The neural control of sequential skilled action

Humans have a remarkable capacity to perform a wide range of skilled actions. Many actions involve a series of separate movements being performed in quick succession to form complex movement sequences. After extended practise, these movement sequences can be executed with incredible speed, accuracy and fluidity. There are competing accounts of the neural mechanism that underlies such skilled sequential action. A long-established theory proposes that the individual elements are fused together behaviourally into a new 'motor primitive' and represented throughout the brain as one holistic action. Holistic control is thought essential for skilled performance across many actions, it is suggested to be a marker of 'true' skill learning and an important goal during the rehabilitation process of stroke patients. However, there is little neural evidence for holistic control in sequential behaviour, with a significant amount of recent electrophysiological/neuroimaging work pointing to an alternative hierarchical mechanism in which the individual movements maintain their independence and are planned through sequence representations in higher-order brain regions. This leads to two significant questions:
1) Under what circumstances does holistic control arise for skilled action?
2) Can we distinguish between holistic vs. hierarchical control within an individual/task?
To address these questions, this project will use a novel behavioural framework that enables the concurrent probing of holistic and hierarchical control of skilled sequential action in humans. Using this framework, the distinct roles of holistic and hierarchical control during skilled sequential behaviour will be identified through a combination of behavioural, neural and causal techniques. The relevance of this work to everyday-life will be shown by using these techniques to establish the role each of these neural control systems play in naturally learnt sequential actions.