Showing papers on "Summation published in 2006"
TL;DR: The extent of TS induced by both paradigms was found to be associated with anxiety level and pain catastrophizing, and the many similarities suggest that the two represent a similar physiological process, even if not precisely the same.
Abstract: Temporal summation (TS) is usually evoked by repetitive mechanical or electrical stimuli, and less commonly by tonic heat pain. The present study aimed to examine the TS induction by repetitive-phasic versus tonic heat pain stimuli. Using 27 normal volunteers, we compared the extent of summation by three calculation methods: start-to-end pain rating difference, percent change, and double-logarithmic regression of successive ratings along the stimulation. Subjects were tested twice, and the reliability of each of the paradigms was obtained. In addition, personality factors related to pain catastrophizing and anxiety level were also correlated with the psychophysical results. Both paradigms induced significant TS, with similar increases for the repetitive-phasic and the tonic paradigms, as measured on 0-100 numerical pain scale (from 52.9+/-11.7 to 80.2+/-15.5, p<0.001; and from 38.5+/-13.3 to 75.8+/-18.3, p<0.001, respectively). The extent of summation was significantly correlated between the two paradigms, when calculated by absolute change (r=0.543, p=0.004) and by regression (r=0.438, p=0.025). Session-to-session variability was similar for both paradigms, relatively large, yet not biased. As with other psychophysical parameters, this poses some limitations on TS assessment in individual patients over time. The extent of TS induced by both paradigms was found to be associated with anxiety level and pain catastrophizing. Despite some dissimilarity between the repetitive-phasic and the tonic paradigms, the many similarities suggest that the two represent a similar physiological process, even if not precisely the same. Future clinical applications of these tests will determine the clinical relevance of the TS paradigms presented in this study.
159 citations
TL;DR: This work has proposed a novel technique of noninvasive transcutaneous electrical stimulation of trigeminal and somatic pain transmission in humans using laser and contact heat evoked pain‐related potentials.
Abstract: Background.—Electrophysiological techniques such as laser and contact heat evoked pain-related potentials are very useful for studying trigeminal and somatic pain transmission in humans. These methods are, however, partly invasive, expensive, and therefore not available for broad clinical use. We recently proposed a novel technique of noninvasive transcutaneous electrical stimulation.
Objective.—To elicit pain-related evoked potentials (PREP) by using a concentric planar electrode and demonstrate their nociceptive specificity.
Methods.—We registered PREP following stimulation of the forehead and hand in 14 healthy volunteers. Latencies, peak-to-peak amplitudes, and conduction velocities of nociceptive fibers have been estimated. Effects of temporal and spatial summation and of cutaneous anesthesia were evaluated.
Results.—Stimulation with the concentric planar electrode produced pinprick-like painful sensation. Cutaneous anesthesia led to abolishment of PREP responses. Estimated mean conduction velocity was 11.61 ± 5.12 m/s, which corresponded well with conduction via A-delta fibers. Spatial as well as temporal summation resulted in a parallel increase of perceived pain intensity and PREP amplitudes.
Conclusion.—The technique is noninvasive, affordable, and easy to perform and allows quantitative assessment of human nociceptive pathways.
120 citations
TL;DR: T Stellate cells fired action potentials in response to even slow depolarizations, showing that their integration window was unlimited so that temporal summation in these cells is limited by the time course of synaptic potentials.
92 citations
TL;DR: It is found that neural summation should greatly increase M. genalis's visual reliability, and predicted spatial summation closely matches the morphology of laminal neurons believed to mediate such summation.
72 citations
TL;DR: In this article, the authors evaluated changes in temporal summation of pressure pain after induction of delayed onset muscle soreness (DOMS) of the trapezius muscle using a computer-controlled algometer.
Abstract: Temporal summation of muscle pain is an important factor in musculoskeletal pain as central integration of repetitive nociceptive input can be facilitated in musculoskeletal pain patients. The aim of this study is to evaluate changes in temporal summation of pressure pain after induction of delayed onset muscle soreness (DOMS) of the trapezius muscle. Sixteen healthy volunteers participated in the study. Temporal summation of pain was induced by sequential pressure stimulation by a computer-controlled algometer. Sequential stimulation consisting of ten stimuli (at pressure pain threshold intensity) was applied over the trapezius muscle. Stimulus duration was 1 s and inter-stimulus intervals (ISI) were 1, 5, 10, and 30 s, respectively. The pain was rated on a continuous visual analogue scale (VAS, 10 cm) after each stimulus and normalised to the VAS score from the first stimulus. DOMS was induced in the right trapezius muscle by eccentric shoulder exercises while the left trapezius muscle served as control. Temporal summation of pressure evoked pain was measured before and 24 h after the exercise. At 24 h after exercise, soreness intensity during shoulder elevation was 3.7±0.2 cm, while no soreness was observed on the control side. When sequential pressure stimulation was applied to the DOMS muscle, VAS scores for 1 s ISI progressively increased to a higher level than before exercise (VAS increase for the last stimulus: 0.8±0.2 cm vs. 0.6±0.1 cm, P<0.05), while VAS scores for ISI 5, 10, and 30 s were not increased. On the control side, significant increases in VAS scores was observed for all ISIs but not affected by contralateral DOMS. Facilitation of temporal summation for 1 s ISI indicated that DOMS may increase the central excitability besides involving peripheral sensitisation. During DOMS there was no potential for further nociceptor sensitisation by repeated noxious pressure stimuli, which may account for the diminishment of temporal summation evoked by pressure stimuli with ISI 5, 10, and 30 s. These data indicate that muscle soreness might facilitate the central components of temporal summation to mechanical stimulation.
66 citations
TL;DR: The spatial summation properties of visual signals were analyzed for geniculocortical afferents in the primary visual cortex of anesthetized paralyzed macaque monkeys, arguing for distinct mechanisms of action for contrast-dependent modulation in cortical and subcortical responses.
Abstract: The spatial summation properties of visual signals were analyzed for geniculocortical afferents in the primary visual cortex (V1) of anesthetized paralyzed macaque monkeys. Afferent input responses were recorded extracellularly during cortical inactivation through superfusion of the cortex with muscimol, allowing investigation of lateral geniculate nucleus of the thalamus (LGN) cell properties in the absence of cortical feedback. Responses from afferent inputs were classified as magno-, parvo-, or koniocellular based on anatomical organization within the cortex, established through histological reconstructions, and visual response wavelength sensitivity. More than 80% of afferents showed strong surround suppression [suppression index (SI) >0.5] and 14% showed negligible surround suppression (SI < 0.2). Afferent responses with weak and strong surround suppression were found throughout cortical input layers 4C and 4A. High-contrast estimates of the spatial extent of the classical surround were similar to the nonclassical surround. The classical and nonclassical surrounds were, on average, 1.5-fold larger than the excitatory center. Unlike neurons within V1, the spatial extent of excitatory summation for geniculocortical afferents was contrast invariant. Nonclassical surround suppression showed slight contrast dependency with estimates larger (20%) at lower contrasts and stronger at higher contrasts (13%). Surround suppression is inherent in cortical input responses and likely derives from lateral inhibition in either the LGN or retina. Although surround suppression within afferent responses increases slightly with contrast, the spatial spread of excitation remains fixed with contrast. This argues for distinct mechanisms of action for contrast-dependent modulation in cortical and subcortical responses.
57 citations
TL;DR: Psychophysical evidence that reliable WU(SP) can be elicited with an advanced pulse design by using a computerized heat-foil/Peltier thermode is obtained, thereby providing an efficient psychophysical test of this phenomenon.
52 citations
TL;DR: Naloxone inhibited the endogenous pain inhibitory systems activated by the spatial summation model, suggesting that these systems have an opioid-mediated component, as previously reported for diffuse noxious inhibitory controls.
49 citations
TL;DR: It is concluded that cortical pooling by multiple spatial mechanisms can account for perimetric spatial summation, whereas probability summation across ganglion cells cannot.
Abstract: Contemporary models of perimetric sensitivity assume probability summation of retinal ganglion cell sensitivities, ignoring cortical processing. To assess the role of cortical processing in perimetric spatial summation, we used a common form of multiple-mechanism spatial vision model in which the stimulus is sampled by receptive fields analogous to those of simple cells in primary visual cortex. Psychophysical threshold was computed by probability summation across the receptive fields. When the receptive fields were nonoriented (like ganglion cells), the spatial summation function had a large nonmonotonic transitional region that was inconsistent with perimetric spatial summation data. When the receptive fields were orientation tuned (like cortical cells), the model was able to give good fits to perimetric spatial summation data. The predictions of the model were evaluated with a masking study, in which noise masks either enlarged the critical area or changed the shape of the spatial summation functions. We conclude that cortical pooling by multiple spatial mechanisms can account for perimetric spatial summation, whereas probability summation across ganglion cells cannot.
48 citations
TL;DR: The results suggest that SS and SD are mutually exclusive functions of the nociceptive systems, and C and A&dgr; nocICEptors are probably similarly involved in these functions.
Abstract: The aims of this study were to explore: (a) the interrelation between spatial summation (SS) and spatial discrimination (SD) of pain, (b) whether the two phenomena are subserved by different sensory channels. SS and SD of pain were measured with contact heat stimuli delivered at slow (0.50 °C/s) and fast (40 °C/s) rise times. Pressure nerve block of the radial nerve was employed to assess whether differential activation of C and Aδ fibers is obtained by these different rates of rise. Two discrete stimuli (each 3 × 3 cm) were applied to the forearm with separation distances between them varying from 0 to 30 cm. A single stimulus or two applied simultaneously were employed. For each distance heat-pain threshold (HPT) and suprathreshold pain ratings were obtained and subjects were asked to report the number of pain spots perceived (SD). SS of HPT occurred at separations smaller than 10 cm whereas significant SD occurred only from a separation of 10 cm and up. SS of suprathreshold sensations was completely accounted for by threshold changes. Stimulation rate did not affect SS or SD. Following nerve block, thresholds obtained with the fast rise stimulation increased significantly (HPT rose from 46.2 to 50.5 °C) but those obtained with slow rise stimuli were not affected by the block, indicating that C and Aδ fibers were activated selectively. The results suggest that: (a) SS and SD are mutually exclusive functions of the nociceptive systems, (b) C and Aδ nociceptors are probably similarly involved in these functions.
48 citations
TL;DR: This work presents rigorous computational support for the hypothesis that receptive field phenomena in V1 largely result from local short-range cortical connections and lateral geniculate nucleus input, and investigates the neural mechanisms of surround suppression and receptive field expansion at low contrast.
Abstract: Neural mechanisms of extraclassical receptive field phenomena in V1 are commonly assumed to result from long-range lateral connections and/or extrastriate feedback. We address two such phenomena: surround suppression and contrast dependent receptive field size. We present rigorous computational support for the hypothesis that the phenomena largely result from local short-range (< 0.5 mm) cortical connections and LGN input. Surround suppression in our simulations results from (A) direct cortical inhibition or (B) suppression of recurrent cortical excitation, or (C) action of both these mechanisms simultaneously. Mechanisms B and C are substantially more prevalent than A. We observe an average growth in the range of spatial summation of excitatory and inhibitory synaptic inputs for low contrast. However, we find this is neither sufficient nor necessary to explain contrast dependent receptive field size, which usually involves additional changes in the relative gain of these inputs.
TL;DR: Dendritic location-dependent differential modulation of coincidence detection and temporal integration by neuronal activity represents a form of activity-dependent and domain-specific plasticity in the function of dendritic information processing.
Abstract: Two major aspects of dendritic integration, coincidence detection and temporal integration, depend critically on the spatial and temporal properties of the dendritic summation of synaptic inputs. Neuronal activity capable of inducing synaptic long-term potentiation (LTP) leads to increased linearity of the spatial summation of synchronous EPSPs. Whether such activity can also modulate the temporal summation of EPSPs is unknown. In the present study, we examined the linearity of the summation of EPSPs spaced by different time intervals in hippocampal CA1 pyramidal neurons, before and after LTP induction. We found that LTP induction resulted in an increased linearity of summation of the potentiated input with another synchronous or asynchronous input, with a striking dendritic location specific selectivity for the timing of the summed inputs. At distal dendrites, LTP induction led to an increased linearity of summation only for EPSPs arriving within 5 ms, thus favoring the summation of coincident inputs. In contrast, LTP induction at proximal dendrites increased the linearity of summation for EPSPs arriving within a time window of > 20 ms. Furthermore, for synaptic inputs at the distal dendrite, enhanced spiking output after LTP induction was observed only for coincidently summed EPSPs, suggesting facilitated coincidence detection. In contrast, for proximal inputs, enhanced spiking output after LTP induction occurred for EPSPs arriving within a broader time window of similar to 20 ms, favoring temporal integration. Such dendritic location-dependent differential modulation of coincidence detection and temporal integration by neuronal activity represents a form of activity-dependent and domain-specific plasticity in the function of dendritic information processing.
TL;DR: The results suggest that the integration of individual synaptic inputs within the neural circuit operates with some redundancy, which might help the postsynaptic neuron to encode in a highly robust way the direction and the velocity of self-motion of the animal.
Abstract: In the brain, sensory information needs often to be read out from the ensemble activity of presynaptic neurons. In the most basic case, this may be accomplished by an individual postsynaptic neuron. In the visual system of the blowfly, an identified motion-sensitive spiking neuron is known to be postsynaptic to an ensemble of graded-potential presynaptic input elements. Both the presynaptic and postsynaptic neurons were shown previously to be capable of representing the velocity of preferred-direction motion reliably and linearly over a large frequency range of velocity fluctuations. Accordingly, the synaptic transfer properties of the connecting excitatory synapses between individual input elements and the postsynaptic neuron were shown to be linear over a similar range of presynaptic membrane potential fluctuations. It was not known, however, how the postsynaptic neuron integrates and reads out the presynaptic ensemble activity. We were able to compare the response properties of the integrating cell before and after eliminating individual presynaptic elements by a laser ablation technique. For most of the input elements, we found that their elimination strongly affected the activity of the postsynaptic neuron but did not degrade its performance to encode motion with constant and time-varying velocity. Our results suggest that the integration of individual synaptic inputs within the neural circuit operates with some redundancy. This feature might help the postsynaptic neuron to encode in a highly robust way the direction and the velocity of self-motion of the animal.
TL;DR: The nature of the spatial summation is consistent with the interpretation that early AMD produces a decrease in cone input to post-receptoral mechanisms in the absence of neural remodelling.
Abstract: We develop the logic for a stimulus that can evaluate cone-dependent spatial summation and detail the modelling and interpretation of thresholds obtained with this stimulus. Fifteen observers participated, including two young normals tested extensively in control experiments, and a clinical trial based on four observers with age-related macular degeneration (AMD), four age-similar controls and five young observers. Monocular spatial summation functions were measured with contrast-modulated Gabor targets that approximated the optimal visual contrast detector. Thresholds were returned from a yes/no adaptive psychophysical algorithm. By fine titration along the size domain it was demonstrated that the spatial summation of normal observers can be adequately described by a two-component model. A reduced set of variables are proposed for clinical applications and the model was applied to data derived using these variables in persons with AMD and age-similar controls. We do not find a significant age-related loss of contrast sensitivity in our normal group. On the other hand, persons with early AMD exhibited a 0.41 log unit loss of sensitivity (P=0.04) from age-similar controls, without any change in their maximum summation area (Amax). The nature of the spatial summation is consistent with the interpretation that early AMD produces a decrease in cone input to post-receptoral mechanisms in the absence of neural remodelling.
TL;DR: The NMDA receptors of tectal neurons can be activated by an intense burst discharge of an individual ganglion cell (likely darkness detector) at physiological conditions and causes a higher level of activity of tECTal neuron network.
TL;DR: It is concluded that both ISO and NE enhance the inhibitory synaptic transmission in the rat SG neurons and their interaction is additive, suggesting that ISO may add to the analgesic action of N2O at the spinal cord dorsal horn level.
Abstract: Volatile inhaled anesthetics and nitrous oxide (N2O) are often used together in clinical practice to produce analgesia. Because the analgesic effect of N2O is, at least in part, mediated by norepinephrine (NE) release in the spinal cord, we examined the interaction between isoflurane (ISO) and NE in the adult rat spinal cord with respect to central nociceptive information processing. The effects of clinically relevant concentrations of ISO (1 MAC) and NE (20 microM) on spontaneous inhibitory transmission in substantia gelatinosa (SG) neurons were examined using the blind whole-cell patch-clamp method. ISO prolonged the decay time and increased the total charge transfer of spontaneous inhibitory postsynaptic currents. NE increased the frequency and mean amplitude of inhibitory postsynaptic currents and the charge transfer as well. Coapplication of both drugs led to an additive increase of the charge transfer and frequent temporal summation of inhibitory postsynaptic currents. We conclude that both ISO and NE enhance the inhibitory synaptic transmission in the rat SG neurons and their interaction is additive, suggesting that ISO may add to the analgesic action of N2O at the spinal cord dorsal horn level.
TL;DR: The results showed that the majority of investigated neurons changed their response patterns with gradual increase of applied stimulus size, and it is suggested that such complex spatial organization of the RF provides the neurophysiological basis for central integration processing of the visual information.
Abstract: The spatial summation in receptive fields (RF) of single neurons in cat's extrastriate area 21a was investigated as a basic neurophysiological substrate for central integration processing of visual information. The results showed that the majority of investigated neurons changed their response patterns with gradual increase of applied stimulus size. In approximately 82% of cases the suppression of neuron discharges was observed when the length of the moving strip exceeded that of the RF. In some neurons the increased size of the moving stimulus leads to the changes in the RF substructure. Receptive fields of neurons recorded at the same microelectrode penetration depth showed a great variety of RF superpositions distributed in a spatially asymmetric manner. As a result, every single RF consists of multiple sub-regions within the RF, differing from each other by the number of superimposed RF-s (density factor). We suggest that such complex spatial organization of the RF provides the neurophysiological basis for central integration processing of the visual information.
TL;DR: Psychophysical results from a motion-impaired stroke patient, WB, whose pattern of deficits over time reveals a systematic shift in spatial scale for processing speed, support the recruitment of high-level visual mechanisms in cases where lower-level function is impaired and suggest that spatial summation may provide an important avenue for investigating functional recovery in patients following damage to visually responsive cortex.
Abstract: Successive stages of cortical processing encode increasingly more complex types of information. In the visual motion system this increasing complexity, complemented by an increase in spatial summation, has proven effective in characterizing the mechanisms mediating visual perception. Here we report psychophysical results from a motion-impaired stroke patient, WB, whose pattern of deficits over time reveals a systematic shift in spatial scale for processing speed. We show that following loss in sensitivity to low-level motion direction WB's representation of speed shifts to larger spatial scales, consistent with recruitment of intact high-level mechanisms. With the recovery of low-level motion processing WB's representation of speed shifts back to small spatial scales. These results support the recruitment of high-level visual mechanisms in cases where lower-level function is impaired and suggest that, as an experimental paradigm, spatial summation may provide an important avenue for investigating functional recovery in patients following damage to visually responsive cortex.
20 Mar 2006
01 Apr 2006
TL;DR: In this article, the authors developed the logic for a stimulus that can evaluate cone-dependent spatial summation and detail the modelling and interpretation of thresholds obtained with this stimulus, which is consistent with the interpretation that early AMD produces a decrease in cone input to post-receptoral mechanisms in the absence of neural remodelling.
Abstract: Background: We develop the logic for a stimulus that can evaluate cone-dependent spatial summation and detail the modelling and interpretation of thresholds obtained with this stimulus. Methods: Fifteen observers participated, including two young normals tested extensively in control experiments, and a clinical trial based on four observers with age related macular degeneration (AMD), four age-similar controls and five young observers. Monocular spatial summation functions were measured with contrast-modulated Gabor targets that approximated the optimal visual contrast detector. Thresholds were returned from a yes/no adaptive psychophysical algorithm. By fine titration along the size domain it was demonstrated that the spatial summation of normal observers can be adequately described by a two-component model. A reduced set of variables are proposed for clinical applications and the model was applied to data derived using these variables in persons with AMD and age-similar controls. Results: We do not find a significant age-related loss of contrast sensitivity in our normal group. On the other hand, persons with early AMD exhibited a 0.41 log unit loss of sensitivity (P=0.04) from age-similar controls, without any change in their maximum summation area (Amax).
Conclusions: The nature of the spatial summation is consistent with the interpretation that early AMD produces a decrease in cone input to post-receptoral mechanisms in the absence of neural remodelling.
TL;DR: This study tested the hypothesis that the pain threshold to electrical stimuli is increased as a result of distraction using a ReliefBand, and found that it was increased during distraction with ReliefBand.
Abstract: Background: Pain is recognized as a cognitive phenomenon, which involves the processing of information. Given that human information processing is largely restricted to a number of simultaneous tasks, many interventions and techniques have been used to modify pain perception by distracting the cognitive processing of pain. This study tested the hypothesis that the pain threshold to electrical stimuli is increased as a result of distraction using a ReliefBand. Methods: Twenty volunteers were enrolled in this study. After attaching surface electrode to the medial plantar nerve territory of left foot, electrical stimuli were delivered to obtain baseline pain threshold and temporal summation threshold. After 15 minutes, while distracting with ReliefBand, the same parameters were obtained. Results: Pain threshold and temporal summation threshold before distraction were 7.9 2.2 mA and 7.0 2.1 mA respectively. During distraction pain threshold and temporal summation threshold were increased to 9.0 2.4 mA and 7.8 2.2 mA respectively. Conclusions: Pain and temporal summation threshold to electrical stimuli were increased during distraction with ReliefBand. Although we applied a technique with weak distracting ability, this distracted the processing of pain perception significantly. Further research about various distraction technique will be required.
Dissertation•
31 May 2006
TL;DR: Preliminary assessment indicates that focal glaucomatous defects detected by standard automated perimetry are replicated by the new MDT.
Abstract: This thesis describes the development of a multi-location motion displacement test (MDT) for the early detection of glaucoma. The test uses line displacement stimuli, which are orientated with the retinal nerve fibre layer (RNFL) and scaled with ganglion cell density. Psychophysical properties of hyperacuity motion displacement were explored and results applied to optimize the stimulus presentation and test format. Investigations included the following: (i) Optical blur: MDT was found to be robust to peripheral astigmatism. The effect of spherical blur was quantified and the implication for discrimination between glaucoma and normal discussed. (ii) Spatial summation properties: equivalent MDT thresholds were demonstrated for equivalent length of single and multi-line stimuli. Equivalent MDT thresholds were also found for stimuli of equivalent energy ( stimulus area * stimulus luminance - background luminance ), in accordance with Ricco's Law. A linear relationship (slope 0.5) was found between log MDT threshold and log relative stimulus energy. A new law is proposed to apply to MDT summation properties, giving the relationship T = KVE T = MDT threshold K = constant E = stimulus energy . This may be used to predict MDT threshold for different configurations of stimuli. (iii) Shortening of response time was observed as stimulus duration is reduced and explained by altered temporal summation properties. The results were applied to modify the subject response window, with benefit of reduced test duration. (iv) Selection of stimulus number and position was made by study of attention, together with application of the anatomical relationship of the RNFL with the optic nerve head. (v) A staircase strategy was developed. Parameters were selected by analysis of results gained within the PhD and earlier studies. Results were pooled to accomplish an operational test. Preliminary assessment indicates that focal glaucomatous defects detected by standard automated perimetry are replicated by the new MDT.
TL;DR: The spatial summation effect on pedestals with difference luminance was investigated to measure the target contrast threshold at different target sizes (spatial summation curve) and pedestal luminance and found that the size and the luminance effects on target detection are separable.
Abstract: We investigated the spatial summation effect on pedestals with difference luminance. The targets were luminance modulation defined by Gaussian functions. The size of the Gaussian spot was determined by the scale parameter (standard deviation, σ) which ranged from 0.13° to 1.04°. The local luminance pedestal (2° radius) had mean luminance ranged from 2.9 to 29cd/m 2 . The no-pedestal condition had a mean luminance 58cd/m 2 . We used a QUEST adaptive threshold seeking procedure and 2AFC paradigm to measure the target contrast threshold at different target sizes (spatial summation curve) and pedestal luminance. The target threshold decreased as the target spatial extent increased with a slope -0.5 on log-log coordinates. However, if the target size was large enough (σ>0.3°), there was little, if any, threshold reduction as the target size further increased. The spatial summation curve had the same shape at all pedestal luminance levels. The effect of the pedestal was to shift the summation curve vertically on log-log coordinates. Hence, the size and the luminance effects on target detection are separable. The visibility of the Gaussian spot can be modeled by a function with a form f(L)*g(σ) where f(L) is a function of local luminance and g(σ) is a function of size.