The challenge

The ability to maintain constant eye-contact with objects of interest during passive and active movements of the body is apparently of great interest for survival. To this end, nature has provided us with a complex, highly flexible structure, the neck. Through the use of about 30 muscles and several sensory systems, the position of the head is controlled. If for instance external accelerations are applied to the body, like when driving a car, acceleration sensors located in the inner ear, the otoliths, help to maintain head position. We have chosen this paradigm as a starting point for our investigation. Modeling the head-neck system represents a challenging task since adequate representations of several sub-systems and their interaction is required. The points to be addressed are:

1. The acceleration sensors, the otoliths.
2. Neural transformations of otolith signals, especially by the vestibular nuclei.
3. The mechanical properties of the muscles as well as their reaction to neural contraction commands.
4. The mechanical response of the neck-head system to external accelerations and muscle contraction.
5. A basic control loop (lambda model) to keep the head in a certain pre-defined position

The Model

Our MKS-simulations of the human neck are to our knowledge the first such simulations that are based on a realistic description of human neck-mechanics and muscles. To incorporate realistic postural reflexes, our model also uses simulated signals from the balance system (LOTO Hagenberg).

Currently our simulation can demonstrate the following responses under simplified conditions:

1. The head drops on the torso if no muscular forces are provided.
2. The head is kept still by the lambda-control if no external accelerations exist.
3. The lambda-control tries to bring the head back to the pre-defined resting position if external accelerations exist.
4. Deviations from the resting position are much smaller if additional otolith input exits