Background
Most humans have the ability to activate the auricular muscles. Although
(intentional) control suggests an involvement of higher cortical centers
underlying posterior auricular muscle (PAM) activation, the cortical
representation of the auricular muscles is still unknown.

Methods
With the purpose of identifying a possible cortical representation area
we performed automated robotic and image-guided transcranial magnetic
stimulation (TMS) mapping (n = 8) and functional magnetic resonance
imaging (fMRI) (n = 13). For topographical comparison, a similar
experimental protocol was applied for the first dorsal interosseus
muscle (FDI) of the hand.

Results
The calculated centers of gravity (COGs) of both muscles were located on
the precentral gyrus with the PAM COGs located more laterally compared
to the FDI. The distance between the mean PAM and mean FDI COG was 26.3
mm. The TMS mapping results were confirmed by fMRI, which showed a
dominance of cortical activation within the precentral gyrus during the
corresponding motor tasks. The correspondence of TMS and fMRI results
was high.

Conclusion
The involvement of the primary motor cortex in PAM activation might
point to an evolved function of the auricular muscles in humans and/or
the ability of intentional (and selective) muscle activation.

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