scholarly journals Intrinsic Stabilization of Output Rates by Spike-Based Hebbian Learning

2001 ◽  
Vol 13 (12) ◽  
pp. 2709-2741 ◽  
Author(s):  
Richard Kempter ◽  
Wulfram Gerstner ◽  
J. Leo van Hemmen
Keyword(s):  
Firing Rate ◽  
Hebbian Learning ◽  
Piecewise Linear ◽  
Poisson Model ◽  
Intrinsic Rate ◽  
Postsynaptic Neuron ◽  
Temporal Correlations ◽  
Spiking Neuron Model ◽  
The Mean

We study analytically a model of long-term synaptic plasticity where synaptic changes are triggered by presynaptic spikes, postsynaptic spikes, and the time differences between presynaptic and postsynaptic spikes. The changes due to correlated input and output spikes are quantified by means of a learning window. We show that plasticity can lead to an intrinsic stabilization of the mean firing rate of the postsynaptic neuron. Subtractive normalization of the synaptic weights (summed over all presynaptic inputs converging on a postsynaptic neuron) follows if, in addition, the mean input rates and the mean input correlations are identical at all synapses. If the integral over the learning window is positive, firing-rate stabilization requires a non-Hebbian component, whereas such a component is not needed if the integral of the learning window is negative. A negative integral corresponds to anti-Hebbian learning in a model with slowly varying firing rates. For spike-based learning, a strict distinction between Hebbian and anti-Hebbian rules is questionable since learning is driven by correlations on the timescale of the learning window. The correlations between presynaptic and postsynaptic firing are evaluated for a piecewise-linear Poisson model and for a noisy spiking neuron model with refractoriness. While a negative integral over the learning window leads to intrinsic rate stabilization, the positive part of the learning window picks up spatial and temporal correlations in the input.

Modeling Synaptic Plasticity in Conjunction with the Timing of Pre- and Postsynaptic Action Potentials

2000 ◽  
Vol 12 (2) ◽  
pp. 385-405 ◽  
Author(s):  
Werner M. Kistler ◽  
J. Leo van Hemmen
Keyword(s):  
Synaptic Plasticity ◽  
Action Potentials ◽  
Neuron Model ◽  
Temporal Distribution ◽  
Temporal Coding ◽  
Synaptic Action ◽  
Temporal Correlations ◽  
Spiking Neuron Model ◽  
Experimental Findings

We present a spiking neuron model that allows for an analytic calculation of the correlations between pre- and postsynaptic spikes. The neuron model is a generalization of the integrate-and-fire model and equipped with a probabilistic spike-triggering mechanism. We show that under certain biologically plausible conditions, pre- and postsynaptic spike trains can be described simultaneously as an inhomogeneous Poisson process. Inspired by experimental findings, we develop a model for synaptic long-term plasticity that relies on the relative timing of pre- and post-synaptic action potentials. Being given an input statistics, we compute the stationary synaptic weights that result from the temporal correlations between the pre- and postsynaptic spikes. By means of both analytic calculations and computer simulations, we show that such a mechanism of synaptic plasticity is able to strengthen those input synapses that convey precisely timed spikes at the expense of synapses that deliver spikes with a broad temporal distribution. This may be of vital importance for any kind of information processing based on spiking neurons and temporal coding.

The postsynaptic induction of nonassociative long-term depression of excitatory synaptic transmission in rat hippocampal slices

1993 ◽  
Vol 69 (1) ◽  
pp. 219-229 ◽  
Author(s):  
G. Christofi ◽  
A. V. Nowicky ◽  
S. R. Bolsover ◽  
L. J. Bindman
Keyword(s):  
Synaptic Transmission ◽  
Hippocampal Slices ◽  
Receptor Subtypes ◽  
Postsynaptic Neuron ◽  
Conditioning Procedure ◽  
Long Term Depression ◽  
Postsynaptic Potentials ◽  
The Mean ◽  
Conditioning Stimuli

1. Long-term depression (LTD) is an activity-dependent reduction in the strength of synaptic transmission that can persist for hours. It is a neural model for processes underlying learning and memory, such as extinction and forgetting. LTD of excitatory postsynaptic potentials (EPSPs) in cells of the CA1 region of hippocampal slices can be induced in an anti-Hebbian paradigm, i.e., by conditioning stimuli that activate the postsynaptic neuron in the absence of evoked synaptic transmission in the test pathway. Past work showed that LTD was not produced consistently in a pharmacologically untreated slice, but it could be induced more reliably when the conditioning stimuli were applied during block of evoked transmitter release. We have now defined further the conditions in which LTD can be obtained using postsynaptic conditioning by investigating 1) whether intracellular conditioning is effective, 2) the requirement for extracellular Ca2+, and 3) the consequences of selective block of glutamate ionotropic receptor subtypes during the conditioning procedure. 2. Intracellular recordings were made from CA1 pyramidal neurons. Test shocks were applied to the stratum radiatum except during conditioning, and the depolarizing slopes and amplitudes of evoked EPSPs were measured. The conditioning procedure activated the postsynaptic neuron either antidromically (via trains of shocks at 100 Hz applied to the axons in the alveus) or intracellularly (via depolarizing pulses of 1.5–3.5 nA). During conditioning, postsynaptic potentials (PSPs) evoked by the conditioning stimuli either were transiently blocked by bathing slices for 5 min in artificial cerebrospinal fluid (CSF) containing a high [Mg2+] or were reduced by glutamate antagonists. 3. When slices were bathed in CSF containing 25 mM Mg2+ and 2 mM Ca2+, evoked PSPs were transiently abolished; conditioning, either by antidromic or intracellular stimulation, always evoked a significant LTD. During the LTD produced by antidromic stimulation, the mean EPSP slope was 52.6 +/- 11.4% (mean +/- SE) of its control at 30–35 min after conditioning (n = 7). The LTD produced by intracellular conditioning was of similar magnitude: the mean EPSP slope was 57.2 +/- 11.6% of its control at 30-35 min postconditioning (n = 7). When slices were bathed in CSF containing 25 mM Mg2+ and 2 mM Ca2+ without conditioning stimuli, there was no LTD (mean EPSP slope 109 +/- 8.1% of its control at 30–35 min after reperfusion with CSF; n = 5).(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Modeling stimulus-dependent variability improves decoding of population neural responses

2017 ◽  
Author(s):  
Abed Ghanbari ◽  
Christopher M. Lee ◽  
Heather L. Read ◽  
Ian H. Stevenson
Keyword(s):  
Firing Rate ◽  
Poisson Model ◽  
Fano Factor ◽  
Response Variability ◽  
Additional Parameter ◽  
Neural Responses ◽  
Stimulus Movement ◽  
Tuning Curves ◽  
The Mean ◽  
Cmp Model

AbstractNeural responses to repeated presentations of an identical stimulus often show substantial trial-to-trial variability. How the mean firing rate varies in response to different stimuli or during different movements (tuning curves) has been extensively modeled in a wide variety of neural systems. However, the variability of neural responses can also have clear tuning independent of the tuning in the mean firing rate. This suggests that the variability could contain information regarding the stimulus/movement beyond what is encoded in the mean firing rate. Here we demonstrate how taking variability into account can improve neural decoding. In a typical neural coding model spike counts are assumed to be Poisson with the mean response depending on an external variable, such as a stimulus or movement. Bayesian decoding methods then use the probabilities under these Poisson tuning models (the likelihood) to estimate the probability of each stimulus given the spikes on a given trial (the posterior). However, under the Poisson model, spike count variability is always exactly equal to the mean (Fano factor = 1). Here we use two alternative models - the Conway-Maxwell-Poisson (CMP) model and Negative Binomial (NB) model - to more flexibly characterize how neural variability depends on external stimuli. These models both contain the Poisson distribution as a special case but have an additional parameter that allows the variance to be greater than the mean (Fano factor >1) or, for the CMP model, less than the mean (Fano factor <1). We find that neural responses in primary motor (M1), visual (V1), and auditory (A1) cortices have diverse tuning in both their mean firing rates and response variability. Across cortical areas, we find that Bayesian decoders using the CMP or NB models improve stimulus/movement estimation accuracy by 4-12% compared to the Poisson model. Moreover, the uncertainty of the non-Poisson decoders more accurately reflects the magnitude of estimation errors. In addition to tuning curves that reflect average neural responses, stimulus-dependent response variability may be an important aspect of the neural code. Modeling this structure could, potentially, lead to improvements in brain machine interfaces.

Acute and Chronic Changes in Platelet Volume and Count After Cardiopulmonary Bypass Induced Thrombocytopenia in Man

1987 ◽  
Vol 57 (01) ◽  
pp. 55-58 ◽  
Author(s):  
J F Martin ◽  
T D Daniel ◽  
E A Trowbridge
Keyword(s):  
Platelet Count ◽  
Mean Platelet Volume ◽  
Artery Bypass ◽  
Bypass Graft ◽  
Control Group ◽  
Artery Bypass Graft ◽  
Platelet Volume ◽  
Young Males ◽  
The Mean

SummaryPatients undergoing surgery for coronary artery bypass graft or heart valve replacement had their platelet count and mean volume measured pre-operatively, immediately post-operatively and serially for up to 48 days after the surgical procedure. The mean pre-operative platelet count of 1.95 ± 0.11 × 1011/1 (n = 26) fell significantly to 1.35 ± 0.09 × 1011/1 immediately post-operatively (p <0.001) (n = 22), without a significant alteration in the mean platelet volume. The average platelet count rose to a maximum of 5.07 ± 0.66 × 1011/1 between days 14 and 17 after surgery while the average mean platelet volume fell from preparative and post-operative values of 7.25 ± 0.14 and 7.20 ± 0.14 fl respectively to a minimum of 6.16 ± 0.16 fl by day 20. Seven patients were followed for 32 days or longer after the operation. By this time they had achieved steady state thrombopoiesis and their average platelet count was 2.44 ± 0.33 × 1011/1, significantly higher than the pre-operative value (p <0.05), while their average mean platelet volume was 6.63 ± 0.21 fl, significantly lower than before surgery (p <0.001). The pre-operative values for the platelet volume and counts of these patients were significantly different from a control group of 32 young males, while the chronic post-operative values were not. These long term changes in platelet volume and count may reflect changes in the thrombopoietic control system secondary to the corrective surgery.

Multi-Center Calibration of the Second Reference Material for Thromboplastin, Rabbit, Plain, Coded CRM 149R

1991 ◽  
Vol 65 (03) ◽  
pp. 263-267 ◽  
Author(s):  
A M H P van den Besselaar ◽  
R M Bertina
Keyword(s):  
Reference Material ◽  
Standard Error ◽  
Standard Errors ◽  
Sensitivity Index ◽  
Long Term Stability ◽  
Significant Bias ◽  
The Mean ◽  
The Relationship ◽  
International Sensitivity Index

SummaryIn a collaborative trial of eleven laboratories which was performed mainly within the framework of the European Community Bureau of Reference (BCR), a second reference material for thromboplastin, rabbit, plain, was calibrated against its predecessor RBT/79. This second reference material (coded CRM 149R) has a mean International Sensitivity Index (ISI) of 1.343 with a standard error of the mean of 0.035. The standard error of the ISI was determined by combination of the standard errors of the ISI of RBT/79 and the slope of the calibration line in this trial.The BCR reference material for thromboplastin, human, plain (coded BCT/099) was also included in this trial for assessment of the long-term stability of the relationship with RBT/79. The results indicated that this relationship has not changed over a period of 8 years. The interlaboratory variation of the slope of the relationship between CRM 149R and RBT/79 was significantly lower than the variation of the slope of the relationship between BCT/099 and RBT/79. In addition to the manual technique, a semi-automatic coagulometer according to Schnitger & Gross was used to determine prothrombin times with CRM 149R. The mean ISI of CRM 149R was not affected by replacement of the manual technique by this particular coagulometer.Two lyophilized plasmas were included in this trial. The mean slope of relationship between RBT/79 and CRM 149R based on the two lyophilized plasmas was the same as the corresponding slope based on fresh plasmas. Tlowever, the mean slope of relationship between RBT/79 and BCT/099 based on the two lyophilized plasmas was 4.9% higher than the mean slope based on fresh plasmas. Thus, the use of these lyophilized plasmas induced a small but significant bias in the slope of relationship between these thromboplastins of different species.

Comparative Study of effectiveness of mobilization with movement (MWM) and End range mobilization (ERM) techniques in frozen shoulder

2018 ◽  
Vol 4 (4) ◽  
pp. 519-522
Author(s):  
Jeyakumar S ◽  
Jagatheesan Alagesan ◽  
T.S. Muthukumar
Keyword(s):  
Range Of Motion ◽  
Frozen Shoulder ◽  
Type I ◽  
Mean Values ◽  
Functional Activities ◽  
Group A ◽  
The Mean ◽  
Group B

Background: Frozen shoulder is disorder of the connective tissue that limits the normal Range of motion of the shoulder in diabetes, frozen shoulder is thought to be caused by changes to the collagen in the shoulder joint as a result of long term Hypoglycemia. Mobilization is a therapeutic movement of the joint. The goal is to restore normal joint motion and rhythm. The use of mobilization with movement for peripheral joints was developed by mulligan. This technique combines a sustained application of manual technique “gliding” force to the joint with concurrent physiologic motion of joint, either actively or passively. This study aims to find out the effects of mobilization with movement and end range mobilization in frozen shoulder in Type I diabetics. Materials and Methods: 30 subjects both male and female, suffering with shoulder pain and clinically diagnosed with frozen shoulder was recruited for the study and divided into two groups with 15 patients each based on convenient sampling method. Group A patients received mobilization with movement and Group B patients received end range mobilization for three weeks. The outcome measurements were SPADI, Functional hand to back scale, abduction range of motion using goniometer and VAS. Results: The mean values of all parameters showed significant differences in group A as compared to group B in terms of decreased pain, increased abduction range and other outcome measures. Conclusion: Based on the results it has been concluded that treating the type 1 diabetic patient with frozen shoulder, mobilization with movement exercise shows better results than end range mobilization in reducing pain and increase functional activities and mobility in frozen shoulder.

PITUITARY-ADRENAL RECOVERY FOLLOWING LONG-TERM CORTICOSTEROID THERAPY

1966 ◽  
Vol 51 (1) ◽  
pp. 63-70 ◽  
Author(s):  
P. F. Roe ◽  
D. M. Mitchell ◽  
G. W. Pennington
Keyword(s):  
Corticosteroid Therapy ◽  
Adrenocortical Function ◽  
Endocrine Disorders ◽  
Marked Rise ◽  
Underlying Condition ◽  
Normal Limits ◽  
Small Rise ◽  
The Mean ◽  
Corticosteroid Drugs

ABSTRACT Adrenocortical function was assessed in 20 patients receiving long-term corticosteroid drugs for a variety of non-endocrine disorders. In all cases plasma 17-hydroxycorticosteroids (17-OHCS) levels were within or above normal limits 48 hours after abruptly stopping their drugs and a further marked rise occurred in 7 patients given metyrapone for 24 h. Urinary 17-OHCS excretion did not show a parallel rise. Taking the group as a whole, a small rise in the mean output occurred 48 hours after stopping therapy, and a further slightly greater rise followed metyrapone. 3 patients had a relapse of their underlying condition during the test in spite of normal plasma and urinary 17-OHCS levels.

Long-term dynamics and destruction of marsh vegetation in the Kolokolkova Bay of the Barents Sea

2012 ◽  
pp. 66-77 ◽  
Author(s):  
I. A. Lavrinenko ◽  
O. V. Lavrinenko ◽  
D. V. Dobrynin
Keyword(s):  
Species Composition ◽  
Plant Communities ◽  
Barents Sea ◽  
Mean Value ◽  
Marsh Vegetation ◽  
Composition And Structure ◽  
The Mean ◽  
Species Composition And Structure

The satellite images show that the area of marshes in the Kolokolkova bay was notstable during the period from 1973 up to 2011. Until 2010 it varied from 357 to 636 ha. After a severe storm happened on July 24–25, 2010 the total area of marshes was reduced up to 43–50 ha. The mean value of NDVI for studied marshes, reflecting the green biomass, varied from 0.13 to 0.32 before the storm in 2010, after the storm the NDVI decreased to 0.10, in 2011 — 0.03. A comparative analysis of species composition and structure of plant communities described in 2002 and 2011, allowed to evaluate the vegetation changes of marshes of the different topographic levels. They are fol­lowing: a total destruction of plant communities of the ass. Puccinellietum phryganodis and ass. Caricetum subspathaceae on low and middle marches; increasing role of halophytic species in plant communities of the ass. Caricetum glareosae vic. Calamagrostis deschampsioides subass. typicum on middle marches; some changes in species composition and structure of plant communities of the ass. Caricetum glareosae vic. Calamagrostis deschampsioides subass. festucetosum rubrae on high marches and ass. Parnassio palustris–Salicetum reptantis in transition zone between marches and tundra without changes of their syntaxonomy; a death of moss cover in plant communities of the ass. Caricetum mackenziei var. Warnstorfia exannulata on brackish coastal bogs. The possible reasons of dramatic vegetation dynamics are discussed. The dating of the storm makes it possible to observe the directions and rates of the succession of marches vegetation.

Long-term outcomes of lumbar microdiscectomy in the pediatric population: a large single-institution case series

2019 ◽  
Vol 24 (5) ◽  
pp. 549-557
Author(s):  
Malia McAvoy ◽  
Heather J. McCrea ◽  
Vamsidhar Chavakula ◽  
Hoon Choi ◽  
Wenya Linda Bi ◽  
...  
Keyword(s):  
Conservative Management ◽  
Functional Outcomes ◽  
Pediatric Patients ◽  
Clinical Presentation ◽  
Case Series ◽  
Csf Leak ◽  
Single Institution ◽  
The Mean

OBJECTIVEFew studies describe long-term functional outcomes of pediatric patients who have undergone lumbar microdiscectomy (LMD) because of the rarity of pediatric disc herniation and the short follow-up periods. The authors analyzed risk factors, clinical presentation, complications, and functional outcomes of a single-institution series of LMD patients over a 19-year period.METHODSA retrospective case series was conducted of pediatric LMD patients at a large pediatric academic hospital from 1998 to 2017. The authors examined premorbid risk factors, clinical presentation, physical examination findings, type and duration of conservative management, indications for surgical intervention, complications, and postoperative outcomes.RESULTSOver the 19-year study period, 199 patients underwent LMD at the authors’ institution. The mean age at presentation was 16.0 years (range 12–18 years), and 55.8% were female. Of these patients, 70.9% participated in competitive sports, and among those who did not play sports, 65.0% had a body mass index greater than 25 kg/m2. Prior to surgery, conservative management had failed in 98.0% of the patients. Only 3 patients (1.5%) presented with cauda equina syndrome requiring emergent microdiscectomy. Complications included 4 cases of postoperative CSF leak (2.0%), 1 case of a noted intraoperative CSF leak, and 3 cases of wound infection (1.5%). At the first postoperative follow-up appointment, minimal or no pain was reported by 93.3% of patients. The mean time to return to sports was 9.8 weeks. During a mean follow-up duration of 8.2 years, 72.9% of patients did not present again after routine postoperative appointments. The total risk of reoperation was a rate of 7.5% (3.5% of patients underwent reoperation for the same level; 4.5% underwent adjacent-level decompression, and one patient [0.5%] ultimately underwent a fusion).CONCLUSIONSMicrodiscectomy is a safe and effective treatment for long-term relief of pain and return to daily activities among pediatric patients with symptomatic lumbar disc disease in whom conservative management has failed.

Deep brain stimulation of the posterior limb of the internal capsule in the treatment of central poststroke neuropathic pain of the lower limb: case series with long-term follow-up and literature review

2020 ◽  
Vol 133 (3) ◽  
pp. 830-838 ◽  
Author(s):  
Andrea Franzini ◽  
Giuseppe Messina ◽  
Vincenzo Levi ◽  
Antonio D’Ammando ◽  
Roberto Cordella ◽  
...  
Keyword(s):  
Neuropathic Pain ◽  
Lower Limb ◽  
Internal Capsule ◽  
Posterior Limb ◽  
Vas Score ◽  
The Mean ◽  
Deep Brain ◽  
Stimulation Of

OBJECTIVECentral poststroke neuropathic pain is a debilitating syndrome that is often resistant to medical therapies. Surgical measures include motor cortex stimulation and deep brain stimulation (DBS), which have been used to relieve pain. The aim of this study was to retrospectively assess the safety and long-term efficacy of DBS of the posterior limb of the internal capsule for relieving central poststroke neuropathic pain and associated spasticity affecting the lower limb.METHODSClinical and surgical data were retrospectively collected and analyzed in all patients who had undergone DBS of the posterior limb of the internal capsule to address central poststroke neuropathic pain refractory to conservative measures. In addition, long-term pain intensity and level of satisfaction gained from stimulation were assessed. Pain was evaluated using the visual analog scale (VAS). Information on gait improvement was obtained from medical records, neurological examination, and interview.RESULTSFour patients have undergone the procedure since 2001. No mortality or morbidity related to the surgery was recorded. In three patients, stimulation of the posterior limb of the internal capsule resulted in long-term pain relief; in a fourth patient, the procedure failed to produce any long-lasting positive effect. Two patients obtained a reduction in spasticity and improved motor capability. Before surgery, the mean VAS score was 9 (range 8–10). In the immediate postoperative period and within 1 week after the DBS system had been turned on, the mean VAS score was significantly lower at a mean of 3 (range 0–6). After a mean follow-up of 5.88 years, the mean VAS score was still reduced at 5.5 (range 3–8). The mean percentage of long-term pain reduction was 38.13%.CONCLUSIONSThis series suggests that stimulation of the posterior limb of the internal capsule is safe and effective in treating patients with chronic neuropathic pain affecting the lower limb. The procedure may be a more targeted treatment method than motor cortex stimulation or other neuromodulation techniques in the subset of patients whose pain and spasticity are referred to the lower limbs.

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