Functional localization of the supplementary motor area

Area of Science:

• Neuroscience
• Cognitive Neuroscience
• Neuroimaging

Background:

• The supplementary motor area (SMA) is vital for planning and executing behaviors.
• Its precise somatotopic organization remains incompletely understood despite evidence suggesting it.
• Functional mapping is essential to clarify SMA's role in complex tasks.

Purpose of the Study:

• To functionally map the supplementary motor area (SMA) using functional magnetic resonance imaging (fMRI).
• To validate fMRI findings with electrocortical stimulation (ECS) and postsurgical symptom analysis.
• To elucidate the somatotopic organization and functional specialization within the SMA.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was employed with 32 healthy volunteers performing motor (finger tapping) and language (reading, lexical decision, verb generation) tasks.
• Statistical Parametric Mapping (SPM8) was used for data analysis.
• Electrocortical stimulation (ECS) was performed on 6 patients during awake craniotomy to map SMA function.

Main Results:

• The lexical decision task activated the most fMRI pixels within the SMA across all subjects.
• Language tasks predominantly activated the anterior SMA, while finger tapping tasks showed different patterns.
• A consistent 'SMA core' in the posterior SMA showed overlap across all tasks, and ECS stimulation here evoked speech arrest and hemiparesis.

Conclusions:

• The posterior SMA, identified as the 'SMA core,' plays a critical role in the execution of diverse tasks, including motor and language functions.
• fMRI and ECS collectively demonstrate a functional organization within the SMA, with the posterior region being essential for execution.
• This research refines our understanding of SMA's somatotopic organization and its involvement in complex behavioral control.