Spike Timing Dependent Plasticity Finds the Start of Repeating Patterns in Continuous Spike Trains

Experimental studies have observed Long Term synaptic Potentiation (LTP) when a presynaptic neuron fires shortly before a postsynaptic neuron, and Long Term Depression (LTD) when the presynaptic neuron fires shortly after, a phenomenon known as Spike Timing Dependant Plasticity (STDP). When a neuron is presented successively with discrete volleys of input spikes STDP has been shown to learn ‘early spike patterns’, that is to concentrate synaptic weights on afferents that consistently fire early, with the result that the postsynaptic spike latency decreases, until it reaches a minimal and stable value. Here, we show that these results still stand in a continuous regime where afferents fire continuously with a constant population rate. As such, STDP is able to solve a very difficult computational problem: to localize a repeating spatio-temporal spike pattern embedded in equally dense ‘distractor’ spike trains. STDP thus enables some form of temporal coding, even in the absence of an explicit time reference. Given that the mechanism exposed here is simple and cheap it is hard to believe that the brain did not evolve to use it

Hair cortisol concentrations in chronic central serous chorioretinopathy

Purpose Central serous chorioretinopathy (CSC), a distinct form of macular degeneration, has been associated with glucocorticoid use and possibly also with an increased endogenous activity of the hypothalamic-pituitary-adrenal (HPA) axis. To estimate long-term glucocorticoid exposure, measurement of hair cortisol concentrations (HCC) has emerged. This cross-sectional study aimed to investigate HCC, as a reflection of chronic endogenous steroid exposure, in a cohort of patients with chronic CSC (cCSC).Methods Hair cortisol concentrations (HCC) were determined in 48 patients with cCSC and 230 population-based controls (Lifelines cohort study), not using exogenous corticosteroids.Results Increased HCC (defined as >10.49 pg/mg) were present in 2 (4%) patients with cCSC and 13 (6%) controls. Mean HCC values were not different between patients and controls, and no difference in HCC was found between patients with active cCSC disease and patients with inactive disease. No correlation between HCC and urinary free cortisol (UFC) levels in patients with cCSC was found.Conclusions This study shows that HCC in patients with cCSC are not elevated compared to population-based controls, and no association between HCC and cCSC severity was found. This finding questions the previous suggestion that cCSC is associated with increased HPA axis activity. In line, HCC do not seem useful in monitoring cCSC disease activity.Clinical epidemiolog

Hair cortisol concentrations in chronic central serous chorioretinopathy

Purpose Central serous chorioretinopathy (CSC), a distinct form of macular degeneration, has been associated with glucocorticoid use and possibly also with an increased endogenous activity of the hypothalamic-pituitary-adrenal (HPA) axis. To estimate long-term glucocorticoid exposure, measurement of hair cortisol concentrations (HCC) has emerged. This cross-sectional study aimed to investigate HCC, as a reflection of chronic endogenous steroid exposure, in a cohort of patients with chronic CSC (cCSC).Methods Hair cortisol concentrations (HCC) were determined in 48 patients with cCSC and 230 population-based controls (Lifelines cohort study), not using exogenous corticosteroids.Results Increased HCC (defined as >10.49 pg/mg) were present in 2 (4%) patients with cCSC and 13 (6%) controls. Mean HCC values were not different between patients and controls, and no difference in HCC was found between patients with active cCSC disease and patients with inactive disease. No correlation between HCC and urinary free cortisol (UFC) levels in patients with cCSC was found.Conclusions This study shows that HCC in patients with cCSC are not elevated compared to population-based controls, and no association between HCC and cCSC severity was found. This finding questions the previous suggestion that cCSC is associated with increased HPA axis activity. In line, HCC do not seem useful in monitoring cCSC disease activity.Clinical epidemiolog

Trimetazidine in heart failure with preserved ejection fraction: a randomized controlled cross‐over trial

Abstract Aims Impaired myocardial energy homeostasis plays an import role in the pathophysiology of heart failure with preserved ejection fraction (HFpEF). Left ventricular relaxation has a high energy demand, and left ventricular diastolic dysfunction has been related to impaired energy homeostasis. This study investigated whether trimetazidine, a fatty acid oxidation inhibitor, could improve myocardial energy homeostasis and consequently improve exercise haemodynamics in patients with HFpEF. Methods and results The DoPING‐HFpEF trial was a phase II single‐centre, double‐blind, placebo‐controlled, randomized cross‐over trial. Patients were randomized to trimetazidine treatment or placebo for 3 months and switched after a 2‐week wash‐out period. The primary endpoint was change in pulmonary capillary wedge pressure, measured with right heart catheterization at multiple stages of bicycling exercise. Secondary endpoint was change in myocardial phosphocreatine/adenosine triphosphate, an index of the myocardial energy status, measured with phosphorus‐31 magnetic resonance spectroscopy. The study included 25 patients (10/15 males/females; mean (standard deviation) age, 66 (10) years; body mass index, 29.8 (4.5) kg/m2); with the diagnosis of HFpEF confirmed with (exercise) right heart catheterization either before or during the trial. There was no effect of trimetazidine on the primary outcome pulmonary capillary wedge pressure at multiple levels of exercise (mean change 0 [95% confidence interval, 95% CI −2, 2] mmHg over multiple levels of exercise, P = 0.60). Myocardial phosphocreatine/adenosine triphosphate in the trimetazidine arm was similar to placebo (1.08 [0.76, 1.76] vs. 1.30 [0.95, 1.86], P = 0.08). There was no change by trimetazidine compared with placebo in the exploratory parameters: 6‐min walking distance (mean change of −6 [95% CI −18, 7] m vs. −5 [95% CI −22, 22] m, respectively, P = 0.93), N‐terminal pro‐B‐type natriuretic peptide (5 (−156, 166) ng/L vs. −13 (−172, 147) ng/L, P = 0.70), overall quality‐of‐life (KCCQ and EQ‐5D‐5L, P = 0.78 and P = 0.51, respectively), parameters for diastolic function measured with echocardiography and cardiac magnetic resonance, or metabolic parameters. Conclusions Trimetazidine did not improve myocardial energy homeostasis and did not improve exercise haemodynamics in patients with HFpEF