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Showing papers on "Summation published in 2002"


Journal ArticleDOI
TL;DR: Comparing intracortical facilitation of I1‐waves with that of I3‐waves using single motor unit and surface electromyographic recordings from the first dorsal interosseous muscle suggests that summation between excitatory postsynaptic potentials and subliminal depolarization of interneurones elicited by S2 directly produces facilitation.
Abstract: In order to elucidate the mechanisms underlying intracortical I-wave facilitation elicited by paired-pulse magnetic stimulation, we compared intracortical facilitation of I1-waves with that of I3-waves using single motor unit and surface electromyographic (EMG) recordings from the first dorsal interosseous muscle (FDI) We used a suprathreshold first stimulus (S1) and a subthreshold second stimulus (S2) In most experiments, both stimuli induced currents in the same direction In others, S1 induced posteriorly directed currents and S2 induced anteriorly directed currents When both stimuli induced anteriorly directed currents (I1-wave effects), an interstimulus interval (ISI) of 15 ms resulted in extra facilitation of the responses to S1 alone The latency of this effect was equivalent to that of the I2-wave from S1 When S1 evoked posteriorly directed currents (I3-wave recruitment), facilitation occurred at a latency corresponding to the I3-wave from S1 This facilitation occurred at an ISI of 15 ms when both S1 and S2 flowed posteriorly, and at an ISI of approximately 35 ms when S1 was posteriorly and S2 was anteriorly directed Based on these findings, we propose the following mechanisms for intracortical I-wave facilitation When S1 and S2 induce currents in the same direction, facilitation is produced by summation between excitatory postsynaptic potentials (EPSPs) elicited by S1 and subliminal depolarization of interneurones elicited by S2 directly When S1 and S2 induce currents in the opposite direction, facilitation is produced by the same mechanism as above or by temporal and spatial summation of EPSPs elicited by two successive stimuli at interneurones or corticospinal neurones of the motor cortex

196 citations


Journal ArticleDOI
TL;DR: The attenuated amount of spatial summation on the fingertip was interpreted as an indication that the mechanism of temporal summation consists of the operations of both neural integration and probability summation.
Abstract: Thresholds were measured for the detection of vibratory stimuli of variable frequency and duration applied to the index fingertip and thenar eminence through contactors of different sizes. The effects of stimulus frequency could be accounted for by the frequency characteristics of the Pacinian (P), non-Pacinian (NP) I, and NP III channels previously determined for the thenar eminence (Bolanowski et al., J Acoust Soc Am 84 : 1680-1694, 1988; Gescheider et al., Somatosens Mot Res 18: 191- 201, 2001). The effect of changing stimulus duration was also essentially identical for both sites, demonstrating the same amount of temporal summation in the P channel. Although the effect of changing stimulus frequency and changing stimulus duration did not differ for the two sites, the effect of varying the size of the stimulus was significantly greater for the thenar eminence than for the fingertip. The attenuated amount of spatial summation on the fingertip was interpreted as an indication that the mechanism of spatia...

170 citations


Journal Article
TL;DR: Results are inconsistent with the hypothesis that spatially nonlinear (M(y) retinal ganglion cells are the physiological substrate of the frequency-doubling illusion, and other mechanisms that may underlie the illusion are investigated.
Abstract: PURPOSE. The frequency-doubling illusion is an apparent doubling of spatial frequency when a sinusoidal grating is modulated rapidly in temporal counterphase. It has been proposed that the illusion arises from a spatially nonlinear ganglion cell class. The current study reexamines this possibility and investigates other mechanisms that may underlie the illusion. METHODS. Responses of macaque magnocellular (MC) retinal ganglion cells were recorded to counterphase-modulated sinusoidal gratings of various spatial frequencies, and linearity of spatial summation was assessed. Human psychophysical thresholds were measured for a variety of phase discrimination and matching tasks. RESULTS. Consistent with lateral geniculate recordings reported by other authors, no evidence was found of a separate nonlinear (My) MC cell class. The small, spatially nonlinear responses found were least at the low spatial frequencies used in clinical testing. Further analysis showed that no spatially modulated signal can be expected from the nonlinear response of a ganglion cell; the nonlinearity of spatial summation gives a doubled response in time but not across space. Psychophysical performance was consistent with an inability to distinguish the temporal phase of counterphase-modulated gratings when the illusion occurs. From 4 to 40 Hz, the zero-crossings of the modulated sinusoidal grating provided a spatial cue and were matched to comparison patterns at twice the stimulus spatial frequency. CONCLUSIONS. These results are inconsistent with the hypothesis that spatially nonlinear (My) retinal ganglion cells are the physiological substrate of the frequency-doubling illusion. A cortical loss of temporal phase discrimination may be the principle cause of the illusion. (Invest Ophthalmol Vis Sci. 2002;43:3590 –3599) T

157 citations


Journal ArticleDOI
01 May 2002-Pain
TL;DR: The findings indicate that temporal summation of mechanically evoked pain is higher in females compared to males, is stimulation frequency dependent and is centrally mediated.
Abstract: Several studies indicate that females are more sensitive to experimentally induced pain than males. Moreover, it was recently shown that temporal summation of heat pain is greater in females than males, suggesting that central processing of nociceptive input may be upregulated in women. Temporal summation of pain has been examined principally using thermal or electrical stimuli. The purpose of this study was to investigate the temporal summation to noxious mechanical stimulation, and examine gender differences in temporal summation of mechanically evoked pain. A sharp probe was used to apply brief mechanical stimuli on the fingers of ten healthy females and ten healthy males. Trains of ten repetitive stimuli were applied at an intensity of 1.2–1.3× the individual subject's pain threshold, at interstimulus intervals (ISIs) ranging from 1 to 6 s. The same or different skin sites were stimulated in any single train of stimuli. The pain ratings for the fifth as well as the tenth stimulus were significantly higher than those for the first stimulus. Also, the pain responses for the tenth stimulus were higher than those for the fifth. There was no overall gender difference in pain ratings, however, there was a significant trial #×gender interaction. Males and females provided comparable magnitude estimates for the first stimulus in the train, but females provided higher pain ratings than males for the fifth as well as the tenth stimulus. Temporal summation occurred across all ISIs, but shorter ISIs (1–3 s) elicited significantly greater temporal summation than longer ISIs (4–6 s). Finally, although higher pain ratings were obtained when the ten consecutive stimuli were applied on the same versus different skin areas, the degree of temporal summation was not significantly different. These findings indicate that temporal summation of mechanically evoked pain is higher in females compared to males, is stimulation frequency dependent and is centrally mediated.

153 citations


Journal ArticleDOI
TL;DR: The results demonstrate that the sound-evoked spike activity of SBCs reflects the integration of acoustically driven excitatory and inhibitory input, which affects the processing of the spectral, temporal, and intensity cues of acoustic signals.
Abstract: Spherical bushy cells (SBCs) of the anteroventral cochlear nucleus (AVCN) receive their main excitatory input from auditory nerve fibers (ANFs) through large synapses, endbulbs of Held. These cells are also the target of inhibitory inputs whose function is not well understood. The present study examines the role of inhibition in the encoding of low-frequency sounds in the gerbil's AVCN. The presynaptic action potentials of endbulb terminals and postsynaptic action potentials of SBCs were monitored simultaneously in extracellular single-unit recordings in vivo. An input-output analysis of presynaptic and postsynaptic activity was performed for both spontaneous and acoustically driven activity. Two-tone stimulation and neuropharmacological experiments allowed the effects of neuronal inhibition and cochlear suppression on SBC activity to be distinguished. Ninety-one percent of SBCs showed significant neuronal inhibition. Inhibitory sidebands enclosed the high- or low-frequency, or both, sides of the excitatory areas of these units; this was reflected as a presynaptic to postsynaptic increase in frequency selectivity of up to one octave. Inhibition also affected the level-dependent responses at the characteristic frequency. Although in all units the presynaptic recordings showed monotonic rate-level functions, this was the case in only half of the postsynaptic recordings. In the other half of SBCs, postsynaptic inhibitory areas overlapped the excitatory areas, resulting in nonmonotonic rate-level functions. The results demonstrate that the sound-evoked spike activity of SBCs reflects the integration of acoustically driven excitatory and inhibitory input. The inhibition specifically affects the processing of the spectral, temporal, and intensity cues of acoustic signals.

118 citations


Journal ArticleDOI
TL;DR: It is demonstrated that simultaneous activation of both capsaicin-sensitive afferent pathways and αβm-ATP-sensitive/capsaic in-insensitive pathways could generate a temporal summation of excitatory inputs onto single lamina V neurons.
Abstract: Using a spinal cord slice preparation and patch-clamp recordings from spinal cord dorsal horn neurons, we examined excitatory and inhibitory circuits connecting to lamina V neurons after the activation of afferent central terminal vanilloid receptor-1 (VR1) receptors and P2X receptors. We found that single neurons in lamina V often received excitatory inputs from two chemically defined afferent pathways. One of these pathways was polysynaptic from capsaicin-sensitive afferent terminals. In this pathway the capsaicin-sensitive afferent input first activated interneurons in superficial laminas, and then the excitatory activity was transmitted onto lamina V neurons. The second excitatory input was monosynaptic from alpha(beta)m-ATP-sensitive/capsaicin-insensitive afferent terminals. Both capsaicin-sensitive and alpha(beta)m-ATP-sensitive/capsaicin-insensitive pathways also recruited polysynaptic inhibitory inputs to lamina V neurons. Furthermore, we demonstrated that simultaneous activation of both capsaicin-sensitive afferent pathways and alpha(beta)m-ATP-sensitive/capsaicin-insensitive pathways could generate a temporal summation of excitatory inputs onto single lamina V neurons. These convergent pathways may provide a mechanism of sensory integration for two chemically defined sensory inputs and may have implications in different sensory states.

102 citations


Journal ArticleDOI
01 Feb 2002-Pain
TL;DR: The results are a shift of the pain perception curve and a positive relation between the surface stimulated and pain perception and inhibitory mechanisms being fully recruited at the beginning of the session with the immersion of the largest surface area.
Abstract: To study the relation between size of the surface stimulated and perceived pain intensity (spatial summation effect), subjects sequentially immersed predetermined segments of the surface of their arm, between the fingertips and the shoulder, in circulating nociceptive hot water. Immersion sessions were of three types: (i) increasing session (immersion beginning at fingertips and increasing to shoulder); (ii) decreasing session (immersion beginning at shoulder and decreasing to fingertips); and (iii) whole arm+increasing session (preliminary immersion of the whole arm up to shoulder, followed by an increasing session from fingertips to shoulder). Results showed a positive spatial summation effect (pain perception positively correlated to the size of the surface stimulated) during both the decreasing session and the whole arm+increasing session. However, no spatial summation effect was found during the increasing session (fingertips to shoulder). In addition, pain perceived for a surface area was less intense during the decreasing session compared to the increasing session. One possible explanation for the lack of a spatial summation effect during the increasing session is that inhibitory mechanisms are gradually recruited at the same time as excitatory afferences, thus 'cancelling out' any measurable spatial summation effect. The results obtained during the decreasing session and the whole arm+increasing session may be explained by inhibitory mechanisms being fully recruited at the beginning of the session with the immersion of the largest surface area (whole arm). The results are a shift of the pain perception curve and a positive relation between the surface stimulated and pain perception.

95 citations


Journal ArticleDOI
TL;DR: The results indicate that contrast changes in the spatial frequency tuning curves result from spatial reorganization of the receptive field, and a fundamental property of receptive field organization, spatial summation, is not contrast invariant.
Abstract: Previous studies on single neurons in primary visual cortex have reported that selectivity for orientation and spatial frequency tuning do not change with stimulus contrast. The prevailing hypothesis is that contrast scales the response magnitude but does not differentially affect particular stimuli. Models where responses are normalized over contrast to maintain constant tuning for parameters such as orientation and spatial frequency have been proposed to explain these results. However, our results indicate that a fundamental property of receptive field organization, spatial summation, is not contrast invariant. We examined the spatial frequency tuning of cells that show contrast-dependent changes in spatial summation and have found that spatial frequency selectivity also depends on stimulus contrast. These results indicate that contrast changes in the spatial frequency tuning curves result from spatial reorganization of the receptive field.

90 citations


01 Jan 2002
TL;DR: In this paper, the authors investigated the relation between size of the surface stimulated and perceived pain intensity (spatial summation effect), and found a positive relationship between the surface stimulation and pain perception.
Abstract: To study the relation between size of the surface stimulated and perceived pain intensity (spatial summation effect), subjects sequentially immersed predetermined segments of the surface of their arm, between the fingertips and the shoulder, in circulating nociceptive hot water. Immersion sessions were of three types: (i) increasing session (immersion beginning at fingertips and increasing to shoulder); (ii) decreasing session (immersion beginning at shoulder and decreasing to fingertips); and (iii) whole arm 1 increasing session (preliminary immersion of the whole arm up to shoulder, followed by an increasing session from fingertips to shoulder). Results showed a positive spatial summation effect (pain perception positively correlated to the size of the surface stimulated) during both the decreasing session and the whole arm 1 increasing session. However, no spatial summation effect was found during the increasing session (fingertips to shoulder). In addition, pain perceived for a surface area was less intense during the decreasing session compared to the increasing session. One possible explanation for the lack of a spatial summation effect during the increasing session is that inhibitory mechanisms are gradually recruited at the same time as excitatory afferences, thus ‘canceling out’ any measurable spatial summation effect. The results obtained during the decreasing session and the whole arm 1 increasing session may be explained by inhibitory mechanisms being fully recruited at the beginning of the session with the immersion of the largest surface area (whole arm). The results are a shift of the pain perception curve and a positive relation between the surface stimulated and pain perception. q 2002 International Association for the Study of Pain. Published by Elsevier Science B.V. All rights reserved.

78 citations


Journal ArticleDOI
TL;DR: The results suggest that, when few inputs are active, the majority of afferent permutations undergo linear integration, maintaining the importance of individual inputs, however, compartment- and connection-specific nonlinear interactions between synapses located close to each other could increase the computational power of individual neurons in a cell type-specific manner.
Abstract: Theoretical studies predict that the modes of integration of coincident inputs depend on their location and timing. To test these models experimentally, we simultaneously recorded from three neocortical neurons in vitro and investigated the effect of the subcellular position of two convergent inputs on the response summation in the common postsynaptic cell. When scattered over the somatodendritic surface, combination of two coincident excitatory or inhibitory synaptic potentials summed linearly in layer 2/3 pyramidal cells, as well as in GABAergic interneurons. Slightly sublinear summation with connection specific kinetics was observed when convergent inputs targeted closely placed sites on the postsynaptic cell. The degree of linearity of summation also depended on the type of connection, the relative timing of inputs, and the activation state of I h . The results suggest that, when few inputs are active, the majority of afferent permutations undergo linear integration, maintaining the importance of individual inputs. However, compartment- and connection-specific nonlinear interactions between synapses located close to each other could increase the computational power of individual neurons in a cell type-specific manner.

67 citations


Journal ArticleDOI
01 Jul 2002-Pain
TL;DR: Compared to participants without a parental history of hypertension, offspring of individuals with hypertension exhibited significantly higher NFR thresholds, suggesting that risk for hypertension may be associated with enhanced activation of central pain inhibition pathways.
Abstract: Previous evidence indicates that individuals with hypertension and those at increased risk for the disorder exhibit decreased pain perception. To test the hypothesis that attenuation of nociceptive processing in individuals at genetic risk for hypertension is related to differential central modulation of nociceptive transmission, the present study examined descending modulation, alpha-motoneuron excitability, and temporal summation of nociceptive input in young adults with and without a parental history of hypertension. Nociceptive flexion (NFR) and non-nociceptive Hoffman reflexes were assessed at rest and during performance of a mental arithmetic task. Temporal summation was assessed by examining NFR threshold in response to a series of five electrical pulses delivered at 2 Hz. Compared to participants without a parental history of hypertension, offspring of individuals with hypertension exhibited significantly higher NFR thresholds, suggesting that risk for hypertension may be associated with enhanced activation of central pain inhibition pathways.

Journal ArticleDOI
Rob W. Clarke1, S Eves1, John Harris1, J.E Peachey1, E Stuart1 
TL;DR: Activity in fine afferent axons augments the reflexogenic potential of all subsequent afferent input, thereby allowing all afferent drive from the sural field to contribute to withdrawal of the heel.

Journal ArticleDOI
TL;DR: It is clear that if temporal summation is more pronounced in muscle than other tissues then this may be an important factor contributing to pain in musculoskeletal syndromes.
Abstract: This study investigated the phenomenon of temporal summation in response to repetitive focused ultrasound stimulation of skin, muscle and joint in human volunteers. Stimulation was carried out using a customdesigned, focused ultrasonic stimulator with a resonant frequency of 1.66 MHz. A series of stand-off attachments were used to ensure that the focal region of the ultrasound beam projected either cutaneousely, within the distal interphalangeal joint of the index finger, or within the first dorsal interosseous muscle. Stimulation was carried out using single pulses and trains of five pulses of different pulse durations (25 ms, 50 ms, 75 ms, 100 ms), and using single pulses and trains of five pulses (50 ms duration) at different frequencies (0.5 Hz, 1 Hz, 2 Hz, 3 Hz, 4 Hz, 5 Hz). Tactile perception thresholds, pain thresholds and summation pain thresholds were recorded. Temporal summation of pain could be elicited by stimulation of both skin, joint and muscle, although the influence of temporal summation appeared to be more pronounced for muscle stimulation. Muscle stimulation also required greater ultrasound intensity compared with joint and skin stimulation. Temporal summation could not be elicited by tactile, low-intensity stimulation. Focused ultrasound is a potent, noninvasive technique with which to investigate temporal summation from somatic structures. A number of factors may account for the higher intensities required to elicit pain in muscle and the increased rate of temporal summation. It is clear, however, that if temporal summation is more pronounced in muscle than other tissues then this may be an important factor contributing to pain in musculoskeletal syndromes.

Journal ArticleDOI
TL;DR: The TNLI can be used to control the firing variability through inhibition; with 80% inhibition to concurrent excitation, firing at high rates is nearly consistent with a Poisson-type firing variability observed in cortical neurons, illustrating how a hardware-realisable neuron model can capitalise on the unique computational capabilities of biological neurons.

Journal ArticleDOI
TL;DR: The temporal and spatial shift during spatial summation may reflect speeding up of the limbic affective reaction and prefrontal cognitive preparation in impending aversion and is deemed essential for integration of bodily sensations, such as pain.

Journal ArticleDOI
TL;DR: The model elucidates the roles played by spatial summation and coincidence detection, showing how synchronization decreases with an increase in both frequency and spatial spread of inputs and under what conditions an enhancement of synchronization of the output relative to the input takes place.
Abstract: The response of leaky integrate-and-fire neurons is analyzed for periodic inputs whose phases vary with their spatial location. The model gives the relationship between the spatial summation distance and the degree of phase locking of the output spikes (i.e., locking to the periodic stochastic inputs, measured by the synchronization index). The synaptic inputs are modeled as an inhomogeneous Poisson process, and the analysis is carried out in the Gaussian approximation. The model has been applied to globular bushy cells of the cochlear nucleus, which receive converging inputs from auditory nerve fibers that originate at neighboring sites in the cochlea. The model elucidates the roles played by spatial summation and coincidence detection, showing how synchronization decreases with an increase in both frequency and spatial spread of inputs. It also shows under what conditions an enhancement of synchronization of the output relative to the input takes place.

Journal ArticleDOI
TL;DR: Studies ranging from cell culture preparations to humans subjects indicate that the decision of whether a synapse will undergo strengthening or weakening critically depends on the temporal order of presynaptic and postsynaptic activity.
Abstract: Long-term modification of synaptic strength is thought to be the basic mechanism underlying the activity-dependent refinement of neural circuits and the formation of memories engrammed on them. Studies ranging from cell culture preparations to humans subjects indicate that the decision of whether a synapse will undergo strengthening or weakening critically depends on the temporal order of presynaptic and postsynaptic activity. At many synapses, potentiation will be induced only when the presynaptic neuron fires an action potential within milliseconds before the postsynaptic neuron fires, whereas weakening will occur when it is the postsynaptic neuron that fires first. Such processes might be important for the remodeling of neural circuits by activity during development and for network functions such as sequence learning and prediction. Ultimately, this synaptic property might also be fundamental for the cognitive process by which we structure our experience through cause and effect relations.

Journal ArticleDOI
TL;DR: Exitatory inputs are generally superior drivers compared with inhibitory inputs in part because spontaneous activity of a postsynaptic neuron is not required in the case of excitatory drive, and simulations suggest a possible reinterpretation of the role of inhibitoryinputs, such as those to the thalamus.
Abstract: Although inhibitory inputs are often viewed as equal but opposite to excitatory inputs, excitatory inputs may alter the firing of postsynaptic cells more effectively than inhibitory inputs. This is because spike cancellation produced by an inhibitory input requires coincidence in time, whereas an excitatory input can add spikes with less temporal constraint. To test for such potential differences, especially in the context of the function of thalamocortical (TC) relay nuclei, we used a stochastic "integrate-and-fire-or-burst" TC neuron model to quantify the detectability of excitatory and inhibitory drive in the presence and absence of the low-threshold Ca2+ current, I(T), and the hyperpolarization-activated cation conductance, I(sag). We find that excitatory inputs are generally superior drivers compared with inhibitory inputs in part because spontaneous activity of a postsynaptic neuron is not required in the case of excitatory drive. Interestingly, the presence of the low-threshold Ca2+ current, I(T) in a postsynaptic neuron allows the robust detection of inhibitory drive over a certain range of spontaneous and driven activity, a range that can be extended by the presence of the hyperpolarization-activated cation conductance, I(sag). These simulations suggest a possible reinterpretation of the role of inhibitory inputs, such as those to the thalamus.

Journal ArticleDOI
TL;DR: It is suggested that adenosine mediates the high-temperature-induced depression of the excitatory synaptic transmission but not that of action potential propagation in rat CA1 neurons.

Journal ArticleDOI
TL;DR: The results support the idea of a spatial reorganization of the mechanisms involved in the task at low contrast, but suggest that additional influences possibly reflecting image segmentation also affect performance.

Journal ArticleDOI
TL;DR: Values indicate the upper limit of temporal summation for chromatic stimuli in the human early visual cortex.
Abstract: The temporal-summation characteristics of the human visual cortex were investigated by recording the magnetic responses to isoluminant red-green gratings. In one condition, exposure duration (ED) of a single-pulse stimulus was varied between 16.7 ms and 200 ms, and in the other, stimulus-onset-asynchrony (SOA) of a double-pulse (presented for 16.7 ms each) stimulus was varied between 16.7 ms and 200 ms. The magnetic responses showed an initial peak at a latency of around 100 ms, the origin of which was estimated to be in the vicinity of the striate cortex. The peak amplitude increased with increasing ED and decreased with increasing SOA, showing a clear sign of temporal summation. The critical ED and SOA estimated from the peak amplitude vs. ED/SOA functions were about 50 ms. These values indicate the upper limit of temporal summation for chromatic stimuli in the human early visual cortex.