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.

Tonic Pain Evoked by Pulsating Heat: Temporal Summation Mechanisms and Perceptual Qualities

Abstract: The properties of a newly developed tonic heat pain model (THPM), which makes use of pulsating contact heat, were investigated in 18 young men. The most important feature of this model is that repetitive heat pulses with an intensity of 1°C above the individual pain threshold are employed. This approach was used to tailor the tonic pain stimulation to the individual pain sensitivity. In the first of two experiments, the effects of pulse frequencies ranging from 5 to 30 pulses per minute (ppm) on ratings of pain intensity and pain unpleasantness (visual analogue scales) were examined. At all frequencies, both ratings increased steadily over the 5-min test period. Frequencies of 15 ppm or more appeared to enhance pain intensity throughout the test period compared to the lower frequencies, but did not appear to alter pain unpleasantness. This suggests that only pain intensity is influenced by slow temporal summation and that a sort of frequency threshold exists for this kind of summation. In the second exper...

Homeostatic Regulation of Synaptic Excitability: Tonic GABAA Receptor Currents Replace Ih in Cortical Pyramidal Neurons of HCN1 Knock-Out Mice

Abstract: Homeostatic control of synaptic efficacy is often mediated by dynamic regulation of excitatory synaptic receptors. Here, we report a novel form of homeostatic synaptic plasticity based on regulation of shunt currents that control dendritosomatic information transfer. In cortical pyramidal neurons from wild-type mice, HCN1 channels underlie a dendritic hyperpolarization-activated cationic current ( I h) that serves to limit temporal summation of synaptic inputs. In HCN1 knock-out mice, as expected, I h is reduced in pyramidal neurons and its effects on synaptic summation are strongly diminished. Unexpectedly, we found a markedly enhanced bicuculline- and L-655,708-sensitive background GABAA current in these cells that could be attributed to selective upregulation of GABAA α5 subunit expression in the cortex of HCN1 knock-out mice. Strikingly, despite diminished I h, baseline sublinear summation of evoked EPSPs was unchanged in pyramidal neurons from HCN1 knock-out mice; however, blocking tonic GABAA currents with bicuculline enhanced synaptic summation more strongly in pyramidal cells from HCN1 knock-out mice than in those cells from wild-type mice. Increasing tonic GABAA receptor conductance in the context of reduced I h, using computational or pharmacological approaches, restored normal baseline synaptic summation, as observed in neurons from HCN1 knock-out mice. These data indicate that upregulation of α5 subunit-mediated GABAA receptor tonic current compensates quantitatively for loss of dendritic I h in cortical pyramidal neurons from HCN1 knock-out mice to maintain normal synaptic summation; they further imply that dendritosomatic synaptic efficacy is a controlled variable for homeostatic regulation of cortical neuron excitability in vivo .

Neural coding of nociceptive stimuli—from rat spinal neurones to human perception

Abstract: Translational studies are key to furthering our understanding of nociceptive signalling and bridging the gaps between molecules and pathways to the patients. This requires use of appropriate preclinical models that accurately depict outcome measures used in humans. Whereas behavioural animal studies classically involve reports related to nociceptive thresholds of, for example, withdrawal, electrophysiological recordings of spinal neurones that receive convergent input from primary afferents permits investigation of suprathreshold events and exploration of the full-range coding of different stimuli. We explored the central processing of nociceptive inputs in a novel parallel investigation between rats and humans. Using radiant laser pulses, we first compared the electrophysiological responses of deep wide dynamic range and superficial nociceptive-specific neurones in the rat dorsal horn with human psychophysics and cortical responses. Secondly, we explored the effects of spatial summation using laser pulses of identical energy and different size. We observed 3 main findings. Firstly, both rodent and human data confirmed that neodymium–yttrium aluminium perovskite laser stimulation is a nociceptive-selective stimulus that never activates Aβ afferents. Secondly, graded laser stimulation elicited similarly graded electrophysiological and behavioural responses in both species. Thirdly, there was a significant degree of spatial summation of laser nociceptive input. The remarkable similarity in rodent and human coding indicates that responses of rat dorsal horn neurones can translate to human nociceptive processing. These findings suggest that recordings of spinal neuronal activity elicited by laser stimuli could be a valuable predictive measure of human pain perception.

The effects of DNIC-type inhibition on temporal summation compared to single pulse processing: does sex matter?

Abstract: A few experimental observations have suggested that diffuse noxious inhibitory control (DNIC)-type inhibition acts preferentially on the pain system if this is in a sensitised state, e.g. after slow temporal summation (wind-up). However, firm evidence is still missing. Furthermore, sex-related factors, which seem to affect temporal summation as well as DNIC effects, might thus also modulate the interaction of these two processes. To answer these questions, we investigated 40 young and pain-free subjects (20 female and 20 male). The conditioning stimulus in our DNIC paradigm was realized by immersion of the hand into a water tub containing either 42 degrees C (non-painful heat) or 46 degrees C (painful heat) hot water. The test stimuli were either single pulses or series of five pulses (0.5 Hz repetition frequency) produced by a pressure algometer. The VAS ratings for the last stimulus in the series were significantly higher than for the single pulse (temporal summation). The ratings were significantly reduced by the 42 degrees C conditioning stimulus and even more by the 46 degrees C conditioning stimulus, suggesting DNIC-like inhibition. This was equally true both for the single pulse and for the series of pulses. Sex differences were not observed for temporal summation, DNIC inhibition or for the interaction of the two processes, although women exhibited significantly lower pressure pain thresholds and higher ratings for the tonic heat stimuli. In conclusion, DNIC-type inhibition apparently does not preferentially act on a sensitised pain system after slow temporal summation. Considering the sex of the subjects does not change this insight.