Various forms of potentials recorded from caudate nucleus neurons

Spontaneous and evoked activity of caudate nucleus neurons was recorded extracellularly in acute experiments on cats. Different forms of potentials were found by analysis of the results. The potentials recorded belong to three types: ordinary action potentials; prepotentials or incomplete spikes differing from ordinary action potentials in their lower amplitude and slower decline, and complex discharges in which a spike of somewhat reduced amplitude is followed by a slow positive-negative wave. In the spontaneous activity prepotentials were observed both in complete action potentials and in isolation. The frequency of the complex discharges was 0.5–1 per second. The slow wave of these discharges blocked prepotential and action potential formation. The origin of these forms of potentials in neurons of the caudate nucleus is discussed and they are compared with analogous forms of potentials described for the Purkinje cells of the cerebellum.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukranian SSR, Kiev. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 149–156, March–April, 1977.     

Comparison of evoked potentials to tones and clicks recorded simulataneously by multiple electrodes from the auditory cortex in unanesthetized cats

Evoked potentials to tones and clicks were recorded simultaneously from seven points of the auditory cortex and one or two points of the somatosensory cortex in unanesthetized cats. Comparison of evoked potentials to tones of equal loudness in the 250–7000 Hz band showed no common pattern of cortical tonotopic distribution. However, an individual dependence of the components of the evoked potential on pitch and on localization of the recording point exists for each animal. With a change in stimulus intensity the absolute and relative values of these components of the evoked potential vary. The initial positive waves are the most variable; besides the two waves already known a third, intermediate wave, particulary sensitive to loudness, was discovered. The negative wave of the primary response increases proportionally to loudness. Evoked potentials to clicks are more uniform over the auditory cortex and more stable than those to tones. Responses appeared in the somatosensory cortex to loud stimuli, more regularly to clicks than to tones. It is concluded that the parameter of pitch is reflected in the cat cortex as a complex spatially-individual distribution of the amplitude and time parameters of the evoked potentials.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 7, No. 2, pp. 115–125, March–April, 1975.     

Mechanisms of interaction between the parietal association and projection areas of the cat neocortex

Changes in evoked potentials in the first visual (VI), first somatic (SI), and parietal areas of the cortex during local cooling of each area were investigated under pentobarbital anesthesia. Two types of interaction were distinguished. Type I interaction was found in all areas in the early stages of local cooling and was reflected in a similar decrease in amplitude of evoked potentials in intact parts of the cortex. In the thalamic association nuclei — the pulvinar and posterolateral nucleus — somatic evoked potentials were unchanged but visual were transformed differently from those in the cortex. Type IIinteraction was found in the later stages of cooling and only between the association area and each of the projection areas. It was reflected in a greater change in amplitude of the evoked potentials and also in their configuration. In response to somatic stimulation in the early stage of type II interaction transformation of evoked potentials in the cortex took place sooner than in the nuclei; in the later stage it took place immediately after transformation of the "subcortical" evoked potentials. In response to photic stimulation transformations of cortical evoked potentials were always preceded by the corresponding transformations in the nuclei. It is suggested that type I interaction is formed by intercortical connections and type II by direct and subcortical relay connections. Differences in the role of the association area in interaction of types I and II when activated by stimuli of different modalities are discussed.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 10, No. 6, pp. 573–581, November–December, 1978.     

Features of evoked potentials in the cerebellar cortex of rabbits

We investigated evoked responses of the cerebellar cortex of rabbits under Nembutal or chloralose anesthesia to stimulation of the sciatic, brachial, and vagus nerves. The parameters of evoked potentials (E Ps), together with features of their distribution throughout the cerebellar cortex, enabled us to divide them provisionally into three types. Evoked potentials of the first type have a latent period of 5–10 msec and a two-phase or more complex shape. Evoked potentials of the second type have a latent period of 10–23 msec and include from one to four components. Evoked potentials of the third type are discharges with long latent periods (20–50 msec) and consist of a series of slow sinusoidal oscillations. Appearance of an initial electronegative component is characteristic of EPs of the cerebellar cortex of rabbits, especially those of the second and third types. Evoked potentials of the first type are local.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 73–80, July–August, 1969.     

Posttetanic changes in hippocampal minimal evoked potentials

Changes in the EEG induced by a single spike were recorded in the hippocampus of an unanesthetized rabbit. Summation of focal electrical activity synchronous with spontaneous single unit discharges at the symmetrical point of contralateral hemisphere revealed no stable potentials which could reflect these changes. In two cases discharges identified as activity of Shaffer's collaterals were recorded in area CA₁. Summation of post-spike changes in evoked activity recorded by the same microelectrode showed stable negative waves with an amplitute of 40–60 µV, which could have been evoked by single spikes. The curve of amplitude of the averaged evoked potentials versus near-threshold current strength stimulating the intrahippocampal pathways was not smooth in most experiments but stepwise in character. It is suggested that the minimal evoked potential corresponding to the first step (amplitude 40–80 µV) reflects a response to stimulation of one fiber. After above-threshold tetanization prolonged posttetanic potentiation of the minimal evoked potentials did not arise in CA₁ in response to stimulation of Shaffer's collaterals. Minimal evoked potentials recorded in area CA₃ in response to stimulation of the dentate fascia showed clear potentiation. The results are in agreement with the hypothesis of the synaptic localization of the mechanisms responsible for prolonged posttetanic potentiation.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 9, No. 2, pp. 124–134, March–April, 1977.     

Restoration of evoked responses in the rat dorsomedial thalamic nucleus after amygdaloid lesion

The changing pattern of focal potentials in the thalamic dorsomedial nucleus, produced by stimulating the periamygdaloid cortex between 2 and 90 days after unilateral destruction of the basolateral amygdaloid nuclei, was investigated during semichronic experiments on anesthetized rats. A comparison was made between the parameters and spatio-temporal characteristics of potentials, as revealed at different stages of functional reorganization of thalamo-limbic interaction. The biggest increase in latency to peak of the principal positive-negative component is seen during the first two months after amygdaloid lesion. The original pattern and numerical features of focal potentials are restored in 2.5 months. The potentials formed during the course of the compensatory process differed from those of animals with an intact CNS, however, the amplitude of their test response to paired stimuli being incompletely restored, especially at interstimulus intervals of 40–150 msec. Findings indicate the high functional plasticity of the neural fibers mediating afferents at the level of the above thalamic association nucleus.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 18, No. 2, pp. 153–161, March–April, 1986.     

Visual acuity thresholds of juvenile loggerhead sea turtles (Caretta caretta): an electrophysiological approach

Visual evoked potentials measure dynamic properties of the visual system by recording transient electric responses of neural tissue identified to correspond to a specific visual stimulus, such as light or a striped grid. In this study, visual evoked potentials were used to test the visual acuity of juvenile loggerhead sea turtles (Caretta caretta) in water. Subject animals were fitted with a Plexiglas goggle filled with filtered seawater. Stimuli of black and white striped gratings were presented to the turtles using a slide projector directing an image onto a screen via a rotatable mirror that shifted the striped pattern laterally one-half cycle. Bioelectric activity was collected using a digital averaging computer and subdermal platinum electrodes, implanted under the head scutes directly above the optic nerve and the contralateral optic tectum. To isolate the response signal from the noise, signal averaging techniques were used when collecting visual evoked potentials. The resulting response waveforms included a robust positive-negative compound that was used to track the turtle's response to visual stimulation. Acuity thresholds for these sea turtles, which were derived from linear regressions analysis of the positive-negative compound amplitudes versus stripe size, ranged from 0.130 to 0.215. This acuity level is comparable to other inshore, shallow water marine species.     

Evoked potentials to electrical stimulation of the facial nerve in the carp tectum mesencephali

Tectal evoked potentials to stimulation of the facial nerve, containing afferent fibers of nonolfactory chemoreception, in the carp are positive evoked potentials with a latent period of 5 to 25 msec which show no phase shift as the microelectrode is advanced to a depth of 600 µ. Depending on the amplitude and latency of evoked potentials seven active zones differing in one or both parameters were distinguished in the ipsilateral tectum mesencephali. The role of impulses from the medulla in the mechanism of tectal evoked potentials to facial nerve stimulation is proved by differences in latent periods and disappearance of the tectal response (although it is preserved in the primary center) after severance of connections between the two parts of the brain. Descending influences from the tectum on the primary center were found: its extirpation disturbs evoked potential generation in several parts of the medullla, so that they either disappear completely or their parameters are modified.A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 1, pp. 39–46, January–February, 1976.     

Analysis of long-latency components of field potentials evoked by stimulation of the cerebral cortex and nerves in the cerebellar paramedian lobule

Field potentials evoked in the graunular layer of the cerebellar paramedian lobule of unanesthetized cats in response to stimulation of the sensomotor cortex and limb nerves contained slow negative waves, appearing after a long latent period, which were generated by granule cells. In the case of nerve stimulation this component was recorded both inside and outside the projection zone of the corresponding limb. Cortical stimulation by single stimuli or series of stimuli not more than 1.8–2.5 times above threshold strength led to the appearance of evoked potentials only inside the corresponding projection zone. The long-latency component of field potentials evoked by cerebral stimulation followed high frequencies of repetitive stimulation and was less sensitive to the action of barbital anesthesia than the analogous component of potentials evoked by nerve stimulation. In the case of combined cerebral and nerve stimulation the long-latency components underwent summation. It is concluded that mossy fibers of slowly-conducting spino- and cerebrocerebellar tracts innervate different granule cells in the cerebellar cortex.Institute of Problems in Information Transmission, Academy of Sciences of the USSR, Moscow. M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 14, No. 4, pp. 379–385, July–August, 1982.     

Retrieval of delayed evoked potentials after amygdaloid stimulation

The effect of amygdaloid stimulation on retrieval of delayed evoked potentials recorded in the cortex, mesencephalic reticular formation, lateral geniculate body, and hippocampus was investigated in unanesthetized curarized cats. Delayed evoked potentials were produced to 10–400 combinations of flashes and hypothalamic stimulation and consisted of potentials arising in response to a conditioned stimulus after a delay equal to the interval between it and the unconditioned stimulus. Amygdaloid stimulation facilitated the retrieval of these potentials if they had first been extinguished or had not appeared during initial testing.Institute of Physiology, Academy of Medical Sciences of the USSR, Siberian Branch, Novosibirsk. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 300–304, May–June, 1976.     

Effect of injury to the lateral reticular nucleus and nuclei of the inferior olive on electrical responses of the cerebellar cortex evoked by vagus nerve stimulation in cats

The role of the lateral reticular nucleus and nuclei of the inferior olive in the formation of cerebellar cortical evoked potentials in response to vagus nerve stimulation was determined in experiments on 28 cats anesthetized with chloralose and pentobarbital. After electrolytic destruction of the lateral reticular nucleus, in response to vagus nerve stimulation, especially ipsilateral, lengthening of the latent period and a decrease in amplitude of evoked potentials were observed; after bilateral destruction of this nucleus, evoked potentials could be completely suppressed. It is concluded that the lateral reticular nucleus relays interoceptive impulses in the vagus nerve system on to the cerebellar cortex. Additional evidence was given by the appearance of spike responses of Purkinje cells, in the form of mainly simple discharges, to stimulation of the vagus nerve. After destruction of the nuclei of the inferior olive, the latent period and the number of components of evoked potentials in response to vagus nerve stimulation remained unchanged but their amplitude was reduced. The role of the nuclei of the inferior olive as a regulator of the intensity of the flow of interoceptive impulses to the cerebellum is discussed.N. I. Pirogov Medical Institute, Vinnitsa. Translated from Neirofiziologiya, Vol. 9, No. 3, pp. 290–299, May–June, 1977.     

Interaction of Tonic and Phasic Pain in Rabbit Ontogenesis

In the experiments on the 20–25-day-old and adult rabbits, effects of tonic pain focus (a subcutaneous injection of formalin into leg dorsal surface) on behavioral and electrophysiological characteristics of acute pain were studied. The effect of the 40–60-min-long tonic pain was seen as a decrease of defensive reaction threshold and an increase of inhibitory effect of brain rewarding zones on evoked potential recorded in thalamus parafascicular complex in response to a nociceptive electrocutaneous stimulation in narcotized rabbits. The changes observed were biphasic and coincided in time with an enhancement of the earlier described [26] specific behavioral responses to formalin injection. It is established that the effect of tonic pain is more expressed by its intensity and duration in the 20–25-day-old than in adult rabbits.     

Neurophysiological analysis of postnatal development of corticostriate connections in rabbits

Evoked potentials were recorded in the caudate nucleus of adult rabbits and young rabbits aged 2–30 days in response to stimulation of the ipsilateral motor cortex. The response of the caudate nucleus in the adult rabbit consisted of a positive-negative complex with latent period of 3–5 msec. Maximal amplitude of the response was observed in the dorsorostral region of the nucleus. As the recording electrode was inserted deeper, the amplitude of the response gradually decreased but without reversal of its polarity. Responses of the caudate nucleus to stimulation of the motor cortex were recorded as early as on the 3rd day after birth. These responses were indistinguishable in configuration from responses of the nucleus of adult rabbits. Their latent period was about 10 msec. Between the 16th and 20th day after birth the latent period of the response decreased considerably — from 9 to 5 msec, and by the 30th day of life it had reached its definitive value. With age the amplitude of the response increased but the threshold of stimulation decreased, The results indicate early functional maturation of connections of the motor cortex with the caudate nucleus and they agree with the results of morphological investigations of the structural development of the afferent systems of this nucleus.Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 3, pp. 284–289, May–June, 1982.     

Spatial configuration of rabbit superior collicular evoked response to punctiform afferent stimulation

Evoked potentials arising in the rabbit superior colliculus in response to punctiform stimulation of the receptive field were studied. This response has only negative polarity at the focus of maximal activity and does not exhibit reversal of the potential which is a characteristic feature of the response to diffuse stimulation. The evoked potential was recorded at depths of between 0.1 and 0.9–1.0 mm from the collicular surface, corresponding to the stratum griseum superficiale. The response disappeared when the stimulating spot was shifted through 4–6° away from the optical position. It is suggested that evoked potentials to punctiform stimulation can give more complete information on the location of different synapses.A. N. Severtsov Institute of Evolutionary Morphology and Ecology of Animals, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 11, No. 5, pp. 441–450, September–October, 1979.     

Variability of cortical evoked potentials to tooth pulp stimulation in unrestrained rats

In unrestrained adult rats evoked potentials were recorded by implanted electrodes in the somatosensory cortex in response to electrical stimulation of the pulp of an upper incisor. The spontaneous EEG, motor activity of the animal, and its respiratory movements were recorded simultaneously. Significant differences were observed in the configuration of the potentials and mean amplitude of the primary complex (P₁+N₁) during states of slow sleep, drowsiness, relaxed wakefulness, grooming, and investigative behavior; the amplitude of the primary complex during marked motor activity was reduced by more than an order of magnitude compared with that observed in a state of motor rest.In a state of relaxed wakefulness negative correlation was recorded between the amplitude of evoked potentials and momentary values of the respiration rate, weaker during periods of intensive motor activity. Meanwhile no direct parallel was observed between changes in potentials and respiration rate over the whole range of behavioral states studied: Depression of potentials was maximal during grooming whereas the respiration rate was maximal during investigative behavior.Paul Flechsig Institute for Brain Research, Karl Marx University, Leipzig, East Germany. Translated from Neirofiziologiya, Vol. 17, No. 1, pp. 27–35, January–February, 1985.     

Functional organization of projection zones of lateral line organs in the midbrain of Raja clavata

The character and distribution of evoked potentials in the midbrain during electrical stimulation of the lateral line nerves were investigated in acute experiments on the ray (Raja clavata). The clearest response was observed on the contralateral side of the dorsal surface. The evoked potentials consisted of several components. The initial high-frequency component is regarded as presynaptic. The principal slow component of the evoked potential corresponds to postsynaptic processes. The lateral line organs have spatially differentiated representation with partial overlapping of the projection zones.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 5, No. 4, pp. 384–391, July–August, 1973.     

Contribution of specific and nonspecific afferent inputs to shaping evoked potentials produced in the cat brain by photic stimulation

Acute and chronic experiments on cats served to show that generation of evoked potentials continued in both the cortex and a number of subcortical structures and that these contained a component matching initial response (except in its reduced amplitude) even after cutting off specific pathways for visual impulse access. This involved severing the optic tract prior to its entry into the lateral geniculate body. Amplitude of primary response decreased less sharply after coagulating the lateral geniculate body, thus preserving a proportion of nonspecific impulse transmission (with pathways via the retino-collicular fibers persisting). Once a major proportion of the nonspecific visual pathways had been destroyed by severing the brachium of the superior colliculi, photic stimulation led to the formation of two-stage evoked potentials with a profile hardly differing from normal. It is presumed that genesis of evoked potentials depends on the quantity rather than the quality of incoming afferents.I. V. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 1, pp. 3–7, January–February, 1988.     

Synaptic processes in neurons of the cervical enlargement of the cat spinal cord during stimulation of propriospinal pathways of the dorsolateral tract

Responses of motoneurons and interneurons of the cervical enlargement of the cat spinal cord were studied by a microelectrode technique during selective stimulation of propriospinal fibers of the dorsolateral tract of the lateral white column. The long descending and ascending pathways were blocked by preliminary (10–16 days earlier) hemisection of the spinal cord cranially and caudally to the segments studied. Stimulation of the dorsolateral tract at a distance of 15–25 mm from the site of recording evoked complex postsynaptic potentials consisting of several successive waves in the motoneurons. The character of the PSPs was not clearly linked with the function of the motoneurons. By their latent periods the components of the PSPs could be placed in three groups. The "primary" components were reproduced in response to stimulation at 50–100/sec whereas the "secondary" and "tertiary" components were weakened or blocked. It is postulated that the "primary" components are evoked through monosynaptic connections between propriospinal fibers of the dorsolateral tract and motoneurons of the forelimb muscles, while the late components are evoked through polysynaptic pathways, including segmental interneurons. Many of these interneurons, located in the ventral horn and intermediate zone, were strongly excited during stimulation of the dorsolateral tract.A. A. Bogomolets' Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 61–69, January–February, 1973.     

Synaptic processes in facial motoneurons evoked by stimulation of the caudal trigeminal nucleus

Field potentials and postsynaptic potentials of facial motoneurons evoked by stimulation of the caudal trigeminal nucleus were investigated in acute experiments on cats by extra- and intra-cellular recording. Pre- and postsynaptic components of field potentials were found. Four types of motoneuron response were distinguished: EPSP with generation of single action potentials; a gradual shift of depolarization inducing grouped action potentials; a rhythmic discharge of action potentials arising at a low level of depolarization; and EPSPs or EPSP-IPSP sequences. The monosynaptic and (chiefly) polysynaptic nature of these responses was demonstrated. The possible mechanism of afferent control over facial motoneurons are discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 272–282, May–June, 1980.