Abstract and Effector-Specific Representations of Motor Sequences Identified with PET

Grafton, Scott T.; Hazeltine, Eliot; Ivry, Richard B. · 1998 · Journal of Neuroscience

DOI: 10.1523/jneurosci.18-22-09420.1998

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Summary

This study investigates the neural mechanisms underlying the acquisition and transfer of sequential motor skills, specifically addressing whether motor sequences are represented abstractly or tied to specific effectors. The authors utilized Positron Emission Tomography (PET) to measure regional cerebral blood flow (rCBF) in twenty healthy subjects performing a serial reaction time task under implicit learning conditions. The experimental design involved two phases: an acquisition phase where subjects responded to visual stimuli using finger movements on a small keyboard, and a transfer phase where they switched to arm movements on a large keyboard. One group (Group A) learned a fixed six-element sequence during acquisition, while a control group (Group B) performed random trials. Both groups subsequently performed the sequence using the new effector. Behavioral results confirmed implicit learning, as Group A showed significant reductions in reaction time when the sequence was introduced and maintained these benefits upon transferring to the large keyboard. Imaging data revealed that sequence acquisition with the small keyboard increased rCBF in a network including the sensorimotor cortex, supplementary motor area (SMA), and rostral inferior parietal cortex. Crucially, during the transfer phase, activity in the inferior parietal cortex remained elevated, indicating that this region encodes the sequence at an abstract level independent of the specific muscles used. In contrast, activity in the sensorimotor cortex shifted to a more dorsal location consistent with the somatotopic representation of the arm, demonstrating effector-specific processing. Additionally, increased rCBF was observed in the cingulate motor area during transfer, suggesting its role in linking abstract sequential representations with the task-relevant effector system. The findings distinguish between abstract and effector-specific components of motor memory. The persistence of activity in the inferior parietal cortex across different effectors supports the existence of a goal-based, abstract representation of the sequence. Meanwhile, the shift in sensorimotor cortex activity confirms that motor execution remains tied to specific body parts. The involvement of the cingulate motor area highlights a neural mechanism for integrating these abstract plans with specific motor outputs. These results provide evidence for a distributed network where different brain regions contribute distinctively to the encoding, storage, and retrieval of sequential motor skills, resolving the puzzle of how implicit learning allows for flexible transfer across different motor effectors.

Key finding

Motor sequence learning involves a dual representation system where the inferior parietal cortex encodes abstract sequence information independent of the effector, while the sensorimotor cortex encodes effector-specific motor details.

Methodology

lab_experiment

Sample size: 20

Provenance

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Topics

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• automaticity skill acquisition