Microsurgical and Tractographic Anatomy of the Supplementary Motor Area Complex in Humans

Objective: To evaluate the microsurgical anatomy of the fiber tract connections of the supplementary motor area (SMA) and pre-SMA, and examine its potential functional role with reference to clinical trials in the literature.

Methods: Ten postmortem formalin-fixed human brains (20 sides) and 1 cadaveric head were prepared following Klingler's method. The fiber dissection was performed in a stepwise fashion, from lateral to medial and also from medial to lateral, under an operating microscope, with 3D images captured at each stage. Our findings were supported by in vivo magnetic resonance imaging tractography in 2 healthy subjects.

Results: The connections of the SMA complex, composed of the pre-SMA and the SMA proper, are composed of short "U" association fibers and the superior longitudinal fasciculus I, cingulum, claustrocortical fibers, callosal fibers, corticospinal tract, frontal aslant tract, and frontostriatal tract. The claustrocortical fibers may play an important role in the integration of motor, language, and limbic functions of the SMA complex. The frontostriatal tract connects the pre-SMA to the putamen and caudate nucleus, and also forms parts of both the internal capsule and the dorsal external capsule.

Conclusions: The SMA complex has numerous connections throughout the cerebrum. An understanding of these connections is important for presurgical planning for lesions in the frontal lobe and helps explain symptoms related to SMA injury.