Showing papers on "Summation published in 1997"
TL;DR: Properties of local synaptic connections in neocortex, studied with dual intracellular recordings in vitro and correlated with cell and synaptic morphology are summarized, showing frequency-dependent, incrementing facilitation at higher presynaptic frequencies.
Abstract: Properties of local synaptic connections in neocortex, studied with dual intracellular recordings in vitro and correlated with cell and synaptic morphology are summarized. The different durations and sensitivities to somatic membrane potential of pyramid-pyramid excitatory postsynaptic potentials (EPSPs) apparently reflect the positions of the synapses on the postsynaptic dendrites. Their time-, frequency- and voltage-dependent properties enable supra-linear summation of several low-frequency inputs arising in the same dendritic region, even if only loosely coincident, but they depress during repetitive firing in any one input. Pyramidal input to classical fast spiking and low threshold spiking interneurones are strikingly different. Here low presynaptic firing rates results in many transmission failures. EPSPs are brief and inputs must be near coincident for summation. However, these synapses display pronounced. frequency-dependent, incrementing facilitation at higher presynaptic frequencies. Once initiated by a brief high-frequency burst, this facilitation is maintained at lower frequencies. GABAA receptor-mediated inhibitory postsynaptic potentials (IPSPs) arising proximally are of very different durations depending on the type of interneurone activated and can prevent and subsequently synchronize firing in their many postsynaptic partners with very different delays (eg. 10-100 ms). Low threshold spiking interneurones, in contrast, generate brief IPSPs only in more distal dendritic regions and have little effect on somatic excitability acting to shunt input distally.
327 citations
TL;DR: Evidence that temporal summation of sensory intensity during series of brief contacts relies on central integration, rather than a sensitization of peripheral receptors, was obtained using two approaches.
Abstract: Temporal summation of sensory intensity was investigated in normal subjects using novel methods of thermal stimulation. A Peltier thermode was heated and then applied in a series of brief (700 ms) contacts to different sites on the glabrous skin of either hand. Repetitive contacts on the thenar or hypothenar eminence, at interstimulus intervals (ISIs) of 3 s, progressively increased the perceived intensity of a thermal sensation that followed each contact at an onset latency > 2 s. Temporal summation of these delayed (late) sensations was proportional to thermode temperature over a range of 45-53 degrees C, progressing from a nonpainful level (warmth) to painful sensations that could be rated as very strong after 10 contacts. Short-latency pain sensations rarely were evoked by such stimuli and never attained levels substantially above pain threshold for the sequences and temperatures presented. Temporal summation produced by brief contacts was greater in rate and amount than increases in sensory intensity resulting from repetitive ramping to the same temperature by a thermode in constant contact with the skin. Variation of the interval between contacts revealed a dependence of sensory intensity on interstimulus interval that is similar to physiological demonstrations of windup, where increasing frequencies of spike train activity are evoked from spinal neurons by repetitive activation of unmyelinated nociceptors. However, substantial summation at repetition rates of > or = 0.33 Hz was observed for temperatures that produced only late sensations of warmth when presented at frequencies < 0.16 Hz. Measurements of subepidermal skin temperature from anesthetized monkeys revealed different time courses for storage and dissipation of heat by the skin than for temporal summation and decay of sensory intensity for the human subjects. For example, negligible heat loss occurred during a 6-s interval between two trials of 10 contacts at 0.33 Hz, but ratings of sensory magnitude decreased from very strong levels of pain to sensations of warmth during the same interval. Evidence that temporal summation of sensory intensity during series of brief contacts relies on central integration, rather than a sensitization of peripheral receptors, was obtained using two approaches. In the first, a moderate degree of temporal summation was observed during alternating stimulation of adjacent but nonoverlapping skin sites at 0.33 Hz. Second, temporal summation was significantly attenuated by prior administration of dextromethorphan, a N-methyl-D-aspartate receptor antagonist.
245 citations
TL;DR: Hippocampal long‐term potentiation is reduced in aged relative to young F‐344 rats when peri‐threshold stimulation protocols are used and the possibility that this LTP‐induction deficit is caused by a reduced overlap of Schaffer‐collateral inputs onto CA1 pyramidal cells is examined.
Abstract: Hippocampal long-term potentiation (LTP) is reduced in aged relative to young F-344 rats when peri-threshold stimulation protocols (several stimulus pulses at 100-200 Hz) are used The present study was designed to examine the possibility that this LTP-induction deficit is caused by a reduced overlap of Schaffer-collateral inputs onto CA1 pyramidal cells (input cooperativity) This reduced input cooperativity would decrease the levels of postsynaptic depolarization during LTP induction, which might account for the age-related LTP deficit Both behavioral data (Morris Water Maze) and electrophysiological data (intracellular recordings from hippocampal slices) were collected from adult and aged F-344 rats To counter the effects of reduced input cooperativity, stimulus intensities were adjusted to elicit baseline excitatory postsynaptic potentials (EPSPs) of equivalent amplitude in aged and young rats Contrary to expectations, however, an age-related LTP-induction deficit was still observed Further evaluation of the electrophysiological data revealed that temporal summation of multiple EPSPs during high-frequency stimulation was impaired in the aged rats Thus, despite the equalization across age groups of the baseline EPSP amplitudes, the cells of aged rats were less depolarized during the LTP-inducing stimulation than were those of young rats This reduced total depolarization was not an artifact of the higher stimulus intensity used on aged animals, nor was it caused by a failure of aged rats' CA1 afferents to follow high-frequency stimulation The present data therefore suggest that there is a deficit in the ability of aged rats' synapses to provide the sustained depolarization necessary to active the LTP-induction cascade
126 citations
TL;DR: It is concluded that, in intact rats, an inhibitory mechanism counteracts the long-lasting increase of excitability of the flexor reflex seen in spinal animals after high-intensity, repetitive stimulation of C-fibers.
Abstract: Gozariu, Manuela, Dominique Bragard, Jean-Claude Willer, and Daniel Le Bars. Temporal summation of C-fiber afferent inputs: competition between facilitatory and inhibitory effects on C-fiber reflex...
95 citations
TL;DR: The study demonstrates that temporal summation of nociceptive input from muscles exists and that the responses to single and repeated nocICEptive stimuli of the referred pain area are facilitated.
Abstract: The aim of the present study was to assess temporal summation within saline-induced, localized and referred muscle pain areas. The sensibility to single and repeated electrical stimuli were assessed in the muscle by means of needle electrodes and in the referred pain area by surface stimulation. The study demonstrates that temporal summation of nociceptive input from muscles exists and that the responses to single and repeated nociceptive stimuli of the referred pain area are facilitated.
95 citations
TL;DR: The study shows that spatial summation of pain is most likely a mechanism acting across segments and is existing from pain threshold to tolerance.
Abstract: The aim was to study spatial summation within and between ipsi- and contralateral dermatomes at different painful temperatures. For heat stimulation we used a computer controlled thermofoil based thermode. The thermode area could be varied in five discrete steps from 3.14 to 15.70 cm2. When we applied the stimuli within a dermatome, the mean heat pain threshold decreased significantly from 45.6 to 43.5 C as the area was increased from minimum (3.14 cm2) to maximum (15.70 cm2). When the areas were increased involving different dermatomes (both ipsi- or contralateral), we found similar decreases in pain threshold. Spatial summation was also found within and between dermatomes at supra-threshold temperatures (46, 48, 50 C).The study shows that spatial summation of pain is most likely a mechanism acting across segments and is existing from pain threshold to tolerance.
93 citations
TL;DR: A physiological and mathematical model of muscle activation is presented which accounts for major effects that occur (during artificial stimulation of human muscle under isometric conditions) and provides significant insight into muscle processes during FES.
80 citations
TL;DR: The lack of significant spatial summation for sharpness threshold is consistent with the theory that perceived sharpness can be evoked by near threshold activity of a single nociceptor, and implies that distinctly suprathreshold activation of nocICEptors is required for mechanically evoked pain perception.
Abstract: Psychophysically, spatial summation can be demonstrated as a decrease in threshold accompanying an increased field of stimulation. The present study examined to what extent different mechanically evoked percepts (pressure, sharpness, and pain) show spatial summation. Various probes were used to apply prescribed forces to the dorsal surface of the digits of 19 healthy subjects. The threshold for three perceptual qualities showed differing degrees of spatial summation: sharpness showed no statistically significant spatial summation; pain demonstrated some significant summation (46% on average); pressure showed the greatest degree of spatial summation (76% on average). The lack of significant spatial summation for sharpness threshold is consistent with the theory that perceived sharpness can be evoked by near threshold activity of a single nociceptor. The modest amount of spatial summation for pain implies that distinctly suprathreshold activation of nociceptors is required for mechanically evoked pain perce...
61 citations
TL;DR: The results are consistent with a common mode of central nociceptive processing for skin and muscle pain intensity but suggest a relatively larger activation of affective mechanisms by muscle afferents.
Abstract: We used psychophysical methods to compare the central processing of nociceptive inputs from skin and muscle in ten normal humans. Both intramuscular electrical and infrared CO2 laser cutaneous stimulation showed increasing but decelerating (downward concave) stimulus-response curves and similar temporal summation characteristics. Intramuscular stimulation was rated significantly more unpleasant than cutaneous stimulation. The results are consistent with a common mode of central nociceptive processing for skin and muscle pain intensity but suggest a relatively larger activation of affective mechanisms by muscle afferents.
44 citations
TL;DR: It is concluded that spinal anaesthesia inhibits temporal summation elicited by repeated electrical stimulation of the sural nerve, and pain to both single and repeated stimulation, and pinprick and cold sensation, disappeared in all patients.
Abstract: In a previous investigation we found that extradural anaesthesia did not adequately inhibit temporal summation of repeated electrical stimuli: pain to repeated stimuli was blocked in only one of 10 patients, and pain thresholds to repeated stimuli were significantly lower than pain thresholds to a single stimulus. In this study we have investigated in 10 patients the effect of spinal anaesthesia on temporal summation, assessed by repeated electrical stimulation of the sural nerve. Plain 0.5% bupivacaine 18 mg was injected at L2-3. The pain threshold to a single electrical stimulus, summation threshold (increase in perception during repeated electrical stimuli with five impulses of the same intensity at 2 Hz), pinprick and cold sensation were assessed. After spinal anaesthesia, pain to both single and repeated stimulation, and pinprick and cold sensation, disappeared in all patients. We conclude that spinal anaesthesia inhibits temporal summation elicited by repeated electrical stimulation.
43 citations
TL;DR: The short‐latency reflex myoclonus that appears to be characteristic of cortical‐basal ganglionic degeneration (CBGD) was investigated in two patients and it is argued that this results from the loss of an intrinsic cortical or corticothalamic inhibitory mechanism.
Abstract: The short-latency reflex myoclonus that appears to be characteristic of cortical-basal ganglionic degeneration (CBGD) was investigated in two patients. Stimulating the digital nerves of the middle finger caused exaggerated reflex activity in the first dorsal interosseus (FDI) muscle of that hand with a latency of 46-51 ms. Magnetic stimulation over the contralateral cortex, delivered 25 ms after the digital nerve stimulus, resulted in greater than expected facilitation of FDI, implying spatial summation. Poststimulus time histograms (PSTH) of individual FDI motor units indicated that this spatial summation was occurring "upstream" from the motoneurons. It is argued that this occurs at the motor cortex. Magnetic stimulation over the cortex in normal subjects results in short-latency facilitation of the contralateral motoneurons followed by inhibition. This inhibition was less in the patients with CBGD. It is argued that this results from the loss of an intrinsic cortical and corticothalamic inhibitory mechanism.
TL;DR: The results indicate that both N-methyl-D-aspartate and non-N- methyl- D- aspartate receptor-mediated synaptic responses are present in dorsal nucleus of the lateral lemniscus neurons of rats at 21-35 days of age.
TL;DR: The formation of neuronal networks in vitro is controlled by cellular mechanisms that favor inhibitory connections in general and specifically enhance the formation of reciprocal connections between pairs of excitatory and inhibitory neurons.
Abstract: Muller, Thomas H., D. Swandulla, and H. U. Zeilhofer. Synaptic connectivity in cultured hypothalamic neuronal networks. J. Neurophysiol. 77: 3218–3225, 1997. We have developed a novel approach to a...
TL;DR: A new method of analysis is used that allows the quantification of firing discontinuities in a spike train and is applied to parietal cells recorded from monkeys during the performance of a tactile short-term memory task, showing that these cells show more firing transitions in active short- term memory than in baseline (intertrial) conditions.
Abstract: Bodner, Mark, Yong-Di Zhou, and Joaquin M. Fuster. Binary mapping of cortical spike trains in short-term memory. J. Neurophysiol. 77: 2219–2222, 1997. Microelectrode studies in monkeys performing short-term memory tasks show the sustained elevated discharge of cortical neurons during the retention of recalled sensory information. Cortical cells that are part of memory networks are assumed to receive numerous inputs of excitatory as well as inhibitory nature and local as well as remote. Thus it is reasonable to postulate that the temporal and spatial summation of diverse inputs on any cell in an activated network will result in temporally discrete groups of spikes in its firing. The activation of a network in active memory supposedly increases the magnitude and diversity of those inputs and thus increases the discontinuities and frequency fluctuations in the firing of cells in the network. In this study we use a new method of analysis that allows the quantification of firing discontinuities in a spike tra...
TL;DR: It is proposed that the mechanical input yields a reflex more resistant to depression of the corticoreticular drive and to narcotic analgesia, because it exploits temporal summation at central synapses, whereas the electrical input exploits spatial summation.
TL;DR: A technique to address the issue of phase cancellation during summation of the compound muscle action potential evoked by supramaximal stimulation and mean amplitude of single motor unit potentials (SMUPs).
Abstract: Current techniques for motor unit number estimation (MUNE) rely on the amplitude of the compound muscle action potential (CMAP) evoked by supramaximal stimulation and mean amplitude of single motor unit potentials (SMUPs). The phase cancellation during summation is not considered. We developed a technique to address this issue. Slow and fast types of motor unit potentials were collected from 5 normal subjects from their abductor pollicis brevis muscles by low-level voluntary contractions, and near-threshold nerve stimulation, respectively. Two of each type of SMUPs were used as templates for reconstructing the best fitted CMAP using a feed-forward neural network. The total number of SMUPs simulated from the four templates during the reconstruction served as MUNE. The mean MUNE was 222 ± 98. The technique is simple and noninvasive, and may be applied in the future for MUNE in patients. © 1997 John Wiley & Sons, Inc. Muscle Nerve, 20, 461–468, 1997
TL;DR: Although SKD tends to be larger with the increase in age, the relationship between SKD and spatial summation was not obvious.
Journal Article•
TL;DR: VLF-EPSPs were found to increase with hyperpolarizing and decreased with depolarizing the membrane, indicating that the descending fibers in the VLF may terminate on the soma or proximal dendrites of MNs, while the EPSPs evoked by the dorsal or ventral root stimulation were insensitive to membrane potential changes.
Abstract: By using the intracellular recording techniques, the electrophysiological characteristics of fast excitatory postsynaptic potentials (EPSP) evoked by ventrolateral funiculus (VLF) stimulation were analyzed in neonate rat motoneurons (MN) of spinal cord slices. The incidences of VLF-EPSPs was 80% (n = 28), among which 2 is preceded by inhibitory postsynaptic potential and 6 followed by slow EPSPs. Considering the distribution skewness of VLF-EPSP latency histogram, it was suggested that short- and long-latency EPSPs correspond respectively to mono- and poly-synaptic transmission respectively. The possible neurotransmitters mediating VLF-EPSPs were excitatory amino acids and non-NMDA receptors were critically involved in these synaptic transmissions, for both VLF-EPSP and glutamate-induced response were similarly and almost completely abolished by kynurenic acid and DNQX. Typical spatial summation of VLF-EPSPs and EPSPs evoked by ventral root stimulation were observed in the same recorded MNs. Most importantly, VLF-EPSPs were found to increase with hyperpolarizing and decreased with depolarizing the membrane, indicating that the descending fibers in the VLF may terminate on the soma or proximal dendrites of MNs, while the EPSPs evoked by the dorsal or ventral root stimulation were insensitive to membrane potential changes, indicating that the primary sensory afferents in the dorsal and ventral roots may contact the distal dendrites of the MNs. The results imply that the commanding signals conducting along the descending fibers in the VLF may directly modulate the MN's activities, whereas messages from the periphery may cause fine changes of the membrane potential subject to integration of the MNs.
Journal Article•
Journal Article•
TL;DR: It is concluded that the RVM is involved in inhibitory feedback mechanisms elicited by temporal summation of C-fibre afferents that both counteract the wind-up phenomenon and trigger long periods of inhibition.
Abstract: In intact rats, an inhibitory mechanism counteracts the increase in excitability of a flexor reflex seen in spinal animals following high-intensity, repetitive stimulation of C-fibres. We tested the hypothesis that the rostral ventromedial medulla (RVM) is involved in these processes. Electromyographic responses elicited by electrical stimulation of the sural nerve, were recorded from the ipsilateral biceps femoris in halothane-anaesthetised, sham-operated or RVM-lesioned rats. There were no significant differences between the C-fibre reflexes in the two groups in terms of their thresholds, latencies, durations or mean recruitment curves. The excitability of the C-fibre reflex was tested following 20 s of high-intensity homotopic electrical conditioning stimuli at 1 Hz. During the conditioning period, the EMG responses first increased in both groups (the wind-up phenomenon), but then decreased in the sham-operated rats and plateaued in the RVM-lesioned rats. These effects were followed by inhibitions that were very much smaller in the RVM-lesioned rats, both in terms of their magnitudes and their durations. It is concluded that the RVM is involved in inhibitory feedback mechanisms elicited by temporal summation of C-fibre afferents that both counteract the wind-up phenomenon and trigger long periods of inhibition.
01 Dec 1997
TL;DR: Two spike train analysis techniques are introduced to establish how the probability of firing in a neuron is dependent on the number of sequential spikes fired in another neuron (temporal summation) and in any other neuron (spatial summation).
Abstract: Two spike train analysis techniques are introduced to establish how the probability of firing in a neuron is dependent on the number of sequential spikes fired in another neuron (temporal summation) and in any other neuron (spatial summation). The Joint InterNeuronal-Arrival-Time/Cross-Interval (J-INAT/CI) Probability Mass Function (PMF) is used to deduce how a sequential (burst) firing pattern in any neuron is contributing to the generation of a spike in a reference neuron. Analogously, the Joint Inter-Spike-ArrivalTime/Cross-Interval (J-LSAT/CI) PMF is defined similar to the former PMF except that the contribution from only one other neuron is considered. These analyses can be used to establish the precise coupling relationship between the firing times of neurons both spatially and temporally.