Christoph Kolodziejski, Bernd Porr, and Florentin Wörgötter (2006)
Fast, flexible and adaptive motor control achieved by pairing neuronal learning with recruitment
In: . Proceedings of the fifteenth annual computational neuroscience meeting CNS*2006, Edinburgh. (export entry)
The motor system must be able to adapt quickly to load changes. In
addition, it is known that also long-term learning exists in the motor
system, which, for example, allows us to learn difficult motor skills
like playing the piano or excelling in sports. It is generally agreed
that many times motor learning occurs through the generation of
forward models for an originally existing control loop. Hence, early
on, the system cumbersomely executes a motor action under tight
closed-loop feedback control, whereas later, after some successful
learning, a forward model has been generated and the system executes a
much improved motion sequence "without thinking". In this study we
show that it is possible to combine temporal sequence learning with
recruitment to learn a forward model of a reflex and to execute it
with the momentarily required strength, which depends on the load. To
this end we employ a learning rule, which we had recently introduced
(Porr and Woergoetter Neural Comp. 15, 831-864, 2003)
and which is similar to spike timing-dependent plasticity. Using this
rule, at a one-arm joint we correlate an earlier disturbance loading
force with the measured position change that this force
induces. Without learning, the position change is originally
compensated with some delay by a reflex like feedback reaction. After learning
the system reacts immediately to the loading pulse and produces the
required counterforce to keep the arm position stable. This works for
constant loads. It is, however, possible to add a simple recruitment
mechanism to this and now the system can learn compensating also different
loads without delay. From an older study (Porr et al, Neural
Comp. 15,865-884,2003) a mathematical proof exists that this type of learning
creates a forward model of the initially existing feedback
loop. Hence, here we were able to show that we can employ learning and
recruitment in a simple motor-control structure to learn anticipatory
load compensation by feed-forward compensation.

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