Response of rabbit visual cortex neurons to direct stimulation by current of different intensities

Response was investigated in 47 rabbit visual cortex neurons to direct intracortical electrical stimulation consisting of single biphasic pulses of increasing intensities within the 150–2,700 µA range. Minimum level for generating all components of response to electrical stimulation remained similar from one neuron to the next, ranging between 150 and 600 µA. Three different patterns of dependence between numbers of spikes at different stages of response and current amplitude were identified: stable, gradual and selective patterns. Percentages of stable dependences were lower for after-discharges in comparison with initial firing (at 11 and 26% respectively) and the proportion of selective dependences were somewhat higher (at 32 and 21%). The selective dependence observed could imply the existence of optimum current levels at which peak neuronal response occurs. At the same time, duration of inhibitory pauses lengthened uniformly in the response of all test neurons during increasing intensity of the electrical stimuli. Findings obtained during this study may have a practical application in matters connected with visual prosthetics in the blind.M. V. Lomonosov State University, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 239–247, March–April, 1989.     

Dynamics of single unit responses of the rabbit visual cortex to repetitive photic stimulation

Single unit responses in the visual cortex of the waking rabbit to repetitive photic stimulation at a frequency of once every 2.5 sec were studied. Depending on the total number of spikes in the response, the dynamics of the responses could be divided into two types: "fast" and "slow." From 5 to 15 stimuli were required to establish a stable level of response with changes of the first type, but 50 to 100 stimuli were needed for the response with changes of the second type. About 50% of all neurons did not change the characteristics of response. In the group of neurons with changing responses, partial habituation was found in 55–59% of cells; there were 25% of neurons with sensitization of discharge and 17–20% with a humpbacked type of response dynamics. A "slow" dynamics of unit responses in most cases was accompanied by changes in the duration of inhibitory pauses in the response; negative correlation of these values was observed in 65% of neurons.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 10, No. 5, pp. 451–459, September–October, 1978.     

Responses of rabbit visual cortical neurons to intracortical electrical stimulation

Responses of rabbit visual cortical neurons to single and repetitive intracortical electrical stimulation were investigated. The stimulating electrode was located 0.7–1.2 mm away from the recording electrode. Response thresholds to single stimulation were as a rule 150–180 µA, whereas to series of stimuli they were 30–60 µA. The latent period to the first spike averaged 5–15 msec but the probability of the initial discharge was very low, namely 3–6%. With an increase in current intensity the duration of the initial inhibitory pause was increased in half of the neurons responding to it, whereas in the rest it was unchanged. After presentation of series of stimuli spontaneous activity was enhanced for a short time (4–6 sec). In about half of the cells the same kinds of discharge dynamics were observed in response to repetitive stimulation (frequency 0.25 Hz) as in responses to light, but more neurons with sensitization of discharge and fewer "habituating" neurons took part in responses to electrical stimulation. It is postulated that stimulation of a given point of the visual cortex evokes excitation of a local neuron hypercolumn and inhibition of neighboring cell columns.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 15, No. 4, pp. 412–419, July–August, 1983.     

New Criteria for the Evaluation of Soil Bacterial Complexes

The initial concentration of prokaryotic microorganisms, the type of their growth, doubling time, and the growth dynamics of bacteria and actinomycetes in three types of soil (meadow, chestnut, and soddy forest) were evaluated by the luminescence microscopic analysis of soil samples incubated in a humid chamber for 1 day. Soddy forest and chestnut soils differed in most of the parameters analyzed. Meadow soil was close to soddy forest soil in some parameters and to chestnut soil in other parameters. All soil suspensions exhibited high growth rates of bacteria and actinomycetes, indicating that the fraction of viable microorganisms in the soils was high.     

Convergence of visual and auditory stimuli on the neurons of the visual cortex in the conscious rabbit

We investigated the visual-cortex neurons of the conscious rabbit during simultaneous stimulation with a clicking sound and a light flash (complex) and during separate application of these stimuli. We tested the development of the reflex with time and of the sound-light association during prolonged rhythmic application of the sound and light. Fifty visual-cortex neurons were studied; 20% of the cells responded with a specific phased reaction and 16% exhibited a specific response to the complex different from the responses to each of its components. Development of a sound-light association was observed in 18% of the cells and a temporal reflex was induced in 25%. In most cases, the conditioned reaction evoked was similar to some informational element in the neuronal response to the complex.M. V. Lomonosov Moscow State University. Institute of Cybernetics, Academy of Sciences of the GruzSSR. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 391–398, July–August, 1970.