1. 1 The BUMP model of response planning: Intermittent predictive control accounts for 10 Hz physiological tremor Robin T. Bye* and Peter D. Neilson Neuroengineering Laboratory, School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney 2052, Australia. *Corresponding author: robin.bye@gmail.com

2. The BUMP model of response planning forms the kernel of Adaptive Model Theory which defines, in computational terms, a basic unit of motor production or BUMP. Each BUMP consists of three processes: (1) analysing sensory information, (2) planning a desired optimal response, and (3) execution of that response. These processes operate in parallel across successive sequential BUMPs. The response planning process requires a discrete time interval in which to generate a minimum acceleration trajectory to connect the actual response with the predicted future state of the target and compensate for executional error. Here we show, by means of a simulation study of constant velocity (ram p) movements, that employing a 100 ms planning interval closely reproduces the measurement discontinuities and power spectra of electromyograms, joint-angles, and angular velocities of 10 Hz physiological tremor reported experimentally. We conclude that intermittent predictive control through sequential operation of BUMPs is a fundamental mechanism of 10 Hz physiological tremor in movement. 2 Abstract

3. Physiological tremor Normal 8-12 Hz tremor due to central- neurogenic and mechanical-reflex components Many types, e.g. rest, posture, motion Tremor during movement (focus of this study) is ~10 Hz and of central origin 10 Hz physiological tremor during constant velocity (ramp) movements is observable in joint angle, angular velocity and EMG signals [1] Cerebello-thalamo-cortical loop is considered neural basis for intermittent motor control of continuous movement [2]

4. Adaptive Model Theory The BUMP model forms the kernel of Adaptive Model Theory, a neuroengineering account of movement control Fusion of adaptive control theory and neuroscience Addresses major human movement science issues - e.g., intermittency, redundancy, resources, nonlinear interactions [3] Three systems for information processing Biologically-feasible neural network solution

5. Three processing systems Response planning (RP) Response execution (RE) system Sensory analysis (SA) system Operate independently and in parallel: The CNS can simultaneously - plan appropriate response to a stimulus (RP system) - execute response to an earlier stimulus (RE system) - detect and store a subsequent stimulus (SA system)

6. Intermittency SA and RE systems operate continuously RP system operates intermittently - system is refractory while operating on “chunks” of information -fixed planning time interval to plan an optimal response trajectory (minimum acceleration) -must predict future state of target and response - planning time interval Tp = 100 ms Leads to repeating SA-RP-RE sequences: BUMPs Movement consists of concatenated submovements Each submovement has a fixed duration of 100 ms

7. SA-RP-RE sequence 7 SARP RE BUMP

8. Basic unit of motor production (BUMP) 8

9. Simulation study Simulator of BUMP model implemented with Matlab/Simulink software Aim: Test simulator’s ability to reproduce results from human experiments Test case: Influential study of physiological tremor in slow finger movements [1] Simulations of ramp and hold movements -with and without visual feedback -with various levels of skill -of a variety of movement speeds Compare real (human) and simulated data -angular position, velocity, acceleration -power spectra

10. Ramp movements (real) 10

11. Ramp movements (sim.) 11

12. Power spectra (real & sim.) 12 RealSimulated

13. Varying speeds (real) 13

14. Varying speeds (sim.) 14

15. Effect of vision (real & sim.) Real 15 Simulated

16. Discussion Simulator closely reproduces the results of [1], i.e. ramp movements (position, velocity, acceleration waveforms) and their power spectra - with and without visual feedback - for high and low level of skill - for a variety of movement speeds Main finding: 10 Hz physiological tremor occurs for all test cases independent of vision, skill, and movement speed

17. Discussion cont’d With vision -secondary 2-3 Hz component occurs for less skilled subjects - “bumpy” movement trajectory Without vision -power of 2-3 Hz component is halved or disappears -smooth movement trajectory Results are independent of movement speed An adaptation paradigm was used to simulate different levels of skill

18. Conclusion 18 1.Vallbo ÅB & Wessberg J (1993). Organization of motor output in slow finger movements in man. Journal of Physiology, 469, 673-691. 2.Gross J, Timmermann L, Kujala J, Dirks M, Schmitz F, Salmelin R & Schnitzler A (2002). The neural basis of intermittent motor control in humans. Proceedings of the National Academy of Sciences of the USA, 99(4), 2299-2302. 3.Neilson PD & Neilson MD (2005). An overview of adaptive model theory: Solving the problems of redundancy, resources, and nonlinear interactions in human movement control. Journal of Neural Engineering, 2(3):S279–S312. We suggest that 10 Hz physiological tremor is the direct result of an intermittently operating predictive neural controller generating BUMPs every 100 ms. References

20. Use this as a master First level First level - Second level