Adaptation and learning in postural control

Sammanfattning: The importance of the ability to use bipedal stance and gait in everyday life cannot be underestimated. Bipedal stance is learned during childhood and constantly adapted to changing circumstances throughout life. Failure to attain and maintain the control of upright posture can have catastrophic consequences. Postural competence needs to be recovered in a multitude of illness, in developmental disorders as well as to age related decreasing function. To meet this end, health professionals utilise a multitude of techniques, mainly based on sensory based training exercises. The overall ambition of this thesis was to enhance knowledge on adaptive behaviour and motor learning of human postural control with the aim to identify new therapeutic concepts for training and rehabilitation. The results demonstrate that postural control learning follow the general paradigm for memory formation, i.e. short-term learning is consolidated to long-term learning through central neural processes during inactivity. Long-term postural learning benefits from training with intervals more than three hours. Postural learning to withstand somatosensory or vestibular perturbations seems to follow different time schedules. Experiences from different postural tasks, if they post different demands, can be transferred to each other. Strategies to withstand postural perturbations include sensory reweighting (i.e. change of the relative importance of the individual sensory systems), and modifications and building of internal models (automatic postural programs). Children (7-9 years of age) had a more efficient consolidation of experiences from postural perturbations then adults. This could possibly be due to neural plasticity or a behaviour of ‘exploratory learning’. Patients suffering from Phobic Postural Vertigo – an anxiety related disorder, were shown to have an impaired adaptation, possibly due to an anxious control of posture which disable the patients to adapt their postural responses. This knowledge led to the development of a new therapeutic concept of ‘PREHAB’ prior to a sensory lesion which was implemented and studied. Patients scheduled for schwannoma surgery pre-treated with gentamicin, in order to produce a gradual sensory deafferentation, performed markedly better on the 6-month follow-up after surgery. Both compaired to before surgery and to other groups not treated with gentamicin and ‘PREHAB’. The effect could be attributed either to a sensory training concomitant with gradual sensory decline or to a separation in time of surgical and sensory trauma, or both in concert. The findings elucidate several important aspects to be taken into account both for rehabilitation of patients as well as for designing future studies on postural control.