Repetitive Transcorneal Alternating Current Stimulation Reduces Brain Idling State After Long-term Vision Loss.

BACKGROUND: Deafferentation of visual system structures following brain or optic nerve injury leaves cortical areas deprived of visual input. Deprived cortical areas have a reduced sensory information processing and are characterized with localized enhanced or synchronized rhythms believed to represent an "idling state". OBJECTIVE/HYPOTHESIS: We hypothesized that cortical idling can be modified with transcorneal alternating current stimulation (tACS) known to modulate cortical oscillations and thus change the functional state of the deafferented areas. METHODS: tACS was applied in rat model of severe optic nerve crush using a protocol similar to our clinical studies (200 µA, 2-8 Hz) for 5 treatment days right after the lesion and at the chronic stage (3 months later). EEG and VEP were recorded over the visual cortices. In vivo confocal neuroimaging of the retina and histology of the optic nerves were performed. RESULTS: Morphological investigations showed massive retinal ganglion cells death and degeneration of the optic nerves after crush. Visual loss was associated with increased EEG spectral power and lower coherence, indicating an "idling state". Stimulation induced a significant decrease of EEG power towards normal values. These effects were especially pronounced in the chronic stage. CONCLUSION: Our results suggest that alternating current injected via the eye is able to modulate visually deprived brain areas and thus reduce cortical idling.

[Activity of Retrosplenial Neurons during the First Days and after a Week Following the Learning of the Operant Food-Acquisition Task].

Activity of single neurons in the retrosplenial cortex of rats during realization of the operant food-acquisition behavior was recorded. In the first group of rats the recordings were made in the first six days after learning of the task and in the second group--following a week of a rest after learning. There were no significant differences in proportion of neurons specialized in relation to the learned behavior; however in the first group 40% of these cells had specific activations only in 80-90%, but not in all (100%) realizations of their specific behavioral acts, while in the second group there were much less relative numbers (4%) of such cells. All neurons with not-100% activations on the early stages after the learning were specialized in relation to acts of approaching and pressing the pedal that rats acquired on the last session of learning. It could be supposed that during the first stages of consolidation of the operant skill some variable set of retrosplenial cortex neurons specialized to new behavioral acts can be involved.

[Optimal signal filtering parameters for tetrode recording of neuronal activity].

Extracellular recording of neuronal spiking is the main method of investigation of involvement of neurons in behavioral tasks. Development of multichannel electrodes made it possible to simultaneously record activity of the same group of neurons from different locations in the brain tissue. That method allows the researches to distinguish spiking of simultaneously recorded neurons by individual set of projection coefficients of amplitude parameters on axes corresponding to different channels of the multichannel electrode. We tested the possibility of effective separation of single unit spiking streams from multiunit activity recorded by tetrode and subjected to different filtering. We described the main limitations for effective spike identification and determined the optimal band of signal filtering for tetrode recording.

Tetanus-induced re-activation of evoked spiking in the post-ischemic dentate gyrus.

This study aimed at investigating and influencing the basic electrophysiological functions and neuronal plasticity in the dentate gyrus in freely moving rats at several time-points after global ischemia. Although neuronal death was induced selectively in the cornu ammonis, subfield 1 (CA1)-region of the hippocampus, we found an additional loss of the population spike in the dentate gyrus after stimulation of the perforant path. Input/output-measurements revealed that as early as 1 day post-ischemia population spike generation in the granular cell layer is greatly decreased when compared with pre-ischemic values and to sham-operated animals, despite an apparently intact morphology of granular cells as evidenced by Nissl-staining. In contrast, the synaptic transmission (excitatory postsynaptic field potential) shows no significant difference when comparing values before and after ischemia and ischemic and sham-operated animals. Despite reduced output function, indicated by very small population spike amplitudes, long lasting potentiation can be induced 10 days after ischemia. Surprisingly, even "silent" populations of neurons, which appear selectively post-ischemia and do not show any evoked population spike, can be re-activated by tetanisation which is followed by a normal appearing long-term potentiation. However, this functional recovery seems to be partial and transient under current conditions: population spike-values do not reach pre-ischemic values and return to the low pre-tetanic baseline values the next day. Electrophysiological measurements ex vivo after ischemia indicate that the neuronal dysfunction in the dentate gyrus is not due to locally destroyed structures but that the activity of granular cells is merely suppressed only under in vivo conditions. In summary, global ischemia leaves a neighboring morphologically intact input area, functionally impaired. However, neuronal function can be partially regenerated by electrophysiological tetanic stimulation.

Long-term potentiation and evoked spike responses in the cingulate cortex of freely mobile rats.

Long-term potentiation of synaptic efficiency is regarded as a major candidate for the role of the physiological mechanism of long-term memory. However, the limited development of concepts of the cellular and subcellular characteristics of the induction of long-term potentiation in animals in conditions of free behavior does not correspond to the importance of this question. The present study was undertaken to determine whether the characteristics of potentiation in the cingulate cortex in response to stimulation of fibers of the subiculo-cingulate tract are truly long-term, i.e., develop through all known phases and last at least 24 h, in freely moving animals. In addition, the study aims included identification of the effects of application of blockers of different types of glutamate receptors on the development of long-term potentiation and identification of the characteristics of spike responses of single cingulate cortex neurons to stimulation of the subiculo-cingulate tract. Long-term potentiation, lasting more than 24 h, was obtained in freely moving adult rats not treated with GABA blockers. Injection of glutamate NMDA synapse blockers led to significant decreases in evoked cingulate cortex potentials in response to test stimulation. Activatory short-latency spike responses were characterized by a low probability of spike generation, and this increased with increases in the stimulation current. These data demonstrated that it is methodologically possible to compare, in freely moving rats, the involvement of individual neurons in the mechanisms involved in learning one or another type of adaptive behavior and the dynamics of their evoked spike activity during the formation of long-term potentiation.

[Long-term potentiation and unit evoked responses in the cingulate cortex of freely moving rats]. / Dolgovremennaia potentsiatsiia i vyzvannye spaikovye otvety v tsinguliarnoi kore svobodnopodvizhnykh krys.

Long-term potentiation (LTP) of synaptic efficacy is considered to be the most probable physiological mechanism of long-term memory. However, lack of understanding of cellular and subcellular mechanisms of LTP induction in freely behaving animals does not correspond to the importance of the problem. It was tested whether the characteristics of potentiation in the cingulate cortex after tetanization of the subiculocingulate tract (SCT) meet the criteria of true LTP (that passes all known stages in its development and lasts for more than a day in freely-behaving animals). Additionally, characteristics of spike responses to SCT stimulation and the effects of application of different glutamate receptor blockers were studied. Without application of GABA receptor blockers, the LTP lasted for more than 24 hours. Application of NMDA glutamate receptor blockers significantly inhibited field potentials evoke by testing stimulation. Short-latency spike responses to SCT stimulation were recorded with low probability that increased with stimulation intensity. The obtained data reveal the possibility to compare the involvement of cingulate neurons in acquisition of adaptive behavior and changes in their spike responses during the LTP development in freely-moving rats.

Formation and realization of individual experience.

This article describes the methodological approach of systemic psychophysiology. In the framework of this approach a wide range of experimental data is analyzed: results of neuronal recordings in vitro and in awake normal and pathological animals learning to perform and performing both complex instrumental and simple behavioral acts. Another block of analyzed data is based on experiments with human subjects who learn and perform the tasks of categorization of words and operator tasks, participate in group game activity, and answer the questionnaires of psychodiagnostic methods. As a result of this analysis, the systemic psychophysiology approach is used to describe qualitatively and quantitatively the formation and realization of individual experience.

[Patterns in the shaping and realization of individual experience]. / Zakonomernosti formirovaniia i realizatsii individual'nogo opyta.

This article describes the methodological approach of systemic psychology. In the framework of this approach a wide range of experimental data is analyzed: results of neuronal recordings in vitro and in awake normal and pathological animals learning to perform and performing both complex instrumental and simple behavioral acts. Another block of analyzed data is based on the experiments with human subjects that learn and perform the tasks of categorization of words and operator tasks, subjects, performing group game activity and answering the questionnaires of psychodiagnostic methods. As a result of this analysis, the system psychology approach is used to describe qualitatively and quantitatively the formation and realization of individual experience.

Distinctions in the neuronal activity of the rabbit limbic cortex under different training strategies.

Limbic cortex neurons as well as the temporal characteristics of the behavioral cycles were recorded in rabbits trained to perform a food-procuring behavior according to different strategies which were distinguished by the sequence of the stages of training. It was demonstrated that additional activations can appear in the nonspecific activity of neurons specialized relative to one of those behavioral acts for which the animal was trained directly in the experimental cage. Such activations appeared, depending upon the training strategy, during different types of the animal's behavior; the temporal characteristics of the behavioral cycles also varied. An inference is drawn regarding the activating influence of preceding experience on the behavioral acts formed directly after it.

[Distinctions in the neuronal activity of the rabbit limbic cortex under different training strategies]. / Razlichiia v aktivnosti neironov limbicheskoi kory krolikov pri raznykh strategiiakh obuchenii.

Rabbits were trained to perform a food-procuring behavioural reaction which consisted in pressing one of the two pedals to get food from one of the two feeders, located in the corners of the cage. Activity of limbic cortex neurons and duration of behavioural cycles varied according to different strategies of learning the same final behavioural act. Neurons which were specifically activated while performing one of the trained behavioural acts could be additionally activated. For neurons of similar specificity these activation appeared at different behavioural acts in accordance with the applied strategy, but always at the stage which in the training sequence preceded specific activation. It is concluded that preceding experience activates the following behaviour. Such kind of activation might play an important role in behavioural act sequence, especially in searching behaviour.

Stability of the behavioral specialization of neurons.

The constancy of the association of the activity of the neurons of the limbic cortex and food-procuring behavior has been analyzed in neurons specially selected on the basis of the criterion of length of recording in experiments in rabbits. Comparison of the activity in the first and second halves of the period was carried on the basis of the average frequency for the time of each half of the recording, the average frequency in each of 10 distinctive acts of cyclical behavior, as well as on the basis of the probability of the presence of activation in these acts. It was demonstrated that behavioral specialization, defined as the presence of 100% activation of the cell in specific acts, did not change in the course of the recording, and was a stable information-containing characteristic of the association of the activity of the neuron with the animal's behavior.

[The stability of the behavioral specialization of the neurons]. / Stabil'nost' povedencheskoi spetsializatsii neironov.

Constancy of connection between the activity of limbic cortex neurones and food-procuring behaviour was studied on rabbits during prolonged unit records. Comparison of activity in the first and the second halves of records was conducted according to the mean frequency during each stage of recording, the mean frequency in each of 10 selected acts of cyclic behaviour and also the probability of activation presence in these acts. It was shown, that behavioural specialization, determined by the criterion of presence of 100% cell activation in specific acts, did not change during recording. The volume of changes in the connection of neurone activity to behaviour in the process of record greatly depended on conditions of recording; at constant mean frequency of neurone activity during the whole time of recording the volume of these changes was minimal.