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The BUMP model of The BUMP model of response planning: response planning:

Intermittent Intermittent predictive control predictive control accounts for 10 Hz accounts for 10 Hz

physiological tremorphysiological tremor

Robin T. Bye* and Peter D. Robin T. Bye* and Peter D. NeilsonNeilson

Neuroengineering Laboratory, School of Electrical Engineering and Neuroengineering Laboratory, School of Electrical Engineering and Telecommunications, University of New South Wales, Sydney Telecommunications, University of New South Wales, Sydney

2052, Australia.2052, Australia.

*Corresponding author: robin.bye@gmail.com *Corresponding author: robin.bye@gmail.com

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

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AbstractAbstract

Physiological tremorPhysiological 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]

Adaptive Model Adaptive Model TheoryTheory

• 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

Three processing Three processing systemssystems

• 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)

IntermittencyIntermittency• 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

SA-RP-RE sequenceSA-RP-RE sequence

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SSAA

RPRP

RREE

BUMP

Basic unit of motor Basic unit of motor production (BUMP)production (BUMP)

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Simulation studySimulation 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

Ramp movements Ramp movements (real)(real)

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Ramp movements Ramp movements (sim.)(sim.)

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

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RealReal SimulatedSimulated

Varying speeds (real)Varying speeds (real)

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Varying speeds (sim.)Varying speeds (sim.)

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Effect of vision (real & Effect of vision (real & sim.)sim.)

RealReal

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SimulatedSimulated

DiscussionDiscussion• 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

Discussion cont’dDiscussion 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

ConclusionConclusion

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1.1. Vallbo ÅB & Wessberg J (1993). Organization of motor output in slow finger movements in Vallbo ÅB & Wessberg J (1993). Organization of motor output in slow finger movements in man. man. Journal of PhysiologyJournal of Physiology, , 469,469, 673-691. 673-691.

2.2. Gross J, Timmermann L, Kujala J, Dirks M, Schmitz F, Salmelin R & Schnitzler A (2002). Gross J, Timmermann L, Kujala J, Dirks M, Schmitz F, Salmelin R & Schnitzler A (2002). The neural basis of intermittent motor control in humans. The neural basis of intermittent motor control in humans. Proceedings of the National Proceedings of the National Academy of Sciences of the USA,Academy of Sciences of the USA, 9999(4), 2299-2302.(4), 2299-2302.

3.3. Neilson PD & Neilson MD (2005). An overview of adaptive model theory: Solving the Neilson PD & Neilson MD (2005). An overview of adaptive model theory: Solving the problems of redundancy, resources, and nonlinear interactions in human movement control. problems of redundancy, resources, and nonlinear interactions in human movement control. Journal of Neural EngineeringJournal of Neural Engineering, , 22(3):S279–S312.(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. ReferencesReferences

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