The vestibular system detects head movement and provides vital information for balance. Unfortunately, over a third of adults over age 40 have a vestibular dysfunction resulting in a significant increased risk of falls. While vestibular therapy can improve symptoms, some patients show little recovery. For physical therapy to be effective, the techniques learned in the clinic must transfer into daily life. The theory of credit assignment has been used to enhance this transfer. Briefly, credit assignment states that when we detect an error between our predicted and actual movement, we can either assign the error to ourselves, as an inaccurate prediction, or to our environment, as external interference. When an error is internalized we update our prediction, to match what we observed, and adapt our motor plan accordingly. As a result, the next time we perform the same movement there is no error. Thus, the goals of this proposal are to understand 1) how sensory information from the vestibular system is interpreted and 2) how this interpretation influences adaptation in motor behavior.
The first aim of this proposal is to characterize a population of neurons, called VO cells. Previous studies have shown that VO neurons receive head movement information from the vestibular system. However, these cells only encode the information when the head is moved by an external perturbation. During a planned head movement, the body can predict the sensory feedback and subtract it from the total feedback signal. In addition, when an unexpected head movement interrupts a planned one, these cells will only encode the perturbation. Thus by monitoring these cells one can infer what part of head velocity the body interprets as an external perturbation.
The second aim i s to examine how this interpretation is linked to the adaptation of a relevant motor behavior. For example, in order to maintain visual stability during head rotation the eyes must counter-rotate. When a head movement is planned, the body predicts and pre-programs the necessary eye movements. We hypothesize that the same system that predicts the feedback signal to suppress VO cells also drive pre-programmed eye movements, hence any change in prediction should be seen in both behaviors. To test this, we will perturb head movements in a predictable way, by adding weight to the head and thus slowing it down. We hypothesize that initially the body will interpret this as an external perturbation but, with time,will update its prediction. Therefore it is expected that VO cells will initially encode an error in hea movement, but will eventually adapt to the new head dynamics. Additionally, eye movements will initially fail to compensate for the change in dynamics but will regain accuracy as the body adapts. A model has been developed that captures VO cell and eye movement behavior. If confirmed, it could further the understanding of vestibular physiology. Moreover, monitoring the progress of adaptation under different motor/sensory conditions could guide improved rehabilitation. Future studies could examine the role of additional sensory inputs (ex. vision) and how adaptation affects other vestibular functions (ex. balance).
The goal of this project is to understand 1) how the body interprets sensory feedback from a planned movement and 2) how that interpretation can affect future planned movements. When sensory feedback is interpreted as an error, our brain will correct the movement plan, and future movements will reflect that change. Understanding this process of adaptation could guide improvements in physical therapy and rehabilitation.
| Haggerty, Stephanie E; King, W Michael (2018) The Interaction of Pre-programmed Eye Movements With the Vestibulo-Ocular Reflex. Front Syst Neurosci 12:4 |
