Neirofiziologiia = Neurophysiology最新文献

Movements of the elbow joint were studied in unanesthetized cats. These movements were evoked by microstimulation of the motor cortex or by vibration of the forepaw and then compared with reaction from direct stimulation of muscles in the anesthetized animals. Interaction of the hysteretic effects in the antagonistic muscles of the joint was studied during stimulation of two points of the motor cortex which produced opposite-directed movements. Coactivation of the antagonists was shown to increase both the joint stiffness and the uncertainty of the equilibrium value of the joint angle. The uncertainty myotatic reflexes during intracortical microstimulation were more significantly depressed in the muscle receiving more intensive activation from the given point in the motor cortex. On the contrary, myotatic reflexes during vibration were well expressed in the both antagonistic muscles. At the same time the uncertainty effects during forepaw vibration were displayed similarly as it was in the cortically evoked movements.

Inhibition of neuronal spike reactions associated with reflex movements and induced by the light flare at different moments during the conditioned stimulation (1 s.) has been found in chronic experiments on cats. The light flare in the interval of maximum probability of the reflex realization has promoted a rise in the neuronal latency by 300-400 ms and a decrease of their duration almost twice. Other realizations of the inhibition effect were weaker.

Orientation tuning (OT) of 225 visual cortex neurons was studied in immobilized cats by their responses to flashing light bars. It was found that 43% of neurons had monomodal OT and preferred the horizontal and vertical orientations, while 57% of neurons had double OT, i.e. they had main preferred orientation (PO) and additional PO (aPO). The mean angle between PO and aPO was equal to 71.4 +/- 2.4 degrees. In half of the cases the second maximum of OT was equal to the first one (mean: 0.7 +/- 0.03 from PO). Orientation characteristics of PO and aPO were practically identical. Under light and middle levels of narcosis half of the neurons with double OT became monomodal and 12% of monomodal neurons receive bimodal OT. Monomodal neurons had more often simple RF and invariance of OT to narcosis. The neurons with double OT had simple and complex RF equally often and their OT changed in narcosis. It is supposed that the neurons with double OT can be an angle and line cross detectors. Monomodal neurons may be the stable bench mark system of orientation coordinates. Interaction of these neuronal systems permits conducting an effective analysis of image features in the primary visual cortex.

The "concentration clamp" technique has been modified to realize fast and short-term application of a transmitter to whole neuron followed by its fast washout. Prolonged glutamate application evoked activation of the desensitized current. The application time was shortened to intervals when the washout corresponded to unfinished desensitization of the current. Shortening of the glutamate application term to some milliseconds resulted in arising of fast currents which maximal amplitude appreciably exceeded that of currents evoked by prolonged glutamate application. The role of both components under real synaptic conditions is discussed.

The excitability of flexors and extensors of the upper and low extremities was studied in healthy people and in patients with spasticity during local thermostimulation of their receptive fields using H-reflex (HR). In healthy people the HR was inhibited during cooling and was enhanced during warming. Thermostimulation of the contralateral side caused a contraverse reaction. In patients cooling of skin followed the rise of HR. The obtained data show that the condition of the thermoreceptive fields can influence reflex excitability of motoneurons. The character of this influence depends on the initial condition of the locomotor generator.

Local cooling (14-16 degrees C) and warming (40-42 degrees C) of different crus areas or healthy volunteers have been studied for their effect on pain sensitivity. The latter was estimated by means of the tibialis anterior flexor reflex (FR) and EMC-recording. It was established that changes in FR parameters depended not on the thermostimulus modality, but on its position. The FR was enhanced when the warm or cold stimulus was applied over the ipsilateral tested flexor muscle, and it was mainly inhibited when the thermostimulus was over the extensor or contralateral flexor. An assumption is made that the loss of the temperature modality is caused by convergence of temperature and pain information to the spinal interneurons of the "bimodal type". These neurons change their impulse activity under the effect of both temperature modalities. Different reactions of FR on thermostimulation of different areas of the crus are explained by the locomotor generation control of afferent information.

Postural reactions evoked in human by bilateral vibration of calf muscles were studied under different conditions: sitting without the feet contact with a support; sitting in an unstable position on the edge of the chair; sitting under conditions of the foot contact with different types of supports (rotating disk, suspended platform, etc.); standing with an asymmetrical load applied to the trunk. It has been shown that local vibration of calf muscles can evoke activation not only of the vibrated muscle or of its antagonist (local effects), but also of extensors and flexors of the knee joint (non-local effects), or of the remote muscular groups, involved in different postural synergies. The concrete pattern of muscle activation is determined by several factors, the most important being the relative position of the body links and interaction of feet with a support. The mental image of the body configuration in the system of internal representation is also very significant.

Neurophysiological effects and dynamics of bound calcium (Ca-b) in command neurons of defense behavior (LP11 and RP11) during food aversion conditioning were studied in snail Helix lucorum. It was found that during associative learning both conditioned reaction and nonspecific facilitation of sensory responses were determined in neurons. The nonspecific facilitation of sensory responses was similar to that found during sensitization development in neurons. However, conditioned response appeared 30 min later than long-term sensitization development. Specific dynamics of the Ca-b level in neurons was obtained after three and more conditioning. The dynamics of the Ca-b level correlated with neurophysiological effects and differed from those measured during sensitization development. It is suggested that molecular mechanisms underlying associative learning and sensitization are different in a command neuron of defense behavior in the snail.

Rapid ballistic food-getting movement characteristics were studied in albino rats. After ablation of the second area of the frontal cortex contralaterally as to the preferred extremity the number of attempts increased and their duration with reorganization of the phase structure of movements decreased. The habit of food extraction was lost after bilateral ablation of the cortex. The obtained results have illustrated significance of the frontal cortex in formation and realization of moving programmes.

Experimental studies on the relations between the afferent flows in A-beta and A-delta and C-fibres of a cutaneous nerve for different stimulations of cutaneous receptors provided the basis for modelling of various digital and graphical codes of the known and unknown sensations.