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At least 973 records · Page 54Linked to original sources
PubMed2004

Magnetic fields in the human hippocampal area evoked by a somatosensory oddball task.

We recorded neuromagnetic fields evoked by a somatosensory oddball task requiring subjects to discriminate target stimuli from nontarget stimuli, which are different in stimulation intensity, with a mental count of the target stimuli. A whole head type 80-channel magnetoencephalography (MEG) system with a 50-mm baseline gradiometer array was used. Targets and nontargets were somatosensory stimuli with an electrical current intensity of twice and three times the sensory threshold, respectively. The source current locations of the evoked magnetic fields in three dimensions and the equivalent current dipole (ECD) moments were calculated by using a single dipole model, assuming the brain as a sphere. In 28 of 63 recording sessions for 7 subjects, the loci of neuronal activities were observed in the left and/or right hippocampal areas. The latency of left hippocampal activity (293 +/- 49 ms) was significantly shorter than that of the right (333 +/- 45 ms) (P = 0.027, non-paired t-test). In view of previous studies that have shown the time window of sensory integration as approximately 200-300 ms, sensory information may be transferred to hippocampal areas following sensory integration.

Adult↗
PubMedDate not supplied

[The effect of different activating influences on the self stimulation reaction].

A study was made of the influence on self-stimulation of non-painful sensory stimuli of different modalities, and of intra-brain stimulations of emotionally positive and neutral points with the wiew to elucidate the specificity of certain functional relations appearing during interaction between emotionally negative and positive conditions. The data obtained attest that the influence of various excitation sites on self-stimulation reactions depends not so much on the strength of the stimuli, as on the specific neurophysiological organization of emotionally negative zones in the brain. A reciprocal enhancement of excitation of self-stimulation zones points to a certain non-specificity of positively reinforced structures.

Acoustic Stimulation↗
PubMed1985

Uncertainties of topodiagnosis of auditory nerve and brain-stem auditory evoked potentials due to rarefaction and condensation stimuli.

Auditory nerve and brain-stem auditory evoked potentials (AN and BAEP) were elicited after separate stimulation with rarefaction and condensation stimuli. There were only few persons with identical patterns in the two opposite phases. Rarefaction stimuli showed a tendency to evoke AN and BAEP with shorter latencies and better synchronization. In diseases of the auditory nerve and brain-stem the phase-dependent differences were even more prominent, indicating different topodiagnostic levels of lesions. The results point to the need for stimulus presentation with rarefaction and condensation stimuli separately and an evaluation of both curves. The alternating mode is the result of summating rarefaction and condensation stimuli.

Brain Stem↗
PubMed1995

Responses of human motoneurons to Ia inputs: effects of background firing rate.

The effects of synchronous Ia volleys on the firing probability of repetitively firing human motoneurons were examined at fast and slow firing rates. Ia afferents of either the median or the posterior tibial nerve were stimulated, while single motor unit activity was recorded from the homonymous muscles. Motoneuron responses to the Ia inputs were quantified by measurement of the magnitude of the short latency excitatory peak in peristimulus time histograms (PSTHs). When the stimuli were given at random with respect to the times of motor unit spikes, the magnitude of the PSTH peak (response probability) was significantly lower at a faster firing rate. In the "triggered" mode of stimulation, stimuli were given at various known times during the interspike interval. In this mode the response probability to the input increased monotonically as the stimuli were delivered progressively later during the interspike interval. The response probability at a fixed delay with respect to the triggering spike was higher at the faster firing rate. The results obtained with the two modes of stimulation are not in contradiction and both may be explained by the nature of membrane voltage trajectories and ionic conductances during the interspike interval described for repetitively firing cat motoneurons.

Adult↗
PubMed1994

Somatic stimulation reduces perception of gut distention in humans.

BACKGROUND/AIMS: Perception of gut symptoms may depend on visceral sensory modulation, but the mechanisms are poorly understood. Based on somatosensory data, we hypothesized that somatic stimulation modulates perception of gut stimuli. METHODS: Perception and gut reflexes were measured in 8 healthy subjects in response to increasing gastric and duodenal distentions (stimulus-response trials) performed alone or with simultaneous application on the hand of either low (just perceivable) or high (nonpainful) transcutaneous electrical nerve stimulation (100 Hz, 100 microseconds). Fixed pressure distentions were performed in stepwise increments by gastric and duodenal barostats to determine the respective thresholds for discomfort. Perception was measured by a questionnaire, and gut reflex responses were measured as isobaric volume changes by the barostats. Individual stimuli of 2 minutes' duration were randomly applied at 10-minute intervals. RESULTS: Somatic stimuli increased the tolerance to gut distention, and this effect was more pronounced with high stimuli. The gastric threshold for discomfort was 7.3 +/- 0.5 mm Hg with high stimuli vs. 5.5 +/- 0.2 mm Hg without stimuli, and the duodenal discomfort threshold was 15.5 +/- 1.5 mm Hg with high stimuli vs. 13.5 +/- 1.4 mm Hg without stimuli; P < 0.05 for both. Somatic stimuli modified neither basal gut tone nor the relaxatory duodenogastric reflex induced by duodenal distention (gastric expansion by 203 +/- 48 mL with high stimuli and 208 +/- 73 mL without stimuli). CONCLUSIONS: Somatic stimulation reduces perception of gut distention without interfering with local and reflex gut responses.

Adult↗
PubMed1992

The functional anatomy of middle-latency auditory evoked potentials: thalamocortical connections.

1. An 8 x 8-channel microelectrode array was used to map epicortical field potentials from a 4.375 x 4.375-mm2 area in the right parietotemporal neocortex of four rats. Potentials were evoked with bilaterally presented click stimuli and with electrical stimulation of the ventral and dorsal divisions of the medial geniculate body. 2. Epicortical responses to click stimuli replicated earlier findings. The responses consisted of a positive-negative biphasic waveform (P1a and N1) in the region of primary auditory cortex (area 41) and a positive monophasic waveform (P1b) in the region of secondary auditory cortex (area 36). Two potential patterns, one at the latency of the N1 and the other at the latency of the P1b, were used to represent activation of cells within areas 41 and 36. A linear combination of these patterns was sufficient to explain from 90 to 94% of the variance of the evoked potential complex at all latencies. 3. In the same animals, epicortical responses to electrical stimulation of the ventral and dorsal divisions of the medial geniculate body were also localized to areas 41 and 36, respectively. A linear combination of potential patterns from these separate stimulation conditions was sufficient to explain from 80 to 93% of the variance of the original click-evoked potential complex at all latencies. 4. These data provide functional evidence for anatomically defined topographical thalamocortical projections to primary and secondary auditory cortex. They suggest that short-latency cortical evoked potentials (10-60 ms poststimulus) are dominated by parallel thalamocortical activation of areas 41 and 36.

Acoustic Stimulation↗
PubMed1997

The transient 40-Hz response, mismatch negativity, and attentional processes in humans.

1. Recent experimental studies on the neurophysiological basis of auditory selective attention and sensory memory forming the sensory-data basis for tuning the selective-attention system in humans are reviewed. 2. The results demonstrate that the transient 40-Hz response is enhanced by selective attention, attenuated in the course of long-term stimulation, but is not affected by changes in auditory stimuli. 3. Therefore, the 40-Hz response seems to be closely related to selective and sustained attention, whereas it does not seem to be associated with passive attention, as it does not reflect the detection of changes in auditory stimuli. 4. Changes in auditory stimulation are registered by pre-attentive sensory memory, indexed by the mismatch negativity (MMN), a change-specific component of the event-related potentials (ERPs). By this time, the transient 40-Hz response has already terminated. The magnitude of stimulus change is reflected in MMN latency. These latency changes predict changes in attentive reaction time (RT). 5. Thus, the pre-attentive memory mechanism seems to govern attentive detection of changes in the auditory environment. 6. It is concluded that the transient 40-Hz response is related to active attention and MMN is related to passive attention.

Attention↗
PubMed2001

Cognitive and neural mechanisms of emotional memory.

A highly adaptive aspect of human memory is the enhancement of explicit, consciously accessible memory for emotional stimuli. Recent findings from neuroimaging, neuropsychological, drug and neural stimulation studies indicate that emotional stimuli engage specific cognitive and neural mechanisms that enhance explicit memory. Emotional arousal influences memory via factors that act during memory encoding (attention and elaboration) and factors that modulate memory consolidation. Across studies, the amygdala has been consistently implicated as playing a key role in enhancing explicit memory for both pleasant and unpleasant emotional stimuli through modulation of encoding and consolidation processes.

Journal Article↗
PubMed1989

Decreased releasability of basophils from patients with cold urticaria after cold exposure.

Histamine release from peripheral blood basophils challenged with C5a, f-met-peptides and calcium ionophore was studied in patients with cold urticaria before and after exposure to low environmental temperatures. Compared to healthy controls, stimulated mediator release before cold exposure was increased in 7 of 11 patients. When challenged by cold exposure mediator release from in vitro-stimulated basophils was decreased. This decrease was more pronounced after stimulation with receptor-mediated stimuli (e.g. C5a) as compared to receptor-unrelated stimuli, e.g. calcium ionophore. In 4 of 11 patients stimulated mediator release before cold exposure was moderately increased. Also after cold exposure only a weak decrease of stimulated histamine release was seen. Levels of activated complement components (C3a) before and after cold exposure failed to provide evidence for complement activation in vivo. Also the number of circulating basophils as well as their cellular histamine content remained normal after cold exposure. The results show that in these patients release of histamine is altered before and after cold exposure. These changes in basophil responsiveness are not due to complement activation in vivo.

Basophils↗
PubMedDate not supplied

Tissue impedance and current flow in the implanted ear. Implications for the cochlear prosthesis.

Tissue impedance was measured in the cochleas of monkeys and guinea pigs implanted with electrode arrays. The impedances were measured within the scala tympani and between the scala tympani and the internal auditory meatus of the modiolus. The measurements revealed several impedance properties. 1) The impedances inside and outside of the scala tympani are resistive for frequencies between 8 Hz and 12.5 kHz. 2). The impedances measured between the scala tympani and the internal auditory meatus were larger in magnitude than the impedances measured in the scala tympani. 3) Impedance was not affected significantly by changing stimulus current flow from 0.45 to 45 microA rms. 4) Impedance magnitude increased rapidly by different factors inside and outside the scala tympani after sacrifice of the subject animals. Measurements of the tissue impedance made in conjunction with measurements of threshold of response to electrical stimulation revealed that the threshold of response to electrical stimuli was lowest when the stimulating currents were highest outside the scala tympani. We conclude that the excitable elements of the auditory nerve are being stimulated within the modiolus rather than within the scala tympani.

Acoustic Impedance Tests↗
PubMed2003

Functional comparison of DCs generated in vivo with Flt3 ligand or in vitro from blood monocytes: differential regulation of function by specific classes of physiologic stimuli.

Dendritic cells (DCs) are a family of leukocytes that initiate T- and B-cell immunity against pathogens. Migration of antigen-loaded DCs from sites of infection into draining lymphoid tissues is fundamental to the priming of T-cell immune responses. In humans, the major peripheral blood DC (PBDC) types, CD1c+ DCs and interleukin 3 receptor-positive (IL-3R+) plasmacytoid DCs, are significantly expanded in vivo with the use of Flt3 ligand (FL). DC-like cells can also be generated from monocyte precursors (MoDCs). A detailed comparison of the functional potential of these types of DCs (in an autologous setting) has yet to be reported. Here, we compared the functional capacity of FL-expanded CD1c+ PBDCs with autologous MoDCs in response to 3 different classes of stimuli: (1) proinflammatory mediators, (2) soluble CD40 ligand trimer (CD40L), and (3) intact bacteria (Escherichia coli). Significant differences in functional capacities were found with respect to changes in phenotype, migratory capacity, cytokine secretion, and T-cell stimulation. MoDCs required specific stimuli for the expression of functions. They responded vigorously to CD40L or E coli, expressing cytokines known to regulate interferon-gamma (IFN-gamma) in T cells (IL-12p70, IL-18, and IL-23), but required prostaglandin E2 (PGE2) during stimulation to migrate to chemokines. In contrast, PBDCs matured in response to minimal stimulation, rapidly acquired migratory function in the absence of PGE2-containing stimuli, and were low cytokine producers. Interestingly, both types of DCs were equivalent with respect to stimulation of allogeneic T-cell proliferation and presentation of peptides to cytotoxic T lymphocyte (CTL) lines. These distinct differences are of particular importance when considering the choice of DC types for clinical applications.

Antigens, CD1↗
PubMed1979

Inhibition in penicillin-induced epileptic foci.

A previous study indicated that the early surface negative component (associated with recurrent inhibition) of the evoked potential recorded from cat pericruciate cortex, subsequent to pyramidal tract stimulation, was altered after application of penicillin to the cortical surface (Van Duijn et al. 1973). This suggested that decreased effectiveness of recurrent inhibition might be the basis for epileptogenicity of penicillin. To verify that recurrent inhibition is functionally decreased in the penicillin epileptic focus and to assess alternative sites for penicillin action, this phenomenon was investigated at the cellular level. Neurons were recorded extracellularly and response to stimuli monitored throughout the transition from normal cortex to epileptogenic cortex. Stimuli employed were peduncular stimulation (to test recurrent inhibitory pathways), epicortical stimulation (to test inhibitory pathways, bypassing the recurrent collateral system), and forepaw footpad shock (to test the responsiveness ofneurons to afferent input). In normal cortex, PT cells were inhibited by peduncular or epicortical stimulation and excited by forepaw stimulation, with the excitation followed by a period of inhibition. In the penicillin focus, inhibition was not observed in response to any of the 3 stimuli, and the excitatory response to forepaw stimulation was maintained. The bursting non-PT cells, most likely candidates for interneurons, exhibited excitation in response to peduncular and epicortical stimulation, consistent with involvement in inhibitory pathways. Nonetheless, in the penicillin focus, excitatory response to peduncular and epicortical stimulation was maintained. Excitatory response to forepaw stimulation was also maintained in the penicillin focus. The results demonstrate a loss of effectiveness of recurrent inhibition measured at the PT cell body in the penicillin focus. Further, the reduction in inhibitory feedback occurs in conjunction with maintained or enhanced excitability of the neurons which are most likely candidates for inhibitory interneurons. Thus, penicillin is most likely exerting its effect at the inhibitory synapses onto PT cells in the cortex, thereby allowing excitatory input to have greater influence on neuronal firing.

Animals↗
PubMed1978

Referred thermal sensations: warmth versus cold.

The present study investigates further the phenomenon of thermal referral, in which thermal sensations are "referred" to the site of nearby tactile stimuli. First demonstrated with three stimulators (Green, B.G. Perception and Psychophysics, 1977, 22, 331-337), the present experiments show that referral also occurs between two contact stimuli. Measurements with two stimulators reveal that (1) on the arm and fingers, warmth refers more strongly that cold, and (2) referral of warmth is affected relatively little by increasing the distance between stimulators; (3) on the fingertips, referral is greater when the thermal sensation refers away from rather than toward the first digit; and (4) the pattern or referral across fingers differs for warmth and cold and appears unrelated to the pattern of peripheral innervation. The phenomenon of referral illustrates that information about locus gathered through the tactile sense is available to the thermal senses, which means that information about stimulus locus and quality can be carried on separate nerve fibers.

Adolescent↗
PubMedDate not supplied

[Limited plasticity of the rabbit visual cortex and hippocampal neurons in the oddball test].

The activity of 41 visual cortex and 20 hippocampal neurons from field CA1 was registered in experiments using oddball-stimulation with different color stimuli varied in intensity. 34% cortical and 37% hippocampal neurons demonstrated plasticity reactions. The significant increase of latest phases of neuronal activity (200-500 and 200-1000 ms after stimulation for cortical neurons and 300-550 ms for hippocampal neurons) was shown in responses to rare deviant stimuli, which had a less intensity than frequently standards. The quantity of the earliest neuronal phase of activity (40-120 ms after stimulation) was stabilized in responses to deviants and standards during the experiment. We propose that such increase of the latest phases of neuronal activity (the limited plasticity) may reflect the mechanisms of orienting reaction.

Action Potentials↗
PubMed1997

Prostaglandin E2 and IL-4 provide naive CD4+ T cells with distinct inhibitory signals for the priming of IFN-gamma production.

We investigated the effects of prostaglandin E2 and IL-4 on the acquisition of cytokine-producing ability by naive CD4(+) T cells in human umbilical cord blood. The presence of PGE2 or IL-4 at primary stimulation inhibited the production of IFN-gamma at secondary stimulation, and the combination of these stimuli resulted in cooperative effects. During primary stimulation with anti-CD3, the intracellular cAMP level was elevated in PGE2-treated cells but not in IL-4-treated or control cells. The signal provided by PGE2, but not by IL-4, was inhibited with RpcAMP, indicating that it was mediated by cAMP. After differentiation into Th2-like cells, cAMP levels in PGE2- and IL-4-treated cells were not different. Our results suggest that both PGE2 and IL-4 play important roles with distinct mechanisms in inhibiting the priming of IFN-gamma production of naive CD4(+) T cells.

CD4-Positive T-Lymphocytes↗
PubMed2006

Effect of morphine on the release of excitatory amino acids in the rat hind instep: Pain is modulated by the interaction between the peripheral opioid and glutamate systems.

Behavioral evidence supports a role for peripheral glutamate receptors in normal nociceptive transmission. In this study, we examined the release of the excitatory amino acids, glutamate and aspartate, in the s.c. perfusate of the rat hind instep by in vivo microdialysis. Antidromic stimulation of the sciatic nerve and noxious stimuli in the form of heat stimulation and local application of capsaicin cream (1%) to the instep caused an increase in excitatory amino acid release. This capsaicin-induced excitatory amino acid release was suppressed by pretreatment with capsaicin. Both systemic (10 mg/kg, i.v.) and local injections (10(-5) M in the perfusate) of morphine inhibited the increase in excitatory amino acid release evoked by local application of capsaicin cream to the instep. This inhibitory effect of morphine was antagonized by naloxone either given systemically (5 mg/kg, i.v.) or locally (10(-5) M). These results suggest that excitatory amino acids are released from small diameter afferent fibers by heat stimulation in the periphery or local application of capsaicin cream, and that activation of opioid receptors, present on the peripheral endings of small-diameter afferent fibers, can regulate noxious stimulus-induced excitatory amino acid release.

Analgesics, Opioid↗
PubMed1999

B7-H1, a third member of the B7 family, co-stimulates T-cell proliferation and interleukin-10 secretion.

The B7 family members B7-1 and B7-2 interact with CD28 and constitute an essential T-cell co-stimulatory pathway in the initiation of antigen-specific humoral and cell-mediated immune response. Here, we describe a third member of the B7 family, called B7-H1 that does not bind CD28, cytotoxic T-lymphocyte A4 or ICOS (inducible co-stimulator). Ligation of B7-H1 co-stimulated T-cell responses to polyclonal stimuli and allogeneic antigens, and preferentially stimulated the production of interleukin-10. Interleukin-2, although produced in small amounts, was required for the effect of B7-H1 co-stimulation. Our studies thus define a previously unknown co-stimulatory molecule that may be involved in the negative regulation of cell-mediated immune responses.

Amino Acid Sequence↗