Effect of dominant motivation on the functional organization of the auditory input into the sensorimotor cortex of the cat brain

To consider the role of dominant motivation in functional organization of acoustic input to the sensorimotor cortex (SMC), a comparison was made of frequency reflection of tonal bursts in the rostral neocortex summary reactions, and for comparison, in the parietal association cortical area (PC), in the normal state, during pregnancy and after the kittens birth. During pregnancy an increase of the amplitude of averaged evoked potentials (AEP) of SMC and PC was observed practically in the whole studied frequency range. After kittens birth the range of changes narrowed and reactions with maximum amplitude were recorded in females to presentation of tonal bursts with frequencies which corresponded to spectral characteristics of their own kittens vocalizations. However, absolute value of changes of AEPs amplitude, observed in PC were less expressed. As a role the obtained data testify that reorganization of frequency selectivity of SMC acoustic input observed under the influence of dominant motivation, conforms to a change of kittens acoustic signals biological meaning for females in lactation period.     

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.     

The effect of acute alcohol administration on auditory evoked potentials in altricial nestlings during the development of natural behavior]

Acute ethanol influence on field L auditory evoked potentials (AEP) was studied in 4-8-days-old altricial nestlings of pied flycatcher. Nestlings were presented with tone pips related with the realization of natural behaviour (2.0 and 5.0 kHz) and bearing no meaning for the behaviour of the young of the age under study (3.0 kHz). Ethanol ingestion was found to reduce the maturity index (MI) of AEP in response to "behavioural" but not to control frequencies; this effect was first observed at day 5, when nestlings eyes opened and defence behaviour appeared, while previously formed feeding behaviour was significantly modified. During the next 2 days alcohol had a greater effect upon the AEP in response to 2.0 kHz tone pips, related with feeding behaviour of increasing complexity than upon the AEP in response to 5.0 kHz, related with the defence behaviour that remained relatively constant. The previous data concerning the effect of alcohol on unit activity are used to support the view that MI increase during the early postembryonic ontogeny is due to the involvement of neurons with newly formed behavioural specializations into the subserving of new behavioural patterns while the decrease of MI under alcohol is due to the depression of activity in these neurons.     

Post-tetanic strengthening of evoked electrical responses of the sensomotor cortex]

A study has been made of the posttetanic potentiation of evoked potentials (PTP EP) in the sensorimotor cortex, appearing in response to VPL stimulation. A distinct PTP EP of the cortical surface has been found as well as considerable differences in its intensity recorded at different portions of deep cortical layers (700 to 1600 mu). Suggestions were made regarding the origin of the phenomena observed.     

Experimental investigation on neural cell survival after dielectrophoretic trapping

Negative dielectrophoretic forces can effectively be used to trap cortical rat neurons. The creation of dielectrophoretic forces requires electric fields of high non-uniformity. High electric field strengths, however, can cause excessive membrane potentials by which cells may unrecoverably be changed or it may lead to cell death. In a previous study it was found that cells trapped at 3 Vtt/14 MHz did not change morphologically as compared to cells that were not exposed to the electric field. This study investigates the viability of fetal cortical rat neurons after being trapped by negative dielectrophoretic forces at frequencies up to 1 MHz. A planar quadrupole micro-electrode structure was used for the creation of a non-uniform electric field. The sinusoidal input signal was varied in amplitude (3 and 5 Vtt) and frequency (10 kHz-1 MHz). The results presented in this paper show that the viability of dielectrophoretically trapped postnatal cortical rat cells was greatly frequency dependent. To preserve viability frequencies above 100 kHz (at 3 Vtt) or 1 MHz (5 Vtt) must be used.     

Intensity dependence of auditory evoked potentials in behaving cats

The intensity dependence of auditory evoked potentials (AEPs) recorded epidurally over the primary (AI) and secondary (AII) areas of the auditory cortex was studied in behaving cats during wakefulness, sleep and anesthesia. Four kHz tones of 50, 60, 70, and 80 dB SPL, presented in random order every 2 ± 0.2 s by a bone conductor, elicited clear changes of the AEP amplitudes with increasing stimulus intensity, but individual components displayed different responses curves. AEP components from the AI region showed saturation of their amplitude with stimulus intensity (P13, P34) or no amplitude increase (N19), while amplitude and intensity were linearly related in the AII area. The intensity dependence of the first positive component (P12/P13) was consistently stronger for the AEP recorded from the AI than from the AII area, while later components exhibited no difference between AI and AII. During slow wave sleep, the intensity dependence of this first positive component increased in the two areas, while that of later components decreased. Pentobarbital anesthesia abolished almost all later components and depressed the intensity dependence of the first positive component both in the AI and AII area. These results indicate that (1) clear intensity dependence of AEP exists in the cat auditory cortex and (2) this intensity dependence, especially that of the first positive AEP component, shares functional similarities to the human augmenting/reducing phenomenon in the auditory modality concerning regional differences and sleep-waking cycle.     

Effect of local surface cooling of the rat cortex on the impulse activity of neurons assumed to be the sources of corticofugal influences

In an experiment on albino rats with electrodermal stimulation of the forepaw evoked potentials (EP) in the neostriatum (NS), the cortical primary response (PR), and impulse reactions of neurons (mainly of layers V and VI of the cortex) were recorded. The zone of leading-off of the potentials in the cortex was subjected to local surface cooling, which led to an increase in the PR amplitude. This facilitation was accompanied by a change in the time parameters of the impulse reactions of the cortical neurons: the latency and duration increased, and a rhythmic organization of activity appeared or intensified (if it was already present). The increase in the PR amplitude and number of spikes in the response of the cortical neurons to stimulus presentation was far less intensive than the sharp increase in EP amplitude in the NS, and did not correspond to it fully in time. The data suggest that the activating influence of the corticofugal signal on EP in the NS is determined not so much by the intensity of the descending signal as by its temporal organization.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 181–189, March–April, 1991.     

Effect of motor deprivation in early ontogeny on evoked potentials of the sensomotor and visual cortex in the rat

The influence of long-term (3 months) locomotor deprivation of rats in a month age, on the evoked potentials (EP) of the sensorimotor and the visual cortex was studied in conditions of presentation of single and paired stimuli. Changes were revealed in both cortical zones. An increase of peak latency of the initial positive EP phase in the sensorimotor cortex, and prolongation of the process of changes in excitability of neural elements, elicited by conditioning stimulus, was revealed both in the sensorimotor and the visual areas. The effect of deprivation on the dynamics of changes in neuronal systems excitability was greater in the visual evoked responses.     

Spectral correlation analysis of the potentials of the neocortex and certain subcortical structures during low-frequency electrical stimulation of nonspecific thalamic nuclei]

The spectral-correlation analysis of biopotentials in the cortex and some other brain structures (the anteroventral thalamic nucleus, dorsal hippocampus, lateral geniculate body, mid-brain reticular formation), in chronic experiments on alert rabbits, revealed that during electrical stimulation of thalamic mid-line nuclei within the ranges of 1-3, 4-7 and 8-10 c/s, there occured a rearrangement of the EEG frequencies; a dominant, narrow-band peak at the stimulation frequency, appeared. The coherence of the biopotentials of different cortical areas, of the cortex and subcortical formations increased during the stimulation at the frequency of the stimulation, reaching maximum values between the potentials of the visual and sensorimotor cortical areas.     

GABA metabolism and the formation of a sensorimotor cortex evoked potential in the presence of excess zinc ions

Changes in GABA content, the enzymatic activity of its metabolism and the formation of sensorimotor cortical evoked potential (EP) were studied following long-term ZnCl2 administration. It has been established that a single ZnCl2 injection at a dose of 0.1 and 1 mg/kg was accompanied by an increase in the amplitude of sensorimotor cortical EP, though GABA accumulation in this brain structure was observed. This might account for the prolongation of the period of the potential appearance. Long-term (for 7, 14, 21 days) ZnCl2 administration at a dose of 0.1 mg/kg produced a sharp depression in the potential appearance and an increase in GABA content by 50% with the enhancement of glutamate decarboxylase activity and the attenuation of GABA-transaminase activity.     

Effects of Temperature on Auditory Sensitivity in Eurythermal Fishes: Common Carp Cyprinus carpio (Family Cyprinidae) versus Wels Catfish Silurus glanis (Family Siluridae)

Background

In ectothermal animals such as fish, -temperature affects physiological and metabolic processes. This includes sensory organs such as the auditory system. The reported effects of temperature on hearing in eurythermal otophysines are contradictory. We therefore investigated the effect on the auditory system in species representing two different orders.

Methodology/Principal Findings

Hearing sensitivity was determined using the auditory evoked potentials (AEP) recording technique. Auditory sensitivity and latency in response to clicks were measured in the common carp Cyprinus carpio (order Cypriniformes) and the Wels catfish Silurus glanis (order Siluriformes) after acclimating fish for at least three weeks to two different water temperatures (15°C, 25°C and again 15°C). Hearing sensitivity increased with temperature in both species. Best hearing was detected between 0.3 and 1 kHz at both temperatures. The maximum increase occurred at 0.8 kHz (7.8 dB) in C. carpio and at 0.5 kHz (10.3 dB) in S. glanis. The improvement differed between species and was in particular more pronounced in the catfish at 4 kHz. The latency in response to single clicks was measured from the onset of the sound stimulus to the most constant positive peak of the AEP. The latency decreased at the higher temperature in both species by 0.37 ms on average.

Conclusions/Significance

The current study shows that higher temperature improves hearing (lower thresholds, shorter latencies) in eurythermal species from different orders of otophysines. Differences in threshold shifts between eurythermal species seem to reflect differences in absolute sensitivity at higher frequencies and they furthermore indicate differences to stenothermal (tropical) species.     

Modulation of the neuronal activity and evoked potentials of the cerebral cortex by stimulation of the dorsal hippocampus]

In experiments on alert rabbits high frequency stimulation of the CA1 field of the dorsal hippocampus reduced the peak latency of the main negative component of the evoked potential (EP) to a light flash in the sensorimotor and occipital tests areas of the cerebral cortex. A single stimulation of the same part of the hippocampus resulted in a gradually developing facilitation of secondary negativity of the EP 5th component, predominantly in the sensorimotor cortex. Investigation of neuronal responses in the same cortical areas to a stimulation of the CA1 field with different parameters has shown that the effects of EP modulation are due to dynamic reorganizations of cortical neuronal activity.     

Changes in evoked potentials to light in the presence of lesions of the diencephalic and brainstem regions of the human brain

Evoked potentials (EPs) to light were studied in groups of patients with tumours of basal-diencephalic localization (24 patients) and at the brain-stem level (24 patients), in comparison with 11 normal subjects. In the first group, a decrease of amplitude and increase of response duration were found in the frontal cortical areas, with simultaneous reduction of intrahemispheric differences due to decrease of low-frequency components in the EP spectra by amplitude in fronto-central parts, and of alpha- and beta-frequencies in the occipital parts of the hemispheres. EP changes resulting from brain-stem tumors were more expressed than in the case of cerebellar tumors. In patients with foci causing a pronounced irritation of the brain-stem, a decrease in responses amplitude was observed accompanied by an amplitude lowering of delta- and theta-frequencies in EPs-spectra in the frontal, central and temporal leads, with no changes in the occipital leads. The obtained data testify to functional inequivalence and independence of different EP frequency components suggesting that the methods of studying the EP frequency structure are informative and efficient.     

Hemispheric interaction in man during perception of visual stimuli]

Averaged evoked potentials (AEP) to verbal (letters) and nonverbal (random shapes) stimuli exposed in the left and right visual fields were registered in healthy subjects with normal vision. Analysis of the later AEP latencies pointed to asymmetry in the temporal parameters of the interhemispheric interaction. The late AEP latency is shorter in the right hemisphere than in the left hemisphere. The difference is more pronounced in responses to nonverbal stimuli. The earlier development of the evoked potential in the right hemisphere (or the later one in the left hemisphere) accounts for the interhemispheric difference in the temporal parameters of the late AEP components. Comparison of the latency of the component P300 to verbal and nonverbal stimuli presented in the ipsilateral or the contralateral visual fields reveals a transfer of the results of the cortical processing of visual information in the course of interhemispheric interaction.     

Aerial hearing thresholds and detection of hearing loss in male California sea lions (Zalophus californianus) using auditory evoked potentials

Auditory evoked potential (AEP) measurements are useful for describing the variability of hearing among individuals in marine mammal populations, an important consideration in terms of basic biology and the design of noise mitigation criteria. In this study, hearing thresholds were measured for 16 male California sea lions at frequencies ranging from 0.5 to 32 kHz using the auditory steady state‐response (ASSR), a frequency‐specific AEP. Audiograms for most sea lions were grossly similar to previously reported psychophysical data in that hearing sensitivity increased with increasing frequency up to a steep reduction in sensitivity between 16 and 32 kHz. Average thresholds were not different from AEP thresholds previously reported for male and female California sea lions. Two sea lions from the current study exhibited abnormal audiograms: a 26‐yr‐old sea lion had impaired hearing with a high‐frequency hearing limit (HFHL) between 8 and 16 kHz, and an 8‐yr‐old sea lion displayed elevated thresholds across most tested frequencies. The auditory brainstem responses (ABRs) for these two individuals and an additional 26‐yr‐old sea lion were aberrant compared to those of other sea lions. Hearing loss may have fitness implications for sea lions that rely on sound during foraging and reproductive activities.     

Activation of duration-sensitive auditory cortical fields in humans

The influence of stimulus duration on auditory evoked potentials (AEPs) was examined for tones varying randomly in duration, location, and frequency in an auditory selective attention task. Stimulus duration effects were isolated as duration difference waves by subtracting AEPs to short duration tones from AEPs to longer duration tones of identical location, frequency and rise time. This analysis revealed that AEP components generally increased in amplitude and decreased in latency with increments in signal duration, with evidence of longer temporal integration times for lower frequency tones. Different temporal integration functions were seen for different N1 subcomponents. The results suggest that different auditory cortical areas have different temporal integration times, and that these functions vary as a function of tone frequency.     

Dynamics of potentials evoked in the auditory pathway and reticular formation of the cat. Studies during waking and sleep stages

Averaged evoked potentials in the inferior colliculus (IC), medial geniculate nucleus (MG) and reticular formation (RF) of chronically implanted and freely moving cats were measured using auditory step functions in the form of tone bursts of 2000 Hz. The most prominent components of the AEP of the inferior colliculus were a positive wave of 13 msec and a negative wave of 40–55 msec latency. The AEP of the medial geniculate nucleus was characterized by a large negative wave peaking at 35–40 msec. During spindle sleep and slow wave sleep stages changes in the AEPs of both nuclei occured.Transient evoked responses of the inferior colliculus, medial geniculate nucleus and reticular formation were transformed to the frequency domain using the Laplace transform (one sided Fourier transform) in order to obtain frequency characteristics of the systems under study. The amplitude characteristics of IC, MG. and RF obtained in this way revealed maxima in alpha (8–13 Hz), beta (18–35 Hz) and higher frequency (50–80 Hz) ranges. During spindle sleep stage a maximum in the theta frequency range (3–8 Hz) and during slow wave sleep maximum in the delta (1–3 Hz) frequency range appeared in the amplitude characteristics of these nuclei.The amplitude characteristics of the inferior colliculus and medial geniculate nucleus were compared with the amplitude characteristics of other brain structures. The comparison of AEPs and amplitude frequency characteristics obtained using these AEPs reveals that the existence of a number of peaks (waves) with different latencies in the time course does not necessarily indicate the existence of different functional structures or neural groups giving rise to these waves. The entire time course of evoked potentials and not the number and latencies of the waves, carries, the whole information concerning different activities and frequency selectivities of brain structures.Supported by Turkish Scientific and Technical Research Council Grant TAG-266.Presented in Part at the VIIIth International Congress of Electroencephalography and Clinical Neurophysiology in Marseilles, September 1–7, 1973.     

Effect of strychnine on the neuronal reactivity of the sensorimotor cortex and the temporary connection in rabbits

On awake nonimmobilized rabbits, evoked activity was studied of the sensorimotor cortex neurons in response to stimulation of the pyramidal tract, medial lemniscus and reticular nucleus of the midbrain tegmentum by stimuli of different frequencies, and driving reaction of cortical neurons to stimulation of these brain structures by series of stimuli of increasing frequency. Conditioned reflexes were also studied, established on the basis of combination of direct stimulation of the sensorimotor cortex and electrocutaneous stimulation. Application of the cortex of low concentration of strychnine solutions (less than 1%) heightened neurons reactivity and provides for the formation of temporary connection. Application of strychnine solutions of higher concentration (greater than 1%) led to opposite effects. Interconnection of electrical and behavioural effects is discussed.     

Neurophysiological Indicators of Voluntary and Involuntary Visual Attention in a Human

The visual evoked potentials (EPs) in response to lateralized and central visual symbols under the conditions of involuntary (passive viewing) and selective attention (when one of the symbols was a target and required a rapid and precise motor reaction) are considered. The evoked potentials in the occipital, parietal, and frontal derivations were recorded in 20 healthy subjects. It was shown that the EP during selective attention are most pronounced and more alike in the parietal derivations. A strong positive correlation was revealed between the EP amplitude ([N1–P3] component) and the EP stability (correlation between the repeated EP). The involuntary and voluntary forms of attention supplement each other: the more expressed the involuntary attention (assessed by the [N1–P3] component) the higher the EP to target stimuli during voluntary attention and the shorter the reaction time. It is suggested that the role of visual attention consists in the increase and stabilization of cortical activity (primarily, the parietal regions) engaged in solving a visual task.     

The development of hearing sensitivity in altricial birds: the absolute thresholds of the generation of evoked potentials]

Thresholds of field L auditory evoked potentials EP were studied in 1.5-9-day-old nestlings of pied flycatcher in response to pure tone signals of different frequencies. According to the tendencies of age dynamics of auditory EP thresholds (2-9 days of life) all hearing range was divided into three separate channels: low-frequency (0.3-1.0 kHz), intermediate-(1.5-4.0 kHz) and high-frequency (5.0-8.0 kHz) ones. The widening of the hearing range in its high-frequency part was demonstrated on days 4-5 of life. The development of auditory sensitivity was shown to continue within all three channels in postembryonic period (days 2-9 post-hatching), each of the channels being characterized by its own age dynamics of auditory EP thresholds. Reproduction of tape-recorded species song during days 1-3 post-hatching resulted in significant decrease of auditory EP thresholds.