Disturbance and restoration of functions after division of spinal afferent pathways in the cat

The possibility and degree of recovery of motor and sensory functions in cats were studied after one-stage or two-stage bilateral division of the posterior columns and spinocervical tracts at the cervical level. Blocking the afferent inflow along these systems led to severe and prolonged disturbances of sensation and motor activity and was accompanied by a sharp decrease in nociceptive sensation. Weak (6–8 V) electrical stimulation of the skin of the limbs, which evoked a primary response of maximal amplitude in intact waking animals, evoked no electrical response in the somatosensory cortex of the chordotomized animals. However, on increasing the intensity of stimulation by 2, 3, or more times, low-amplitude negative waves with a spike latency of about 15 msec, together with slow late waves, were recorded in foci of maximal activity of the cortex. Recovery of motor activity and, to some extent, of proprioception was observed 2–4 months after injury; responses to tactile stimulation were not restored. In the course of compensatory reconstruction evoked activity in the somatosensory cortex did not recover. It is concluded that the recovery of motor activity in cats after injury to the afferent systems of the spinal cord can take place despite a considerable defect of somatic sensation.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 3, pp. 281–288, May–June, 1973.     

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.     

Evoked Potentials of the Somatic Cortex and EMG Reactions of the Shoulder Muscles Elicited by Passive Extension of the Elbow Joint in Unanesthetized Cats

We recorded electromyographic (EMG) reactions from the flexors of the elbow joint and evoked potentials (EP) from the somatic cortex (fields 3, 4, and 6) of unanesthetized cats. These reactions were elicited by perturbation of an external extensor loading applied to the arm and evoking passive extension of the elbow joint. Perturbation of the loading was performed in two modes: (i) with different fixed force moments within a 0.04–0.2 N·m range, but with a constant rate of change in this moment (3.2 N·m·sec^–1), and (ii) with a constant force moment magnitude (0.2 N·m), but with different rates of change in this moment (from 0.1 to 6.4 N·m·sec^–1). When the elbow joint was passively extended, an EMG response was generated in the m. biceps brachii. The amplitude of this response correlated with the amplitude of perturbation of the external loading, and the time course of the response was rather close to that of the evoked passive moment. It was possible to differentiate several (up to seven) successive components in EP recorded from the three above-mentioned cortical fields; among them, the component N(50–60) was the most stable and clearly manifested. Its amplitude did not depend on the level of external loading and decreased with a decrease in the rate of loading perturbation. The time course of the N(50–60) changed insignificantly with variation of temporal parameters of the stimulus and of the evoked movement. We conclude that the spinal level and the cortical level responsible for formation of the stretch reflex differ significantly from each other in their functional roles. Reactions of the spinal level (which could be characterized by changes in EMG) are to a greater extent related to a change in the position of the limb link, while reactions of the cortical level (EP) are determined by the arrival of information about changes in the forces applied to the joint. Neurons of the somatic cortex, which are excited in the course of the stretch reflex, cannot be considered the main source responsible for generation of the M2 component of the myographic response. It is supposed that the cortical level predetermines the formation of non-reflex motor commands related to motor reflexes closed in the somatic brain cortex.     

Changes in amplitude and temporal characteristics of evoked potentials in the sensomotor cortex after division of the spinocervical tracts in cats

Temporal and amplitude characteristics of evoked potentials of the sensomotor cortex in waking cats were studied during variation in the intensity of electrodermal stimulation. The results obtained in experiments on intact animals and on the same animals for several months after division of the spinocervical tracts at the cervical level were compared. After blocking of the inflow of afferent impulses along these tracts of the spinal cord, statistically significant changes in evoked potentials were observed, mainly in response to medium and strong stimulation. These changes were more clear in the motor and second somatosensory areas of the cortex. A decrease in sensitivity to pain also was found. During recovery of the motor functions, cutaneous sensation remained impaired and the amplitude characteristics of the evoked somatosensory activity were not restored. The results suggest that thinner fibers predominate among the primary afferent fibers of the spinocervical tract, and their projections are more widely represented in the second somatosensory and motor areas of the cortex.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 5, pp. 516–523, September–October, 1972.     

Activation of various areas of the ventral horn of lumbar segments during stimulation of the motor cortex

Focal potentials (FP) in segments L₆–L₇ of the ventral horn, evoked by stimulation of the motor cortex with series of stimuli of threshold magnitude for the flexor nerve response, were studied in acute experiments on cats. Appreciable differences were found to exist between the FP arising in the medial zone (layer VIII of Rexed) and those in the inner and outer parts of the lateral zone (layer IX). The FP of the medial zone appear earlier than in other zones (with a latency of 5–12 msec); they are multiphasic, negative components predominating over the positive ones. The FP from the inner part of layer IX possess the largest amplitude (up to 500 µV), a latency of 7–13 msec, a large first negative phase, and marked late positivity. Positive — negative FP (latency 9–15 msec) of small amplitude are recorded from the outermost portion of the ventral horn. The FP of the three zones mentioned above differ also with respect to other functional criteria. The FP of the medial zone are assumed to reflect the realization at the segmental level of the extrapyramidal component of descending cortical activity, the FP of both lateral zones reflecting reciprocal interrelations between postsynaptic processes in the motoneurons of flexor and extensor nuclei during implementation of a cortical motor reaction.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 3, No. 2, pp. 175–184, March–April, 1971.     

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.     

Role of tonic motor units in flexor reflex evoked by impulsation from a focus of inflammation

The reactions of single motor units (MU) of the flexor muscles (musculus tibialis anterior and musculus biceps femoris) to tactile (light touch), nociceptive (strong compression), and electrical stimulation of the skin of the same extremity were investigated in unanesthetized spinal rats and cats. These reactions were compared with the reactions of the same MU to impulsation from a focus of inflammation evoked on the same extremity. It is shown that the smaller the motor units (judging by the amplitude of its action potential), the higher its sensitivity to exciting and the lower its sensitivity to inhibitory effects from the flexor reflex afferents (FRA), the longer its after-discharges and the more pronounced its capacity for prolonged discharges in response to prolonged stimulation of the FRA. These functional properties of the small MU are characteristic of the tonic motor neurons and the slow muscle fibers innervated by them. It is shown that prolonged impulsation from a focus of inflammation evokes the continuous activity of precisely these (tonic) MU. The activity of the large (phasic) MU ceases 2–3 min after injury which causes a focus of inflammation. Such selective activation of only some of the tonic MU is evidently due to the fact that the prolonged exciting synaptic effect of impulsation from the focus of inflammation causes accommodation of the phasic motor neurons.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 3, pp. 308–315, May–June 1971.     

A study of the time and frequency characteristics of the potentials evoked in the acoustical cortex

Evoked potentials in the auditory cortex of the cat are measured by applying auditory stimulations in the form of tone bursts of 700 Hz. Transient evoked potentials obtained in this way are transformed to the frequency domain using a Laplace Transform. The amplitude frequency characteristic obtained with this semi-empirical method depicts maxima of EEG-amplitude in frequency ranges of 10–13 Hz and 60–80 Hz. The correlation between the time course of evoked potentials and spontaneous activity of the brain and the efficiency of the method used are pointed out.     

Effect of local cooling of the cortex on evoked potentials in the reticular formation in response to somatosensory stimulation

Potentials evoked in nuclei of the reticular formation by electrodermal stimulation of the limbs were investigated in acute experiments on unanesthetized, immobilized rats during cooling of the somatosensory cortex in the area of representation of one forelimb. Evoked potentials in the reticular formation were found to depend on the degree of cold inhibition of the cortical primary response to the same stimulation. The peak time of the main negative wave increased from 40–50 to 60–80 msec with a simultaneous decrease in its amplitude or its total disappearance in the case of deep cooling of the cortex. Cooling of the cortex had a similar although weaker effect on the earlier wave of the evoked potential with a peak time of 14 msec, recorded in the ventral reticular nucleus. In parallel recordings of potentials evoked by stimulation of other limbs they remained unchanged at these same points of the reticular formation or were reduced in amplitude while preserving the same temporal parameters. Cooling of the cortex thus selectively delays the development and reduces the amplitude of the response to stimulation of the limb in whose area of representation transformation of the afferent signal into a corticofugal volley is blocked. Consequently the normal development of both late and early components of the potential evoked in the reticular formation by somatic stimulation requires an additional volley, descending from the cortex, and formed as a result of transformation of the same afferent signal in the corresponding point of the somatosensory cortex.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 1, pp. 32–38, January–February, 1981.     

Effects of tractotomy on reflex activity in the lumbar segment of the rat spinal cord previously disrupted by severing the sciatic nerve

Evoked electrical discharges in the spinal cord roots and dorsal surface ipsilateral to the previously severed sciatic nerve (as well as on the contralateral side) were investigated in rats one, three, seven, and 14 days after tractotomy. Monosynaptic reflex discharges in the ventral roots were found to return to 20–40% of the level of this parameter as measured on the contralateral side within seven and 14 days after tractotomy. Mean amplitude of antidromic dorsal root discharges, afferent peak, and the N₁ component of potential(s) at the dorsal surface ipsilateral to the severed nerve barely altered, remaining significantly lower than on the contralateral side. Mechanisms are suggested for the increase in monosynaptic reflex ventral root discharges ipsilateral to the severed nerve following tractotomy — thought to be largely due to raised sensitivity to transmitter at the motoneuronal membrane resulting from degeneration of synapses of descending pathways.Medical Institute of the Ukrainian Ministry of Health, Dnepropetrovsk. Translated from Neirofiziologiya, Vol. 21, No. 3, pp. 366–371, May–June, 1989.     

The modulation of corticospinal excitability during motor imagery of actions with objects

We investigated whether corticospinal excitability during motor imagery of actions (the power or the pincer grip) with objects was influenced by actually touching objects (tactile input) and by the congruency of posture with the imagined action (proprioceptive input). Corticospinal excitability was assessed by monitoring motor evoked potentials (MEPs) in the first dorsal interosseous following transcranial magnetic stimulation over the motor cortex. MEPs were recorded during imagery of the power grip of a larger-sized ball (7 cm) or the pincer grip of a smaller-sized ball (3 cm)--with or without passively holding the larger-sized ball with the holding posture or the smaller-sized ball with the pinching posture. During imagery of the power grip, MEPs amplitude was increased only while the actual posture was the same as the imagined action (the holding posture). On the other hand, during imagery of the pincer grip while touching the ball, MEPs amplitude was enhanced in both postures. To examine the pure effect of touching (tactile input), we recorded MEPs during imagery of the power and pincer grip while touching various areas of an open palm with a flat foam pad. The MEPs amplitude was not affected by the palmer touching. These findings suggest that corticospinal excitability during imagery with an object is modulated by actually touching an object through the combination of tactile and proprioceptive inputs.     

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.     

Evoked potentials and unit activity in the cat somatosensory cortex

Investigation of unit activity of the cat somatosensory cortex has shown that the principal role in the genesis of the primary response, the response to stimulation of the thalamic relay nucleus, the callosal response, and certain other forms of evoked potentials (EPs) of the somatosensory cortex is played by neurons not usually responding by spike generation during EP development. The EPs reflect what the cortical neurons received from the afferent volley, and the level of their polarization, but they are not a reliable indicator of fast nervous processes in the cerebral cortex. The EPs reflect postsynaptic potentials (PSPs) of neurons not directly participating actively in the analysis of information reaching the cortex.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 2, No, 4, pp. 360–367, July–August, 1970.     

Electrical activity of neurons in the cat cortex during cooling

Changes of the activity of cortical neurons were studied in the posterior crucial gyrus and in the middle parts of the suprasylvian and ectosylvian gyri on cooling the brain to 18°C and below. In exact experiments it was noted that cooling the cortex to 18.8–21.8° causes a complete cessation of neuron activity. The kinetics of the change of activity under these conditions follows a definite order: first an increase of the frequency of spike discharges is observed (31–27°), then a decrease of their amplitude (at 25–22°), and finally a complete disappearance of neuron activity (at 21.8–18.8°). Discontinuation of the cooling leads to restoration of the activity of the nerve cells in inverse order: low-amplitude high-frequency discharges manifest (at 23–26°), the amplitude of the spikes increases (at 29–31°) and then the initial activity is restored (at 31–32°). The decrease of neuron activity depends on the rate of temperature drop in the cortex. The faster the cortex is cooled, the lower is the temperature at which the neurons cease to function. And conversely, slow cooling of the cortex causes an inactivation of the spike potentials at a higher temperature.S. M. Kirov Gorki State Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 1, pp. 59–63, January–February, 1970.     

Analysis of evoked potentials of the cerebellar cortex

Evoked potentials (EP) of the cerebellar cortex in response to stimulation of peripheral nerves are characterized by a two-phase positive-negative oscillation of the potential having a latent period of 10–25 msec. The electropositive phase can contain up to three components. The latent period of component I comprises 3–9 msec. The latent period and amplitude of this component are distinguished by considerable stability, which indicates the predominant significance of presynaptic processes in its formation. The sign of component II changes at a depth of 500 µ (and more), which corresponds to the position of the granular cell layer. At this level there arises in the neurons a response with a latent period of 4–10 msec in the form of a group (3–10) of impulses with a frequency of up to 200 per sec. It is concluded that the granular cells participate in the formation of component II and partially participate in the formation of components I and III of the EP. Responses to stimulation of the nerves appear synchronously with the EP in 24% of responding Purkinje cells; they fall on the maximum electropositive deviation or component III of the EP. Microinjections of 1% strychnine into the cerebellar cortex cause an increase of EP amplitude; impulse activity of the neurons is intensified. This indicates participation of postsynaptic processes in the formation of EP. No shifts in the EP of the cerebellar cortex were observed after intracortical injection of 0.1% atropine.N. I. Pirogov Vinnitsa Medical Institute. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 429–433, July–August, 1970.     

Evoked potentials in the visual and association cortex of alert cats during paired uniform stimulation of the lateral geniculate body and pulvinar

Recovery curves of evoked potentials in the association and visual cortex during paired stimulation of the pulvinar in chronic experiments on alert cats were shown to be similar in character. Depression of the test response was observed only if the interval between stimuli was of the order of 10 msec, but if it was 40 msec considerable (2–4 times) facilitation of the second response was observed, mainly on account of an increase in the negative component N₁. Facilitation was less marked if the intervals were from 60 to 100 msec, and they decreased gradually to an interval of 200 msec. The recovery curve of cortical evoked potentials during paired stimulation of the lateral geniculate body differed considerably from the recovery curve during paired stimulation of the pulvinar and was characterized by a gradual increase in amplitude of the second response — from its almost total suppression with an interval of 10 msec to slight facilitation with an interval of 200 msec. If intervals of 10 to 80 msec were used, the test response was restored more slowly in the association cortex than in the visual cortex. The results are discussed from the standpoint of differences in the character of intracortical spread of excitation as a result of activation of geniculo-cortical and pulvinar-cortical pathways of conduction of information.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 16, No. 4, pp. 497–505, July–August, 1984.     

Effects of quinine on calcium current in mollusk neurons

The effects of quinine on the peak amplitude and the decay of calcium currents (I_Ca) were investigated in nonidentified neurons isolated fromHelix pomatia. A concentration of 1×10^–5–5×10^–4 M quinine was found to produce a reversible dose-dependent deceleration in the decline of I_Ca ("lead" effect) and a reversible, slowly evolving dose-dependent reduction in I_Ca amplitude ("lag" effect). A reduction in amplitude down to half control level is observed at a quinine concentration of 6 ×10^–5 M, while the current-voltage relationship of I_Ca shifts by 5–10 mV towards negative potentials. Results show that quinine successfully blocks calcium channels inHelix pomatia neurons.Institute of Brain Research, All-Union Mental Health Research Center, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 19, No. 3, pp. 413–417, May–June, 1987.     

Pyramidal and extrapyramidal synaptic effects upon chronically deafferented motoneurons of the spinal cord of a cat

By means of intracellular recording technique, studies have been made of the electrical activity of -motoneurons of the seventh lumbar segment in cats with chronic rhizotomy of the dorsal root fibers (L₄-S₂). Postsynaptic potentials of the reticular formation of the midbrain, medulla, and ventral columns of the spinal cord were compared with the reactions recorded from nonoperated animals; these potentials were evoked by stimulation of the motor cortex, red nucleus, and Deuters' nuclei. Deafferentiation did not cause statistically reliable variations in the amplitude of the descending monosynaptic E PSPs. Extrapyramidal short-latent disynaptic E PSPs and IPSPs remained also practically unchanged, while the responses of deafferented motoneurons to cortico-spinal impulses were considerably facilitated; this effect was retained in pyramidal cats. Deafferentation was not accompanied by variations in the dependence of the discharge frequency on the depolarizing current strength or by the variation in the threshold and input resistance of the motoneuron membranes. This suggests that intensification of the pyramidal synaptic action upon deafferented motoneurons was caused by the variation on the intermediate neuronal level.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 1, No. 1, pp. 35–46, July–August, 1969.     

Sprouting and formation of new synapses in motor structures of the central nervous system

The investigations of sprouting and reactive synaptogenesis in motor structures of the spinal cord, brain stem, thalamus, and cerebral cortex are reviewed. The reactions of the neurons and neuronal connections to injury and the ability of the nervous system to recover the impaired connections in the early postnatal period are compared with those in adult animals. The sprouting phenomenon appearing in the intact central nervous system is analyzed too. The mechanisms of synaptic reorganization of the nervous centers are discussed.Neirofiziologiya/Neurophysiology, Vol. 26, No. 4, pp. 299–314, June–July, 1994.     

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.