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PubMed1995

Seasonal variation in coronary heart disease in Scotland.

STUDY OBJECTIVE: Seasonality of coronary heart disease (CHD) was examined to determine whether fatal and non-fatal disease have the same annual rhythm. DESIGN: Time series analysis was carried out on retrospective data over a 10 year period and analysed by age groups ( < 45 to > 75 years) and gender. SETTING: Data by month were obtained for the years 1962-71. The Registrar General provided information on deaths and the Research and Intelligence Unit of the Scottish Home and Health Department on hospital admissions. SUBJECTS: In Scotland, between 1962 and 1971, 123 000 patients were admitted to hospital for CHD, of whom 29 000 died. There were a further 97 000 CHD deaths outside hospital. These two groups were also examined as one (coronary incidence) - that is, all coronary deaths and coronary admissions discharged alive. STATISTICAL ANALYSIS AND MAIN RESULTS: Where there was a single annual peak, the sine curve was analysed by cosinor analysis. When there were two peaks the analysis was by normal approximation to Poisson distribution. In younger men (under 45 years) admitted to hospital there was a dominant spring peak and an autumn trough. A bimodal pattern of spring and winter peaks was evident for hospital admissions in older male age groups: with increasing age the spring peak diminished and the winter peak increased. In contrast, female hospital admissions showed a dominant winter/summer pattern of seasonal variation. In male and female CHD deaths seasonal variation showed a dominant pattern of winter peaks and summer troughs, with the winter peak spreading into spring in the two youngest male age groups. CHD incidence in women showed a winter/summer rhythm, but in men the spring peak was dominant up to the age of 55. CONCLUSION: The male, age related spring peak in CHD hospital admissions suggests there is an androgenic risk factor for myocardial infarction operating through an unknown effector mechanism. As age advances and reproduction becomes less important, the well defined winter/summer pattern of seasonal variation of CHD is superimposed, and shows a close relationship with the environment, especially temperature, or the autumn and early winter fall in temperature.

Adult↗
PubMed1996

Daily mortality and air pollutants: findings from Köln, Germany.

STUDY OBJECTIVE AND DESIGN: For the APHEA study, the short term effects of air pollutants on human health were investigated in a comparable way in various European cities. Daily mortality was used as one of the health effects indicators. This report aims to demonstrate the steps in epidemiological model building in this type of time series analysis aimed at detecting short term effects under a poisson distribution assumption and shows the tools for decision making. In addition, it assesses the impact of these steps on the pollution effect estimates. SETTING: Köln, Germany, is a city of one million inhabitants. It is densely populated with a warm, humid, unfavourable climate and a high traffic density. In previous studies, smog episodes were found to increase mortality and higher sulphur dioxide (SO2) levels were connected with increases in the number of episodes of croup. PARTICIPANTS, MATERIALS AND METHODS: Daily total mortality was obtained for 1975-85. SO2, total suspended particulates, and nitrogen dioxide (NO2) data were available from two to five stations for the city area, and size fractionated PM7 data from a neighbouring city. The main tools were time series plots of the raw data, predicted and residual data, the partial autocorrelation function and periodogram of the residuals, cross correlations of prefiltered series, plots of categorised influences, chi 2 statistics of influences and sensitivity analyses taking overdispersion and autocorrelation into account. RESULTS AND CONCLUSIONS: With regard to model building, it is concluded that seasonal and epidemic correction are the most important steps. The actual model chosen depends very much on the properties of the data set. For the pollution effect estimates, trend, season, and epidemic corrections are important to avoid overestimation of the effect, while an appropriate short term meterology influence correction model may actually prevent underestimation. When the model leaves very little over-dispersion and autocorrelation in the residuals, which indicates a good fit, correction for them has consequently little impact. Given the model, most of the range of SO2 values (5th centile to 95th centile) led to a 3-4% increase in mortality (significant), particulates led to a 2% increase (borderline significant, less data than for SO2), and NO2 had no relationship with mortality (measurements possibly not representative of actual exposure). Effects were usually delayed by a day.

Air Pollutants↗
PubMed2006

Retrospective mortality cohort study of Italian workers compensated for silicosis.

OBJECTIVES: To estimate cause specific mortality in a large cohort of Italian workers compensated for silicosis. METHODS: The cohort included 14 929 subjects (14,098 men and 831 women) compensated for silicosis between 1946 and 1979, alive on 1 January 1980, and resident in Tuscany (a region of central Italy with 3,547,000 inhabitants). Mortality follow up ranged from 1980 to 1999. Vital status and the causes of death were determined by linkage with the regional mortality registry and with the national mortality database. The cohort mortality rates were compared to the rates of the local reference population. SMRs and their 95% confidence intervals were computed assuming a Poisson distribution of the observed deaths. Specific SMR analyses were performed according to the level of disability, the year of compensation assignment, and the job type. RESULTS: A significant excess mortality was observed in male silicotics for cancer of the lung, trachea, and bronchus and cancer of the liver, respiratory diseases (silicosis, asbestosis, antracosilicosis, and other pneumoconiosis), and for tubercolosis. Statistically significant mortality excess was observed in female silicotics for respiratory diseases (specifically silicosis and other pneumoconiosis) and tuberculosis. Analyses for period of compensation assignment showed a twofold increased SMR for biliary tract cancer among female workers and for liver cancer among male workers compensated before 1970. CONCLUSIONS: The excess mortality from respiratory tract cancers and respiratory tract diseases detected in Italian compensated silicotics are in agreement with previous epidemiological studies. Although the twofold increased risk for liver cancer among males is suggestive of a possible association with silica dust exposure, the finding needs to be confirmed.

Adult↗
PubMed2007

Cancer mortality in a synthetic spinning plant in Besançon, France.

OBJECTIVES: To assess the mortality of a cohort of workers in a synthetic textile spinning plant and to evaluate the relationship between mortality from lung, liver and bladder cancer and the processes or the products used. METHODS: The study population consisted of male workers present for at least 6 months in the plant from 1968 to 1984. The cohort was followed until 1999. Vital status and the causes of death were determined by consulting national registries. The population of the Franche-Comté region was used for comparison. In total, 17 groups of exposure were assessed by the industrial hygienist, based on the consensus of an expert group that determined the exposure levels of each job to selected occupational hazards. Each worker was assigned to one or several groups, according to his occupational history. Confounding factors could not be assessed. Standardised mortality ratios (SMR) and 95% bilateral confidence intervals were calculated based on an assumed Poisson distribution of the number of cases to compare the plant mortality and the population mortality. Internal analyses were performed with Cox models in order to assess the risks of death related to the various exposures. RESULTS: In the whole cohort, mortality from all malignant neoplasms was lower than expected, but this was not significant. All the estimated SMRs were lower than or close to 1. The "hot -line fitters" (RR = 2.13; n = 9; 1.06 to 4.29) and the "fibre-drawing workers" (RR = 1.83; n = 20;1.09 to 3.07) experienced a statistically significant excess in mortality from lung cancer. A slightly elevated but not significant risk of death related to lung cancer (RR = 1.5; n = 41; 0.8 to 2.7) was observed in the groups with the highest exposure to mineral fibres. A statistically significant increase in cancer deaths was observed for workers with high exposure to dust (higher intensity: RR = 1.42; n = 79; 1.06 to 1.89). CONCLUSION: Some findings, mainly of lung cancer, justify further exploration in other plants in this industry.

Epidemiologic Methods↗
PubMed2006

Risk of leukaemia among children living near the Solway coast of Dumfries and Galloway Health Board area, Scotland, 1975-2002.

OBJECTIVE: To investigate allegations of an excess risk of leukaemia among children living near the Solway Firth coast of Dumfries and Galloway Health Board area in Scotland, UK. METHODS: Incident cases of childhood leukaemia (International Classification of Diseases, 10th revision, C91-C95, patients aged 0-14 years) for two almost equal calendar periods of diagnosis (1975-89 and 1990-2002) were selected from the Scottish Cancer Registry database and allocated to predetermined study areas, on the basis of proximity of residence to the Solway coast. Expected numbers of childhood leukaemia cases for the study areas were calculated by applying Scotland's age-specific, sex-specific and calendar period-specific rates to estimates of the person-years at risk in each study area. The ratios of observed to expected cases or standardised incidence ratios (SIRs) were calculated overall and for each sex and calendar period category. Exact 95% confidence intervals (CIs) for the SIRs were calculated assuming a Poisson distribution for the observed number of cases of childhood leukaemia. RESULTS: No statistically significantly increased SIRs were found in boys, girls or both combined for any of the areas or periods of diagnosis studied. For the total period of observation (1975-2002), and the more immediate coastal area studied, the SIR for both sexes combined was 1.22 (95% CI 0.53 to 2.40). CONCLUSION: No statistically significant evidence was found of an excess risk of childhood leukaemia in the vicinity of the Solway Firth coast of Dumfries and Galloway Health Board area in Scotland.

Adolescent↗
PubMed1988

Incidence of laryngeal cancer and exposure to acid mists.

To determine the relation between exposure to acid mist and laryngeal cancer, the smoking habits, drinking habits, and incidence of laryngeal cancer of 879 male steelworkers exposed to acid mists during pickling operations was ascertained. Sulphuric acid mist was the primary exposure for most men in this cohort. These men had all worked in a pickling operation for a minimum of six months before 1965, with an average duration of exposure of 9.5 years. Exposures to sulphuric acid in the 1970s averaged about 0.2 mg/m3, and earlier exposures were probably similar. Interviews were conducted with all cohort members or their next of kin in 1986 and medical records of decedents were reviewed. Nine workers were identified who had been diagnosed as having laryngeal cancer, using a conservative case definition that required medical record confirmation for any case among decedents and confirmation by a physician for any case among live individuals. Using data from national surveys of cancer incidence as referent rates, 3.44 laryngeal cancers would have been expected. Excess smoking by the exposed cohort compared with the United States population resulted in an upward adjustment of the expected number of cases of laryngeal cancer to 3.92. The standardised incidence rate ratio for laryngeal cancer was 2.30 (9/3.92), with a one sided p value of 0.01 (assuming a Poisson distribution). The finding of excess laryngeal cancer in this cohort is consistent with four other studies published since 1981.

Alcohol Drinking↗
PubMed1997

Lameness and foot lesions in adult British dairy goats.

In the first population-based study of lameness and foot lesions in adult goats in the UK, a random sample of 307 adult goats from four large commercial dairy farms was examined. The overall proportion of lame goats was 9.1 per cent (2.6 to 24.4 per cent). The abnormalities detected were horn separation (29.6 per cent), white line lesions (13.0 per cent) slippering (10.1 per cent), abscess of the sole (4.2 per cent), foreign body, and granulomatous lesions (1.0 per cent). Between 83.1 and 95.5 per cent of the goats had overgrown horn on at least one foot. The number of feet of individual goats with horn separation followed a Poisson distribution suggesting that it was associated with environmental rather than genetic or nutritional factors. Horn separation, abscess of the sole and footrot were significantly associated with lameness, but white line lesions, slippering and granulomatous lesions were not. There were differences between the farms in the prevalence of lameness and foot lesions. Routine foot trimming was associated with a lower prevalence of lameness.

Animal Husbandry↗
PubMed1981

Ag-NORs variation and banding homologies in two species of Bovidae: Bubalus bubalis and Bos taurus.

G,Q and R-binding pattern comparisons between the Murrah type of Bubalus bubalis L. (2n - 50) and the Holstein Friesian breed of Bos taurus L. (2n = 60) chromosomes revealed that the autosomes are similar in both species; in the former, the five pairs of submetacentrics correspond to centric fusions of chromosomes 1-29, 2-22, 8-19, 5-28 and 16-25 in the latter. Silver staining on somatic cells of buffalo revealed telomeric AG-NORs located on six pairs of autosomes, identified as 3p, 4p, 8, 21, 23 and 24. Only one pair of nucleolus organizer chromosomes is common to both species, namely the 4p of buffalo which corresponds to the 28 of cattle. The remaining NORs are located on different pairs. Out of 18 individuals, the number of Ag-NORs per cell varied between 3 and 10, with a mean value of 6.3 +/- 1.7; the mean number of nucleolar associations per cell was between 0.1 and 1.8. In the total population of 317 cells the two variables followed the binomial and the Poisson distributions, respectively, and their correlation coefficient was not statistically significant (r = +0.36). In addition to the mean number of Ag-NORs, the mean number of nucleolar associations per cell should be used for a better understanding of the differences among individuals.

Animals↗
PubMed2005

Accommodation of requests for emergency US and CT: applications of queueing theory to scheduling of urgent studies.

The purpose of this study was to determine whether queueing theory would allow prediction of optimal number of schedule slots to be reserved for urgent computed tomography (CT) and ultrasonography (US). Institutional review board approval was obtained; informed consent was exempted. Emergency studies were modeled as a Poisson process; slots were reserved such that rate of rescheduling of routine studies to accommodate emergencies was predicted to be below a certain level. Model was tested with 3 years of emergency US and CT requests. US and CT requests showed Poisson distribution. US rescheduling was near that predicted. CT rescheduling exceeded that predicted, which reflected increasing CT use. By using more recent CT data for prediction, a more concordant rescheduling rate resulted.

Appointments and Schedules↗
PubMed1983

Uptake of latex particles by macrophages: characterization using flow cytometry.

Flow cytometry can be used to characterize the uptake of particles by small samples of pulmonary macrophages both quickly and accurately. We found that there was a linear relationship between the number of fluorescent latex particles and the fluorescent intensity associated with each cell up to 47 particles/cell. Macrophages lavaged from the lungs of Syrian golden hamsters were metabolically and functionally stable for 3 h of incubation; the average intracellular concentrations of Na+ and K+ were 29 +/- 2 and 158 +/- 6 mM, respectively. Particle uptake was significantly inhibited by removing divalent cations with ethylenediaminetetraacetic acid and lowering the incubation temperature (37 degrees C) to 24 and 3 degrees C. The cell-to-cell variability in the uptake of particles was greater than the Poisson distribution would predict based on the mean number of particles per cell.

Animals↗
PubMed1977

Phagocytosis: quantification of rates and intercellular heterogeneity.

We present a method which permits analysis of phagocytic behavior in small samples of macrophages. Both overall phagocytic kinetics and intercellular variability in particle uptake were measured. Macrophages lavaged from Syrian golden hamster lungs were incubated (5 min at 37 degrees C) with 2- to 4-mum plastic particles at 4.6, 6.9, 9.1, and 16.0 X 10(6) part./ml. Harvested macrophages ranged from 0.6 to 4.0 X 10(6) cells per animal. To concentrate the cells and separate them from cell-free substrate after termination of phagocytosis, 30-60% of each flask's contents were centrifuged (400 X g, 20 min) atop a Metrizamide subphase (34% wt/vol, rho = 1.18). Cells were collected from the interface, fixed, and visually scored for number of particles phagocytized. Phagocytic rates followed Michaelis-Menten kinetics with Vmax = 0.63 +/- 0.18 (SEM) part./viable cell per min and Km = 8.5 +/- 2.7 (SEM) X 10(6) part./ml. In every case (23/23 flasks from 6 animals) particle uptake exhibited greater (P less than 0.01) cell-to-cell variability in avidity for substrate than the Poisson distribution would predict from mean number of particles phagocytized per viable cell.

Animals↗
PubMed2002

Postsynaptic dorsal column and cuneate correlations in the raccoon: a re-evaluation by parallel-cascade analysis.

In a previous study, we reported evidence for correlations between the firing of postsynaptic dorsal column (PSDC) neurons and cuneate neurons with overlapping receptive fields on the glabrous skin of the raccoon forepaw. The evidence was based on cross-correlation and frequency response analyses of spontaneously firing neurons. However, cross-correlation without white noise Gaussian analog inputs or Poisson distributed pulse train inputs is difficult to interpret because of the inherent convolution with the autocorrelation of the unknown input signals. While the data suggested positive correlations in the spinocuneate direction for most neuron pairs, we could not estimate the temporal characteristics of these putative connections. We have now re-analyzed these data using a parallel-cascade method to estimate the first- and second-order kernels of a Volterra series approximation to the spinocuneate system. This unbiased analysis suggests that a positive correlation occurs after about 5 ms, probably followed by a negative correlation at about 12 ms. Second-order kernels also had repeatable structure, indicating dual pathways with time separations of at least 10 ms.

Animals↗
PubMed1988

Nonlinear systems analysis of the hippocampal perforant path-dentate projection. II. Effects of random impulse train stimulation.

1. Nonlinear systems analytic techniques were used to characterize transformational properties of the network of neurons activated by perforant path input to the rabbit hippocampus. Trains of 4,064 impulses with randomly varying interimpulse intervals were used to stimulate perforant path fibers, and amplitudes of evoked dentate granule cell population spikes were measured. Interimpulse intervals of the random stimulus train were determined by a Poisson distribution with a mean interimpulse interval of 500 ms, and with intervals ranging from 1 to 5,000 ms. The response of dentate granule cells to this stimulation was assumed to reflect activity in the larger hippocampal network, because other subpopulations of neurons activated monosynaptically and polysynaptically within the hippocampal formation contribute to granule cell excitability through multiple feedforward and feedback pathways. System properties were characterized both for halothane anesthetized and chronically implanted, unanesthetized preparations. 2. Second-order kernel analysis showed that population spike amplitude was highly dependent on interimpulse interval. When population spikes of all latencies were included in the same analysis, stimulation impulses produced near-total suppression of spike amplitude when they were preceded 10-20 ms by another impulse in the train. Spike suppression extended to approximately 50 ms and was inversely related to length of the interimpulse interval. Suppression of granule cell response to intervals within the range of 10-50 ms was not influenced by halothane anesthesia. 3. Interstimulus intervals greater than approximately 50 ms resulted in a facilitation of population spike amplitude, with maximum facilitation occurring in response to intervals of 90-100 ms. The magnitude of maximum facilitation was significantly greater for anesthetized (129%) than for unanesthetized (74%) preparations. The range of intervals resulting in facilitation for unanesthetized animals could extend to 1,000-1,100 ms (average range, 61-714 ms). This was much greater than observed for population spikes recorded from anesthetized animals (50-364 ms), which exhibited suppression in response to intervals of approximately 300-700 ms. 4. Further analysis revealed that the nature of nonlinearities in population spike amplitude may depend on spike latency. For example, population spikes of "short" latency (3-4 or 4-5 ms, depending on the animal) exhibited only facilitation in response to interstimulus intervals of 1-4 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Nonlinear systems analysis of the hippocampal perforant path-dentate projection. III. Comparison of random train and paired impulse stimulation.

1. The transformational properties of the network of hippocampal neurons activated monosynaptically and polysynaptically by electrical stimulation of the perforant path were analyzed using random impulse train and paired impulse stimuli. In response to both types of input, the amplitudes of granule cell population spikes evoked in the dentate gyrus were used as the measure of network output. The random stimulus train consisted of a series of 4,064 electrical impulses, with interimpulse intervals determined by a Poisson distribution; the mean interimpulse interval of the train was 500 ms, and the range was 1-5,000 ms. Paired impulse stimuli consisted of pairs of impulses separated by 10-1,200 ms; impulses pairs were delivered once every 20 s. The procedures were applied to both anesthetized and chronically implanted, unanesthetized preparations. 2. Nonlinear systems analysis of population spike responses evoked during random train stimulation revealed that dentate granule cell output to any impulse was highly dependent on the interval since a prior impulse. Data from anesthetized animals showed that population spike amplitudes were markedly suppressed in response to intervals less than 50 ms, facilitated in response to intervals of approximately 100 ms, suppressed slightly in response to intervals of 300-700 ms, and unaffected by intervals greater than 700 ms. Data from unanesthetized animals showed similar results except that facilitation rather than suppression of spike amplitude was observed in response to intervals of 300-700 ms, and could extend to intervals as great as 1,000 ms. 3. The results of paired impulse stimulation applied to the same preparations also showed that granule cell response was highly dependent on interimpulse interval. However, nonlinearities observed with paired impulse stimulation differed from those revealed by a random impulse signal. Compared to results of random train stimulation, a paired impulse format produced greater magnitude spike suppression in response to short interimpulse intervals (e.g., 10-20 ms), maximum facilitation in response to shorter interstimulus intervals (50 ms rather than 100 ms), greater magnitude spike facilitation, and greater suppression in response to intervals greater than or equal to 300 ms. Furthermore, there were virtually no differences in the nonlinearities of granule cell response recorded from anesthetized and unanesthetized animals when a paired impulse format was used, whereas several differences were observed with random train stimuli. 4.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1995

Synchrony between single-unit activity and local field potentials in relation to periodicity coding in primary auditory cortex.

1. We recorded responses from 136 single units and the corresponding local field potentials (LFPs) from the same electrode at 44 positions in the primary auditory cortex of 25 juvenile, ketamine-anesthetized cats in response to periodic click trains with click repetition rates between 1 and 32 Hz; to Poisson-distributed click trains with an average click rate of 4 Hz; and under spontaneous conditions. The aim of the study is to evaluate the synchrony between LFPs and single-unit responses, to compare their coding of periodic stimuli, and to elucidate mechanisms that limit this periodicity coding in primary auditory cortex. 2. We obtained averaged LFPs either as click-triggered averages, the classical evoked potentials, or as spike-triggered averages. We quantified LFPs by initial negative peak-to-positive peak amplitude. In addition, we obtained trigger events from negativegoing level crossings (at approximately 2 SD below the mean) of the 100-Hz low-pass electrode signal. We analyzed these LFP triggers similarly to single-unit spikes. 3. The average ratio of the LFP amplitude in response to the second click in a train and the LFP amplitude to the first click as a function of click rate was low-pass with a slight resonance at approximately 10 Hz, and, above that frequency, decreasing with a slope of approximately 24 dB/octave. We found the 50% point at approximately 16 Hz. In contrast, the LFP amplitude averaged over entire click trains was low-pass with a similar resonance but a high-frequency slope of 12 dB/octave and a 50% point at approximately 12 Hz. 4. The LFP amplitude for click repetition rates between 5 and 11 Hz often showed augmentation, i.e., the amplitude increased in response to the first few clicks in the train and thereafter decreased. This augmentation was paralleled by an increase in the probability of firing in single units simultaneously recorded on the same electrode. 5. We calculated temporal modulation transfer functions (tMTFs) for single-unit spikes and for LFP triggers. They were typically bandpass with a best modulating frequency of 10 Hz and similar shape for both single-unit spikes and LFP triggers. The tMTF per click, obtained by dividing the tMTF by the number of clicks in the train, was low-pass with a 50% cutoff frequency at approximately Hz, similar to that for the average LFP amplitude. 6. the close similarity of the tMTFs for single-unit spikes and LFP triggers suggests that single-unit tMTFs can be predicted from LFP level crossings.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1995

Oscillations in the activity of a potassium channel at the presynaptic nerve terminal.

1. Periodic oscillations were detected in the activity of single macromolecules: potassium channels. 2. When potassium channels are repeatedly activated in isolated patches from fused synaptosomes of Torpedo electric organ, their behavior exhibits a departure from random activation. 3. The departure from random behavior is demonstrated by the runs test and by the lack of fit to Poisson distribution. 4. Under appropriate experimental conditions, the channels display periodic oscillations with a periodicity of approximately 20 s when activated at a rate of 1.25 Hz. 5. The oscillations do not arise from sampling, recording, or computational artifacts. 6. It is conceivable that single-channel oscillations play a role in the generation of membrane oscillations and thus may contribute to the oscillatory behavior of the nervous system.

Animals↗
PubMed1998

Spatiotemporal structure of cortical activity: properties and behavioral relevance.

The study was designed to reveal occurrences of precise firing sequences (PFSs) in cortical activity and to test their behavioral relevance. Two monkeys were trained to perform a delayed-response paradigm and to open puzzle boxes. Extracellular activity was recorded from neurons in premotor and prefrontal areas with an array of six microelectrodes. An algorithm was developed to detect PFSs, defined as a set of three spikes and two intervals with a precision of +/-1 ms repeating significantly more than expected by chance. The expected level of repetition was computed based on the firing rate and the pairwise correlation of the participating units, assuming a Poisson distribution of event counts. Accordingly, the search for PFSs was corrected for rate modulations. PFSs were found in 24/25 recording sessions. Most PFSs (76%) were composed of spikes of more than one unit but usually not more than two units (67%). The PFSs spanned hundreds of milliseconds, and the average interval between two events within the PFSs was 200 ms. No traces of periodic oscillations were found in the PFS intervals. The bins of the matrix that were defined as PFSs were isolated temporally: the spikes that generated PFSs were not associated with high-frequency bursts or rapid coherent rate fluctuations. A given PFS tended to be correlated with the animal's behavior. Furthermore, for 19% of the PFS pairs that shared the same unit composition, each member of the pair was associated with a different type of behavior. The PFSs often appeared in clusters that were associated with particular phases of the behavior. The firing rate of single units did not provide a full explanation for the timing and structure of these clusters. A reduced spike train (RST) was defined for each unit by taking all spikes of that unit that were part of any PFS. In 88% of the cases the degree of modulation of the RST was higher than that of the complete spike train. The results suggest that relevant information is carried by the fine temporal structure of cortical activity. A coding scheme that involves such temporal structures is rich and sufficiently flexible to facilitate a rapid organization of cortical neurons into functional groups. The results can be accounted for by the synfire chain model, which suggests that cortical activity is mediated by synchronous activation of neural groups in a reverberatory mode.

Algorithms↗
PubMed1998

Physiological signs of the activation of bag2 and chain intrafusal muscle fibers of gastrocnemius muscle spindles in the cat.

A method is described for identifying the effect of single gamma static (gamma(s)) axons on bag2 or chain intrafusal fibers using random (Poisson-distributed) stimuli. The cross-correlogram of the stimuli with the firing of spindle primary afferents took one of three forms. A large, simple, brief response was taken to indicate pure chain fiber activation and a small, prolonged response to indicate pure bag2 activation. A compound response with brief and prolonged components was taken to be a sign of mixed innervation. The correlogram components could be well fitted with lognormal curves. They could also be transformed into curves of gain as a function of frequency, which were convenient for estimating the strength of the effects. In 68 effects of gammas axons on Ia afferents, 16 were pure chain, 17 pure bag2, and 35 mixed. This distribution was significantly different (P < 0. 05) from that expected from chance nonspecific innervation of chain and bag2 fibers. Making use of the estimates of the strength of chain and bag2 effects derived from the gain curves, the classification was modified by treating mixed responses that had one effect more than five times stronger than the other as belonging to the dominant type. The distribution was then as follows: chain 16, bag2 28, and mixed 24. This differed very significantly from the prediction of chance distribution (P < 0.001). This evidence for some degree of specific innervation of chain and bag2 fibers is discussed in relation to previous work and with regard to the ways in which the two fiber types might be used in natural movements.

Action Potentials↗