Practical scan-length considerations for mapping upper limb movements to the somatosensory/motor cortex at 7T: A...

Area of Science:

• Neuroscience
• Neuroimaging
• Motor Control

Background:

• Functional magnetic resonance imaging (fMRI) is widely used to study the motor cortex (M1) and upper limb movements.
• Research has primarily focused on fMRI applications, with limited attention to optimizing fMRI protocols for motor experiments.
• The influence of scan duration on M1 activation during diverse upper limb tasks is not well understood, despite scan length constraints in typical sessions.

Purpose of the Study:

• To investigate the effect of scan length on M1 activations during various upper limb movements using 7T fMRI.
• To determine optimal scanning durations for different types of upper limb movements to achieve consistent statistical power.
• To propose a practical, adaptable fMRI protocol for upper limb motor tasks within standard session lengths.

Main Methods:

• A single male participant performed eight distinct upper limb movements (fingers, wrist, elbow) with both arms across 16 task runs (88 minutes total fMRI).
• Standard activation analyses (Z > 3.1, p < 0.01) were conducted for varying numbers of runs (2 to 8) for each arm.
• fMRI activations were compared across different run counts to assess the impact of scan length and identify movement-specific activation patterns.

Main Results:

• Diminishing returns were observed, with M1 activations plateauing as the number of runs increased.
• Two categories of movements emerged: those with generally higher activation and those with lower activation.
• Movements with lower activation required longer scanning durations to achieve comparable statistical power to those with higher activation.

Conclusions:

• A 'one size does not fit all' approach is recommended for fMRI protocol design in upper limb motor studies.
• Tailored protocols, assigning different numbers of runs based on movement type, can optimize scan efficiency within 60-, 75-, or 90-minute sessions.
• The findings provide practical guidance for researchers designing fMRI experiments involving upper limb movements, enhancing data acquisition and analysis.