Effect of T-activin on the formation of conditioned reflex and manifestations of unconditioned reflex of avoidance in August strain rats]

It has been revealed that intraperitoneal injection of T-activin (humoral factor of the thymus) to August rats leads to more rapid and stable conditioned reflex formation to a sound and to a decrease of avoidance time when electric current is given to a shuttle chamber. Furthermore, less amount of uneffective series in testing unconditioned avoidance is registered in the test animals. A positive T-activin effect on conditioned reflex formation and unconditioned reflex manifestation is probably connected with its ability to alter hippocampus functional parameters and (or) with anti-stressor properties of the preparation.     

Reversal time distribution in the perception of visual ambiguous stimuli

Reversal of perspective for ambiguous optical stimuli (Necker cube, Schröder staircase, honeycomb) has been studied, determining the statistical distribution of time intervals spent on each percept. The experimental distributions can be fitted with the gamma function, characterized by two parameters n, b. The two parameters are not independent, showing a correlatiomn = 0.74.Subsequent intervals appear to be largely independent; from the beta distribution for the fraction of time spent on a given percept, one can show that the subjects differ only in regard to the variance of this variable.     

The conditioned avoidance reflex and intersignal movements: the correlation of the cardiac and motor components]

In five dogs correlation was studied of heart rate (HR) and motor component of conditioned avoidance reflex (CAR), elaborated by Petropavlovski? method. Stable CAR was expressed in lifting and long (not less than 5-10 sec) holding of the paw on definite height (5-10 cm) for the avoidance of painful electrocutaneous paw stimulation in response to conditioned acoustic stimulus. The level of defensive excitation, evaluated by heart rate change was maximum before the beginning of the conditioned motor reaction. Immediately after lifting and placing the paw in the zone of security a sharp decrease of defensive excitation level ("drive" reduction) took place. Intertrial motor reactions of two types were revealed. The first type imitated the conditioned motor reaction, the second one the usual phasic bending of the paw. Against the background of intertrial movement of the first, operant type a decrease of defensive motivation took similarity as it occurred against the background of CAR during the performance response.     

The effect of phenamine and caffeine on caudate inhibition of conditioned reflex avoidance reactions in cats]

In cats with a preliminarily learned conditioned avoidance reaction, stimulation of the caudate nucleus inhibited behavioral response by lengthening its latency and reducing the number of conditioned reactions. Intensity of the inhibitory effect did not substantially depend on the localization of electrodes in the head or body of the nucleus and weakened within a few experimental days. D,1-amphetamine (0.5 to 4 mg/kg) and caffeine (10 to 10 mg/kg) suppressed the caudate inhibition, but the action of the drugs was manifested in different ways. The influence of large doses of d,1-amphetamine was characterized by a serious disturbance of behaviour and caudate inhibition of conditioned responses.     

Neurophysiologic mechanisms of the formation of the signal significance of words in yound children]

It has been established by means of the auto- and cross-correlation EEG analysis of children in the second year of life that different functional systems of relationships of cortical structures are formed during the word perception depending on whether it is an indifferent or signal stimulus for the child. In response to indifferent words, synphasic oscillations of the biopotentials appear in the infero-parietal and temporal, as well as in the temporal and frontal zones of the dominant hemisphere, without enhancement of the periodic processes and without appearance of a common rhythm. Signal verbal stimuli produce enhanced highly synchronous, synphasic interconnections of the infero-parietal biopotentials not only with temporal, but more considerably so with the frontal activity of the left hemisphere. This is accompanied by increased periodicity of processes between them and the appearance of a predominant rhythm 4--5 osc/sec.     

Level dependent signal flow in the light pupil reflex

Latency of pupillary responses to light stimuli are smaller for larger steps of light, and larger for smaller steps of light (Alpern 1954; Lowenstein et al. 1964; Lee et al. 1969; Terdiman et al. 1969; Cibis et al. 1977; and many others). Miller and Thompson (1978), however, reported negligible change in pupil cycle time (period of high gain instability oscillations) with increased mean brightness. Sandberg and Stark (1968) reportd a negligible reduction in phase lag of pupillary responses to sinusoidal light stimuli as the modulation coefficient (m) increased. To resolve the inconsistency between the well-documented dependence of latency upon brightness, and the apparent absence of level dependence in the phase characteristics (as reflected directly in the responses to sinusoidal stimuli and indirectly in pupil cycle time experiments) we measured: 1. Latency to step stimuli of light, 2. Phase of responses to sinusoidal light stimuli and 3. Period (pupil cycle time) of high gain instability oscillations. The dependence of pupillary latency upon stimulus level (both light and accommodation) and the interaction between accommodation and light responses were investigated. We show that most of the level dependence of light-pupil latency resides in the afferent path. In the companion papers, we demonstrate that: 1. Phase of pupillary response to sinusoidal light stimuli is reduced by increased mean light level, but is independent of pupil size and accommodative stimulus level; and 2. The period of high gain oscillations is shown to decrease with increased mean light level. Taken together, these results imply the existence of a Level Dependent Signal Flow (LDSF) operator that resides in the light-pupil pathway, but not in the accommodation-pupil pathway. We propose a systems model of this operator in which the neural signals controlling pupil size are treated as waves whose phase velocity increases in response to brighter stimuli, and decreases in response to dimmer stimuli. When parameters of the model are adjusted to fit measured pupillary latency over a range of light levels, the model exhibits reduced phase lag in response to increased mean light level in the sinusoidal paradigm, and it exhibits reduced pupil cycle time in the high-gain oscillation paradigm. The model exhibits saturation of the LDSF effect in all paradigms at high light levels, as do experimental results. It simulates directional asymmetry of pupillary response to positive and negative steps of light, with constriction more rapid than dilatation. Finally, it simulates tonic pupillary constriction in response to modulation of a light simulus without changing average light level (Varju 1964; Troelstra 1968). All of these stimulated results are in accord with experimental observation.