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A model of functional recovery after significant loss of neural tissue: biofeedback based healing of vestibular dysfunction
BMC Neuroscience volume 11, Article number: P111 (2010)
Vestibular dysfunction can significantly affect balance, posture, and gait. Hundreds of patients suffering from significant loss of neural (vestibular) tissue were helped with a new treatment using biofeedback – a strip of electrodes feeding head-tilt information onto the tongue surface [1, 2]. The success rate is stunning but the neural processes associated with this treatment are, to date, not understood in detail.
We present a model that can explain how a minor fraction of remaining vestibular tissue, trained using biofeedback, regains the ability to balance the modeled organism in an upright position.
Our model contains 4 populations of rate-coded units with sigmoid activation functions that are either not or fully connected via activity modulated Hebbian synapses (see Figure 1). A vestibular apparatus (VA) senses the tilt level of the modeled organism. VA is connected to a hidden population (HL) connected to a motor control population (BA), generating balancing actions and thereby closing a control loop by influencing the current tilt level. A second loop, the biofeedback, contains a population mimicking the signal of the mentioned tongue strip (TS).
VA and TS create population-coded output because their units are broadly tuned to different preferred tilt levels. HL and BA use winner take all dynamics. All units receive, in addition to the afferent input, a constant amount of white noise. Feedback connections from BA to HL force these populations to commit to a common, converged state.
Destroyed VA-units reduce the total input to HL. Homeostatic input normalization iteratively strengthens remaining postsynaptic processes to regain the desired input strength.
After destruction of a significant amount of VA-nodes (>90%) the remaining efferent signal does not exceed HL’s noise level and the entire system turns non-functional. During homeostatic input normalization the tuning of remaining efferent VA connections broadens and causes the system to settle in a non-functional state.
Biofeedback substitutes missing vestibular data and re-enables BA to generate sensible actions. BA-HL-feedback forces HL’s output to be correlated with the sensed tilt angles. Thus, activity modulated Hebbian learning re-sharpens VA’s efferent tuning and the modeled organism relearns to balance in an upright position – even without biofeedback. Phenomenologically this effect is also observed in human patients.
Tyler M, Danilov YP, Bach-Y-Rita P: Closing an open-loop control system: vestibular substitution through the tongue. J Integr Neurosci. 2003, 2 (2): 159-164. 10.1142/S0219635203000263.
Danilov YP, Tyler ME, Skinner KL, Hogle RA, Bach-y-Rita P: Efficacy of electrotactile vestibular substitution in patients with peripheral and central vestibular loss. J Vestib Res. 2007, 17 (23): 119-130.
The authors would like to thank ETH Research Grant ETH-23 08-1.
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Jug, F., Krautz, C. & Steger, A. A model of functional recovery after significant loss of neural tissue: biofeedback based healing of vestibular dysfunction. BMC Neurosci 11, P111 (2010) doi:10.1186/1471-2202-11-S1-P111
- Upright Position
- Vestibular Apparatus
- Efferent Signal
- Hebbian Learning
- Vestibular Dysfunction