[Evaluation by humans of signals modulating different sound movement directions and particulars of perception of such signals in patients with temporal epilepsy].

In patients with epileptic lesions in the hippocampus as well as in the temporal lobe and hippocampus simultaneously, studies were made on the perception of sound signals imitating sound source movement. It was established that hippocampal lesion results in disturbance of estimation of sound spatial characteristics which manifests in a change accuracy of localization and shortening of subjective sound image movement trajectory. Maximum disturbances of localization function are observed during lesions of hippocampus and temporal lobe. Possible neurophysiological mechanism underling observed disturbances are considered.

Responses of cat primary auditory cortex neurons to moving stimuli with dynamically changing interaural delays.

The spike responses of individual neurons in the primary auditory cortex were studied in anesthetized cats during exposure to stationary and moving stimuli with static or dynamically changing interaural delays (deltaT). Static stimuli were tones and clicks. Dynamic stimuli were created using series of synphase and antiphase clicks with interaural delays which changed over time. Sensitivity to changes in deltaT was predominantly present in neurons with low characteristic frequencies (less than 2.8 kHz). Changes in deltaT in moving stimuli induced responses in neurons sensitive to changes in deltaT in the stationary stimulus. The effect of movement could be a relationship between the level of spike activity and the direction and rate of change of deltaT or it could be a displacement of the tuning curve for the response to deltaT (the deltaT function) in the direction opposite to that of the direction of the change in deltaT. The magnitude of the effects of movement depended on the position of the period for changes in deltaT relative to the deltaT function. The greatest effects were seen with changes in deltaT on the sloping part of the deltaT function.

[Responses of neurons in the primary auditory cortex of the cat to the auditory motion stimuli with variable interaural delay]. / Reaktsiia neironov pervichnoy slukhovoi kory koshki na dvizhushcheisia stimul s dinamicheski izmeniaiushcheisia mezhushnoi zaderzhkoy.

Unit responses in the primary auditory cortex of anesthetized cats to stationary and apparently moving stimuli resulted from a static and dynamically varying interaural delay (ITD) were recorded. The static stimuli consisted of binaurally presented tones and clicks. The dynamic stimuli were produced by in-phase and out-of-phase binaurally presented click trains with time-varying ITD. Sensitivity to ITDs was mostly seen in responses of the neurons with low characteristic frequency (below 2.8 kHz). All cells sampled with static stimuli responded to simulated motion. A motion effect could take the form of a difference in response magnitude depending on the direction of stimulus motion and a shift in the ITD-function opposite the direction of motion. The magnitude of motion effects was influenced by the position of motion trajectory relative to the ITD-function. The greatest motion effect was produced by motion crossing the ITD-function slopes.

Methods for estimating structure of trace reactions of neurons in medial geniculate body.

The trace reactions of neurons in the medial geniculate body during the action of various auditory signals were investigated in anesthetized cats. Using the traditional peristimulus histogram (PSTH) method to analyze the impulse activity, trace reactions were found in some neurons that possessed a definite time structure with a varying degree of periodicity. Prolonged, diffuse changes in the level of activity were demonstrated in another group of neurons. The trace reactions of the second group of neurons were evaluated by averaging for a multitude of responses the individual PSTHs obtained for each response using the procedure of eliminating time shifts. Elimination in this way of the physiological variation in the time of reaction onset made it possible to establish the presence of a time structure in the trace reactions of a number of neurons in the second group.

[Various ways of assessing the structure of trace reactions of neurons of the medial geniculate body]. / Nekotorye sposoby otsenki struktury sledovykh reaktsii neironov vnutrennego kolenchatogo tela.

Afterdischarges of the medial geniculate body units were recorded in anesthetized cats following different sound stimuli. With traditional PSTH-technique, a periodicity of afterdischarges was found in some neurons whereas others showed diffuse and prolonged changes of their activity. To estimate the diffuse afterdischarges a special method was used. The procedure of eliminating time shift in neuronal responses was employed followed by averaging the individual PSTHs. A consequent diminution of time dispersion of neuronal responses revealed a distinct time structure in the diffuse afterdischarges.

[Conditions affecting the nature of the neuronal afterdischarges in the medial geniculate body of the cat]. / Usloviia, vliiaiushchie na kharakter sledovykh reaktsii neironov vnutrennego kolenchatogo tela koshki.

Sound signals induced afterdischarges in 20-40% medial geniculate body units. Dorsal neurons of the MGB had afterdischarges in the form of an augmentation of the activity level after cessation of the stimulation. The ventral MGB neurons revealed rhythmic afterdischarges more often, their pattern depending on the parameters of stimuli. When moving sound source or synthetized speech-like sounds were used, the dorsal MGB neurons and numerous ventral neurons showed afterdischarges in the form of an augmentation of the activity level. After pure tone stimulation of the ventral MGB units, many of them revealed rhythmic afterdischarges. The level of anesthesia in the experiments seems to be important.

[Neuronal afterdischarges of the medial geniculate body in the cat after the action of a rhythmic sound sequence]. / Sledovye reaktsii neironov vnutrennego kolenchatogo tela koshki pri deistvii ritmicheskoi zvukovoi posledovatel'nosti.

22% of neurons in the cat medial geniculate body under the effect of rhythmic sound stimuli developed afterdischarges the temporal structure of which and the amount of pulses in them being dependent on the stimulation rhythm, although no obvious driving phenomenon occurred. Changes of the firing rate in the afterdischarge related to changes in stimulation rhythm could be significant at the PST's epochs corresponding to the moment of the occurrence. The afterdischarges a periodic structure had mostly frequencies from 2 to 8 Hz, their low-frequency component being of the 0.2-0.7 Hz order.

[Selectivity of trace reactions of medial geniculate neurons to the rate of simulated movement of a sound source in the cat]. / Izbiratel'nost' sledovykh reaktsii neironov vnutrennego kolenchatogo tela koshki k skorosti imitiruemogo dvizheniia istochnika zvuka.

33 out of 90 neurons of the cat medial geniculate body revealed the selectivity of their afterdischarges to movement of sound when velocity of the movement changed from 30 to 180 deg/s. There was a specific velocity of the movement for each neuron. 76% of the neurons preferred the movement of 45--90 deg/s. 9 neurons had a periodic character of responses. The selective afterdischarges occurred in 39% of dorsal neurons and in 39% of ventral ones. The afterdischarges can be dependent on the direction of sound source movement, too.

[Response of medial geniculate body responses to the velocity of simulated sound source movement in the cat]. / Reaktsii neironov vnutrennego kolenchatogo tela koshki na skorost' imitiruemogo dvizheniia istochnika zvuka.

36 neurons (39%) of the anaesthetized cat medical geniculate body responded to simulated motion of the sound source (with angular velocity of 30 to 180 degrees/sec) selectivity with a certain speed of firing rate changing specific for each neuron during action of the signal. Selective response to a certain velocity of the sound motion occurred in 55% of neurons of the dorsal portion and in 27% of the ventral portion of the medial geniculate body. Response of these neurons reflected the whole range of experimental velocities. 75% of neurons revealed most obvious responses to the sound motion velocity of 30--90%/sec. The selective response to a certain velocity of the sound motion seems to depend on the direction of motion.