Central Adaptive Mechanisms Research Articles

Effect of spaceflight on thresholds of perception of angular and linear motion

Psychophysical studies of vestibular function have been carried out in order to study adaptation within the vestibular sensory system to the weightless environment of orbital spaceflight. No significant change in the threshold of detection of whole-body angular acceleration was found, either during flight or post-flight. Experiments involving the perception of whole-body linear acceleration have yielded somewhat inconsistent results, although the weight of evidence points to an elevation and increased variability of threshold in the first few days following spaceflight. Although a change in the excitability of the saccular and macular otoliths in microgravity cannot be excluded, it is more probable that this decreased sensitivity is a manifestation of a central adaptive mechanism, in which the "weighting" of gravi-receptor information is reduced. Enhancement of the ability to detect linear acceleration stimuli, exhibited by some astronauts in microgravity, may be a manifestation of heightened utilization of cutaneous rather than otolithic cues.

Benign paroxysmal positional vertigo. Clinical observations by vestibular habituation training and by posturography.

Vestibular Habituation Training (VHT) is the treatment of choice for paroxysmal positional vertigo (ppv). The origin of the disturbance is peripheral and the data observed in the cases treated confirm that it is not located in horizontal canal function. However, canal dysfunction can be present together with ppv. Usually a separate course is observed for the phenomena attributed to horizontal dysfunction and those to the ppv lesion. The specificity of the Dix-Hallpike manoeuvres linked to the typical ppv is also confirmed by the data obtained by testing for VHT (VHT-test-battery). Ppv can have a repercussion upon the vestibulospinal reflex. That the same ppv disturbance can coincide with normal as well as with abnormal posturographic data, pleads for the intervention of central adaptive mechanisms. The effect of VHT is due to stimulation of these central adaptive mechanisms and not to any impact upon the peripheral lesion.

Posturography measuring instability in vestibular dysfunction in the elderly.

Balance dysfunction may be a cause of falling in the elderly. Disturbance of the vestibular system may have a repercussion upon balance performance, causing instability. Unilateral vestibular hypofunction (UVH) and its disturbing influence upon the vestibulospinal reflex (VSR), measured by the postural sway, has been studied. This influence is dependent on the interfering action of central adaptive and compensatory mechanisms. This central compensation may be different for vestibulo-ocular reflex (VOR) and the VSR. This comparative study shows that the elaboration of compensation in elderly people is less efficacious at the VSR level than at the VOR level. The influence of visual fixation is also stressed by comparing the posturographic recordings made with eyes open and eyes closed.

Cyclic AMP in the organs and tissues during adaptation to extremal factors

Extremal factors of different nature (hypoxic hypoxia, carbon monoxide poisoning, exposure to chemicals and to noise, hypokinesia) caused similar changes in the cyclic AMP level in the organs of albino rats (liver, cerebral hemispheres, heart). A considerable increase in the cyclic AMP concentration was found in the first stages, followed by a progressive fall during subsequent exposure, especially if the intensity of the factor was high. It is suggested that the universality of this response reflects one of the central adaptive mechanisms of the cell and of the organism as a whole.