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PubMed2000

In-vivo assessment of 5-HT2A and 5-HT2C antagonistic properties of newer antipsychotics.

The effects of serotonin (5-HT) receptor ligands on the MK 212 (6-chloro-2[1-piperazinyl]pyrazine) discriminative stimulus and quipazine-induced head twitches were studied in rats. 5-HT1A (8-OH-DPAT) and preferential 5-HT2A (DOI) receptor agonists did not generalize to the discriminative stimulus. The 5-HT2B/2C-receptor antagonist, SB 206553 (5-methyl-1-(3-pyridylcarbamoyl)-1,2,3,5-tetrahydropyrrolo[2 ,3-f]indole), and the 5-HT2A/2C-receptor antagonist, ritanserin, acted as potent antagonists, whereas the 5-HT2A-receptor antagonist, MDL 100.151 ([(+/-)-alpha-(2,3-dimethoxyphenyl)-1-[2-(4-fluorophenylethyl)]-4- piperidine-methanol), produced minor and inconsistent inhibition. SB 206553 was a weak antagonist against quipazine-induced head twitches, whereas MDL 100.151 and ritanserin were potent antagonists. This suggests that the MK 212 discriminative stimulus is mediated by 5-HT2C receptors, while quipazine-induced head twitches are mediated primarily by 5-HT2A receptors. The effects on quipazine-induced head twitches were comparable to previously published effects on the DOI discriminative stimulus. 5-HT2A- and 5-HT2C-receptor antagonistic potencies of clozapine, olanzapine, risperidone, sertindole and ziprasidone were compared in the same models. Clozapine showed similar potencies in both models, while sertindole, olanzapine and risperidone inhibited quipazine-induced effects more potently than the MK 212 discriminative stimulus. Ziprasidone exerted a minor preference for 5-HT2A- compared to 5-HT2C-receptor-mediated effects. The ratio between in vivo inhibitory potencies at 5-HT2A and 5-HT2C receptors did not correlate with corresponding ratios from in-vitro affinity and ex-vivo occupancy studies in the literature.

Animals↗
PubMed1999

Effects of antidepressants in rats trained to discriminate the beta-2 adrenergic agonist clenbuterol.

The ability of indirectly acting agonists such as norepinephrine uptake inhibitors, serotonin reuptake inhibitors, and atypical antidepressants to substitute for clenbuterol, a beta-2 adrenergic agonist, was examined in rats trained to discriminate 0.03 mg/kg clenbuterol and saline using a fixed-ratio 10 (FR 10) schedule with water reinforcement. The beta-2 selective adrenergic agonist clenbuterol produced an orderly dose-response relationship, and its discriminative stimulus effects were antagonized by the beta-adrenergic antagonist propranolol. It was found that the effects of tricyclic antidepressants and selective norepinephrine uptake inhibitors did not generalize to the discriminative stimulus effects of clenbuterol, with the exception of high doses of protriptyline. Moreover, compounds from other drug classes, including fluoxetine and phenelzine, did not substitute for clenbuterol. Atypical antidepressants, such as trazodone, rolipram, and bupropion also did not engender drug-appropriate responding. Prenalterol and dobutamine, both purported to be beta-1 adrenergic receptor agonists, partially substituted for clenbuterol, but at relatively high doses. The present results show that the antidepressants tested do not share discriminative stimulus effects with clenbuterol, a beta-2 adrenergic agonist.

Adrenergic beta-Agonists↗
PubMed2004

Pain in a balance: noxious events engage opposing processes that concurrently modulate nociceptive reactivity.

Studies have shown that noxious cutaneous stimulation engages physiologically different antinociceptive systems to inhibit a spinal reflex, tail withdrawal from radiant heat. Two experiments are reported that examine the relationship between the inhibition of the tail-flick response and brain-mediated responses to nociception. The induction of a spinally mediated antinociception was accompanied by an increase in latency to vocalize to a noxious thermal stimulus, suggesting pain inhibition. Physiological manipulations that eliminated the inhibition of the tail-flick reflex restored vocalization to thermal stimulation and revealed a concurrent sensitization that generally heightened behavioral reactivity. The results suggest that net pain is regulated by 2 opposing processes, a selective inhibition of nociceptive signals within the spinal cord and a general sensitization that heightens stimulus processing.

Afferent Pathways↗
PubMed2001

Discriminative stimulus properties of indorenate, a 5-HT1A, 5-HT1B and 5-HT2C agonist: a study in rats.

Indorenate (INDO), initially described as an antihypertensive agent, also has some effects on behaviour, with anxiolytic and anorectic actions being reported. The aim of the present experiment was to examine the activity of INDO at the behavioural level at various serotonin (5-hydroxytryptamine, 5-HT) receptor sites by comparing its stimulus properties with those of other 5-HT receptor agonists and by examining its interactions with some 5-HT antagonists. Rats were trained to discriminate between 10.0 mg/kg INDO (administered intraperitoneally (90 min before the start of the session) from saline. A Fixed Ratio 10 (FR10) schedule of reinforcement was in effect in each drug condition. During generalization test sessions, the discrimination index (DI, responses to drug lever/responses to drug + saline lever) was calculated from the responses emitted before the first reinforcer of the session. DI was a function of the dose of INDO employed. Generalization to the discriminative stimulus properties of INDO was observed with the 5-HT1A receptor agonist 8-OH-DPAT (1.0 mg/kg produced 90% generalization) and the 5-HT(1B/2C) receptor agonist 1-(3-trifluoromethylphenyl) piperazine (TFMPP) (3.0 mg/kg produced up to 75% generalization). Yohimbine (5.6 mg/kg), buspirone (1.0 mg/kg), 6-chloro-2-(1-piperaziny)pyrazine (1.0 mg/kg) and m-chlorophenylpiperazine (mCPP) (1.0 mg/kg) induced a DI of 70%, 50% and 48% and 55%, respectively. In generalization tests, ritanserin (0.01-1.0 mg/kg) induced saline-like responding. NAN-190 (3.0 mg/kg), a 5-HT1A receptor antagonist, was able to reduce the DI of INDO to 50%. Although the 5-HT(2C/2A) receptor antagonists cinanserin (10.0 mg/kg) and metergoline (0.3 mg/kg) were able to reduce the stimulus properties of INDO to 60% and 30%, respectively, only ritanserin (1.0 mg/kg) reduced the stimulus properties of INDO to 25% with a clear dose-response relationship. The results suggest that INDO acts as an agonist at 5-HT1A receptor sites, but its activity at 5-HT(1B/2C) receptor sites also contributes to its discriminative function.

5-Methoxytryptamine↗
PubMed1986

Functional organization of the electroreceptive midbrain in an elasmobranch (Platyrhinoidis triseriata). A single-unit study.

The response properties of 322 single units in the electroreceptive midbrain (lateral mesencephalic nucleus, LMN) of the thornback ray, Platyrhinoidis triseriata, were studied using uniform and local electric fields. Tactile, visual, or auditory stimuli were also presented to test for multimodality. Most LMN electrosensory units (81%) are silent in the absence of stimulation. Those with spontaneous activity fired irregularly at 0.5 to 5 impulses/s, the lower values being more common. Two units had firing rates greater than 10/s. Midbrain electrosensory units are largely phasic, responding with one or a few spikes per stimulus onset or offset or both, but the adaptation characteristics of some neurons are complex. The same neuron can exhibit phasic or phasic-tonic responses, depending upon orientation of the electric field. Tonic units without any initial phasic over-shoot were not recorded. Even the phasic-tonic units adapt to a step stimulus within several seconds. Unit thresholds are generally lower than 0.3 microV/cm, the weakest stimulus delivered, although thresholds as high as 5 microV/cm were recorded, Neuronal responses reach a maximum, with few exceptions, at 100 microV/cm and decrease rapidly at higher intensities. LMN neurons are highly sensitive to stimulus repetition rates: most responded to frequencies of 5 pulses/s or less; none responded to rates greater than 10/s. Three distinct response patterns are recognized. Best frequencies in response to sinusoidal stimuli range from 0.2 Hz (the lowest frequency delivered) to 4 Hz. Responses decrease rapidly at 8 Hz or greater, and no units responded to frequencies greater than 32 Hz. Most LMN neurons have small, well defined excitatory electroreceptive fields (RFs) exhibiting no surround inhibition, at least as detectable by methods employed here. Seventy-eight percent of units recorded had RFs restricted to the ventral surface: of these, 98% were contralateral. The remaining 22% of units had disjunct dorsal and ventral receptive fields. Electrosensory RFs on the ventral surface are somatotopically organized. Anterior, middle, and posterior body surfaces are mapped at the rostral, middle, and caudal levels, respectively, of the contralateral LMN. The lateral, middle, and medial body are mapped at medial, middle, and lateral levels of the nucleus. Moreover, the RFs of all units isolated in a given dorsoventral electrode track are nearly superimposable. About 40% of LMN, measured from the dorsal surface, is devoted to input from ventral electroreceptors located in a small region rostral and lateral to the mouth.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2004

Characterizing spatial and temporal features of autobiographical memory retrieval networks: a partial least squares approach.

Conway (Conway, M.A., 1992. A structural model of autobiographical memory. In: Conway, M.A., Spinnler, H., Wagenaar, W.A. (Eds.), Theoretical Perspectives on Autobiological Memory. Kluwer Academic Publishers, Dordrecht, The Netherlands, pp. 167-194) proposed that two types of autobiographical memories (AMs) exist within a hierarchical AM system: unique, specific events and repeated, general memories. There is little research on whether retrieval of these AMs relies on different neural substrates. To investigate this issue, we used a multivariate image analysis technique, spatiotemporal partial least squares (PLS), to identify distributed patterns of activity most related to AM tasks that we have found to be associated with a medial and left-lateralized network. Using PLS, specific and general memories were more strongly associated with different parts of this retrieval network. Specific AM retrieval was associated more with activation of regions involved in imagery in episodic memory, including the left precuneus, left superior parietal lobule and right cuneus, whereas general AM retrieval was associated with activation of the right inferior temporal gyrus, right medial frontal cortex, and left thalamus. These two patterns emerged at different lags after stimulus onset, with the general AM pattern peaking between 2 and 6 s, and the specific AM pattern between 6 and 8 s. These lag differences are consistent with Conway's theory which posits that general AMs are the preferred level of entry to the AM system. A seed PLS analysis revealed that the regions functionally connected to the hippocampus during retrieval did not differentiate specific from general AM retrieval, which confirms our earlier univariate analysis indicating that some aspects of the memory retrieval network are shared by these memories.

Adult↗
PubMed1981

Spinal motoneuronal excitability in hyperkinesis: H-reflex recovery function and homosynaptic depression during wakefulness.

Variations in amplitude of the spinal monosynaptic H-reflex were examined during relaxed wakefulness in three unmedicated groups of subjects, hyperactive children (n=5), an age-matched group of control children (n=5), and a group of young adults (n=10), using techniques involving equal intensity percutaneous stimuli delivered in pairs or trains at varying rates. The paired-stimuli procedure generates a recovery function, the outstanding features of which are early depression, a peak of facilitation occurring between 100-300 msec, and complete recovery by 2-5 sec. Trains of stimuli delivered at rates greater than or equal to 1/sec effect a reduction in reflex amplitude which is termed homosynaptic depression. Both procedures revealed differences between hyperkinetic children and comparison groups. The paired-stimulus technique revealed a generalized reduction in excitability for hyperkinetic children for intervals extending up to 800 msec. In particular, hyperkinetic children were characterized by a significantly increased variability at the longer stimulus intervals. Hyperkinetic children also showed a more rapid reduction in reflex amplitude to initial stimuli in stimulus trains delivered at rates greater than or equal to 1/sec. Trains of stimuli at rates effecting facilitation in terms of the paired stimulus technique, i.e., 3,4 and 5/sec, revealed sustained amplitude enhancement for control subjects only. The recovery function data are consonant with spinal motoneuronal hypoexcitability in hyperkinetic children. Possible neruophysiological and neurochemical mechanisms underlying the reduced capability of hyperkinetic children to respond to rapidly delivered, repetitive stimuli are discussed.

Adult↗
PubMed1994

Activity of inferior temporal neurons during orientation discrimination with successively presented gratings.

1. We recorded from inferior temporal (IT) cells in three monkeys while they performed an orientation discrimination task with successively presented gratings. Histological reconstruction of two monkey brains indicated that most recordings were from TE3. The task was exactly the same as the one used in a previous V1 study, allowing direct comparison. 2. One quarter of IT cells were responsive to the grating. Response strength and variability of the cells excited by the grating (n = 341) were similar to those in V1, whereas response latency was on average 40 ms longer than in V1. 3. In one third of the responsive cells orientation had a significant effect. Sensitivity for orientation was captured by the orientation sensitivity index, which ranged from 0 to 0.95 with a median of 0.23. Orientation sensitivity of IT cells was on average much less than that of V1 cells. More cells preferred horizontal and vertical than oblique orientations. 4. The differences in responsiveness and orientation sensitivity among individual animals could be accounted for by the anterior/posterior difference in recording position. 5. Task-related behavioral effects were examined in 283 cells that were responsive to the visual stimuli. Order effects were examined in "same" trials and occurred in half of the IT cells in each of the three monkeys. In these cells there was on average a threefold difference in response between the first stimulus (S1) and the second stimulus in same trials (S2same). In two monkeys the average response to S2same was less than that to S1, whereas in the third monkey the average response to S1 was smaller than that to S2same. 6. IT cells also exhibited same/different effects, whereby response to a physically identical second stimulus differed between same and "different" trials. Generally cells responded more to the second stimulus in different trials than to S2same but the opposite also occurred. For a subset of these cells we could show that the correct/error type of the trial had no effect and that the response occurred before the saccadic response. 7. These context effects were modulations of the gain of the orientation tuning curves for the different types of responses. The tuning for orientation of these different responses was similar. 8. One third of the responsive IT cells exhibited an increased activity in the interstimulus interval (ISI), fitting the definition of delay cells. This activity was maintained when the ISI was lengthened from 300 to 800 ms. The orientation tuning of this response was similar to that for S1 responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1979

Responses of single units in the monkey superior colliculus to moving stimuli.

1. Single unit responses of pan-directional cells to moving and stationary flashing stimuli were studied in the superficial layers of the superior colliculus in paralysed, anaesthetized rhesus monkeys. The aim of this study was to see how far cell responses to moving stimuli fit in with what would be expected from their responses to stationary flashing stimuli. 2. Both the leading and the trailing edge of a moving stimulus evoke a transient response. If the diameter of moving light spots is increased the strength of the leading edge response increases, reaches a maximum and decreases to a constant value which is similar to the behaviour of the on response when the diameter of flashing spots is increased. The strength of the trailing edge response increases and reaches the same strength as that of the leading edge response. If the width of a long moving slit is increased, the strength of the leading edge response is the same at all slit widths, while the strength of the trailing edge response shows a course similar to that of the trailing edge response if the spot diameter is increased. If the length of a wide moving slit is increased both the leading and the trailing edge responses decrease. These results indicate that the strength of both leading and trailing edge responses is dependent on the degree the inhibitory surround is activated. 3. The leading and the trailing edge of a stimulus evoke their responses at the same position in the receptive field independent of the direction of movement. 4. Increasing the velocity of a moving stimulus shows that in general the leading edge response is present up to higher velocities than the trailing edge response independent of the sign of contrast. The burst duration to moving stimuli decreases with increasing stimulus velocity and appears to be determined by the time a moving edge is present in the receptive field centre. When this time becomes shorter than 10--20 ms, the burst duration for moving stimuli is constant and about the same as for flashing stimuli. This indicates that, although spatial receptive field properties can vary considerably, temporal receptive field properties show a strong similarity among different units. 5. The response latencies to light and dark moving edges are the same, which in turn are about equal to the response latencies to stationary flashing stimuli. 6. Stimulation experiments show that the general response characteristics to moving stimuli can be predicted by using a set of receptive field parameters derived from responses to stationary flashing stimuli. The most important variable of moving stimuli appears to be the period of time a moving contour is present within the receptive field centre, besides the degree of activation of the inhibitory surround.

Animals↗
PubMed1998

Selective serotonin reuptake inhibitors potentiate 8-OH-DPAT-induced stimulus control in the pigeon.

The effects of two selective serotonin reuptake inhibitors, fluoxetine and citalopram, and a nonselective monoamine reuptake inhibitor, imipramine, were characterized in pigeons that had been trained to discriminate 0.64 mg/kg of 8-hydroxy-(2-di-n-propylamino)tetralin hydrobromide (8-OH-DPAT), a 5-HT1A receptor agonist, from saline. Neither fluoxetine, citalopram, nor imipramine generalized to the 8-OH-DPAT-induced stimulus cue. However, when administered in addition to 8-OH-DPAT, both fluoxetine (10 mg/kg) and citalopram (10 mg/kg) lowered the ED50 for generalization of 8-OH-DPAT from 0.16 mg/kg (8-OH-DPAT by itself) to 0.05 mg/kg (fluoxetine + 8-OH-DPAT) and 0.06 mg/kg (citalopram + 8-OH-DPAT). Under similar conditions, imipramine (1 mg/kg) had no effect on the generalization curve for 8-OH-DPAT. The data support the hypothesis that activation of the 5-HT1A receptor may be relevant to the mechanism of action of serotonin reuptake inhibitors.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed1998

Discriminative stimulus functions of CNS sedative drugs assessed by drug versus drug discrimination procedures in gerbils.

This study is concerned with dissecting out differences in the discriminative stimulus attributes between drugs from broader pharmacological categories such as sedative/hypnotics where generalization tests often indicate shared stimulus effects. To this end, the discriminative stimulus effects of three to five doses of either chlordiazepoxide (CDP), chlormethiazole (CMZ), ethanol (ETOH), and pentobarbital (P-barb) were studied with gerbils in a two-choice, T-maze task. When the discrimination was based upon the presence versus the absence of drug administration, speed of acquiring the discrimination increased dose-dependently for all four drugs with log of sessions to criterion being a linear function of log dose. The slopes of all four lines were similar. The acquisition of a discrimination based on different doses of the training drug was then examined. A two-to-one ratio of high to low doses was used. Discriminative control developed with CMZ, ETOH, and P-barb, but not with CDP. The side of the T-maze that correlated with the lower training dose was always selected in tests with saline. Gerbils were then trained to discriminate between two drugs using at least two different dose combinations. The CDP versus CMZ, CDP versus ETOH, CMZ versus P-barb, CMZ versus ETOH discriminations were acquired. The CDP versus P-barb discrimination was obtained across doses only after an additional training procedure was instituted such that the P-barb dose was incremented gradually from low to higher doses during discrimination training; the CDP training doses were 20 and 30 mg/kg in two different groups of gerbils, respectively and the dose of P-barb was incremented by 2.5 mg/kg until the final dose of 20 mg/kg was reached with the barbiturate. Thus, although often shown to share similar stimulus effects, members of the broad pharmacological class of CNS sedatives/hypnotics nonetheless were shown to be discriminable from one another. Non-drug tests (vehicle) were used to assess stimulus control between pairs of drugs, equal control being implicated when responding was evenly distributed across the two training conditions.

Animals↗
PubMed1986

Category specific dissociations in naming and recognition by aphasic patients.

Two studies examined category specific retrieval deficits in aphasic patients. The first study tested naming performance of 24 aphasic patients for pictures of objects representing 16 semantic categories. Instances of deviantly high and low naming scores relative to a patient's general level of naming ability were encountered, most notably for letters, body parts and colors. The second study compared name production versus name recognition for 117 aphasic patients across six stimulus categories. Although a general superiority of name recognition over name production was found, thirteen patients, predominantly fluent aphasics, accounted for most instances of correct naming in the absence of correct name recognition. Letters, body parts and colors were again most notable. Several issues in lexical access for name recognition versus name production are discussed.

Adult↗
PubMed1994

Interactions of clozapine with the stimulus effects of DOM and LSD.

Two groups of rats were trained with the 5-HT2 agonists 2,5-dimethoxy-4-methylamphetamine (DOM) or lysergic acid diethylamide (LSD) in a two-lever discrimination task. Tests of generalization and antagonism were then carried out with clozapine. DOM did not generalize to clozapine. Partial antagonism of DOM was observed with 0.3, 1, and 2 mg/kg clozapine and statistically significant full antagonism with 3 mg/kg. LSD did not fully generalize to clozapine. Partial antagonism of LSD was observed with 3 and 4 mg/kg clozapine. Because clozapine is known to block muscarinic as well as 5-HT2 receptors, atropine was studied in DOM-trained rats. DOM partially generalized to 3 mg/kg atropine. Partial attenuation of DOM stimulus effects was observed with 3 mg/kg atropine, and no attenuation with 5 mg/kg. A combination of 2 mg/kg clozapine and 3 mg/kg atropine vs. DOM produced response suppression in five of seven rats. The atropine test results do not exclude the possibility of an antimuscarinic component in the observed attenuation of DOM and LSD stimulus effects by clozapine.

DOM 2,5-Dimethoxy-4-Methylamphetamine↗
PubMed1995

Anesthetic actions within the spinal cord: contributions to the state of general anesthesia.

The behavioral state known as general anesthesia is the result of actions of general anesthetic agents at multiple sites within the neuraxis. The most common end point used to measure the presence of anesthesia is absence of movement following the presentation of a noxious stimulus. The actions of general anesthetics within the spinal cord have been shown to contribute significantly to the suppression of pain-evoked movements, an important component of clinical anesthesia. Studies in the spinal cord are likely to increase our understanding of the pharmacology by which general anesthetics alter the transmission of somatomotor information. It now appears that the pharmacology responsible for the production of anesthesia is agent- and site-selective, and not the result of a unitary mechanism of action.

Anesthesia, General↗
PubMed2005

Neuronal mechanisms of repetition priming in occipitotemporal cortex: spatiotemporal evidence from functional magnetic resonance imaging and electroencephalography.

Repeated stimulus presentation (priming) is generally associated with a reduction in neuronal firing, macroscopically mirrored by a decrease in oscillatory electrophysiological markers as well as reduced hemodynamic responses. However, these repetition effects seem to be dependent on stimulus familiarity. We investigate the spatiotemporal correlates of repetition priming in cortical word-recognition networks and their modulation by stimulus familiarity (i.e., words vs pseudowords). Event-related functional magnetic resonance imaging results show reduced activation for repeated words in occipitotemporal cortical regions. Electroencephalogram recordings reveal a significant reduction of induced gamma-band responses (GBRs) between 200 and 350 ms after stimulus onset, accompanied by a decrease in phase synchrony between electrode positions. Pseudoword repetition, in contrast, leads to an activation increase in the same areas, to increased GBRs, and to an increased phase coupling. This spatiotemporal repetition by stimulus type interaction suggests that qualitatively distinct mechanisms are recruited during repetition priming of familiar and unfamiliar stimuli. Repetition of familiar stimuli leads to a "sharpening" of extrastriate object representations, whereas the repetition of unfamiliar stimuli results in the "formation" of a novel cortical network by means of synchronized oscillatory activity. In addition to isolating these mechanisms, the present study provides the first evidence for a possible link between induced electrophysiological and hemodynamic measures of brain activity.

Adult↗
PubMedDate not supplied

Brainstem correlates of gustatory similarity in the hamster.

Responses of neurons in the nucleus tractus solitarius (NTS) and parabrachial pons (Pb pons) of the hamster to 10 gustatory stimuli were compared to behavioral similarities among these compounds. Animals were given a conditioned taste aversion to one of the 10 stimuli by pairing it with an induced gastrointestinal illness. Following this procedure, the degree of generalization of the learned taste aversion to each of the other compounds was measured. Behavioral similarity profiles were derived for each stimulus from the similarities in the generalization profiles of each pair of compounds. The across-neuron correlations in the firing rates evoked by these stimuli in the NTS cells corresponded quite well to these behavioral profiles, as did these neural correlations among Pb pontine cells, except for those correlations involving quinine. Sucrose-best cells in the Pb pons are too broadly responsive to account for the behavioral similarity functions for sweet-tasting stimuli, although other best-stimulus categories of cells (NaCl- and HCl-best) showed response profiles quite similar to the behavioral profiles, as did all best-stimulus classes of cells in the NTS.

Animals↗
PubMed1992

Effects of stimulus intensity on posterior tibial nerve somatosensory evoked potentials.

Relationships between stimulus intensity and peak latencies and amplitudes in posterior tibial nerve somatosensory evoked potential patterns were evaluated in ten healthy subjects. Eight intermediate latency peaks between 30 and 125 milliseconds (ms) after stimulus onset and seven amplitudes were analyzed. In general, there was a decrease in latency with each increase in stimulus intensity over a five step intensity range between 5 and 19 milliamps (mA) for most peaks. Similarly, increases in amplitudes generally occurred with increases in stimulus intensity for most peaks. Later peaks N105 and P115 as well as amplitudes P90-N105 and N105-P115 were least sensitive to stimulus intensity changes. The greatest changes in peak latency and amplitude occurred as stimulus intensity was increased from 7 to 11 mA. Beyond 11 mA relatively little change was observed in either peak latencies or amplitudes. Under anesthesia, by contrast, there was no stimulus intensity-peak latency interaction and beyond 11 mA there were decreases in amplitudes. Possible reasons for these findings are discussed.

Adult↗