Reduction of the postexcitatory cortical inhibition upon paired-click auditory stimulation in patients with Parkinson's disease.

OBJECTIVES: The aims of this study were: to investigate the postexcitatory inhibition of cortical evoked potentials on auditory paired-click stimulation in patients with Parkinson's disease (PD), to analyze the correlation of N1-P2 amplitude ratios (A2/A1) with latency of the P300 auditory event-related potential and to determine the influence of Levodopa intake on postexcitatory inhibition and P300 latency. METHODS: The central (Cz) auditory evoked potentials were recorded in 61 patients with PD and 21 age-matched healthy subjects. RESULTS: Postexcitatory inhibition in auditory cortex in PD was significantly reduced for interstimulus intervals 500, 700 and 900ms compared to control group. The degree of this reduction correlated positively with the potential P300 latency and negatively with the summary score of the Mini Mental State Examination (MMSE) which was used to study general cognitive status of the PD patients. Increase of the postexcitatory inhibition towards normal values and decrease of the P300 latency were observed (P<0.001) following the administration of Levodopa. CONCLUSIONS: The findings of this study testify that inhibitory processes in auditory cortex are deficient in PD patients. The positive effect of Levodopa administration indicates an important role of dopamine-dependent neural mechanisms in modulation of inhibitory processes in the auditory sensory system. SIGNIFICANCE: The results show that inability of the brain to provide normal inhibition in PD is accompanied by the decline of cognitive indices, including parameters of evoked potential P300 that is related to fundamental aspects of cognitive functions, such as attention and memory.

Two phases of the contingent negative variation in humans: association with motor and mental functions.

The question of the relationship between contingent negative variation and the mechanisms controlling motor and mental functions has received inadequate study. The aims of the present work were to investigate the relationship between the early and late phases of contingent negative variation and the state of motor and mental functions in patients with Parkinson's disease and to study the effects of levodopa on contingent negative variation. Patients with Parkinson's disease showed significant decreases in the amplitudes and areas of both phases of contingent negative variation as compared with subjects of similar age. Correlation analysis demonstrated a negative relationship between the extent of impairment of coordinatory muscle interactions and the amplitudes of both phases of this variation (p < 0.01). There was a positive relationship between the magnitudes of both phases and the state of mental functions, particularly memory (p < 0.05). Treatment of patients with Parkinson's disease with levodopa was followed by a significant increase in the late phase (p < 0.05). The results obtained here provide evidence for the important role of structures supporting both direct motor control and mental functions in forming both phases of contingent negative variation. The greater effect of levodopa on the late phase of contingent negative variation suggests that the efferent system of the basal ganglia has a greater role in generating the late phase than in organizing the early phase of the variation.

[Two phases of the contingent negative variation in humans: connection with motor and mental functions].

The question of dependence of the contingent negative variation (CNV) on the regulating mechanisms of motor and mental functions is not sufficiently studied. The tasks of the present work were: to investigate the dependence of the CNV early and late phases on the state of motor and mental functions in patients with Parkinson's disease (PD), and to elucidate the levodopa influence on the CNV parameters. 18 healthy subjects and 56 patients with PD were studied. In PD patients, significant reductions of amplitudes and squares of two CNV phases were observed. A negative correlation of the degree of coordinating muscle relationships disturbance with amplitudes of two CNV phases was found (p < 0.01). A positive interdependence between values of the both CNV phases and the state of mental functions was established, memory in particular (p < 0.05). After levodopa administration in PD patients, the early CNV phase did not significantly change, whereas the late CNV phase significantly increased (p < 0.05). Results of the investigation suggest an important role of the structures ensuring both direct motor control and mental functions in two CNV phases formation. A more obvious levodopa influence on the late CNV phase suggest participation of the basal ganglia efferent system in generation of the late CNV phase rather than in organization of the early CNV phase.

[Effect of cerebrolysin on the electroencephalographic indices of brain activity in Parkinson's disease]. / Elektroéntsefalograficheskie pokazateli deiatel'nosti mozga pri lechenii tserebrolizinom bolezni Parkinsona.

Cerebrolysin is a brain-derived peptide drug that increases the BBB-GLUT1 and MAP2 genes expression, thus exerting a neuroprotective effect. The present study aimed at investigating in patients with Parkinson's disease (PD) influence of Cerebrolysin infusions (intravenously, 10 ml during 10 days) combined with levodopa treatment on the electroencephalographic (EEG) indices of brain activity: P300 potential, contingent negative variation (CNV) and recovery functions of the cortical auditory evoked potentials, which reflect the postexcitatory inhibition at the paired stimulation. Nineteen PD patients, mean age 61.4 +/- 1.7 years; disease stage according to M.M. Hoehn and M.D. Yahr, 1967-2.2 +/- 0.1) and 18 age-matched healthy controls were studied. In the patients with essential differences of the EEG indices, comparing to the normal values, statistically significant changes were revealed: a decrease of P300 latency from 419.4 +/- 23.5 to 356.3 +/- 18.4 ms (8 patients, 42%); an increase of CNV duration from 423.1 +/- 93.3 to 600.6 +/- 38.5 ms; 2-fold increase of CNV mean amplitude and 3-fold increase of CNV square (8 patients, 42%) and strengthening of postexcitatory inhibition in auditory system at the paired stimulation (13 patients, 68%). In conclusion, Cerebrolysin may be recommended as an additional neuroprotective drug for brain functions improvement in the complex pathogenetic therapy of earlier PD stages.

Effect of stimulation of beta-adrenergic receptors on neuronal activity in primary motor cortex of the rat.

Modulatory influence of beta1- and beta2-subtypes of adrenergic receptors (ARs) on the background neuronal activity and cerebellocortical transmission was characterized in the rat primary motor cortex (M1). Microiontophoretic administration of non-selective beta-ARs agonist isoproterenol significantly decreased firing rate and responses to superior cerebellar peduncle stimulation in 82% of studied neurons in a dose-dependent manner. Similar changes were induced by ejection of selective beta1-ARs agonist dobutamine, while fenoterol (selective beta2-ARs agonist) increased or reduced firing rate in 32% and 19% of M1 neurons, respectively. Non-selective beta-ARs antagonist propranolol enhanced both the background and evoked activity in 84% of tested neurons. These data provided the functional evidence for beta-ARs-mediated inhibition (predominantly through beta1-subtype) of cerebellocortical input to M1. The possible mechanism of the positive therapeutic effect of propranolol in tremor-predominant Parkinson's disease is discussed.

[The use of amantadine sulfate in combined therapy of Parkinson's disease]. / Primenenie amantadina sul'fata v kompleksnoi terapii bolezni Parkinsona.

The efficacy of PK-Merz medication has been studied in 17 patients with Parkinson's disease (PD), who have developed a resistance to levodopa as a result of a long-term treatment. The efficacy was evaluated according to clinical symptoms (UPDRS) and electromyography (EMG) indices. The summary motor score measured by UPDRS estimated as 49-79 (58.1 +/- 3.2) one hour after a single levodopa/carbidopa intake, decreased to 36-65 (45.2 +/- 2.9, p < 0.05) after levodopa/carbidopa combination with i.v. PK-Merz infusion. The biceps and triceps resting EMG amplitude and values of its variance also decreased significantly (p < 0.01). The percentage of the registered burst muscle discharges of 4-7 Hz frequency reduced from 32 to 13%. Under functional stress, the reflex antagonist muscle co-activation decreased in the majority of the patients. Selective correlations were found between the EMG indices and some UPDRS PD symptom scores. PK-Merz improves both motor functions and muscle coordination in PD.

[Regional distribution of the brain steady potential level in patients with Parkinson's disease]. / Regional'noe raspredelenie urovnia postoiannogo potentsiala golovnogo mozga u bol'nykh Parkinsonizmom.

Regional distribution of the brain steady potential level (SPL) was shown to depend on the predominant clinical symptom in parkinsonian patients. Those with prevailing bradykinesia revealed a statistically significant decrease in the SPL in the frontal area as compared with the healthy subjects or the patients with prevailing tremor.

Influence of the blockade of D2 dopamine receptors of the cat neostriatum on the baseline activity and saccadic eye movement-associated reactions of neurons of the reticular portion of the substantia nigra.

The activity of neurons of the reticular portion of the substantia nigra before and after the microinjection of haloperidol (25 micrograms/5 microliters) into the head of the caudate nucleus on the ipsilateral side was investigated under chronic experimental conditions in cats, using the extracellular microelectrode pickup technique. A significant (p < 0.05) increase, from 34 to 61%, of neurons with the burst type of spontaneous activity was established after the injection of haloperidol. A significant increase in the ratio of the number of excitatory responses to inhibitory responses, from 0.04 to 0.4, was identified among the reactions associated with saccadic eye movements following the microinjection of haloperidol. The number of orienting saccades in response to the visual stimulus decreased against this background from 58 to 37%. The identified changes are regarded as a result of the disinhibition of GABAergic neurons of the reticular portion of the substantia nigra under the influence of the blockade of D2 dopamine receptors of the neostriatum.

Electrophysiological investigation of thalamic neuronal mechanisms of motor disorders in parkinsonism: an influence of D2ergic transmission blockade on excitation and inhibition of relay neurons in motor thalamic nuclei of cat.

In acute experiments on cats anaesthetized with ketamine (25 mg/kg, i.m.) and immobilized with myorelaxine (2 mg/kg, i.v.) the activity of two groups of motor thalamic (nucleus ventralis anterior thalami-nucleus ventralis lateralis thalami) relay neurons was studied. The neurons (n = 7) receiving afferents from deep cerebellar nuclei and projecting to the motor area 4 gamma were included in the first group, and those (n = 12) receiving afferents from nucleus entopeduncularis and projecting to the supplementary motor area 6 were included in the second one. All changes in the background activity and reactions to cerebellothalamic or nucleus entopeduncularis stimulation developing under the influence of D2 receptor antagonist haloperidol (1.5-1.7 mg/kg, i.v.) have been studied in the same cell. Under haloperidol influence both groups of neurons showed a reliable decrease of background activity and generation of high frequency discharges accompanied by a shift in the mode of interspike interval histograms. A regular decrease of probability and increase of response latencies after stimulation of afferent input were observed in neurons receiving afferents from the cerebellum. In nucleus ventralis anterior thalami-nucleus ventralis lateralis thalami neurons with an inhibitory input from nucleus entopeduncularis, a shortening of inhibition from 17.5 +/- 3.6 to 9.1 +/- 1.8 ms (P < 0.05) under the haloperidol influence was evident. If the inhibition evoked by nucleus entopeduncularis stimulation consisted of two phases separated by a period of excitation (n = 4), the duration of the second phase of inhibition after haloperidol injection regularly increased and the excitation separating the phase of inhibition after haloperidol injection regularly increased and the excitation separating the phases of inhibition became more prominent. Observation on the spontaneous activity and reactions of the same neuron for 2 h or more showed a gradual moderation of the changes evoked by haloperidol. On the basis of data obtained it is concluded that the blockade of D2 receptors is followed by the increase of inhibitory processes in the relay neurons of motor thalamic nuclei. The suggestion is discussed that during the blockade of D2 receptors afferent impulsation to the motor cortex is being restricted and its influence on segmental apparatus of the spinal cord decreases. These conditions are beneficial for the development of spasticity (rigidity). At the same time, hyperpolarization of the relay neurons promotes the development of oscillatory processes at least in part of them and creates conditions for forming of tremor generators.

[The effect of a blockade of the dopamine D2 receptors in the cat neostriatum on the neuronal background activity and reactions of the reticular portion of the substantia nigra related to saccadic eye movements]. / Vliianie blokady D2 dofaminovykh retseptorov neostriatuma koshki na fonovuiu aktivnost' i reaktsii neironov retikuliarnoi chasti chernoi substantsii, sviazannye s sakkadicheskimi dvizheniia glaz.

In cats, the activity of the substantia nigra reticular part's neurons was extracellularly recorded prior to and after haloperidol administration into the head of the caudate nucleus. The number of neurons with burst-type firing increased after the administration from 34 to 61 per cent. The excitatory/inhibitory responses ratio associated with saccadic eyes movements also increased from 0.04 to 0.4. The above changes seem to follow a disinhibition of the GABA-ergic neurons under the effect of blockade of the neostriatum D2 dopamine receptors.

Participation of nucleus entopeduncularis in motor instrumental reflex and entopeduncular influences on motor thalamic nuclei in normal and MPTP-treated cats.

Activity of entopeduncular neurons was studied in chronic experiments on cats during performance of instrumental movement: pedal pressing and holding. One-hundred and twenty-four neurons were extracellularly investigated in intact animals and 81 neurons in cats treated with N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (5 mg/kg daily, intramuscularly for five days). The mean discharge frequency of nucleus entopeduncularis neurons recorded 48-72 h after the last MPTP injection increased from 12.9 +/- 1.5 to 22.1 +/- 1.4 impulses/s, but dropped to preinjection values within the next ten days. In intact animals and in MPTP-treated cats 23 and 17%, respectively, of neurons changed their activity before or during the movement performance. Along with nucleus entopeduncularis neurons that changed their activity simultaneously with instrumental movement performance, 16% of nucleus entopeduncularis nerve cells in intact cats and 12% in MPTP-treated cats responded 50-800 ms before the myogramme of working forepaw biceps was started. Excitatory responses associated with movement performance in MPTP-exposed cats were more pronounced, indicating enhancement of nucleus entopeduncularis neuronal activity in animals with injured nigrostriatal system. Since nucleus entopeduncularis neurons are inhibitory cells, the increase in their activity had to be accompanied by reinforcement of inhibitory influence on neurons in motor thalamic nuclei. In order to test this hypothesis, two groups of acute experiments were performed on ketamine-anaesthetized and myorelaxine-immobilized cats. Neuronal responses in ventral anterior and ventral lateral thalamic nuclei to nucleus entopeduncularis stimulation were investigated in normal and MPTP-treated animals in doses that were identical to those administered in chronic experiments. In intact cats, 28% of neurons responded to nucleus entopeduncularis stimulation with the latency shorter than 7 ms. In half of the inhibited neurons after the first phase of inhibition lasting 18 +/- 2 ms, the second inhibitory phase was recorded. The duration of the latter was 24 +/- 4 ms. Although in MPTP-treated cats the number of neurons inhibited by nucleus entopeduncularis stimulation was practically the same as in normal ones (24.5%), the first phase tended to be shorter, and a statistically significant increase of the second inhibitory phase duration (up to 50 +/- 11 ms) was found. It was suggested that changes in the inhibitory processes in motor thalamic neurons receiving afferents from nucleus entopeduncularis could be explained by GABAB-mediated hyperpolarization of the neuronal membrane, evoked by increasing pallidothalamic inhibitory influences.

[Effect of nucleus entopeduncularis stimulation on thalamic nuclei motor neurons under normal conditions and after injury of the nigrostriatal dopaminergic system produced by the neurotoxin MPTP]. / Vliianie razdrazheniia éntopedunkuliarnogo iadra na neirony motornykh iader talamusa v norme i na fone porazheniia nigrostriatnoi dofaminergicheskoi sistemy neirotoksinom MFTP.

Two groups of acute experiments were performed on cats anesthetized by ketamine and immobilized by myorelaxine to study reactions of neurons in ventral anterior (VA) and ventral lateral (VL) thalamic nuclei to stimulation of nucleus entopeduncularis (nEp) in normal animals and in those treated with chronic injections of neurotoxin--N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 5 mg/kg, i.m., daily, for five days). It was established that in normal cats 28% of the neurons studied have responded to nEp stimulation by inhibition with the latency shorter than 7 ms. In a half of inhibiting neurons after the first phase of inhibition which lasted 18 +/- 2 ms, the second inhibitory phase was registered. The duration of the latter was 25 +/- 4 ms. In MPTP-treated cats the number of neurons inhibited after nEp stimulation was practically the same as in normal ones (24.5%). A tendency of the first phase shortening and a statistically significant increase of the second inhibition phase duration up to 50 +/- 11 ms were found. It was suggested that changes in the inhibitory processes in VA-VL neurons receiving afferents from nEp might be explained by hyperpolarization of the nerve cell membrane evoked by increasing pallidothalamic inhibitory influences. That hyperpolarization created conditions for a decrease in Cl(-)-dependent and an increase in Ca(2+)-dependent K(+)-related phases of inhibitory postsynaptic potentials.

[Effect of catecholaminergic transmission deficiency on neuronal responses of the ventrolateral thalamic nucleus evoked by stimulation of the cerebellar and pallidal inputs]. / Vliianie nedostatochnosti katekholaminergicheskoi peredachi na reaktsii neironov ventrolateral'nogo iadra talamusa, vyzvannye stimuliatsiei mozzhechkovogo i pallidarnogo vkhodov.

Neuronal responses of the ventrolateral thalamic nucleus (VL) to the afferent stimulation were studied in chronic experiments on cats before and after injection of haloperidol and droperidol in cataleptic doses. As distinct from the reactions of intact animals, after injection of neuroleptics the initial excitative VL neuronal responses to the cerebellar stimulation were characterized by the irregularity of manifestation and the variability of the latent period, the responses in the form of burst discharges appeared. During pallidal stimulation a statistically significant increase in the number of initial inhibitory responses consisting of two periods of the background activity suppression with an excitation phase separating them was observed, while monophase inhibitory reactions prevailed (68%) in intact animals. Under neuroleptics the reactions with rhythmic alternation of excitative and inhibitory periods of the impulsive activity with frequency 3-5/s. occurred. It is suggested that revealed peculiarities of the neuronal reactions result from the hyperpolarizing state of the VL neurons because of the augmented external inhibitory actions due to a blockade of dopamine receptors of the nigrostriatal system or because of the reduced depolarizing influences under the break of the central alpha-adrenergic transmission.

Influence of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced injury of dopaminergic nigrostriatal system on movement components of the instrumental reflex and motor thalamic neurons' reactions in the cat.

Peculiarities of excitation and inhibition in ventral lateral and ventral anterior thalamic neurons were studied in cats with movement disorders (bradykinesia and muscle rigidity) induced by injury of nigrostriatal dopaminergic neurons with neurotoxin N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (5 mg/kg daily, intramuscularly for five days). As was shown in chronic experiments, mean discharge frequency of neurons related to initiation of upper limb movements increased. Excitation of these neurons coincided with movement initiation, flexion and extension becoming more prominent and prolonged as compared with normal animals. In parallel to those changes, bradykinesia developed. In acute experiments performed under ketalar anaesthesia and myorelaxine immobilization it was found that neurotoxin caused a decrease of the inhibition duration and effectiveness in relay and non-relay thalamic motor nuclei neurons. The inhibition deficiency was accompanied by a shortening of latencies of orthodromic responses evoked by red nucleus stimulation. Two days after the last neurotoxin injection, light microscope examination revealed that about 48% of neurons located in the pars compacta of substantia nigra were destroyed. Electron microscopic analysis showed hydropic changes in perykaria and dendrites in most neurons of the substantia nigra pars compacta that are typical of the light type of degeneration. Pathomorphological processes in the synaptic apparatus were also found. The content of dopamine in the caudate nucleus fell to 30% as compared with intact animals. The suggestion is made that the deficiency of inhibition developed in motor thalamic neurons in response to nigrostriatal system destruction results from attenuation of dopamine-modulated direct GABAergic nigrothalamic influences and/or might be connected with increased inhibition of inhibitory interneurons of the same thalamic nuclei conditioned by pallidum disinhibition.

[The effect of the experimentally induced failure of catecholaminergic transmission on the neuronal activity of the thalamic ventrolateral nucleus]. / Vliianie éksperimental'no vyzvannoi nedostatochnosti katekholaminergicheskoi peredachi na aktivnost' neironov ventrolateral'nogo iadra talamusa.

In chronic experiments on cats the background activity of 272 neurons of the ventrolateral thalamic nucleus was registered extracellularly before and after the systemic injection of haloperidol and droperidol (neuroleptics) in cataleptic doses. Autocorrelation and spectral analyses have revealed rhythmic changes in the frequency of the background neuronal activity with periodicity measured by parts of seconds (0.2-0.8 s), seconds (1.5-10 s) and second tens (12-30 s). Just as the number of neurons with individual forms of the rhythmic activity did not exceed 6-8% in intact animals, after administration of neuroleptics it increased to 18-30%. A rise of the neurons' number with two rhythmic processes in the same impulsive flow was observed. Experimental results were compared with clinical data. In patients with parkinsonism the number of neurons with different variants of fluctuations in the rhythmic frequency of the spike activity reached 19-46%, in patients with torsion-muscle dystonia it did not exceed 4-8%. It is supposed that the genesis of augmented rhythmic impulsation of the thalamic neurons in patients with parkinsonism is connected with a break of the catecholaminergic transmission both of the dopaminergic and alpha-adrenergic one.

[The effect of the systemic administration of neuroleptics on the neuronal background activity of the ventrolateral thalamic nucleus in the cat]. / Vliianie sistemnogo vvedeniia neiroleptikov na fonovuiu aktivnost' neironov ventrolateral'nogo iadra talamusa koshki.

The background activity of 272 neurons of the ventrolateral thalamic nucleus was registered extracellularly in chronic experiments on cats in drowsy state before and after systemic injection of haloperidol and droperidol in cataleptic doses. In intact animals the neuronal activity was characterized by the burst discharges with short duration (5-50 ms) and high intraburst frequency (200-450/s). In 15% of investigated cells the rhythmic sequences of burst discharges with frequency of 2-2.5, rarely 3-4/s were revealed. After injection of haloperidol and droperidol the amount of neurons with rhythmic activity increased to 22% and 30%, respectively. The predominant burst frequency augmented to 3-5/s. In a third of cells long rhythmic discharges lasting for 80-300 ms were registered. After chronic haloperidol administration (10 days) relatively low intraburst frequency (60-170/s) was observed in 37% of cells. It is suggested that the above changes are a result of strengthening of the inhibitory influences on the ventrolateral neurons from substantia nigra and reticular thalamic nucleus because of blockage of the dopamine and alpha-adrenergic receptors.

[Excitation and inhibition processes in the neurons of the thalamic motor nuclei of normal cats and following an N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced lesion of the nigrostriatal dopaminergic system]. / Protsessy vozbuzhdeniia i tormozheniia v neironakh motornykh iader talamusa koshek v norme i posle porazheniia nigrostriatnoi dofaminergicheskoi sistemy, vyzvannogo N-metil-4-fenil-1,2,3,6-tetragidropiridinom.

Peculiarities of excitation and inhibition evoked in motor thalamic nuclei (VA-VL) neurons by electrical stimulation of red nucleus were studied on intact cats and after injection of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP; 5 mg/kg i.m., p.d. during five days). Two days after the last injection as much as 48% of nigral neurons were destroyed and the content of dopamine in the caudate nucleus fell to 30% as compared to intact animals. Before acute experiments all cats were anaesthetized with ketalar and immobilized with myorelaxine. It was found that MPTP injections caused a decrease of the inhibition duration and effectiveness in relay and nonrelay VA-VL neurons. The inhibition deficiency was accompanied by shortening of latencies of orthodromic responses evoked by red nucleus stimulation and facilitation of antidromic spikes invasion into somata of relay neurons after motor cortex stimulation. It was suggested that the reduction of GABAergic nigro-thalamic influences modulated by dopamine underlay the developing deficiency of inhibition.

[Rhythmic background activity of the thalamic neurons of patients with extrapyramidal movement disorders]. / Ritmicheskaia fonovaia aktivnost' talamicheskikh neironov u bol'nykh s ékstrapiramidnymi dvigatel'nymi narusheniiami.

When applying the microelectrode method in neurosurgical clinic to differentiate white matter and thalamic nuclei the background activity of 123 thalamic neurons has been registered in 30 patients with motor extrapyramidal disorders. The recordings were performed from ventral oral anterior, ventral oral posterior and adjacent reticular thalamic nuclei. Autocorrelation functions and spectral density functions for the activity of 44 cells were analyzed. In patients with parkinsonism and double athetosis a number of cells (48%) with rhythmic activity were revealed. Regular fluctuations of background neuronal discharges with different frequencies were observed: in the range of thetha-rhythm (5-7 Hz), deltha-rhythm (1-4 Hz), with second (2-10 s) and decasecond (15-40 s) periods. The possibility of simultaneous presence of several regular periodic processes was established: in 8 neurons 2 or 3 waves of acceleration and slowing down of spike discharges have occurred. The question is discussed about the origin and the significance of rhythmic fluctuations of thalamic neuronal discharges.

Spontaneous and evoked activity of neurons in deep structures of the brain during their anodal polarization.

The influence of anodal polarization on the spontaneous activity of neurons in the caudate nucleus, medial geniculate body, and the median center of the thalamus and on the evoked impulse activity of neurons in the medial geniculate body was investigated during auditory stimulation. The impulse activity was recorded extracellularly with glass and metallic microelectrodes. Nichrome polarizing electrodes of 0.2 mm diameter with an uninsulated tip of 0.3 mm were inserted into the foregoing structures in a packet. Current parameters evoking the reversible suppression of spontaneous and evoked neuronal activity were determined: 300-500 microA during exposure for 1-3 min at a distance of up to 3 mm from the polarizing electrode. After the cessation of polarization, a prolonged aftereffect was observed: The inhibition of evoked discharges lasted 4-10 min, and the evoked impulse responses disappeared for 5-20 min.

[Use of the microelectrode method for differentiation of white matter from thalamic nuclei during stereotaxic procedures]. / Ispol'zovanie mikroélektrodnogo metoda dlia differentsirovaniia belogo veshchestva i iader talamusa pri stereotaksicheskikh operatsiiakh.

Two hundred and three neurograms were recorded from the ventrolateral and reticular nuclei of the thalamus in 29 patients. Pulsed neuron activity was encountered in 116 cases. Reactions to motor tests were recorded from 26 neurons. The authors constructed maps of the location of the cerebral areas studied in relation to the main intracerebral guiding points. A large number of cells (44%) with rhythmic pulsed discharges with a frequency of 3-7 Hz were found in patients with parkinsonism and double athetosis. A great variability of background and induced activity of the thalamic nuclei under similar conditions of study was revealed.