In 17 healthy volunteers, we studied movements of the forearm, which included episodes of positioning on the target level. The trajectory of the non-ballistic (relatively slow) movement looked like a double trapezium (flexion of the elbow joint from the state of full extension, 0 deg, positioning on the 50 deg level, further flexion to the limit angle of 100 deg, and a similar reverse sequence). The command trajectory and the trajectory of the realized movement were visualized with movements of cursors on a monitor in time/joint angle coordinates. We compared parameters of the tracking movements (in the presence of visual feedback) and their blindfold reproduction (with the complete absence of visual control). It was found that blindfold reproduction movements differ from sample tracking movements and their reproduction with partial limitation of visual control [16] in higher peak velocities and shorter durations, i.e., a trend toward conversion of such movements into ballistic ones was observed. Under conditions of elimination of visual control, movements that led to positioning were mostly hypermetric, i.e., positioning was usually accompanied by positive systematic errors (whose sign coincided with the direction of the preceding movement phase). The mean intragroup value of the systematic error of the first positioning (after flexion to the target level) was +6.73 ± 1.15 deg, while the respective mean for the second positioning (after extension to the same level) was +4.00 ± 1.31 deg. The nonlinear properties of stretch receptors of muscles whose activity provides the formation of a "proprioceptive" estimate of the joint angle are considered the crucial reason for systematic errors of blindfold positioning.

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State of the afferent, central, and efferent links of the somatic segmental reflex mechanisms was studied in the persons, involved in the cleanup and repair after the catastrophe at the Chernobyl' nuclear power station in 1986; clinical and electroneuromyographic tests were performed. Among 233 investigated individuals, 100 persons received rather high absorbed dc~.s and suffered from acute radiation syndrome (group I). Among the rest of the investigated individuals subjected to lower doses, 49 persons worked at the nuclear plants before and after their participation in the cleanup of the catastrophe (group II), while 84 persons were Involved only in the works carried out in 1986 (group liD. Comparison with a control group (20 persons) showed that the amplitude of evoked potentials (EP), recorded from the projections of n. medianus after supramaximum transcutaneous stimulations of the branches of this nerve, Innervating II and llI fingers, considerably decreased in cleanup workers (on average, by 9.3, 50.8, and 10.0% In groups I-III, respectively), The conduction velocity for EP also dropped (at the finger-wrist region to a greater extent than at the wrist-elbow region, by 12.3-15.0% and 1.1-5.4%, respectively). The maximum amplitude of M responses, recorded from the m~ abductor pollicis after stimulation of the n. medianus, decreased in the groups of cleanup workers by 14.8-17.4%, while the conduction velocity via efferent fibers of the n. rned/anus demonstrated only a slight In'end toward a drop in group II. In the groups of cleanup workers the thresholds of H reflex and M response in the m. soleus, evoked by stimulation of the n. tibialis post., increased, while the amplitudes of these responses decreased. At the same time, the latencies of H and M responses showed no considerable changes. In nearly all cases, the shifts of the above parameters were the greatest in group II. Thus, radiation factors, related to the Chernobyl' catastrophe, induce significant functional distortions in the somatic segmental reflex mechanisms, especially in the distal parts of their afferent and, to a somewhat le.~er extent, efferent links. The crucial significance of the duration of radiation influence in the development of the above changes is emphasized. A concept for radiation-induced genesis of the above phenomena is justified. Microcirculatory and metabolic impairments, largely related to the dysfunction of the sympathetic section of the autonomic nervous system, together with direct influences of radiation on the components of the peripheral and central nervous system, are regarded as probable mechanisms of the above modifications; these changes are induced upon long-lasting irradiation even in the case of its low intensity.