Changes in EEG power, acoustic evoked potentials and heart rate after mildly arousing non-acoustic priming stimuli in carp (Cyprinus carpio).

1. Changes in EEG power spectrum of carp to a priming non-acoustic stimulus followed by acoustic clicks were compared to those due to acoustic clicks delivered alone. Recordings were made from the telencephalon, midbrain and medulla. Acoustic evoked potentials (AEPs) to the clicks were also recorded. 2. EEG power changes to non-acoustic stimuli occurred over the whole 1-40 Hz frequency range and were regionally specific and consistent. 3. The changes in the EEG midfrequency 12-24 Hz power spectrum to non-acoustic stimuli were significantly correlated with changes in the AEP to subsequent clicks. An elevated medullary AEP amplitude and reduced duration were correlated with increased medullary EEG power and increased midbrain AEP duration. 4. Telencephalic EEG power changes were inversely related to changes in medullary and midbrain AEP amplitude.     

Sustained potential shifts,alterations in acoustic evoked potential amplitude and bradycardiac responses to the onset of illumination in the goldfish (Carassius auratus)

Sustained potential shift's (SPSs) and changes in acoustic evoked potential (AEP) amplitudes were recorded from medullary and mid-brain regions in restrained goldfish (Carassius auratus) in response to the onset of illumination against a sensory background restricted to repetitive (1/s) acoustic stimulation. At the tectal surface, a long duration negative SPS, significant 5–10 s after the onset of illumination, was recorded with a maximum negativity of ca. 145 V. Changes in acoustic responsiveness were also most apparent in the mid-brain where attenuations in AEP amplitude of ca. 15% were recorded.In general, AEPs exhibited attenuated amplitudes in response to the onset of illumination, perhaps reflecting attentional rather than arousal processes, arousal generally being associated with heightened sensory responsiveness. Changes in the amplitude of the medullary AEPs were directly related to the magnitude of bradycardiac responses such that lesser attenuations of the medullary AEP were associated with greater magnitude bradycardiac responses, suggesting a possible interaction of attentional and arousal processes.In response to repeated onset of illumination, SPSs tended towards increasing positivity (increasing in positivity at the medullary surface; decreasing in negativity at the tectal surface). The attenuation of AEPs recorded from the medulla and mid-brain habituated in response to stimulus repetition.Changes in amplitude of AEPs (AEP) recorded from the telencephalon and the torus semicircularis region of the mid-brain were correlated with locally recorded SPSs. At the telencephalon, this correlation was inverse; enhanced AEP amplitudes being associated with SPS negativity, attenuated AEP amplitudes with SPS positivity. In the torus semicircularis, experiential changes in SPS and AEP were directly correlated. As the SPS is considered to reflect glial redistribution of [K⁺]_e (Roitbak 1983), glia may contribute to changes in measures of sensory responsivity, such as the AEP, during changes in behavioural state.Abbreviations AEP Acoustic Evoked Potential - AEP Event-related change in amplitude of AEP following onset of illumination - SPS Sustained Potential Shift - [K⁺]_e Extracellular concentration of K⁺     

Changes in early acoustic-evoked potentials by mildly arousing priming stimuli in carp (Cyprinus carpio).

1. Averaged acoustic-evoked potential (AEPs) in the medulla and midbrain were recorded, as were changes in heart rate, indicating arousal, to a previous non-acoustic priming stimulus. 2. Useful AEP measures were amplitude of the early biphasic wave (less than 10 msec) in medulla and amplitude and duration of this wave in midbrain. 3. There was a negative regression of heart rate and medullary AEP amplitude especially evident for a 2 sec light stimulus. Decreased AEP amplitude in both regions was induced by water movement and an increase in midbrain AEP duration by the tactile stimulus. 4. Arousal effects even on these early AEP measures are specific to the form of arousing stimulus.     

Visual unit,EEG and sustained potential shift responses to biologically significant stimuli in the brain of toads (Bufo bufo)

Summary Visual unit activity, EEG changes and sustained potential shifts (SPS) were recorded from the toad tectum whilst the animal was presented with a visual stimulus. Telencephalic EEGs were also recorded.On the surface of the tectum, retinal unit activity preceded a sustained negative shift in potential and an increase in the amplitude and dominant frequency of the EEG. In deeper layers of the tectum, T5 units with configurational selectivity for wormlike stimuli were found. The activity of these units followed a pronounced SPS and EEG change.Visual unit activity was most pronounced during the negative-going phase of the synchronised EEG, when there was also a small decrease in amplitude of neuronal spikes. Similarities between the latencies and durations of EEGs and SPSs, and their response decrements, on repeated stimulus presentation, implies a close relationship between them not shared by the visual units studied. The specific activity of tectal units is discussed in relation to the correlated EEG and SPS changes, which may form part of an adaptive sensitizing mechanism.Abbreviations EEG electroencephalogram - ERF excitatory receptive field - SPS sustained potential shift - T4, T5 tectal neurons     

Dendritic and sustained shifts in potential to electrical stimulation of the anuran tectal surface.

1. Recordings of dendritic potentials and sustained potential shifts (SPS) were made from the brain of immobilised frogs during surface tectal electrical stimulation. 2. Single pulses evoked dendritic responses; trains caused decay of dendritic responses on the background of the evoked SPS. 3. The tectal surface SPS declined with distance from the stimulating electrode. 4. The negative surface SPS declined with tectal depth to ca 300 microns, then reversed polarity and increased in amplitude with depth up to 700 microns.     

Processing of ampullary input in the brain: comparison of sensitivity and evoked responses among elasmobranch and siluriform fishes

1. Averaged evoked potentials (AEP) in response to pulses and sine waves of electric current, either as a homogeneous field or a large dipole field around the fish, have been recorded from the brain in 5 genera of elasmobranchs and 10 genera of siluriform fishes. 2. In the elasmobranchs, AEP's and spike-hash bursts are described from medulla, cerebellum, mesencephalon and telencephalon. A complex sequence of early and late waves is found in each level. Two sets of factors influence the latency and amplitude of the component waves. One is stimulus parameters including intensity, stimulus orientation, sign of the change of current, position of dipole, serial number in the first few cycles of a train as well as interval or frequency of a regular series. Separate component peaks of the complex AEP appear to have different dependencies upon these factors. To sinusoidal stimuli the best response by a certain criterion is at 20--30 Hz in a shark (Carcharhinus), 10--15 Hz in a ray (Potamotrygon); these are much higher than the values based on behavior from previous authors. The lowest threshold, with moderate averaging, was 0.015 muV/cm (= 0.8 nA/cm2) in marine species, less than 50 muV/cm (= 0.7 nA/cm2) in the freshwater ray. 3. The other set of factors determining AEP is brain parameters, including the recording locus, the type of electrode and electrode advance and the state of the brain (anesthesia, etc.). There is evidence of topographic segregation of some stimulus parameters, but mapping was not undertaken. Responsive regions are described in the several brain levels. 4. The best loci for electric AEP are distinct from those for acoustic and photic AEPs. No interaction between these was found. 5. All of the siluriforms tested show electroreception by the criterion of high sensitivity AEP. No obvious specialization was noted among the diverse species, but most were represented by a single experiment. Taken together with the previously known species, the sample of nine families of this large order suggests that this is a general characteristic of the order. 6. The best responses were found in the region of the torus semicircularis and in the lateral lobe. The lowest threshold by the criterion used was less than 0.15 mV/cm (= 2 nA/cm2), but some were nearly 2 mV/cm. Compared to much lower values in Ictalurus, this suggests species differences although part of the difference may be due to failure to record from the optimal locus. The AEP may be useful as a method of suveying for other electroreceptive groups. It is also potentially useful to reveal discriminable parameters of importance, such as dipole position, orientation, polarity and frequency.     

Fast habituation of the long-latency auditory evoked potential in the awake albino rat

Fast habituation of the long-latency, vertex-recorded auditory evoked potential (AEP) peaks in humans was first described by Callaway (1973) as a reduction in AEP amplitude that occurs to the second of a pair of acoustic stimuli when both stimuli are presented with an interstimulus interval (ISI) of no more than 10 sec. When acoustic stimuli are presented in pairs with an ISI of 2 sec and an interpair interval (IPI) of approximately 10 sec, reduction in amplitude to the second tone occurs by as much as 30–50%. Fast habituation may depend somewhat on a subject's anticipation of the stimulus and on other factors related to attention and orienting. Studies in our laboratory have demonstrated this amplitude decrement to the second tone of a pair in human infants, children and adults and have explored the implications of this finding with respect to attentional processes and the allocation of cerebral resources. In the present investigation we describe an animal model of fast habituation. Here, vertex-recorded AEPs were obtained to paired tone stimuli delivered to awake adult male Sprague-Dawley rats chronically implanted with skull electrodes. Findings showed: (a) an AEP wave form with 8 distinct peaks, (b) for one component there was a marked decrement in amplitude from tone 1 to tone 2 in recordings obtained from an electrode placed slightly to the right of midline, and (c) that there were no significant differences in peak latencies across tones. This methodology may further our understanding of fast habituation in humans and may prove useful for studies of attention, orienting, and resource allocation using techniques that are not possible for use with human subjects.     

Cortical evoked potentials as indicators of auditory-visual cross-modal association in young adults

Auditory evoked potentials (AEPs) were studied from scalp locations Cz and Oz on 37 adults aged 20-22 years during sensori-sensorial association of a weak sound (S) and a strong flash of light (L). After sound alone repetition (habituation), S-L association modified AEP: first, it caused a generalized orienting response expressed as increasing of Cz and Oz amplitude AEPs. Then, this pattern gave way to an activation limited to the Oz lead: the increase of amplitude was then concomitant with shortened latencies when compared to sound-alone-habituated responses. Inter-individual differences were observed since these occipital modifications were recorded only on 26 subjects. The other 11 subjects did not exhibit any occipital modifications following S-L association. For them, the main modification was a strong decrease of Cz AEP induced by S-L association. These two groups also differed in their capacity to ignore irrelevant stimuli which is higher in the first group (AEP amplitude habituation with sound-alone repetition) than in the second one (no AEP habituation).     

The antidromic activation of tectal neurons by electrical stimuli applied to the caudal medulla oblongata in the toad,Bufo bufo L.

In order to specify the tectal projection to the bulbar/spinal regions, the antidromic responses of the physiologically identified tectal neurons as well as the gross antidromic field responses in the optic tectum to electrical stimuli applied to the caudal medulla were examined in the paralyzed common toad, Bufo bufo. The antidromic field potential was recorded in the optic tectum in response to electrical stimuli applied to the ventral paramedian portion of the contralateral caudal medulla (where the crossed tecto-spinal pathway of Rubinson (1968) and Lázár (1969) runs), but generally not when they were applied to various parts of the ipsilateral caudal medulla. The antidromic field potential was largest at the superficial part of Layer 6 or at the border between Layers 6 and 7 of the optic tectum, indicating that neurons in these layers project to the contralateral caudal medulla. Mapping experiments of the antidromic field potential over the optic tectum showed that the antidromic field potential was recorded mainly in the lateral part of it, indicating that this part of the optic tectum is the main source of projection neurons to the contralateral caudal medulla. Various classes of tectal neurons as well as retinal ganglion neurons were identified from the characteristics of the response properties to moving visual stimuli and the properties of the receptive fields. Of these, the Class T1, T2, T3, T4, T5(1), T5(2), T5(3), and T5(4) tectal neurons were activated antidromically by stimuli applied to the contralateral caudal medulla. Only a limited proportion of the Class T5(1) neurons was activated antidromically by stimuli applied to the ipsilateral caudal medulla. On the other hand, the Class T7 and T8 neurons, as well as the Class R2, R3, and R4 retinal neurons, were not activated antidromically by stimuli applied to the caudal medulla of either side. These results suggest a possibility that these tectal neurons which project to the medullary regions form the substrate of the sensorimotor interfacing and contribute to the initiation or coordination of the visually guided behavior, such as prey-catching.     

Hemispheric asymetry of the evoked electrical activity of the cerebral cortex to letter and non-verbal stimuli]

Average evoked potentials (AEP) were recorded in practically healthy subjects to "meaningless" figures and letters, presented to different halves of the visual field. Analysis of the amplitudes of AEP late components to verbal and non-verbal stimuli reveals hemispheric asymmetry. A higher amplitude of the late positive evoked response (P300) to a "direct" stimulation both by verbal and non-verbal stimuli (in the contralateral field of vision) is recorded in the left hemisphere than in the right one. Similar stimulation of the right hemisphere does not reveal sucha difference. In the left hemisphere the P300 wave is of a clearly greater amplitude to a "direct" stimulation (contralateral visual field) than to an "indirect" one (ipsilateral visual field), regardless of the nature of the stimulus. No such difference is observed in the right hemisphere. The magnitude of the late negative wave (component N200) to non-verbal stimuli is greater in the right hemisphere both in response to "direct" and "indirect" stimulations. No intrahemispheric difference has been found in the amplitude of late evoked responses of the cerebral cortex to verbal and non-verbal stimuli.     

Temporal resolution of the Florida manatee (<Emphasis Type="Italic">Trichechus manatus latirostris</Emphasis>) auditory system

Auditory evoked potential (AEP) measurements of two Florida manatees (Trichechus manatus latirostris) were measured in response to amplitude modulated tones. The AEP measurements showed weak responses to test stimuli from 4 kHz to 40 kHz. The manatee modulation rate transfer function (MRTF) is maximally sensitive to 150 and 600 Hz amplitude modulation (AM) rates. The 600 Hz AM rate is midway between the AM sensitivities of terrestrial mammals (chinchillas, gerbils, and humans) (80–150 Hz) and dolphins (1,000–1,200 Hz). Audiograms estimated from the input–output functions of the EPs greatly underestimate behavioral hearing thresholds measured in two other manatees. This underestimation is probably due to the electrodes being located several centimeters from the brain.     

Colon Necrosis Due to Sodium Polystyrene Sulfonate with and without Sorbitol: An Experimental Study in Rats

Introduction

Based on a single rat study by Lillemoe et al, the consensus has been formed to implicate sorbitol rather than sodium polystyrene sulfonate (SPS) as the culprit for colon necrosis in humans treated with SPS and sorbitol. We tested the hypothesis that colon necrosis by sorbitol in the experiment was due to the high osmolality and volume of sorbitol rather than its chemical nature.

Methods

26 rats underwent 5/6 nephrectomy. They were divided into 6 groups and given enema solutions under anesthesia (normal saline, 33% sorbitol, 33% mannitol, SPS in 33% sorbitol, SPS in normal saline, and SPS in distilled water). They were sacrificed after 48 hours of enema administration or earlier if they were very sick. The gross appearance of the colon was visually inspected, and then sliced colon tissues were examined under light microscopy.

Results

1 rat from the sorbitol and 1 from the mannitol group had foci of ischemic colonic changes. The rats receiving SPS enema, in sorbitol, normal saline, distilled water, had crystal deposition with colonic necrosis and mucosal erosion. All the rats not given SPS survived until sacrificed at 48 h whereas 11 of 13 rats that received SPS in sorbitol, normal saline or distilled water died or were clearly dying and sacrificed sooner. There was no difference between sorbitol and mannitol when given without SPS.

Conclusions

In a surgical uremic rat model, SPS enema given alone or with sorbitol or mannitol seemed to cause colon necrosis and high mortality rate, whereas 33% sorbitol without SPS did not.     

Evoked potentials of the human cerebral cortex to perceptible and imperceptible sound stimuli

Evoked potentials averaged with the help of an electronic computer (AEP) to brief sound stimuli of subthreshold (3–10 dB below the threshold of the signal's audibility), threshold, and superthreshold (10–60 dB above the threshold) intensity were recorded from the vertex and occipital region of the cranium in healthy people. The dynamics of the changes in the AEP with an increase in the intensity of the sound from subthreshold to superthreshold (60 dB) values was shown. The time and amplitude parameters of AEP to imperceptible and perceptible sound stimuli differed significantly. The most constant, and in many cases the only component of the AEP to an imperceptible stimulus was a long-latent, low-amplitude, slow positive oscillation. The participation of the cerebral cortex in the neural mechanisms of reactions to imperceptible sound stimuli is discussed.V. P. Serbskii Central Scientific-Research Institute of Forensic Psychiatry, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 115–122, March–April, 1971.     

Comparative study of the rod and cone contributions to the generation of b-wave ERG and tectal evoked potential in the dark-adapted carp

Amplitudes and peak latencies as functions of wave length and monochromatic light intensity were investigated for b-wave ERG and tectal evoked potentials (EP) in the dark-adapted carp (Cyprinus carpio L). It was found, that independently of light intensity b-wave action spectra had one maximum in the medium wave band, corresponding to rod sensitivity area. For tectal EP, similar action spectra with maximum in the middle-wave were seen at low light intensity only. The b-wave amplitude growth was significant for the whole band of light intensities, and these changes were accompanied with a slight decrease in peak latency (to 50-100 ms). Tectal EP amplitude increased when low-intensity light was changed for medium intensity light and did not considerably increase to brighter light stimuli. However, tectal EP time latency significantly decreased (to 100-200 ms) during light intensity increasing. This differences show that retinal rod system, which in responsible for ERG b-wave in darkness, is not a key factor in the generation of tectal EP.     

Single-trial latency variability does not contribute to fast habituation of the long-latency averaged auditory evoked potential in the albino rat

Fas habituation (FH) is defined as a general reduction in long-latency, vertex-recorded, averaged auditory evoked potential (AEP) amplitude that occurs in response to the second of a pair of acoustic stimuli. Our laboratory has been studying FH in a variety of human populations with different paradigms and has interpreted it to be a measure of neural attentional mechanism(s) and/or resource allocation related to the processing of cognitive information. We have also reported an analogous phenomenon in the rat. In the present investigation, we examined the relationship between FH (viz., averaged AEP component amplitude decrement) and the single-trial latency variability of the AEP peaks comprising that component. Specifically, AEPs were obtained to 60 paired-tone stimuli from unanesthetized and restrained albino rats previously implanted with chronic skull electrodes. Using a template-matching algorithm similar to that used by Michalewski et al. (Electroenceph. clin. Neurophysiol., 1986, 65:59–71), the latency variability for each animal was computed for the N1 and P2 peaks of the single-trial AEPs that were used to compose the averaged wave form. Findings indicated that (a) there was no difference in single-trial latency variability for these peaks either within or across tones, and (b) there was no relationship between single-trial latency variability for either the N1 or the P2 peaks and the overall peak-to-peak amplitude (N1-P2) of the averaged wave form in response to the second tone. Thus, FH of the N1-P2 (i.e. Peak 2) amplitude in the rat is not due to an increase in latency variability across tones.     

Suppression of "fast" IPSP,superposed on "slow", as a possible cause of priming in murine hippocampus

Intra- and extracellular response in area CA1 to stimulation of two independent afferent inputs, one a priming or conditioned and the other a test or primed input (C1 and C2, respectively) were recorded in surviving murine hippocampal slices. Duration and amplitude of test field potentials (FP) and of excitatory postsynaptic potentials (EPSP), were measured, as well as amplitude of "fast" and "slow" components of inhibitory postsynaptic potentials or stimulation varying between 0 and 1 sec. Conditioning brought about an increase in the duration of FP, in duration and amplitude of EPSP, and suppression of IPSP at intervals of between 50 and 500 msec peaking at 200 msec (i.e., priming effect). These changes correlated with level of IPSP_b in response to conditioned stimuli. The most pronounced effect could be seen in neurons manifesting hyperpolarizing IPSP in response to test stimuli. Suppression of test IPSP_a after superposition on IPSP_b is thought to bring about the increase in test FP and EPSP seen during priming.Institute for Brain Research, All-Union Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 730–739, November–December, 1990.     

Hearing conspecific vocal signals alters peripheral auditory sensitivity

We investigated whether hearing advertisement calls over several nights, as happens in natural frog choruses, modified the responses of the peripheral auditory system in the green treefrog, Hyla cinerea. Using auditory evoked potentials (AEP), we found that exposure to 10 nights of a simulated male chorus lowered auditory thresholds in males and females, while exposure to random tones had no effect in males, but did result in lower thresholds in females. The threshold change was larger at the lower frequencies stimulating the amphibian papilla than at higher frequencies stimulating the basilar papilla. Suprathreshold responses to tonal stimuli were assessed for two peaks in the AEP recordings. For the peak P1 (assessed for 0.8–1.25 kHz), peak amplitude increased following chorus exposure. For peak P2 (assessed for 2–4 kHz), peak amplitude decreased at frequencies between 2.5 and 4.0 kHz, but remained unaltered at 2.0 kHz. Our results show for the first time, to our knowledge, that hearing dynamic social stimuli, like frog choruses, can alter the responses of the auditory periphery in a way that could enhance the detection of and response to conspecific acoustic communication signals.     

Characteristics of evoked potentials and single neuron responses in the cat sensorimotor cortex to sound stimuli with different frequencies.

The characteristics of the averaged evoked potentials (AEP) (experiments with awake non-paralysed animals), of the evoked potentials (EP) and of the responses of single sensorimotor cortical neurons (acute experiments) of cats to tone-bursts with frequencies within 0.1-6.0 kHz were studied. Response selectivity to the tone-burst frequencies which are energetically pronounced in some biologically significant sounds for the cat was observed. The averaged curve of the dependence of the amplitude of AEP in the somatosensory cortical region (S1) on the tone-burst frequency has reliable maximum values at the frequencies of 0.8, 1.6 and 2.0-3.0 kHz. Most pronounced changes in the heart rhythm were observed within the tone-burst frequency ranges in which the AEP of the highest amplitudes were recorded. The amplitude of the AEP was found to increase during the conditioned reflex elaboration. The curve of the dependence of the probability of the EP occurrence on the frequency at equal sound pressure levels had maximum values at the frequencies of 1.6 and 3.2 kHz. The highest amplitude values of EP were found at frequencies of 0.8, 1.6 and 3.2 kHz. More than half of the recorded neurons revealed the lowest values of the response thresholds and the maximum values of the occurrence probability under suprathreshold stimulation at frequencies close to 0.8, 1.6, and 3.2 kHz. It is supposed that the above mentioned feature of the input frequency organization in sensorimotor cortex is connected with the selectivity as to the biological significance of acoustic stimuli.     

Auditory evoked potentials to indifferent and meaningful stimuli in young children

Auditory evoked potentials (AEP) of the frontal, central and parietal cortical areas of the left hemisphere in response to an indifferent sound stimulus and to a stimulus with same physical characteristics, but with acquired informational significance, were studied in healthy children of the 3-d year of life. In the last case the amplitude of the AEPs in all recorded areas rose and the latencies of late components in the parietal area became longer. Moreover, the components of AEP got more complex owing to a greater manifestation of the late positive component P3 in all recorded areas and particularly in the parietal one.     

KILLER WHALE (ORCINUS ORCA) AUDITORY EVOKED POTENTIALS TO RHYTHMIC CLICKS

Temporal auditory mechanisms were measured in killer whales ( Orcinus orca ) by recording auditory evoked potentials (AEPs) to clicks. Clicks were presented at rates from 10/sec to 1,600/sec. At low rates, clicks evoked an AEP similar to the auditory brainstem response (ABR) of other odontocetes; however, peak latencies of the main waves were 3–3.7 msec longer than in bottlenose dolphins. Fourier analysis of the ABR showed a prominent peak at 300–400 Hz and a smaller one at 800–1,200 Hz. High-rate click presentation (more than 100/sec) evoked a rate-following response (RFR). The RFR amplitude depended little on rate up to 400/sec, decreased at higher rates and became undetectable at 1,120/sec. Fourier analysis showed that RFR fundamental amplitude dependence on frequency closely resembled the ABR spectrum. The fundamental could follow clicks to around 1,000/sec, although higher harmonics of lower rates could arise at frequencies as high as 1,200 Hz. Both RFR fundamental phase dependence on frequency and the response lag after a click train indicated an RFR group delay of around 7.5 msec. This corresponds to the latency of ABR waves PIII-NIV, which indicates the RFR originates as a rhythmic, overlapping ABR sequence. The data suggest the killer whale auditory system can follow high click rates, an ability that may have been selected for as a function of high-frequency hearing and the use of rapid clicks in echolocation.