Somatosensory evoked potentials during natural and learning rearrangements of posture accompanied by limb elevation in dogs.

Changes in the functional state of the sensorimotor cortex associated with reorganization of the natural pattern of postural rearrangement before limb elevation (the "diagonal" patten and of an artificial rearrangement (the "unilateral" pattern) were studied in dogs. The state of cortical structures on postural rearrangement was assessed in terms of the pattern of somatosensory evoked potentials produced in response to stimulation of the forelimb during postural preparation of the animal for elevating the hindlimb (acquired avoidance response to a sound signal). Evoked potentials during the natural postural preparation (the "diagonal" pattern) were compared with those during the altered pattern of postural preparation (the "unilateral" pattern), this preparation taking place prior to elevation of the limb. Controls consisted of evoked potentials in the resting state. Decreases were seen in the latencies and amplitudes of most components of evoked potentials during postural rearrangement. In general, changes in evoked potentials were less marked in the "unilateral" pattern than in the "diagonal" pattern, though the differences were significant only for the amplitude of the first negative component. Changes in evoked potentials were similar regardless of whether the supporting forces of the limb to which the test stimulus was applied increased or decreased during postural rearrangement. It is suggested that differences in evoked potentials may reflect changes in the interaction between neuronal populations within the sensorimotor cortex during reorganization of the pattern of postural rearrangement associated with learning.

[Somatosensory evoked potentials during natural and learned patterns of postural adjustment, accompanying limb movements in dogs]. / Somatosensornye vyzvannye potentsialy vo vremia natural'noi i vyuchennoi perestroiki pozy, soprovozhdaiushchei pod''em konechnosti u sobak.

A goal of the study was to investigate cortical reorganization corresponding to inhibition of innate motor patterns during motor learning. Functional changes in the sensorimotor cortex during learned rearrangement of the natural diagonal pattern of postural adjustment (PA) accompanying a hindlimb movement into a new one, the so-called unilateral pattern, were studied in dogs by testing somatosensory evoked potentials (SEP) in response to stimulation of a forelimb during PA immediately before the limb movement onset. During PA the latency and the amplitude of several SEP components decreased. In general, changes in SEP were less pronounced in the learned unilateral pattern of postural adjustment in comparison with the innate diagonal pattern, but the difference was significant only for some SEP components. The SEP late positivity in the learned postural pattern was replaced by a negativity. The SEP changes were similar independently of whether the test stimulus was applied on the forelimb loaded or unloaded during postural adjustment. The data suggest that changes in interrelations between different neuronal populations in the sensorimotor cortex during formation and realization of a learned motor program can be reflected in SEP changes.

[Somatosensory evoked potentials during long-term isometric muscle contraction]. / Issledovanie somatosensornykh vyzvannykh potentsialov vo vremia dlitel'nogo izometricheskogo sokrashcheniia myshts.

The effect of sustained isometric contraction on somatosensory evoked potentials (SEPs) was studied. An attenuation of early SEP components N20--P30, P30--N35) was observed during the last minute of the endurance time. The late components (P45--N55, N55--P100) showed a significant increase of the amplitude during the first minute of the contraction. The amplitude of N35--P45 did not change during voluntary contraction, although it was decreased immediately after the contraction. An increase of the integrated EMG of forearm flexors was observed in the last minute of the endurance time. The maximal voluntary contraction was decreased immediately after the sustained contraction. The observed changes in SEPs could be attributed to possible changes in sensory information and motor command due to motor task.

Computerized system for posturographic research based on the ADAPT language for analysis of analogue signals.

A description is given of a system for posture analysis based on a specialized language ADAPT for analysis of analogue data, guaranteeing: 1. Analogue-to-digital conversion of the input signals with dialogue determination of the conversion parameters and monitoring of the signals on the screen. 2. Storage of the data on a diskette in a format guaranteeing high density of the data and fast exchange with the computer. 3. Calculation of the following parameters of the stabilogram and statokinesigram separately for open and for closed eyes: a) Anterior-posterior and lateral components of the path of the projection of the force centre SPAP and SPLAT; b) Mean frequency of the sways: fAP and fLAT; c) Ratio between the anterior-posterior and the lateral sways: AP/LAT. d) Surface A covered by the shifting of the centre of force; e) The path (SP) of the centre of application of the force; f) Mean amplitude (MA) of the sways for one second; g) Mean frequency (MF) of the sways. Romberg's coefficients are calculated for all parameters. 4. High speed of the calculations. 5. Graphic and digital display of all results on the screen from where they can be transferred to a printer, if necessary.

Somatosensory evoked potential of the stretch-reflex (T-reflex).

Averaging of EEG recorded monopolarly from C3, contralateral to the activated limb, in the stretch reflex shows the presence of somatosensory evoked potential (SSEP) with characteristic shape: four constant waves--P29, N84, P202 and N294, and four inconstant waves--N31, P74, P99 and N123. Comparison of this SSEP with the SSEP in children, evoked in the stretch reflex, shows shorter latencies of the waves in adults. On the basis of data from the different series of experiments, it is assumed that kinesthetic signalization plays a dominant role in the genesis of SSEP of the T-reflex. Studies have shown that SSEP of the T-reflex is succeptible to habituation upon long repetition of the stretch reflex.