Responses of afferent and efferent neurons to auditory inputs in the vestibular nerve of the frog

Summary In the frog, the spontaneous discharges of afferent fibres from the horizontal semicircular canal (HC) and of efferent vestibular units were recorded by means of glass micropipettes filled with 2 mol/l NaCl as well as during acoustic stimulation; pure tones 300–2,000 Hz and clicks 150/s, 80–100 dB re 10^–5 N/m² were used. The activity of 56% of the efferent fibres recorded was increased by such stimulations while the discharge of the others was not modified. In intact preparations the activity of 34.4% of the afferent fibres recorded was either increased or decreased by sound stimulation depending on the unit; the discharge of the others (65.6%) was not modified (Fig. 3). Section of both saccular nerves did not change the percentage of the units modulated by sound showing that the saccules have probably no effect on this modulation (Fig. 4). In preparations where the contralateral auditory papillae were eliminated, 21.1% of the afferent units were facilitated and no unit was inhibited (Fig. 5), while in preparations where the ipsilateral auditory organs were eliminated 21.1% of the afferent units were inhibited and no unit was facilitated (Fig. 6). Therefore, in intact preparations one can assume that decrease and increase of the HC afferent fibre discharges were due to stimulation of the contralateral and the ipsilateral auditory organs, respectively. Such a modulation of canal afferent discharges being mediated by efferent vestibular fibres, it can be postulated that the efferent vestibular system has a double influence upon the hair cells of the vestibular epithelium: one inhibitory and the other facilitatory. Such a double effect is discussed.Abbreviations EVS efferent vestibular system - HC horizontal semicircular canal     

Responses of the neurons of the cortical secondary auditory area to acoustic and non-acoustic stimuli in cats

The responses of the cortical secondary auditory area (AII) to the non-acoustic stimuli (electrical stimulation of the skin in the vibrissae area and light flash) and their combination with acoustic stimulation (sound click or tone) were studied in experiments on cats anesthetized by kalipsol using extra- and intracellular recording. Of the total number of neurons, 69% of the units generating spike responses to the acoustic stimulation responded to the non-acoustic stimulation too. The responses to the modal-nonspecific stimulation, as a rule, were weak and variable; they were mostly represented by a tonic change in the neuronal discharge frequency. The nonspecific stimulation evoked primary excitatory and inhibitory postsynaptic potentials in 77% and 20% of the examined neurons, respectively. We found that synaptic effects of the nonspecific and specific stimulations interact with each other, ensuring considerable modulation of the latter (mostly a significant facilitation resulting from the EPSP summation and suppression of an inhibitory component of the response to acoustic stimulation). Possible participation of the midbrain reticular formation in the transmission of the modal-nonspecific influences to the cortical neurons is considered; stimulation of this structure evoked responses similar to those evoked by the modal-nonspecific sensory stimuli.Neirofiziologiya/Neurophhysiology, Vol. 26, No. 5, pp. 356–364, September–October, 1994.     

Unit responses in the cat auditory cortex to medial geniculate body stimulation

Responses of 98 auditory cortical neurons to electrical stimulation of the medial geniculate body (MGB) were recorded (45 extracellulary, 53 intracellularly) in experiments on cats immobilized with tubocurarine. Responses of the same neurons to clicks were recorded for comparison. Of the total number of neurons, 75 (76%) responded both to MGB stimulation and to clicks, and 23 (24%) to MGB stimulation only. The latent period of extracellularly recorded action potentials of auditory cortical neurons in response to clicks varied from 7 to 28 msec (late responses were disregarded), and that to MGB stimulation varied from 1.5 to 12.5 msec. For EPSPs these values were 8–13 and 1–4 msec respectively. The latent period of IPSPs arising in response to MGB stimulation varied from 2.2 to 6.5 msec; for 34% of neurons it did not exceed 3 msec. The difference between the latent periods of responses to clicks and to MGB stimulation varied for different neurons from 6 to 21 msec. Responses of 11% of neurons to MGB stimulation, recorded intracellularly, consisted of sub-threshold EPSPs, while responses of 23% of neurons began with an EPSP which was either followed by an action potential and subsequent IPSP or was at once cut off by an IPSP; 66% of neurons responded with primary IPSPs. Neurons responding to MGB stimulation by primary IPSPs are distributed irregularly in the depth of the cortex: there are very few in layers III and IV and many more at a depth of 1.6–2 mm. Conversely, excited neurons are predominant in layer III and IV, and they are few in number at a depth of 1.6–2 mm. It is concluded that the afferent volley reaching the auditory cortex induces excitation of some neurons therein and, at the same time, by the principle of reciprocity, induces inhibition of others. This afferent inhibition takes place with the participation of inhibitory interneurons, and in some cells the inhibition is recurrent. The existence of reciprocal relationships between neurons in different layers of the auditory cortex is postulated.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 4, No. 1, pp. 23–31, January–February, 1972.     

Interaction between responses evoked by acoustic and somatosensory stimuli in neurons of the magnocellular part of the medial geniculate body

Interaction between responses to acoustic clicks and to electrodermal stimulation of the contralateral forelimb was investigated in 78 neurons in the magnocellular part of the medial geniculate body of curarized cats. Of this number, 33 neurons responded by discharges both to clicks and to electrodermal stimulation, 25 responded to clicks only, and 20 to electrodermal stimulation only, or to stimulation of the dorsal funiculus of the spinal cord. Conditioning stimulation evoked inhibition of the response to the testing stimulus in 32 of 33 neurons responding by spike discharges to both clicks and electrodermal stimulation. Electrodermal stimulation inhibited responses to clicks in all the neurons tested which responded only to clicks, whereas clicks evoked inhibition of responses to electrodermal stimulation (or to stimulation of the dorsal funiculus) in only four of the 20 neurons which responded to these types of stimulation only. It is suggested that inhibition of excitability arising in neurons of the magnocellular part of the medial geniculate body during interaction between auditory and somatosensory afferent volleys is based on postsynaptic inhibition.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 12, No. 4, pp. 368–374, July–August, 1980.     

Thermostimulation-Induced Modulation of Conditioned Reflex Movement-Related Reactions of Cortical Neurons of the Cat

In awake cats trained to perform a food-procuring conditioned operant reflex (placing movement), we studied impulse reactions of 86 neurons of the motor cortex (field 4) related to realization of the above movements. As conditioning stimuli (CS) initiating the reflex, we used either non-noxious electrocutaneous stimulation (ECS) of the contralateral forelimb or an acoustic stimulus (sound click). Impulsation of cortical neurons was recorded under conditions of (i) isolated presentation of the CS (control), (ii) presentation of the CS (either ECS or acoustic stimulus) combined with thermostimulation (heating with a miniature electric bulb) of the skin of the working forelimb, and (iii) the same, but with stimulation of the resting forelimb. When we recorded spike activity of neurons within the projection motor zone of the resting limb subjected to ESC, alternating thermostimulation of both forelimbs resulted in considerable intensification and an increase in the duration of neuronal responses, especially in cases where thermostimulation was applied to the working limb ipsilateral to the recording site (a two- to threefold increase). When spike reactions were recorded within the motor cortex of the working forelimb, thermostimulation resulted in a considerable increase in the intensity of these reactions and a decrease in their latency, but only when such stimulation was applied to the working forelimb. Thermostimulation of the resting (ipsilateral, subjected to ESC) limb evoked opposite effects (the intensity of neuronal reactions dropped). In both situations, placing movements remained within the control limits. When sound click was used as a distant CS, thermostimulation of the working limb enhanced neuronal responses, increased their duration by 50-100%, and also increased the time of forestalling of the movement initiation by spike neuronal reactions. Thermostimulation of the resting forelimb in this situation also suppressed neuronal reactions. We conclude that foreign stimulations directed toward modifications of the receptor model of the operant reflex experimental situation formed in the animal result in a decrease in the intensity of the spike responses of field-4 neurons and prolongation of the latencies of these responses, while stimulations promoting the inflow of afferent information to the cortical projection of the working limb evoke opposite effects, an increase in the intensity of neuronal spike responses and a decrease in their latencies.     

Responses of motor cortex neurons of the cat to auditory stimulation and their role in the instrumental food reflex

The responses of motor cortex neurons in the cat to the presentation of a single auditory click and a series of 10 clicks presented with 1,000/sec frequency were studied under conditions of chronic experiments before and after the development of an instrumental food reflex. After reflex development a single presentation of a positive conditioned stimulus (single click) markedly influenced for 7 sec the appearance of instrumental movements. At the same time, the immediate responses of motor cortex neurons to presentation of the conditioned auditory stimulus had no impact on the appearance in the motor cortex of discharges leading to the realization of instrumental movements. Consequently, motor cortex neurons do not require activation from afferent sensory inputs for the generation of such discharges. The immediate neuronal responses to conditioned stimulation did not inhibit the realization of the instrumental reflex. It is proposed that they are associated with the realization of motor function in the unconditioned defensive response evoked by the presentation of an auditory stimulus. The presence or absence of responses to auditory conditioned stimulation was dependent upon the signal meaning of the stimulus, its physical parameters, and the degree of excitability of the animal.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 4, pp. 539–550, July–August, 1985.     

Postsynaptic Reactions in Somatosensory Cortex Neurons Activated by Stimulation of Nociceptors: Modulation upon Stimulation of the Central Grey, <Emphasis Type="Italic">Locus Coeruleus</Emphasis>, and <Emphasis Type="Italic">Substantia Nigra</Emphasis>

In experiments on cats, we studied the effects of electrical stimulation of the cerebral central grey (CG), locus coeruleus (LC), and substantia nigra (SN) on postsynaptic processes evoked by nociceptive volleys in somatosensory cortex neurons. Nineteen cells activated exclusively by stimulation of nociceptors (intense stimulation of the dental pulp) and 26 cells activated by both nociceptive and non-nociceptive (near-threshold) stimulations of the n. infraorbitalis and thalamic nucl. ventroposteromedialis (VPM) were intracellularly recorded (nociceptive and convergent cortical neurons, respectively). In neurons of both groups, stimulation of both nociceptive afferents and the VPM evoked complex responses having on EPSP-spike-IPSP patterns (duration of IPSPs about 200-300 msec). Electrical stimulation of the СG, which per se could activate the examined cortical neurons, induced prolonged suppression of synaptic responses evoked by stimulation of nociceptors; maximum inhibition was observed at 600- to 800-msec-long conditioning–test intervals. A certain parallelism was observed between the conditioning effects of СG stimulation and effects of systemic introduction of morphine. Isolated stimulations of the LC and SN by short high-frequency pulse series evoked primary complex EPSPs in a part of the examined cortical neurons, while high-amplitude IPSPs (up to 120 msec long) were observed in other units. Independently of the type of the primary response, conditioning stimulations of the LC and SN induced long-lasting (several seconds) suppression of synaptic responses evoked in cortical neurons by stimulation of nociceptive inputs. Mechanisms of modulating influences coming from opioidergic, noradrenergic, and dopaminergic cerebral systems to neurons of the somatosensory cortex activated upon excitation of high-threshold (nociceptive) afferent inputs are discussed.     

Evoked potentials of the auditory cortex of the porpoise,Phocoena phocoena

Summary Evoked potential (EP) recordings in the auditory cortex of the porpoise,Phocoena phocoena, were used to obtain data characterizing the auditory perception of this dolphin. The frequency threshold curves showed that the lowest EP thresholds were within 120–130 kHz. An additional sensitivity peak was observed between 20 and 30 kHz. The minimal EP threshold to noise burst was 3·10^–4–10^/s-3 Pa. The threshold for response to modulations in sound intensity was below 0.5 dB and about 0.1% for frequency modulations. Special attention was paid to the dependence of the auditory cortex EP on the temporal parameters of the acoustic stimuli: sound burst duration, rise time, and repetition rate. The data indicate that the porpoise auditory cortex is adapted to detect ultrasonic, brief, fast rising, and closely spaced sounds like echolocating clicks.Abbreviation EP evoked potential     

Mechanisms of corticofugal control of the activity of “vagal” viscerosensory neurons in theNucleus tractus solitarii

In experiemnts on cats under chloralose-nembutal anesthesia, we studied viscerosensory neurons in thenucl. tractus solitarii identified by their responses to stimulation of then. vagus. The responses of these cells to stimulation of the secondary sensorimotor cortex (zoneS2) and dorsal regions of field 25 of the limbic cortex (DLC) were recorded. A substantial part of the “vagal” viscerosensory units demonstrated convergent properties and responded toS2 and DLC stimulations by phasic responses. The short latencies of these responses were indicative of oligosynaptic and, in some cases, even monosynaptic transmission of corticofugal influences on a considerable part of such neurons. Using paired stimulation allowed us to demonstrate that the effects of stimulation of the visceral afferent fiber undergo long-lasting suppression exerted by descending corticofugal volleys. The mechanisms of cortical control of the activity of bulbar viscerosensory neurons are discussed.     

Responses of units in the magnocellular part of the medial geniculate body to acoustic and somatosensory stimulation

Responses of 150 neurons in the magnocellular part of the medial geniculate body to clicks and to electrodermal stimulation of the contralateral forelimb were investigated in cats immobilized with myorelaxin. Of the total number of neurons 65% were bimodal, 16.6% responded only to clicks, and 15.4% only to electrodermal stimulation. The unitary responses were excitatory (spike potentials) and inhibitory (inhibition of spontaneous activity). Responses beginning with excitation occurred more frequently to stimulation by clicks than to electrodermal stimulation, whereas initial inhibition occurred more often to electrodermal stimulation. The latent period of the initial spike potentials in response to clicks and to electrodermal stimulation was 5–27 and 6–33 (mean 11.6 and 16.2) msec respectively. Positive correlation was found between the latent periods of spike potentials recorded in the same neurons in response to clicks and to electrodermal stimulation, and also to electrodermal stimulation and to stimulation of the dorsal funiculus of the spinal cord. It is concluded that the magnocellular division of the medial genicculate body is a transitional structure between the posterior ventral nucleus and the parvocellular division of the medial geniculate body, and that in addition, it is connected more closely with the auditory than with the somatosensory system. It is suggested that the somatosensory input into the magnocellular division of the medial geniculate body is formed mainly by fibers of the medial lemniscus.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 10, No. 2, pp. 133–141, March–April, 1978.     

Responses of parietal associative neurons to stimulation of primary sensory areas

Responses of 251 neurons in the anterior part of the middle suprasylvian gyrus to stimulation of primary sensory (auditory, visual, somatosensory) areas and also to acoustic, visual, and somatosensory stimuli were studied in acute experiments on cats anesthetized with chloralose (40 mg/kg) and pentobarbital (20 mg/kg). Three groups of neurons were distinguished by their responses to stimulation of the primary sensory areas: those responding by an increased firing rate (117) or by inhibition (35) and those not responding (99). Responses of 193 neurons to stimulation of the peripheral afferent systems were analyzed. Neurons of the parietal associative cortex responded more frequently to cortical stimulation than to peripheral. By the duration of the latent period of their response to cortical stimulation the neurons were divided into three groups: those with short (less than 20 msec), medium (20–30 msec), and long latent periods (over 30 msec). The first group was the largest.Kemerovo State Medical Institute. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 524–530, September–October, 1972.     

Unit responses of the auditory cortex of waking cats at rest and after defensive conditioning

In chronic experiments with glass microelectrodes responses of 288 spontaneously active neurons in the auditory cortex were investigated in cats at rest (123 neurons) and after defensive conditioning to sound (165 neurons). In the first situation 43% of neurons did not respond to acoustic stimulation. Most (about 60%) responses of the reacting neurons showed marked inhibition. Conditioning caused an increase (up to 72%) in the number of neurons responding to acoustic stimulation, the appearance of tonic responses, a severalfold increase in the amplitude of the responses, an increase in the number of responses of activation type, and stabilization of their form. The results point to increased excitability of neurons in this cortical area.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 25–34, January–February, 1979.     

Organization of the Connections between the Parietal Associative Zone and the Primary Sensory Zones in the Cat Neocortex

In acute experiments on cats, we studied the impulse activity of 262 neurons of the parietal associative zone (PAZ, field 5). Among them, 129 cells [100 silent units and 29 units generating background activity (BA)] were identified as output neurons, while 133 cells with the BA were interneurons of the intrinsic cortical neuronal circuits. Electrical stimulation of the primary visual, auditory, or somatosensory cortices evoked no impulse responses in silent output PAZ neurons, while output neurons with the BA and interneurons (more than 65 and 80% of the cell units, respectively) generated clear responses (more frequently, phasic). Stimulation of the auditory and visual cortices exerted mostly inhibitory effects, while stimulation of the somatosensory cortex provided mostly excitatory influences. The ratios of neurons generating primary excitatory and inhibitory responses to stimulation of the visual, auditory, and somatic cortices were 0.3:1, 0.6:1, and 3.2:1, respectively. More than 95% of the field-5 neurons were influenced from the primary sensory zones via di- and/or polysynaptic pathways. Monosynaptic excitatory inputs from the visual cortex were identified for 3.8% of interneurons and 6.9% of output PAZ neurons; for the auditory cortical inputs, the respective figures were 1.7 and 3.5%. Monosynaptic connections with the somatic cortex were found only for 4% of the interneurons under study. It has been concluded that interaction of heteromodal signals coming to the PAZ via the corticopetal and associative inputs occurs on neurons of all the cortical layers.     

大鼠初级听皮层神经元对声音空间信息的编码

尽管大脑听皮层神经元对声音空间信息的编码已有不少的研究报道,但其编码机制并不十分清楚,相关研究在大鼠的初级听皮层也未见详细的研究报道．用神经电生理学方法在大鼠初级听皮层考察了151个听神经元的听空间反应域,分析了神经元对来自不同空间方位声刺激反应的放电数和平均首次发放潜伏期的关系．结果表明,多数(52.32%)神经元对来自对侧听空间的声刺激反应较强,表现为对侧偏好型特征,其他神经元分别归类为同侧偏好型(18.54%)、中间偏好型(18.54%)、全向型(3.31%)和复杂型(7.28%)．多数神经元偏好的听空间区域的几何中心位于记录部位对侧听空间的中部和上部．绝大多数初级听皮层神经元对来自偏好听空间的声刺激反应的放电数较多、反应潜伏期较短,对来自非偏好听空间的声刺激反应的放电数较少、反应潜伏期较长,放电数与平均首次发放潜伏期呈显著负相关．在对声音空间信息的编码中,大脑初级听皮层可能综合放电数和潜伏期的信息以实现对声源方位的编码．     

Reaction of neurons of the medial geniculate body to acoustic stimulation

Responses of medial geniculate body (MGB) neurons to pure tones and clicks were studied in acute experiments in immobilized cats, preliminary operations being performed under calypsol anaesthesia. MGB units were identified by their reactions to cortical zone AI and brachium of inferior colliculus stimulations. When tonal stimuli were applied relay neurons of pars principalis of MGB usually demonstrated either unimodal tuning curves with narrow frequency band or fragmental ones with several narrow bands. On-response with subsequent inhibition of the background activity or without such an inhibitory period was most frequent type of the reaction (66.6%) of relay MGB neurons to tonal stimulation. The group of relay neurons with the tonic type of reaction (9.1%) was classified for which the duration of tonic response depends on the duration of tonal stimulus. Change of the excitatory reaction to the inhibitory one when the characteristic tone frequency is changed by non-characteristic++ ones is supposed to be a mechanism supplying sharpness of tuning at relay MGB neurons. It is concluded that responses of acoustic cortical neurons to sound stimulation depend to a great extent on the pattern of impulsation that comes from MGB relay units.     

The auditory cortex

The division of the auditory cortex into various fields, functional aspects of these fields, and neuronal coding in the primary auditory cortical field (AI) are reviewed with stress on features that may be common to mammals. On the basis of 14 topographies and clustered distributions of neuronal response characteristics in the primary auditory cortical field, a hypothesis is developed of how a certain complex acoustic pattern may be encoded in an equivalent spatial activity pattern in AI, generated by time-coordinated firing of groups of neurons. The auditory cortex, demonstrated specifically for AI, appears to perform sound analysis by synthesis, i.e. by combining spatially distributed coincident or time-coordinated neuronal responses. The dynamics of sounds and the plasticity of cortical responses are considered as a topic for research. Accepted: 25 July 1997     

Response of cat auditory cortex neurons to tonal stimulation during and after nembutal anesthesia

During acute experiments on 20 cats a comparative study was made of neuronal reaction to a tone, as recorded during the first few hours after administration of Nembutal and after an interval of 10–30 h. No spontaneous activity was seen in 89% of auditory cortex neurons of the anesthetized cats; these produced a sterotyped on- response to the optimal frequency tone. Late neuronal spike discharges at distinct intervals of 100–150 msec appeared in response to the setting up of acoustic stimulation after a brief latent reaction lasting 9–15 msec. It was shown that this stimulation did not produce an off-response in the cortical neurons. When the animals emerged from Nembutal anesthesia, the neurons reacted very differently to the optimal frequency tone. About 76% of the cells produced an on, on-off or off response, while about 21% responded with either tonic spike discharges or total inhibition of these throughout the acoustic stimulation. In unanesthetized cats the vast majority of AI cortical neurons were capable of reacting as long as the stimulus lasted. It is shown how this ability is lost under deep Nembutal anesthetic.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 17, No. 6, pp. 728–737, November–December, 1985.     

Response properties of auditory activated cells in the occipital cortex of the blind mole rat: an electrophysiological study

Previous studies have demonstrated that despite its blindness, the subterranean blind mole rat (Spalax ehrenbergi) possesses a noticeable lateral geniculate nucleus and a typical cyto-architectural occipital cortex that are reciprocally connected. These two areas, as revealed by the metabolic tracer 2-deoxyglucose, are activated by auditory stimuli. Using single unit recordings, we show that about 57% of 325 cells located within the occipital cortex of anesthetized mole rats responded to at least one of the following auditory stimuli — white noise, pure tones, clicks, and amplitude modulated tones — with the latter two being the most effective. About 85% of cells driven by either contralateral or ipsilateral stimulation also responded to binaural stimulation; about 13% responded only to binaural stimulation; and 2% were driven exclusively by contralateral stimulation. Comparing responsiveness and response strength to these three modes of stimulation revealed a contralateral predominance. Mean latency (±SD) of ipsilateral and contralateral responses were 48.5±32.6 ms and 33.5±9.4 ms, respectively. Characteristic frequencies could be divided into two distinct subgroups ranging between 80 and 125 Hz and between 2,500 and 4,400 Hz, corresponding to the most intensive spectral components of the vibratory intraspecific communication signals and airborne vocalizations.Abbreviations BMF best modulation frequency - CF characteristic frequency - 2-DG 2-deoxyglucose - dLGN dorsal lateral geniculate nucleus - IC inferior colliculus - LGN lateral geniculate nucleus - OC occipital cortex - MTF modulation transfer function - SAM sinusoidally amplitude modulation - SC superior colliculus     

Response of parietal association cortex neurons to acoustic stimulation before and after auditory cortex blockage in the cat

The effect of auditory cortex blockade on response patterns of parietal association cortex neurons responding to different frequency tones was investigated in the cat. Blockade was produced by two methods: bilateral isolation and application of a 6% Nembutal solution to the auditory cortex surface. Frequency threshold curves were plotted for all test neurons. The majority of test neurons (84%) displayed one or two characteristic frequencies before blockade, as against only 63% of all neurons responding following blockade. Changes also affect the range of frequencies at which the cells could respond. Virtually all test neurons responded to application of a broad spectrum of frequencies under normal conditions. After blockade of the auditory cortex 69% of neurons no longer responded to tones above 8–10 kHz. This would suggest that mainly information on high frequency tones is transmitted via the auditory cortex. The question of where acoustic information for parietal association cortex neurons mostly originates is also discussed; association thalamic nuclei are thought to be the main source.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 18, No. 3, pp. 354–360, May–June, 1986.     

Responses of neurons in the rat auditory and associative cortices to tonal stimuli

Activity of single neurons and mass evoked potentials (EP) were recorded from the auditory (area 41) and associative (area 39) cortices in acute experiments on rats anesthetized with urethane, nembutal, or chloralose; pure tones were used as acoustic stimuli. The EP appearing in response to a wide range of sound tones on the surface of the auditory and associative cortices were dissimilar in their latency and shape. For neurons exhibiting stable responses, the frequency-threshold curves (FTC) were plotted.Weak and variable responses of neurons were observed under slight urethane anesthesia. Nembutal anesthesia increased the responsiveness of neurons and the probability of appearing of late components in the responses. Chloralose anesthesia was characterized by extension of frequency range perceived by a neuron, while its sharpness of tuning remained unchanged. Under all types of anesthesia employed, the responses recorded from the associative cortex neurons had longer latencies than those recorded from the auditory cortex neurons. Neurons exhibiting the frequency selectivity were much less numerous in the associative cortex than in the auditory cortex. The former neurons were often characterized by intermittent FTC and they responded to a more extended frequency range. No clear tonotopic organization was found in the associative cortex.Neirofiziologiya/Neurophysiology, Vol. 25, No. 5, pp. 343–349, September–October, 1993.