV and several potential prognostic factors including PSAL, PSAD, stage, Gleason score, and pretreatment prostatic acid phosphatase (PAP). In univariate analyses, PSACV, PSAL, and PSAD proved to be the most significant predictors of both biochemical and local control. In multivariate analyses using Cox proportional hazards models with PSAL, PSAD, PSACV, and PAP as continuous variables, PSAL, PSACV, and Gleason score were significant in predicting biochemical control. Only PSAL was significantly correlated with local control. However, when these analyses were restricted to patients with intermediate PSALs (4-20 ng/ml), only PSACV was significant for predicting both biochemical and local control. CONCLUSION: PSACV was highly correlated with actuarial local and biochemical control and was superior to both PSAL and PSAD in predicting these outcomes in patients with PSALs between 4 and 20 ng/ml.

Adenocarcinoma↗

PubMed2004

Parallel processing in an identified neural circuit: the Aplysia californica gill-withdrawal response model system.

The response of the gill of Aplysia calfornica Cooper to weak to moderate tactile stimulation of the siphon, the gill-withdrawal response or GWR, has been an important model system for work aimed at understanding the relationship between neural plasticity and simple forms of non-associative and associative learning. Interest in the GWR has been based largely on the hypothesis that the response could be explained adequately by parallel monosynaptic reflex arcs between six parietovisceral ganglion (PVG) gill motor neurons (GMNs) and a cluster of sensory neurons termed the LE cluster. This hypothesis, the Kupfermann-Kandel model, made clear, falsifiable predictions that have stimulated experimental work for many years. Here, we review tests of three predictions of the Kupfermann-Kandel model: (1) that the GWR is a simple, reflexive behaviour graded with stimulus intensity; (2) that central nervous system (CNS) pathways are necessary and sufficient for the GWR; and (3) that activity in six identified GMNs is sufficient to account for the GWR. The available data suggest that (1) a variety of action patterns occur in the context of the GWR; (2) the PVG is not necessary and the diffuse peripheral nervous system (PNS) is sufficient to mediate these action patterns; and (3) the role of any individual GMN in the behaviour varies. Both the control of gill-withdrawal responses, and plasticity in these responses, are broadly distributed across both PNS and CNS pathways. The Kupfermann-Kandel model is inconsistent with the available data and therefore stands rejected. There is, no known causal connection or correlation between the observed plasticity at the identified synapses in this system and behavioural changes during non-associative and associative learning paradigms. Critical examination of these well-studied central pathways suggests that they represent a 'wetware' neural network, architecturally similar to the neural network models of the widely used 'Perceptron' and/or 'Back-propagation' type. Such models may offer a more biologically realistic representation of nervous system organisation than has been thought. In this model, the six parallel GMNs of the CNS correspond to a hidden layer within one module of the gill-control system. That is, the gill-control system appears to be organised as a distributed system with several parallel modules, some of which are neural networks in their own right. A new model is presented here which predicts that the six GMNs serve as components of a 'push-pull' gain control system, along with known but largely unidentified inhibitory motor neurons from the PVG. This 'push-pull' gain control system sets the responsiveness of the peripheral gill motor system. Neither causal nor correlational links between specific forms of neural plasticity and behavioural plasticity have been demonstrated in the GWR model system. However, the GWR model system does provide an opportunity to observe and describe directly the physiological and biochemical mechanisms of distributed representation and parallel processing in a largely identifiable 'wetware' neural network.

Animals↗

PubMed2004

Supplementary motor area provides an efferent signal for sensory suppression.

Voluntary actions produce suppression of neural activity in sensory areas, and reduced levels of conscious sensation. Recent computational models of motor control have linked sensory suppression to motor prediction: an efferent signal from motor areas may cancel the sensory reafferences predicted as a consequence of movement. Direct evidence for the efferent mechanism in sensory suppression has been lacking. We investigated the perceived size of finger-muscle twitches (MEPs) evoked by TMS in eight normal subjects. Subjects freely chose on each trial whether to make or withhold a voluntary flexion of the right index finger, in synchrony with an instructional stimulus. A test MEP occurred at the instructed time of action. The subject then relaxed and a second reference MEP occurred a few seconds later. Subjects judged which of the two MEPs was larger. Subjects perceived the first test MEP to be smaller in trials where they made voluntary actions than on trials where they did not, demonstrating sensory suppression. On randomly selected trials, a conditioning prepulse was delivered over the supplementary motor area (SMA) 10 ms before the pulse producing the test MEP. The SMA prepulse reduced and almost abolished the sensory suppression effect in voluntary action trials. We suggest the SMA may provide an efferent signal which is used by other brain areas to modulate somatosensory activity during self-generated movement.

Adult↗