Summation

About: Summation is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 45593 citations. The topic is also known as: summation & sum of a sequence.

Frequency-Dependent Synaptic Dynamics Differentially Tune CA1 and CA2 Pyramidal Neuron Responses to Cortical Input.

Abstract: Entorhinal cortex (EC) neurons make monosynaptic connections onto distal apical dendrites of CA1 and CA2 pyramidal neurons (PNs) through the perforant path (PP) projection. Previous studies show that differences in dendritic properties and synaptic input density enable the PP inputs to produce a much stronger excitation of CA2 compared to CA1 PNs. Here, using mice of both sexes, we report that the difference in PP efficacy varies substantially as a function of presynaptic firing rate. Although a single PP stimulus evokes a 5-6 fold greater EPSP in CA2 compared to CA1, a brief high-frequency train of PP stimuli evokes a strongly facilitating postsynaptic response in CA1, with relatively little change in CA2. Furthermore, we demonstrate that blockade of NMDARs significantly reduces strong temporal summation in CA1, but has little impact on that in CA2. As a result of the differences in the frequency- and NMDAR-dependent temporal summation, naturalistic patterns of presynaptic activity evoke CA1 and CA2 responses with distinct dynamics, differentially tuning CA1 and CA2 responses to bursts of presynaptic firing versus single presynaptic spikes, respectively. Significance Statement Recent studies have demonstrated abundant entorhinal cortical innervation and efficient dendritic propagation enable hippocampal CA2 pyramidal neurons to produce robust excitation evoked by single cortical stimuli, compared to CA1. Here we uncovered, unexpectedly, that the difference in efficacy of cortical excitation varies substantially as a function of presynaptic firing rate. A burst of stimuli evokes a strongly facilitating response in CA1, but not in CA2. As a result, postsynaptic response of CA1 and CA2 to presynaptic naturalistic firing displays contrasting temporal dynamics, which depends on the activation of NMDARs. Thus our findings provide a synaptic mechanism by which hippocampal neurons dynamically respond to irregular, high-frequency burst firing in entorhinal cortex in behaving animals.

Dissociation of nociceptive modulation of a human jaw reflex from the influence of stress

Abstract: In human beings, inhibitory jaw reflexes can be depressed by painful stimulation of remote parts of the body. Since similar effects can be produced by the stress of anticipating pain, we wished to investigate whether the effects of remote painful stimuli are dependent on stress. EMG recordings were made from a masseter muscle while subjects maintained activity in the muscle at ∼12.5% of maximum using visual feedback. The protocols involved three sequences: (1) “standard controls” in which reflexes were evoked by electrical test stimuli applied to the upper lip; (2) “standard conditioning” in which painful electrical conditioning stimuli were applied over the sural nerve 100 ms before the test stimuli; (3) “random sequences” in which test-only and conditioning-test combinations were employed in a double-blind, random, order. Data are presented as means ± SEMs. In the standard controls, the stimuli evoked clear inhibitory reflexes (latency 37 ± 1.3 ms, duration 62 ± 5.6 ms; n = 10) in all the subjects. During standard conditioning, the reflex magnitude was reduced significantly (by 50.0 ± 8.5%, P = 0.0002, one-sample t-test). When the test-only and conditioning-test responses were extracted from the random sequences, there was also a significant reduction in the reflex magnitude following conditioning (by 34.6 ± 5.5%, P = 0.0002, one-sample t-test) albeit less so than between the standard sequences (P = 0.03, paired t-test). A second series of experiments suggested that these lesser effects during the random sequences were not substantially due to any loss of temporal summation of the conditioning mechanisms. The evidence for this was that application of pairs of conditioning stimuli did not produce a significantly greater effect than single conditioning stimuli within a random sequence (39.9 ± 9.6% as opposed to 32.7 ± 9.1% reductions in the reflex, P = 0.117, paired t-test). Therefore since any stress in the random sequences would not have been “tied” to the conditioned responses alone, the effects of remote painful stimuli on this inhibitory jaw reflex cannot be entirely secondary to stress.

On Temporal Summation in Chaotic Neural Network with Incremental Learning

Abstract: The incremental learning is a method to compose an associate memory using a chaotic neural network and provides larger capacity than correlative learning in compensation for a large amount of computation. A chaotic neuron has spatiotemporal summation in it and the temporal summation makes the learning stable to input noise. When there is no noise in input, the neuron may not need temporal summation. In this paper, to reduce the computations, a simplified network without temporal summation is introduced and investigated through the computer simulations comparing with the network as in the past, which is called here the usual network. It turns out that the simplified network has the same capacity in comparison with the usual network and can learn faster than the usual one, but that the simplified network loses the learning ability in noisy inputs. To improve this ability, the parameters in the chaotic neural network are adjusted.