Showing papers on "Summation published in 2021"
TL;DR: In this article, the authors describe the spatial summation of pain as a function of the size or distance of a stimulated area(s) and test how this function is shaped by the intensity and SSp test paradigm.
Abstract: When nociceptive stimulation affects a larger body area, pain increases. This effect is called spatial summation of pain (SSp). The aim of this study was to describe SSp as a function of the size or distance of a stimulated area(s) and to test how this function is shaped by the intensity and SSp test paradigm. Thirty-one healthy volunteers participated in a within-subject experiment. Participants were exposed to area-based and distanced-based SSp. For area-based SSp, electrocutaneous noxious stimuli were applied by up to 5 electrodes (5 areas) forming a line-like pattern; for distance-based SSp, the same position and lengths of stimuli were used but only 2 electrodes were stimulated. Each paradigm was repeated using pain of low, moderate, and high intensity. It was found that the pattern of pain intensity followed a logarithmic (power) rather than a linear function. The dynamics of the pain increase were significantly different across pain intensities, with more summation occurring when pain was perceived as low. Results indicated that area-based SSp is more painful than distance-based SSp when low and moderate but not when high pain intensity is induced. Presented findings have important implications for all studies in which the spatial dimension of pain is measured. When the area or separation between nociceptive stimulation increases, pain does not increase linearly and the pattern of the pain increase is a result of the interaction between intensity and the number of nociceptive sites. A power function should be considered when predicting the size of a nociceptive source.
9 citations
TL;DR: In this article, the integration and population coding of higher-order stimuli in the somatosensory and visual cortices of awake mice were investigated using two-photon calcium imaging across cortical layers.
Abstract: How cortical circuits build representations of complex objects is poorly understood. Individual neurons must integrate broadly over space, yet simultaneously obtain sharp tuning to specific global stimulus features. Groups of neurons identifying different global features must then assemble into a population that forms a comprehensive code for these global stimulus properties. Although the logic for how single neurons summate over their spatial inputs has been well explored in anesthetized animals, how large groups of neurons compose a flexible population code of higher-order features in awake animals is not known. To address this question, we probed the integration and population coding of higher-order stimuli in the somatosensory and visual cortices of awake mice using two-photon calcium imaging across cortical layers. We developed a novel tactile stimulator that allowed the precise measurement of spatial summation even in actively whisking mice. Using this system, we found a sparse but comprehensive population code for higher-order tactile features that depends on a heterogeneous and neuron-specific logic of spatial summation beyond the receptive field. Different somatosensory cortical neurons summed specific combinations of sensory inputs supra-linearly, but integrated other inputs sub-linearly, leading to selective responses to higher-order features. Visual cortical populations employed a nearly identical scheme to generate a comprehensive population code for contextual stimuli. These results suggest that a heterogeneous logic of input-specific supra-linear summation may represent a widespread cortical mechanism for the synthesis of sparse higher-order feature codes in neural populations. This may explain how the brain exploits the thalamocortical expansion of dimensionality to encode arbitrary complex features of sensory stimuli.
8 citations
TL;DR: The current experiment showed that spatial summation of pain behaves similarly for electrocutaneous and mechanical stimuli.
Abstract: Spatial acuity measured by 2-point discrimination (2PD) threshold and spatial summation of pain (SSp) are useful paradigms to probe the pain system in humans. Whether the results of these paradigms are influenced by different stimulus modalities and intensities is unclear. The aim of this study was to test 2PD controlling the stimulus modality and the intensity and to investigate the effect of modality on SSp. Thirty-seven healthy volunteers were tested for 2PDs with 2 stimulus modalities (electrocutaneous and mechanical) and intensity (noxious and innocuous). For each condition, participants received stimuli to either 1 or 2 points on their lower back with different distances (2-14 cm, steps of 2 cm). It was found that 2PDs were significantly smaller for noxious stimuli for both modalities. By contrast, between-modality comparison reproduced previous reports of impaired acuity for noxious stimulation. Higher pain intensities were reported when a larger area was stimulated (SSp), independent of the modality. Furthermore, reported pain intensities were higher when the distance between 2 stimulated areas was increased from 2 to 6 cm (P < 0.001), 8 cm (P < 0.01), and 14 cm (P < 0.01). 2PDs determined by mechanical and electrocutaneous stimuli were significantly correlated within both stimulus intensities, ie, innocuous (r = 0.34, P < 0.05) and noxious (r = 0.35, P < 0.05). The current results show 3 novel findings: (1) the precision of the pain system might be higher than in the innocuous (tactile) system when mechanical and electrocutaneous modalities are used, (2) the pattern of distance-based and area-based SSp seems to be comparable irrespective of the modality applied (mechanical and electrocutaneous), and (3) both modalities are moderately correlated.
6 citations
TL;DR: In this article, the authors show that full-field threshold vision is more sensitive than at absolute threshold, requiring the absorption of ~1000 photons across ~91.96 million rods.
6 citations
TL;DR: In this article, the authors show that the difference in PP efficacy varies substantially as a function of presynaptic firing rate and demonstrate that postsynaptic response of CA1 and CA2 pyramidal neurons to naturalistic firing displays contrasting temporal dynamics, which depends on the activation of NMDARs.
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.
5 citations
TL;DR: In this paper, the effect of affective touch on the temporal summation of second pain (TSSP) was investigated in patients with chronic pain, and it was found that AT brought about a decrease of participants' pain as opposed to both discriminative touch and no touch.
3 citations
28 Apr 2021
TL;DR: In this paper, the authors presented a method to use the electrotactile display at a lower threshold by applying two sub-threshold stimuli placed nearby, which is tested on fourteen subjects over a frequency range from 20 to 1280 Hz in the tuning curve.
Abstract: Electrotactile displays provide tactile feedback using electrical currents. However, prolonged usage of them causes skin irritation and burns. This study presents a novel method to use the electrotactile display at a lower threshold by applying two subthreshold electrotactile stimuli placed nearby. This method is tested on fourteen subjects over a frequency range from 20 to 1280 Hz in the tuning curve. Two Psychophysical experiments have been conducted to measure their thresholds for individual stimuli and presented together. In the first experiment, the frequencies of both the stimuli were the same, and it showed 36% to 18% reduction in EPT of the second stimulus when the first stimulus was at 10% to 50% of its threshold. In the second experiment, Meissner and Pacinian were selectively stimulated by applying stimuli at their resonant frequencies (30 and 250 Hz, respectively), results showed slightly more reduction in the case of 250 Hz compared to 30 Hz.
3 citations
TL;DR: Findings suggested that music listening could strengthen components of the inhibitory descending pain pathways operating at the dorsal spinal cord level.
Abstract: Passive music listening has shown its capacity to soothe pain in several clinical and experimental studies. This phenomenon—known as music-induced analgesia—could partly be explained by the modulation of pain signals in response to the stimulation of brain and brainstem centers. We hypothesized that music-induced analgesia may involve inhibitory descending pain systems. We assessed pain-related responses to endogenous pain control mechanisms known to depend on descending pain modulation: peak of first pain (PP), temporal summation (TS), and diffuse noxious inhibitory control (DNIC). Twenty-seven healthy participants (14 men, 13 women) were exposed to a conditioned pain modulation paradigm during a 20-minute relaxing music session and a silence condition. Pain was continually measured with a visual analogue scale. Pain ratings were significantly lower with music listening (p < .02). Repeated measures ANOVA indicated significant differences between conditions within PP and TS (p < .05) but not in DNIC. Those findings suggested that music listening could strengthen components of the inhibitory descending pain pathways operating at the dorsal spinal cord level.
2 citations
TL;DR: In this article, the authors used GEVIs to identify areas of brain slices in which the neuropil was in a sustained depolarization (plateau), long after the stimulus onset.
Abstract: In a typical electrophysiology experiment, synaptic stimulus is delivered in a cortical layer (1-6) and neuronal responses are recorded intracellularly in individual neurons. We recreated this standard electrophysiological paradigm in brain slices of mice expressing genetically encoded voltage indicators (GEVIs). This allowed us to monitor membrane voltages in the target pyramidal neurons (whole-cell), and population voltages in the surrounding neuropil (optical imaging), simultaneously. Pyramidal neurons have complex dendritic trees that span multiple cortical layers. GEVI imaging revealed areas of the brain slice that experienced the strongest depolarization on a specific synaptic stimulus (location and intensity), thus identifying cortical layers that contribute the most afferent activity to the recorded somatic voltage waveform. By combining whole-cell with GEVI imaging, we obtained a crude distribution of activated synaptic afferents in respect to the dendritic tree of a pyramidal cell. Synaptically evoked voltage waves propagating through the cortical neuropil (dendrites and axons) were not static but rather they changed on a millisecond scale. Voltage imaging can identify areas of brain slices in which the neuropil was in a sustained depolarization (plateau), long after the stimulus onset. Upon a barrage of synaptic inputs, a cortical pyramidal neuron experiences: (a) weak temporal summation of evoked voltage transients (EPSPs); and (b) afterhyperpolarization (intracellular recording), which are not represented in the GEVI population imaging signal (optical signal). To explain these findings [(a) and (b)], we used four voltage indicators (ArcLightD, chi-VSFP, Archon1, and di-4-ANEPPS) with different optical sensitivity, optical response speed, labeling strategy, and a target neuron type. All four imaging methods were used in an identical experimental paradigm: layer 1 (L1) synaptic stimulation, to allow direct comparisons. The population voltage signal showed paired-pulse facilitation, caused in part by additional recruitment of new neurons and dendrites. "Synaptic stimulation" delivered in L1 depolarizes almost an entire cortical column to some degree.
2 citations
TL;DR: In this article, DeRidder burst waveform generated EMG responses under all inter-burst frequencies including temporal summation, deeper fiber recruitment, and compounded action potentials.
Abstract: Background Intraoperative neuromonitoring (IONM) for spinal cord stimulation (SCS) uses electromyography (EMG) responses to determine myotomal coverage as a marker for dermatomal coverage. Objective These responses can be utilized to evaluate the effects of stimulation platforms on the nervous system. Methods Eight patients were tested at inter-burst frequencies of 10 Hz, 20 Hz, 30 Hz, and 40 Hz using DeRidder Burst stimulation to determine the amplitude of onset of post-synaptic signal generation. Three patients had additional data recording amplitude of onset of tonic stimulation prior to and post DeRidder Burst stimulation at each inter-burst frequency. This represented post-synaptic excitability. Results In all patients, the DeRidder Burst waveform generated EMG responses under all inter-burst frequencies including temporal summation, deeper fiber recruitment, and compounded action potentials. There was a non-significant decrease of 7.6-7.8% in amplitudes to generate response under 40 Hz, compared to the other frequencies. However, there was a 73.1% reduction in energy requirements at 10 Hz. The enhanced post-synaptic excitability effect was demonstrated at all frequencies. Conclusion DeRidder Burst has similar effects of temporal summation, deeper fiber recruitment, and compounded action potentials under IONM at 40 Hz, 30 Hz, 20 Hz, and 10 Hz. In addition, the hyperexcitability phenomenon was also observed regardless of the frequency. This demonstrates that postsynaptic responses captured via IONM may be a sensitive biomarker to SCS mechanism of action. In addition, lower inter-burst frequencies may have a similar clinical effect on pain relief thus reducing power consumption even further than current dosing paradigms.
2 citations
TL;DR: In this paper, the spatial characteristics of chromatic mechanisms using stimuli, modulated from an achromatic background to each pole of the “red-green” cardinal axis in DKL space at 20 deg eccentricity, were examined.
Abstract: Green stimuli are more difficult to detect than red stimuli in the retinal periphery, as reported previously. We examined the spatial characteristics of chromatic mechanisms using stimuli, modulated from an achromatic background to each pole of the “red–green” cardinal axis in DKL space at 20 deg eccentricity. The “blue–yellow” cardinal axis was also studied for comparison. By measuring both grating discrimination at the resolution limit (resolution acuity) and spatial summation, assessed by the Michaelis–Menten function, we demonstrated a marked “red–green” asymmetry. The resolution acuity was worse and spatial summation more extended for “green” compared to “red” stimuli, while showing significant individual variations. Ricco’s area was also measured, but not determined for “green” spots because of the poor small stimuli detection. These results cannot be explained by differences in L- and M-cone numerosity and/or spatial arrangement, but rather have postreceptoral origin, probably at the cortical level.
TL;DR: Tempo-spatial integration of electrical noxious stimuli was studied using the nociceptive withdrawal reflex and a perceived intensity as mentioned in this paper, where the Tibialis anterior and biceps femoris muscles were differential...
Abstract: Tempo-spatial integration of electrical noxious stimuli was studied using the nociceptive withdrawal reflex and a perceived intensity. Tibialis anterior and biceps femoris muscles were differential...
23 Mar 2021
TL;DR: Both paradigms were roughly equivalent in the ability to evoke temporal summation (although response to one modality did not predict response to the other), but the TENS paradigm appeared to be less apt to induce a CPM response than the thermode + CPTest paradigm.
Abstract: Background: Temporal summation and conditioned pain modulation (CPM) can be measured using a thermode and cold pressor test (CPTest). Unfortunately, these complex and expensive tools are ill-suited for routine clinical assessments. Aims: We aimed to compare the temporal summation and CPM obtained with the thermode + CPTest paradigm to those obtained with a novel paradigm using transcutaneous electrical nerve stimulation (TENS). Methods: We assessed temporal summation and CPM in 29 healthy participants, using two paradigms (random order): TENS, and thermode + CPTest. In the TENS paradigm, both the conditioning stimulus (CS) and the test stimulus (TS) were delivered using TENS; in the thermode + CPTest paradigm, the CS consisted of a CPTest and the TS was delivered using a thermode. We compared the average temporal summation and CPM evoked by the two paradigms. Results: Average temporal summation was similar for both modalities (P = 0.90), and the number of participants showing temporal summation was similar in both paradigms (19 with thermode vs. 18 with TENS; P = 1.00). Average CPM response was larger following the thermode + CPTest than following the TENS (P = 0.005), and more participants showed CPM with the thermode + CPTest paradigm compared to the TENS paradigm (24 vs. 14; P = 0.01). Conclusions: Both paradigms were roughly equivalent in the ability to evoke temporal summation (although response to one modality did not predict response to the other), but the TENS paradigm appeared to be less apt to induce a CPM response than the thermode + CPTest paradigm.
27 Sep 2021
TL;DR: It is pointed out that the nociceptive system is more accurate than the tactile system when controlling for the stimulus modality and intensity in healthy pain-free individuals and shows that the pattern of distance-based and areabased spatial summation of pain is modality independent.
Abstract: Previous studies investigating spatial acuity measured by two-point discrimination threshold concluded that the nociceptive system is less accurate than the innocuous tactile system. In the discussed article, the authors point out that the nociceptive system is more accurate than the tactile system when controlling for the stimulus modality and intensity in healthy pain-free individuals. Furthermore, this article shows that the pattern of distance-based and areabased spatial summation of pain is modality independent.
TL;DR: In this article, the authors examined whether the CPM effect would be different on pain induced by temporal summation than single stimuli in a group of low back pain patients, and found that repeated pressure pain may be better suited as the test stimuli, than single pressure pain and temporal summary of pressure pain, as the effect in absolute terms was greater.
TL;DR: In this paper, the authors determined the relationship between the temporal pattern of spiking activity of a single thalamic neuron and the degree of cortical activation as well as that between the firing rate of the single neuron and cortical activation.
Abstract: Neuron activity in the sensory cortices mainly depends on feedforward thalamic inputs. High-frequency activity of a thalamic input can be temporally integrated by a neuron in the sensory cortex and is likely to induce larger depolarization. However, feedforward inhibition (FFI) and depression of excitatory synaptic transmission in thalamocortical pathways attenuate depolarization induced by the latter part of high-frequency spiking activity and the temporal summation may not be effective. The spiking activity of a thalamic neuron in a specific temporal pattern may circumvent FFI and depression of excitatory synapses. The present study determined the relationship between the temporal pattern of spiking activity of a single thalamic neuron and the degree of cortical activation as well as that between the firing rate of spiking activity of a single thalamic neuron and the degree of cortical activation. Spiking activity of a thalamic neuron was recorded extracellularly from the lateral geniculate nucleus (LGN) in male Long-Evans rats. Degree of cortical activation was assessed by simultaneous recording of local field potential (LFP) from the visual cortex. A specific temporal pattern appearing in three consecutive spikes of an LGN neuron induced larger cortical LFP modulation than high-frequency spiking activity during a short period. These findings indicate that spiking activity of thalamic inputs is integrated by a synaptic mechanism sensitive to an input temporal pattern.
TL;DR: In this paper, the effects of non-polarized near-infrared ray irradiation on pressure pain threshold, tactile perception threshold and temporal summation were examined in 10 healthy adults.
Abstract: Effects of non-polarized near-infrared ray irradiation on pressure pain threshold, tactile perception threshold and temporal summation were examined. The subjects were 10 healthy adults. All subjects were participated in both irradiation and control groups. The irradiation group, non-polarized near-infrared rays were applied to thenar eminence of non-dominant hand. The control group was not irradiated. Pressure pain threshold, tactile perception threshold and temporal summation were measured before and after irradiation. The pressure pain threshold value showed a significant increase after non-polarized near-infrared ray irradiation in the irradiation group, but the tactile perception threshold and visual analogue scale value reflecting the temporal summation did not change in the both groups. It was suggested that non-polarized near-infrared ray irradiation increased the pressure pain threshold. On the other hand, it was considered that non-polarized near-infrared ray irradiation does not affect the tactile perception threshold and the temporal summation.