Effects of click intensity and frequency on the brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 20 common marmosets (Callithrix jacchus) to investigate the effects of click frequency up to 99 kHz, in consideration of the higher hearing range of the marmoset, and intensity on wave forms and peak latencies. According to the results of BAEP recordings at frequencies of 4, 32, and 99 kHz, the number of components recorded was affected by the stimulus intensity and the clicks at an intensity of 80 dB peak equivalent sound pressure level (pe SPL) had the maximum number of clear components. Therefore, it was indicated that click stimulations at an intensity of 80 dB pe SPL over a broad range of frequencies appears to be useful for recording the maximum number of components in marmosets and may increase the information obtainable from BAEPs. BAEP latencies were prolonged as the stimulus intensity decreased from 100 to 50 dB pe SPL. The effects of stimulus frequency on the wave latencies and amplitudes in response to 80 dB pe SPL at frequencies between 0.5 and 99 kHz revealed various changes: the amplitude of wave I increased at 16 and 32 kHz, but that of waves III and V increased at 4-8 and 64-99 kHz. These increases in amplitudes of the waves may correlate with higher synchronous activity of the peripheral or central auditory pathways.     

Informed consent for epidural analgesia in labor

Characteristics and reproducibility of bulbocavernosus reflex (BCR) and pudendal somatosensory evoked potentials (PSEP) elicited by mechanical stimulation in children were tested. Twenty-five male children aged 5-14 years without uroneurological complaints were enrolled in the study. In addition to electrical stimulation, a specially constructed electromechanical hammer triggered by an oscilloscope was used for mechanical stimulation of distal penis. All responses were detected by surface electrodes. The latencies and amplitudes of averaged as well as latencies of single BCR on single and double electrical stimuli were determined. Mechanical stimulation was described as much less unpleasant than electrical stimulation. Both mechanical/electrical stimulation elicited consistent and reproducible responses in high percentages of children (BCR: average, 80%/71%, single, 94%/100%; PSEP: 96%/96%, respectively). BCR latencies were significantly longer and PSEP amplitudes were significantly higher on mechanical stimulation. The compliance with mechanical was much better than with the electrical stimulation and the former can be recommended for clinical use. The effective mechanical stimulus delivered by a particular mechanical stimulator has a characteristic 'delay' (as to the actual point of triggering the oscilloscope ray) which influences the latency reading of responses; appropriate control data are therefore necessary.     

The ontogeny of interstimulus interval (ISI) discrimination of the conditioned eyeblink response in rats.

Discrimination of the eyeblink conditioned response (CR) between conditioned stimuli (CSs) of different durations and modalities was examined across development in rats. Interstimulus interval (ISI) discrimination was evident at Postnatal Days 23-34 in Experiment 1, and earlier CR peak latencies and enhanced CR amplitudes were seen to the long CS in the ISI discrimination group relative to a control group receiving the short CS without reinforcement. Experiment 2 showed that early CR peak latencies and enhanced CR amplitudes to the long CS in the ISI discrimination group were due to associative pairing of the short CS and unconditioned stimulus. Experiment 3 demonstrated ISI discrimination in adults that was improved relative to younger subjects, but with no enhancement of CR amplitude to the long CS in the ISI discrimination group. Cerebellar cortical maturation may influence the ontogeny of CR timing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional characteristics of lateral interactions between rods in the retina of the snapping turtle

1. Intracellular recordings were made of the slow hyperpolarizing light responses of single rods in the retina of the snapping turtle. Physiological criteria used to identify rods were verified by intracellular injections of Procion Yellow. 2. The amplitudes of the responses elicited by fixed intensity flashes increased as the stimulus was enlarged to a diameter of 300 mum. Scattered light was found incapable of accounting for this effect, which must result from summative interaction of rods with neighbouring receptors. Effects of summative interaction were observed even at stimulus intensities that produced maximal responses. Enlarging the diameter of the higher intensity stimuli from 100 to 300 mum increased the peak response amplitude by almost 50%; it also produced a distinct initial peak of the response which we term overshoot. The amplitude of this overshoot was graded with stimulus size. 3. Complete intensity-response relationships were determined using stimulus diameters of 100 and 750 mum for each rod. With the smaller stimulus the intensity response range was 4-5 log units, and with the larger stimulus this was increased to 5-0 log units. For intensities below about 60 quanta/mum2 per flash (514 nm) the amplitudes elicited by the large stimulus followed a sigmoid-shaped curve. However, at higher intensities an additional lobe appeared on the intensity-response relationship. The appearance of this lobe correlated with the emergence of the overshoot on the response wave form. 4. Determinations of rod flash sensitivity (mV per quantum per mum2) showed that it increased with stimulus size up to a stimulus diameter of about 300 mum. With diameters between 50 and 150 mum, a linear relationship existed between the flash sensitivity and stimulus area. Absolute quantal sensitivities increased with stimulus area by a factor of 26, from a value of 28 muV per photoisomerization per rod with a stimulus 25 mum in diameter, to 720 muV per photoisomerization per rod with a stimulus 300 mum in diameter. 5. By comparison, red-sensitive cones showed increased sensitivity as a function of stimulus size only up to a stimulus diameter of 120 mum. Their over-all sensitivity was lower than that of rods and proved linear with stimulus diameter rather than with stimulus area. 6. Simultaneous recordings were made from rod-cone pairs to determine whether the overshoot, and hence the lobe on the amplitude-intensity function, could result from a cone input to the rod response. The time course of the cone response proved much too rapid to fit the overshoot of the rod response. 7. The spectral sensitivity of the dark-adapted rod response closely followed the difference spectrum of the rod photopigment for wave-lengths greater than 450 nm. This was true throughout the intensity range of the response, including low intensities where response averaging was necessary. 8. At low response amplitudes (approximately 1 mV), about 70% of the 40 rods tested showed responses to long wave-length stimuli consisting of two components...     

Management of neurogenic bladder dysfunctions following acute traumatic cervical central cord syndrome (incomplete tetraplegia) [proceedings]

The bases for variations of the middle-component (8-50 ms) auditory averaged electroencephalic response (AER) to clicks during the averaging process were explored by examining (1) the trend of the mean variance of the averaged waveform, (2) averaged waveforms generated by successive blocks of stimuli fractioned from a total of 512 stimuli, and (3) averaged waveforms generated by successive, but partially overlapping, blocks of responses recorded for a train of 512 stimuli. These analyses indicated no systematic changes in peak latencies or peak-to-peak amplitudes as stimulation progressed. Fluctuations in middle AER waveform are more readily explained by non-stationarity of the background electrophysiologic noise. Previously reported amplitude reduction with increasing stimulus number possibly can be explained by progressive reduction of the background noise on which the consistent-amplitude middle components are superimposed.     

Effects of halothane and sevoflurane on the electroretinogram of dogs

OBJECTIVE: To study the effects of halothane and sevoflurane on the electroretinogram of dogs. ANIMALS: 6 clinically normal Beagles. PROCEDURE: Beagles were paralyzed by continuous IV administration of muscle relaxant and were artificially ventilated with a gas mixture of nitrous oxide and oxygen during experiments. Corneal electroretinograms were recorded, using full-field stimuli under several recording conditions before and during 1% halothane or 2% sevoflurane inhalation. RESULTS: The amplitude of the scotopic threshold response (STR) and b-wave was significantly decreased by halothane or sevoflurane inhalation, but the degree of decrease in the STR was much greater. In contrast, the amplitudes of oscillatory potentials were increased. The peak latencies of the 3 components tended to be prolonged by inhalation of the anesthetic. There seemed to be no difference between the effects of halothane and sevoflurane. CONCLUSIONS: Halothane and sevoflurane strongly depressed the STR in Beagles while moderately depressing the b-wave and increasing oscillatory potential amplitudes. Thus, neither is an appropriate anesthetic for use in recording of the STR in dogs.     

The adequate stimulus for avian short latency vestibular responses to linear translation

Transient linear acceleration stimuli have been shown to elicit eighth nerve vestibular compound action potentials in birds and mammals. The present study was undertaken to better define the nature of the adequate stimulus for neurons generating the response in the chicken (Gallus domesticus). In particular, the study evaluated the question of whether the neurons studied are most sensitive to the maximum level of linear acceleration achieved or to the rate of change in acceleration (da/dt, or jerk). To do this, vestibular response thresholds were measured as a function of stimulus onset slope. Traditional computer signal averaging was used to record responses to pulsed linear acceleration stimuli. Stimulus onset slope was systematically varied. Acceleration thresholds decreased with increasing stimulus onset slope (decreasing stimulus rise time). When stimuli were expressed in units of jerk (g/ms), thresholds were virtually constant for all stimulus rise times. Moreover, stimuli having identical jerk magnitudes but widely varying peak acceleration levels produced virtually identical responses. Vestibular response thresholds, latencies and amplitudes appear to be determined strictly by stimulus jerk magnitudes. Stimulus attributes such as peak acceleration or rise time alone do not provide sufficient information to predict response parameter quantities. Indeed, the major response parameters were shown to be virtually independent of peak acceleration levels or rise time when these stimulus features were isolated and considered separately. It is concluded that the neurons generating short latency vestibular evoked potentials do so as "jerk encoders" in the chicken. Primary afferents classified as "irregular", and which traditionally fall into the broad category of "dynamic" or "phasic" neurons, would seem to be the most likely candidates for the neural generators of short latency vestibular compound action potentials.     

Event-related potential measures of 24-hour retention in 5-month-old infants.

Two experiments using event-related potentials (ERPs) investigated 24-hr recognition memory in infants. In each, ERPs were recorded to 100 identical stimuli in 5-mo-olds. After 24 hrs, 50 of these familiar stimuli and 50 novel stimuli were presented. In Exp 1, the 2 stimuli were a tone and a click. The amplitude of a negative peak (N2; approximate latency?=?350 msec) of the auditory ERP was larger on Day 2 for the familiar stimuli compared with ERPs for both Day 1-familiar stimuli and Day 2-novel stimuli. Trial-to-trial latency variability of N2 decreased from Day 1 to Day 2 for the familiar stimuli. In Exp 2, 2 tones differing only in frequency (pitch) were used. The results replicated those of Exp 1. In addition, an earlier positive peak (P2; approximate latency?=?200 msec) showed larger amplitudes and smaller latency variability to the familiar stimulus on Day 2. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactions of pluronic block copolymers with brain microvessel endothelial cells: evidence of two potential pathways for drug absorption

The effect of stimulus size on the pattern onset-offset visual evoked potential elicited with stimuli of two different wavelengths is studied under intensive yellow adaptation: (1) The onset response obtained with a 460 nm pattern is of negative polarity (N1) and saturates in amplitude with a stimulus radius of 7 deg. The onset response obtained with a 550 nm pattern is of positive polarity and continues to increase up to the maximum size (32.2 deg). (2) The peak time of N1 (460 nm) decreases with increasing stimulus size, that of P1 (550 nm) remains constant. These results are discussed as reflecting either varying retinal and brain anatomy, or cone activity, color-opponent activity, or luminance contrast activity.     

Brainstem auditory evoked potentials in young children before and after tympanostomy tube placement

To evaluate the effect of tympanostomy tube placement upon the hearing function of infants and young children, brainstem auditory evoked potentials (BAEP) were recorded in a group of young children (mean age 22 mos) receiving this treatment for otitis media with effusion (OME). For comparison, a group of healthy infants with normal behavioral audiometry were also tested with BAEP. Hearing loss was estimated for each ear using peak V latency-intensity curves. To evaluate the immediate effect of tube placement, 98 ears in 52 children were tested immediately before and after tube insertion. The 63 ears with effusion had prolonged peak latencies that decreased significantly (P < 0.001) immediately after tube placement and a mean hearing loss estimate of 22 dB that improved significantly (P < 0.0001) to 11 dB immediately after tube insertion. The 35 ears without effusion at myringotomy had a mean hearing loss estimate of 8 dB that did not change significantly after tube insertion. To evaluate the short-term effect of tube presence, 39 ears in 25 children were tested 3 weeks to 18 months after tube insertion. The 28 ears with dry tubes had a mean hearing loss estimate of 3 dB, and the 11 ears with otorrhea had a mean hearing loss estimate of 31 dB. The magnitude of mean hearing loss estimates in these young children with OME and the improvement in hearing function with tube placement is similar to that reported in older children studied with BAEP and audiometry. The study groups with a history of otitis media that had resolved by the time of testing had isolated prolongation of mean III-V interpeak latencies compared to normals (P < 0.01). These studies show that BAEP techniques are useful in estimating hearing loss in children with OME who are difficult to test by behavioral audiometry and show changes in rostral brainstem transmission in very young children with a history of OME.     

The rotatory machines in the history of psychiatry

In this study, we recorded the event-related potentials (ERPs) elicited by stimuli appearing at attended and unattended locations. The voltage amplitudes and latencies of the P1, N1, P2, N2 and P3 visual components showed statistically significant differences in the attended condition with respect to the unattended one. The power spectral density of the EEG following stimulus onset was calculated. The difference between the spectral densities of the attended and unattended conditions was computed. Statistically significant differences were found in the decrease of alpha (9-11 Hz) and the increase of beta (15-17 Hz) frequencies during the attention condition with respect to the unattended condition. These results suggest that the arrival of a visual stimulus during the attended condition generates a complex reorganization of neuronal activity in both time and frequency domains.     

Neural retinal contribution to the slow negative potential of the canine electroretinogram

To establish the normal waveform of the electrical responses from canine eyes, electroretinograms and the light peak were recorded in hybrid and beagle dogs under general anesthesia and artificial ventilation. The neural retinal and retinal pigment epithelial components were pharmacologically isolated by intravitreal glutamate injection and systemic sodium iodate administration, respectively. The a- and b-waves elicited by either flash or rectangular stimuli, the oscillatory potentials elicited by flash stimuli and the light peak elicited either by a single maintained illumination or by repetitive stimuli were almost identical with those of other vertebrates thus far studied. In contrast, in response to rectangular (several-second duration) stimuli, the c-wave was usually absent and was replaced by a slow cornea-negative potential that had a time course similar to that of the c-wave in other species. This slow negative potential was elicited at such low stimulus intensities that the a-wave was absent, was deepened by an intravenous administration of sodium iodate, was not affected by an intravitreal injection of sodium glutamate and was shallowed during the light peak. These results suggest that the slow negative potential that replaces the c-wave consists of large slow PIII, small retinal pigment epithelial c-wave and negligible contribution from the late photoreceptor potential and the dc component of the PII.     

Synergy between two calcium channel blockers, verapamil and fantofarone (SR33557), in reversing chloroquine resistance in Plasmodium falciparum

Transcranial magnetic stimuli at different stimulus intensities were applied in six healthy subjects to test the hypothesis that, in different intrinsic hand muscles, the duration of the resultant cortically evoked silent periods (C-SPs) from each stimulus would be positively correlated between muscles, indicating a common inhibitory mechanism. A figure-of-eight coil discharging through a Magstim 200 stimulator delivered 25 stimuli at each stimulus intensity at a minimum of five intensities ranging from 55% to 160% of the individual resting motor threshold. In each subject, simultaneous surface recordings from pairs of muscles were made from the first dorsal interosseous (FDI), opponents pollicis (OP), abductor pollicis brevis (APB) and abductor digiti minimi (ADM). The C-SP durations within all three muscle pairs tested were highly correlated (P<0.001). The amplitude of the preceding compound-muscle action potentials (CMAPs) was positively correlated between FDI and OP, but not between APB and ADM or FDI and ADM. C-SP duration was linearly related to stimulus intensity, but did not correlate with the latency or amplitude of the preceding CMAP. SPs elicited by peripheral nerve stimuli in pairs of hand muscles did not co-vary significantly. The results provide evidence that inhibitory influences of cortical origin are distributed widely to intrinsic hand muscles. In contrast, covariation of excitatory effects only appears between muscles synergistically involved in a motor task.     

Release of renin from glomeruli isolated from rat kidney

Cardiovascular and behavioural responses elicited by novel, noxious or aversive stimuli have been studied in dogs and cats. Hindlimb blood flow, heart rate and arterial blood pressure increased in dogs when an orienting response was elicited by a novel stimulus (a sound). Similar cardiovascular responses occurred in dogs to mild noxious stimulus and in cats displaying a threatening posture when confronted by a dog. The cardiovascular components of the orienting response to a sound habituated with repetition of the sound. In two dogs however sensitization (increase) of the response occurred with reped by repetition of the confrontations: the vasodilation in the muscles waned and eventually was replaced by vasoconstriction while the cardiac acceleration and pressor response persisted. The threatening response was the most persistent. The modification of the behavioural and cardiovascular aspect of the response was not developing in parallel. The cardiovascular pattern was altered before any apparent changes of the behavioural pattern occurred. The cardiovascular responses of the noxious stimulus in dogs and cardiovascular components of the defence reaction in cats were readily conditioned to a sound. The possible role of the modification of the cardiovascular pattern in defence reactions in pathogenesis of hypertension is discussed.     

Vestibular-evoked electromyographic responses in soleus: a comparison between click and galvanic stimulation

The aim of this study was to demonstrate, if possible, vestibulospinal reflex responses in soleus using a stimulus known to be capable of exciting vestibular afferents, namely 100-dB (NHL) clicks. We were able to show short-latency electromyographic (EMG) responses after clicks in five of eight normal subjects, and then we compared these responses with those after transmastoid galvanic stimulation (12 normal subjects). Stimulation of the side towards which the head was rotated (i.e. the side facing backwards) with either clicks or the cathode (anode applied to the opposite side) gave an initial excitatory response in soleus, while click or cathodal stimulation of the opposite side (i.e. the side facing forwards) gave an initial inhibitory response. Onset latencies and modulation with changes in postural task were identical for both click- and galvanic-evoked responses. In addition, there was a significant correlation between the amplitudes of the responses in soleus after click and galvanic stimulation (R2=0.72). These similarities suggest that the earliest reflex responses in soleus after clicks and galvanic stimulation may be mediated by a common central pathway. In contrast, there was no correlation between the amplitudes of responses evoked by 100-dB clicks in soleus and those evoked by the same stimulus in the sternocleidomastoid. We conclude that vestibular activation by clicks can evoke reflex responses in lower-limb muscles and these responses have similar characteristics to the earliest responses evoked by galvanic vestibular stimulation.     

Middle and long latency auditory evoked potentials in cat. II. Component distributions and dependence on stimulus factors

The middle (10-50 ms) and long (50-600 ms) latency periods of the auditory evoked potential (AEP) were investigated in muscle-paralyzed, artificially respired cats with respect to two issues: (1) the distribution of components across the skull, and (2) the effects of changing stimulus intensity on component latencies and amplitudes. The distributional data were gathered during a behavioral study in which four behavioral tasks related to classical pupillary conditioning were used to vary attentional and arousal processes. The distributions across the skull surface (averaged across tasks) of 12 peaks and troughs (P10, N13, P17, N22, P31, N41, P55, N70, N100, N140, P260 and N520) and seven principal components derived from the set of waveforms collected during this experiment are reported. Both peak amplitudes and principal component scores were distributed differentially across the skull surface. In the second experiment, acoustic stimulus intensity was varied, and AEPs collected from a vertex and temporal electrode site. In general, increasing stimulus intensity had a stronger influence on the earlier portions of the AEP, where increased amplitude and decreased latency was the rule, than on later ones. The relationships between cat and human AEP components were discussed based on both the data presented in this paper and in previous papers.     

Effects of regional stimulation using a miniature stimulator implanted in feline posterior biceps femoris

The effects of placement of a miniature implantable stimulator on motor unit recruitment were examined in the posterior head of cat biceps femoris. The implantable stimulator (13-mm long x 2-mm diameter) was injected either proximally near the main nerve branch, or distally near the muscle insertion, through a 12-gauge hypodermic needle. Glycogen-depletion methods were used to map the distribution of fibers activated by electrical stimulation. Muscle fibers were found to be depleted at most or all proximodistal levels of the muscle, but the density of depleted fibers varied transversely according to the stimulus strength and proximity of the device to the nerve-entry site. Thus, muscle cross sections often had a "patchy" appearance produced because different proportions of depleted fibers intermingled with undepleted fibers in different parts of the cross section. In other preparations, the force of muscle contraction was measured when stimuli of varying strengths were delivered by the stimulator positioned at the same proximal or distal sites within the muscle. Devices placed close to the nerve-entry site produced the greatest forces. Those placed more distally produced less force. As stimulus current and/or pulse width increased, muscle force increased, often in steps, until a maximum was reached, which was usually limited by the compliance voltage of the device to less than the force produced by whole nerve stimulation.     

Intensity discrimination and auditory brainstem responses in cochlear implant and normal-hearing listeners

Intensity-discrimination limens (IDLs) and auditory brainstem responses (ABRs) were measured as a function of stimulus intensity in 6 cochlear implant (CI) and 8 normal-hearing (NH) listeners. Pulse-train stimuli were delivered electrically to the auditory nerve in CI listeners and acoustically in NH listeners. In CI listeners, the IDLs expressed as Weber fractions decreased monotonically with increasing intensity. In NH listeners, a nonmonotonic IDL function showing a peak a midintensities was observed. ABR wave amplitudes increased regularly with intensity only in CI listeners. Results support the notion that the slight decrease in Weber's fractions with increasing sound intensity--generally referred to as "the near-miss to Weber's law"--is subtended by retrocochlear processes, whereas the increase in Weber's fractions at midlevels--known as "the severe departure from Weber's law"--originates in cochlear mechanisms.     

Transient-evoked and 2F1-F2 distortion product oto-acoustic emissions in dogs: preliminary findings

Transient (click)-evoked oto-acoustic emissions (TEOAEs) and distortion product oto-acoustic emissions (DPOAEs) were recorded in a feasibility study in 7 healthy mixed-breed dogs using the ILO 92 OAE analyser (Otodynamics, Hartfield, UK). Five dogs were found to have normal hearing in both ears and 2 dogs in the left ear only following otoscopy, tympanometry and auditory brainstem response audiometry. Twelve sets of TEOAEs (click-evoked) to 80 dB peSPL click stimulus and 9 sets of DPOAEs (2F1-F2) to 8 different stimulus levels of the primary tones (L1/L2) were collected at 11 test frequencies (F2) in these normal-hearing dogs. TEOAEs were successfully recorded in 11 of the 12 ears using the default user setting and in all 12 ears using the quickscreen program. DPOAEs were successfully recorded in all 9 ears tested. While the TEOAEs parameters matched those for humans, the average signal-to-noise ratio of DPOAEs was considerably higher in the dogs. Stimulus levels at 55/55, 55/45 and 55/35 dB SPL were demonstrated to produce DPOAEs that seem to reflect the active dynamic status of the outer hair cell system. Postmortem DPOAEs at these stimulus levels and TEOAEs at 80 Db peSPL could not be elicited 5 min following euthanasia of dogs. However, DPOAEs could still be recorded albeit with reduced amplitude at stimulus levels where L1 > 55 dB SPL. The results suggest that TEOAEs and DPOAEs in dogs have the potential to provide valuable insights into their mechanisms of generation, and the specific role and behaviour of outer hair cells of the cochlea in certain pathological conditions, particularly in drug-induced ototoxicity, in humans.