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PubMed1983

Nocifensive responses to cutaneous thermal stimuli in the cat: stimulus-response profiles, latencies, and afferent activity.

Rapid-onset thermal pulses (38 degrees C X s-1) ranging from 43 to 60 degrees C (adapting temperature, 38 degrees C) were applied by contact thermodes to the shaved outer thighs of 29 partially restrained cats while they were eating (coincident stimuli) or between eating periods (noncoincident stimuli). The stimulus-associated probability and latency of three putative nocifensor responses were determined: interruption of eating or of exploration for food, hindlimb movement, and vocalization. These behavioral responses terminated the stimulus. An analysis of response trends and latencies supports the interpretation that these are unlearned escape responses to noxious stimuli. Response threshold was defined as the lowest temperature at which the average response probabilities at the test temperature and at 38 degrees C were outside one another's 95% confidence limits. Average threshold varies with the type of response and the behavior at the time of stimulation. Noncoincident stimuli elicit both interrupt and movement responses at 47 degrees C and vocalization at 53 degrees C. Coincident stimuli also elicit interrupt responses at 47 degrees C but are associated with an increased hindlimb movement threshold (51 degrees C) and vocalization threshold (55 degrees C). The lowest threshold determined for an individual cat was 43 degrees C. Response probability increases as a nonmonotonic function of stimulus intensity. Maximum sensitivity to increases in temperature occurs at stimulus intensities between 50 and 55 degrees C. Above 55 degrees C, some cats show an attenuation of response sensitivity. Special tests failed to reveal any evidence that receptor sensitization or suppression affected the stimulus-response profiles. The average response latency for all behaviors of all cats is 2.3 +/- 0.12 (SE)s from the onset of the stimulus pulse plateau. Most responses occurred within 2.5 s. No significant relationship was found between response latency and type of response or stimulus intensity. The composition and time of onset of heat-evoked afferent activity in the lateral femoral cutaneous nerve was investigated in six cats by colliding antidromic A-delta- and C-fiber volleys with the orthodromic discharge evoked by the thermodes used in the behavioral studies. There was no evidence that noxious thermal pulses evoked activity in A-delta-afferents, but C-fibers could be shown to become active at approximately 46 degrees C, at or before the onset of the thermal pulse plateau.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1984

Activation of the capacity for sodium-induced pinocytosis in Amoeba proteus.

Amoebae treated with cycloheximide or starved for 8-10 days lose their pinocytotic response to Na+. Their capacity for Na+-induced pinocytosis was activated after application of various physical or chemical stimuli (electrical stimulation, mechanical shearing forces, osmotic pressure, UV-light, alkali metal ions, capsaicin, and indole). The degree of activation was related to the intensity and duration of the stimulus and lasted several hours after the stimulus had been withdrawn. The dose-response curves of activating stimuli were always biphasic. Strong activating agents reduced the sensitivity of the amoeba to the inducer. At concentrations lower than those which induced pinocytosis, but in the same order of efficacy, inorganic cations were potent activating agents. Like induction of pinocytosis, activation by cations required minute amounts of Ca2+ and was inhibited by high concentrations of this ion. Activation may therefore be an early event during the induction of pinocytosis. Capsaicin and indole were potent activators, indicating that specific chemical stimuli may increase the capacity for pinocytosis. The activation may be the result of a secretory process adding area and structures to the old membrane which are necessary for the induction of pinocytosis.

Action Potentials↗

PubMed2004

EEG-dependent ERP recording: using TMS to increase the incidence of a selected pre-stimulus pattern.

EEG dependent event-related potential (ERP) recording (interactive ERP) is an extension to ERP paradigms whereby stimuli are initiated in response to a selected pattern of background EEG. This form of recording is critically dependent upon the incidence of the particular pattern of interest. We introduce here a process that modifies the EEG in a predictable manner so as to increase the incidence of a particular pattern. Transcranial magnetic stimulation (TMS) stimuli are applied in response to a selected pattern of pre-TMS activity, and the post-TMS response is characterized by the incidence of a defined pattern of EEG activity. Analysis of validation test results obtained with the TMS modification part of the process verifies an increased incidence of the response pattern after TMS stimuli, compared with placebo stimuli. The TMS modification procedure is then combined with interactive ERP recording in a two step process to affect the ERP response to sensory stimuli. The post-TMS pattern from the first step becomes the pre-stimulus pattern of the interactive ERP recording in the second step. The TMS modified interactive ERP (TMIERP) process is illustrated here using an auditory oddball paradigm. The amplitude of the P300 peak obtained using this process was significantly higher than that obtained using the standard auditory oddball paradigm.

Acoustic Stimulation↗

PubMed1994

Pharmacological manipulations of the alpha 2-noradrenergic system. Effects on cognition.

Electrophysiological and neurosurgical lesion studies with experimental animals have implicated the ascending dorsal noradrenergic bundle of the locus coeruleus system in cognitive process such as memory, learning and selective attention. However, it has also been suggested that noradrenaline (norepinephrine) is crucial in certain cognitive functions associated with the frontal lobes, particularly the prevention of distractibility by irrelevant stimuli. The alpha 2-receptors of the prefrontal cortex appear to be of particular importance in this respect. Studies with humans and experimental primates provide substantial support for this view. The aged primate brain is prone to degeneration of the locus coeruleus, as well as profound catecholamine depletion in the prefrontal cortex, and so is ideal for psychopharmacological investigation of the role of noradrenaline in frontal lobe function. Elderly monkeys show deficits in performance of the delayed response task, which can be reversed directly by both the mixed alpha 1/alpha 2-agonist clonidine, the more specific alpha 2-agonist guanfacine and also, indirectly, by the alpha 2-antagonist yohimbine. It is suggested that these results can be explained by an attenuation of the distracting properties of irrelevant stimuli following stimulation of noradrenergic activity. Conversely, distractibility is magnified whenever noradrenergic activity is reduced. This is supported by similar findings in psychopharmacological studies of healthy humans. The exception to this is when the locus coeruleus is likely to be firing, e.g. in times of stress or when novel stimuli are encountered. Clonidine attenuates locus coeruleus firing on such occasions, and so counteracts any beneficial (or deleterious) effects of stress on task performance. alpha 2-Adrenoceptor agents have little therapeutic value in patients with dementia of the Alzheimer's type. However, they may have some clinical use in patients who have a cognitive symptomatology similar to that of patients who have received neurosurgical excisions to the frontal lobes, e.g. deficits in working memory, executive function or focused attention, with relative sparing of episodic short term memory. Patients with Korsakoff's disease, attention deficit disorder or schizophrenia may benefit from treatment with alpha 2-agents. In particular, idazoxan has putative therapeutic effects in patients with a neurodegenerative disorder, namely dementia of frontal type.

Aging↗

PubMedDate not supplied

Do rods influence the hue of foveal stimuli?

To understand the generality and mechanisms of previously reported rod hue biases, we examined whether they are present for small foveal stimuli by comparing the wavelengths of the three spectral unique hues under dark-adapted and flash-bleached conditions. Rod green bias (shift of unique yellow) and rod blue bias (shift of unique green) were found for some observers with 1 degrees -diameter foveal stimuli, the size most likely to stimulate rods. Smaller stimuli (0.2 degrees and 0.6 degrees diameter), which were least likely to stimulate rods, produced no large or consistent differences between dark-adapted and bleached conditions. This suggests that rod hue biases result from the local stimulation of rods by light, not from remote suppression by dark-adapted, unstimulated rods, and not from bleaching light artifacts.

Adult↗

PubMed1980

Electrophysiology of mouse parotid acini: effects of electrical field stimulation and ionophoresis of neurotransmitters.

1. Intracellular micro-electrode recordings of membrane potential and input resistance were made from surface acini of mouse parotid glands placed in a Perspex tissue bath through which oxygenated physiological saline solutions were circulated. The acinar cells were stimulated by microionophoresis of both acetylcholine (ACh) and adrenaline (Ad) from extracellular micropipettes, and by electrical field stimulation via a pair of platinum electrodes. 2. The acinar cells had a mean resting membrane potential of -64.9 mV +/- 0.6 S.E. The input resistance of the unstimulated cell was 4.63 M omega +/- 0.19 S.E. In a number of cells spontaneous miniature depolarizations were observed, associated with synchronous reductions in input resistance. 3. The responses to ionophoresis of both ACh and Ad and the response to supra-maximal field stimulation were identical. Stimulation always evoked a marked decrease in input resistance associated with an initial potential change, generally followed by a delayed hyperpolarization during which the input resistance returned to normal. 4. Field-stimulation responses could be evoked to single shock (1-2 msec) and to low frequency (1-4 Hz) stimulation. The latency for this response was 245 msec +/- 12 S.E. 5. The field-stimulation response was shown to be susceptible to blockade of nerve conduction in sodium-free or tetrodotoxin- (TTX-) containing media; and to blockade of neurotransmitter release in calcium-free media. 6. The field-stimulation and ACh responses were recorded at different levels of membrane potential within the same cells by applying either hyperpolarizing or depolarizing direct current through the recording electrode. The membrane potential at which the initial potential change undergoes reversal, i.e. changes from a depolarization to a hyperpolarization, is known as the equilibrium or reversal potential, EFS and EACh respectively. The field-stimulation (FS) and ACh responses underwent simultaneous reversal at about -60 mV, i.e. EFS = EACh. Equilibrium potentials were also determined indirectly by analysis of the responses evoked by each stimulus in the manner described by Trautwein & Dudel (1958). Using this technique the equilibrium potentials of the responses to all three stimuli, field stimulation, ACh and Ad, were again about -60mV, i.e. EFS = EACh = EAd. 7. Both the field-stimulation and ACh responses were abolished by atrophine (10(-6) M) while the response to Ad persisted. Atropine also abolished all spontaneous activity. The alpha-adrenergic blocker phentolamine (10(-5) M) abolished the response to Ad but left the field-stimulation response unaffected. 8. Electrical field stimulation of isolated segments of salivary gland evoked release of endogenous neurotransmitter as a consequence of neural excitation. The technique of field stimulation thus makes it possible to investigate the functional innervation of a gland using the in vitro preparation. In the mouse parotid gland the field stimulus response was mediated by ACh released from parasympathetic nerve endings.

Acetylcholine↗

PubMed1988

Physiology and pharmacology of the parietal cell.

The parietal cells possess the unique capacity to produce large quantities of acid at a high concentration, and this is reflected in unique properties at the cellular level. The cells are comparatively large, and they are equipped with secretory canaliculi, a multitude of mitochondria, and cytoplasmic tubulovesicles. During secretion many of the tubulovesicles merge with the secretory canaliculi, which then expand. In the process H+, K+-ATPase is transferred from the tubulovesicular membrane to the secretory membrane. This enzyme catalyses the final step in the production of HCl. Parietal cell activity is regulated through receptors on the basolateral cell surfaces. In the isolated gland and in the isolated parietal-cell fractions, stimulation of receptors for histamine evokes higher secretion than receptor stimulation with cholinergic compounds or with gastrin. In these experimental models, specific inhibitors are required to block acid secretion; for example histamine H2-receptor antagonists will block histamine-induced secretion but will be inactive when secretion is evoked by gastrin or by cholinergic stimulation. These stimuli cause a more or less marked increase in the intracellular levels of Ca2+, which acts as a second messenger, leading to the activation of phosphokinases and, ultimately, to morphological transformation of the parietal cells and acid secretion. Another such intracellular messenger is cAMP, which is formed in response to histamine stimulation only; prostaglandins may prevent this process and block acid secretion. The final step in the production of acid requires K+ and Cl- channels in the secretory membrane and the H+, K+-ATPase-catalysed exchange of K+ for H+ across this membrane. This reaction consumes large amounts of energy and depends on the aerobic production of ATP by the parietal cells. Substituted benzimidazoles, such as omeprazole, accumulate in the acid compartments of the parietal cells and inhibit the H+, K+-ATPase, thereby blocking acid production.

Gastric Acid↗

PubMed1989

[The effect of procainamide on the inducibility of ventricular tachycardia using programmed stimulation].

The effect of intravenously administered procainamide (0.5-1 g, mean 0.966 g) on the inducibility of sustained ventricular tachycardia by programmed ventricular stimulation was tested in 15 patients (12 men and 3 women, mean age 57.2 +/- 16.6 years) with confirmed sustained ventricular tachycardia. Eleven patients had a previous myocardial infarction and two had congestive heart failure. The programmed ventricular stimulation (1-3 premature stimuli following after ventricular stimulation at a rate of 100/120 and 140/min. and a number of quick stimuli with a rising frequency from the apex of the right ventricle at an intensity equal to twice the diastolic threshold) was administered before and after procainamide administration. Sustained ventricular tachycardia was induced during the controlled examination in all 15 patients (100% sensitivity). Induced ventricular tachycardia had a haemodynamically important course with a rapid onset of unconsciousness in three patients whose index of risk of ventricular tachycardia (ratio of its frequency and the ejection fraction at rest) was significantly higher than in the remaining 12 patients (9.0 +/- 2.2 as compared with 4.9 +/- 1.2). Procainamide prevented the induction of sustained ventricular tachycardia in six patients (group I), i. e. in 40%. In the remaining nine patients (group II) ventricular tachycardia induced after procainamide had a significantly lower frequency (192 +/- 34/min.), as compared with controls (214 +/- 42/min.), but its haemodynamic impact was not affected. Patients of group I had, as compared with group II, a significantly higher ejection fraction (47 +/- 14% as compared with 35 +/- 10%) and a significantly lower index of the risk of tachycardia (4.5 +/- 1.3 as compared with 6.5 +/- 2.4).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗

PubMed1999

Pharmacological regulation of descending cortical control of the nociceptive processing.

Clinical and experimental data indicate that the cerebral cortex plays an important role in pain perception and endogenous antinociceptive system function. Moreover, the enhancement of descending inhibitory cortical control may be involved in the mechanisms of analgetic effect of some agents. The present study was designed to investigate the effect of cortical electrical stimulation (as a model of descending inhibitory control) on the behavioral and electrophysiological signs of nociceptive response, decipher the mechanisms involved therein and evaluate the action of central analgesics (both opioid and non-opioid) on descending cortical control. In acute experiments in cats the inhibitory cortical influence on neuronal activity produced by nociceptive stimuli (electrical stimulation of tooth pulp, C-fibers of afferent somatic nerves, afferent cardiac structures) was most marked after stimulation of the first and second sensory and fronto-orbital areas. In chronic experiments on rats cortical stimulation reduced behavioral signs of visceral pain (writhing test) and also delayed the development of neuropathic pain syndrome along with lowering its intensity. Mu-opioid receptor agonists (morphine, fentanyl) potentiated the inhibitory cortical effect on the evoked neuronal activity. Pentazocine, which has pronounced kappa-receptor agonistic activity, was less effective. Naloxone eliminated the effects of both cortical stimulation and opioid analgesics. Serotonin receptor antagonist methysergide as well as p-chlorophenylalanine significantly decreased inhibitory cortical control and opioids effect. Monoamine re-uptake inhibitors with analgetic properties (imipramine, fluoxetine) potentiated the inhibitory effect of cortical stimulation. Adrenoceptor, dopamine, acetylcholine, GABA-receptor agents and antagonists of NMDA receptors had minor or no effect. Among non-narcotic analgesics, inhibitors of cyclooxygenase, metamysole and ketorolak increased only moderately the descending cortical control of nociception. Thus, the cerebral cortex is able to control the nociceptive processing in different pain syndromes (somatic, visceral or neuropathic pain). Opioidergic and serotonergic systems play the key role in this control. The effect over the cortical descending control is likely to be one of the components of the analgetic effect exerted by opioids and some other central analgesics.

Analgesics, Non-Narcotic↗

PubMed2005

Effect of romifidine on the nociceptive withdrawal reflex and temporal summation in conscious horses.

OBJECTIVE: To investigate the action of a single IV administration of romifidine on the thresholds of the nociceptive withdrawal reflex (NWR) and temporal summation in conscious horses. ANIMALS: 10 adult horses. PROCEDURE: Single electrical stimulations were applied on the digital nerves to evoke NWR from the left forelimb and hind limb. Repeated electrical stimulations (10 stimuli, 5 Hz) were given to obtain temporal summation. Surface electromyographic reflex activity was recorded from the common digital extensor and cranial tibial muscles. After baseline assessment of NWR and temporal summation thresholds, romifidine (80 microg x kg(-1), IV) was administered. Successive determinations of NWR and temporal summation thresholds were performed 5, 25, and 55 minutes after administration. RESULTS: Romifidine significantly increased the current intensities necessary to evoke NWR and temporal summation in forelimbs and hind limbs of horses. Values were significantly higher than baseline values 55 minutes after romifidine administration. After administration of romifidine, a facilitation of reflex components of tactile origin was observed when repeated stimulations were applied. CONCLUSIONS AND CLINICAL RELEVANCE: Results confirm antinociceptive activity of romifidine and may represent an objective demonstration of the well-known hypersensitivity to tactile stimuli observed in horses receiving alpha2-adrenoreceptor agonists in clinical practice. Romifidine can be included in analgesic and anesthetic protocols to provide additional analgesia in horses.

Adrenergic alpha-Agonists↗

PubMed1990

Multisensory regulation of maternal behavior and masculine sexual behavior: a revised view.

Frank Beach's view of the multisensory regulation in Norway rats of copulation in males (12) and of pup retrieval in females (23) is critically analyzed and revised in terms of Lashley's influence, Beach's other work, and current neurobiological knowledge. Beach's view was that no single sensory stimulus is essential to elicit these behaviors, but that all relevant stimuli available summate in the neocortex; consequently, (a) sexual "arousal" is increased in males, leading to copulation, and (b) the "efficiency," or likelihood, of retrieval is increased in postpartum mothers. The revised view is based on a component analysis in which each of these behaviors consists of a chain of motoric responses elicited by somatosensory stimulation. Distal stimuli emanating from the female or pups induce proximity by provoking orientation, attention and arousal; the meaning of these stimuli is largely learned by conditioned associations during the initial executions of the behavior, although odors may have a prepotent influence for some individuals. Stimuli are integrated in a multisensory manner by both subcortical and neocortical mechanisms. Generalizations concerning the reproductive behavior of other mammalian species are suggested.

Animals↗

PubMed1995

Response to single twitch or single burst stimulation of the ulnar nerve as predictive guide for intubating conditions.

Disappearance of response to single twitch stimulation (STS) or train-of-four stimulation (TOF) of the ulnar nerve is insufficient as predictive guide for intubating conditions during onset of non-depolarizing neuromuscular block. Double burst stimulation (DBS) appears to be a more reliable indicator of the optimal time for intubation. In the present study, the disappearance of tactile detectable response to 0.1 Hz single twitch stimulation (STS) of the ulnar nerve was compared with disappearance of response to 0.1 Hz single burst stimulation (three stimuli at 50 Hz = SBS) as predictor for optimal intubating conditions during onset of block induced by 0.08 mg.kg-1 of vecuronium in 100 patients under light general anaesthesia where thiopentone was used as the sole anaesthetic. Intubation was performed immediately after disappearance of the twitch response. Likewise 0.05 Hz STS and 0.05 Hz SBS stimulation were compared under identical circumstances in another 100 patients. Intubating conditions were unacceptable in 10%, 14%, 8% and 10% of the patients in the 0.1 Hz STS, 0.1 Hz SBS, 0.05 Hz STS and 0.05 Hz SBS groups, respectively. There were no significant differences between the groups. In conclusion, neither absence of response to STS stimulation nor absence of response to SBS stimulation of the ulnar nerve at either 0.1 Hz or 0.05 Hz frequency does guarantee acceptable intubating conditions during onset of neuromuscular block induced by vecuronium 0.08 mg.kg-1 when thiopentone is used as the sole anaesthetic.

Adult↗

PubMedDate not supplied

[Neurochemical analysis and pharmacological regulation of the corticofugal control of the nociceptive signals in the afferent pathways].

Experimental and clinical data indicate that the cerebral cortex plays an important role in pain perception and endogenous antinociceptive system function. Moreover, the enhancement of descending inhibitory cortical control may be involved in the mechanisms of analgesic effect of some agents. The present study was designed to investigate the effect of cortical electrical stimulation (as a model of descending inhibitory control) on the behavioral and electrophysiological signs of nociceptive response, elucidate the mechanisms involved therein and evaluate the action of central analgesics (both opioid and non-opioid) on descending cortical control. In acute experiments on cats, the inhibitor y cortical influence upon neuronal activity produced by nociceptive stimuli (electrical stimulation of tooth pulp, C-fibers of afferent somatic nerves, afferent cardiac structures) was most marked after stimulation of the first and second sensory and fron-to-orbital areas. In chronic experiments on rats, cortical stimulation reduced behavioral signs of visceral pain (writhing test) and also delayed the development of neuropathic pain syndrome along with lowering its intensity. mu-Opioid receptor agonists (morphine, fentanyl) potentiated the inhibitory cortical effect on the evoked neuronal activity. Pentazocine, which has pronounced kappa-receptor agonist activity, was less effective. Naloxone eliminated the effects of both cortical stimulation and opioid analgesics. Serotonin receptor antagonist methysergide, as well as p-chlorophenylalanine significantly decreased inhibitory cortical control and the effect of opioids. Monoamine re-uptake inhibitors with analgesic properties (imipramine, fluoxetine) potentiated the inhibitory effect of cortical stimulation. Adreno-, dopamine-, acetylcholine-, GABA-receptor agents and antagonists of NMDA receptors had minor or no effect. Among non-narcotic analgesics, the cyclooxygenase inhibitors metamysole and ketorolak increased only moderately the descending cortical control of nociception. Thus, the cerebral cortex is able to control the nociceptive processing in different pain syndromes (somatic, visceral or neuropathic pain). Opioidergic and serotonergic systems play the key role in this control. Action through the cortical descending control is likely to be one of the components of the analgesic effect exerted by opioids and some other central analgesics.

Action Potentials↗

PubMed1990

Role of cholecystokinin in bombesin- and meal-stimulated pancreatic polypeptide secretion in dogs.

This study was undertaken to delineate the role of cholecystokinin (CCK) in bombesin- and meal-stimulated pancreatic polypeptide (PP) secretion in seven conscious dogs by studying: (1) the stimulatory effect of similar plasma levels of CCK induced by a meal and infusions of bombesin and the synthetic CCK analog cerulein on plasma PP, and (2) the inhibition of PP secretion by the CCK-receptor antagonist CR-1409 during these three stimuli. The stimulation of PP secretion during bombesin (11.0 +/- 1.6 nM/hr) and after the meal (8.9 +/- 2.0 nM/hr) were significantly (P less than 0.05) greater than during infusion of the CCK analog cerulein (2.7 +/- 0.4 nM/hr). CR-1409 significantly inhibited the bombesin- and meal-stimulated PP secretion to 2.0 +/- 0.4 nM/hr (81%; P less than 0.05) and 3.1 +/- 1.2 nM/hr (47%; P less than 0.05), respectively, while the cerulein-stimulated PP release was almost abolished to 0.2 +/- 0.1 nM/hr (93%; P less than 0.05) by the drug. These findings point to an important role for CCK in the regulation of bombesin- and meal-stimulated PP secretion.

Animals↗

PubMed1991

[Termination of atrial flutter using esophageal stimulation].

The risk of possible complications in atrial flutter leads to attempts to use all available therapeutic possibilities to eliminate this disorder of the cardiac rhythm. By oesophageal stimulation the sinus rhythm was restored in 40% and a change to atrial fibrillation was achieved in 50% of the patients. The advantages of this method include above all speed and the minimal risk of complications; the disadvantage of the method is the unpleasant sensation when the electrode is inserted and the painful perception of the stimuli. Oesophageal stimulation can be recommended as the method of choice in treatment of atrial flutter.

Atrial Flutter↗

PubMed2007

Interhemispheric inhibition in distal and proximal arm representations in the primary motor cortex.

Interhemispheric inhibitory interactions (IHI) operate between homologous distal hand representations in primary motor cortex (M1). It is not known whether proximal arm representations exhibit comparable effects on their homologous counterparts. We studied IHI in different arm representations, targeting triceps brachii (TB, n = 13), first dorsal interosseous (FDI, n = 13), and biceps brachii (BB, n = 7) muscles in healthy volunteers. Transcranial magnetic stimulation test stimuli (TS) were delivered to M1 contralateral to the target muscle preceded 10 ms by a conditioning stimulus (CS) to the opposite M1 at 110-150% resting motor threshold (RMT). IHI was calculated as the ratio between motor-evoked potential (MEP) amplitudes in conditioned relative to unconditioned trials. Mean RMTs were 38.9, 46.9, and 46.0% of stimulator output in FDI, TB, and BB muscles, respectively. IHI was 0.45 +/- 0.41 (FDI), 0.78 +/- 0.38 (TB), and 0.52 +/- 0.32 (BB, P < 0.01) when test MEP amplitudes were matched and 0.28 +/- 0.17 (FDI) and 0.85 +/- 0.31 (TB, P < 0.05) when TS intensities expressed as percentage RMT were matched. Significant IHI (P < 0.05) was identified with minimal CS intensities (expressed as percentage stimulator output) in the 30 s for FDI, 60 s for TB, and 40 s for BB. Additionally, a CS of roughly 120% RMT suppressed the test MEP but not a test H-reflex in BB, suggesting IHI observed in BB is likely mediated by a supraspinal mechanism. We conclude that IHI differs between different arm muscle representations, comparable between BB and FDI but lesser for TB. This finding suggests the amount of IHI between different arm representations does not strictly follow a proximal-to-distal gradient, but may be related to the role of each muscle in functional movement synergies.

Adult↗

PubMed2003

Effect of stimulus frequency on human cerebral hemodynamic responses to electric median nerve stimulation: a near-infrared spectroscopic study.

We examined the effect of stimulus frequency on optically recorded hemodynamic responses to electric median nerve stimulation. Electric stimuli were delivered to the right median nerve with an intensity of 90% of motor threshold. Four different stimulus frequencies (2, 5, 10, and 20 Hz) were administered in each subject. By means of a multi-channel near-infrared spectroscopic instrument, changes in concentration of oxygenated hemoglobin were continuously measured over the left scalp. After 20 Hz stimulation, we found two spatially and temporally distinct hemodynamic responses. One lasted beyond 60 s, and the center of this response was located over the secondary somatosensory area. The other had a transient duration starting immediately after the stimulus onset and was located in the primary somatosensory hand area. Both responses were linearly augmented as a function of the stimulus frequency. Since temporal activation patterns are different in two somatosensory areas, real-time optical monitoring is necessary in evaluation of hemodynamic responses to electric nerve stimulation.

Adult↗

PubMed1999

Across-species comparisons of psychophysical detection thresholds for electrical stimulation of the cochlea: I. Sinusoidal stimuli.

Several species have been, and continue to be, used as subjects in studies of electrical stimulation of the cochlea. Few attempts, however, have been made to determine if data obtained from different species are quantitatively or qualitatively similar. The present work compares psychophysical absolute detection threshold vs. frequency functions for sinusoidal stimuli obtained from humans, nonhuman primates, cats, and guinea pigs. Threshold data for monopolar and bipolar electrode configurations from both previously published and unpublished studies are compared. In general, within all four species, significant intersubject variation in detection threshold level was found, but slopes of threshold vs. frequency functions were relatively well conserved within a species, under the conditions studied. With one exception (cat bipolar stimulation), threshold functions reached a minimum at or near 100 Hz across species and electrode configurations. In all cases, thresholds were significantly lower for monopolar, as compared with bipolar, configurations. Statistically, there were no significant differences in absolute threshold level across species. Threshold levels increased with frequency above 100 Hz at a rate of 3.0-7.9 dB/octave, depending on both electrode configuration and species. Slopes were steeper for monopolar than for bipolar configurations. When slopes were averaged between 200 and 2000 Hz, no statistically significant differences in overall slopes were found, nor was there a significant interaction between electrode configuration and species. There were, however, consistent species differences within more restricted regions of the function. Human functions for both monopolar and bipolar stimulation were steeper than all animal functions in the range of 100-300 Hz. Within this range, the differences between slopes for human and nonhuman subjects were statistically significant. In addition, differences were noted in the frequency at which slope decreased, with slopes for nonhuman subjects showing the decrease at higher frequencies than did those for human subjects. These differences may be true species differences, or may reflect the influence of confounding variables associated with each experimental-subject model.

Animals↗