Supplementary motor area

Supplementary motor area
Paskari · CC BY-SA 3.0 · source
Name	Supplementary motor area
Latin	area praemotoria supplementaris
Location	Medial frontal lobe
System	Nervous system

Supplementary motor area The supplementary motor area is a medial frontal cortical region implicated in planning and coordinating complex voluntary movements, sequencing motor actions, and preparing internally generated movements. Located on the medial surface of the hemisphere anterior to the primary motor cortex, it interfaces with premotor, cingulate, parietal, thalamic, basal ganglia, and cerebellar structures to support motor planning, bimanual coordination, and aspects of motor imagery and speech production.

Anatomy

The region lies on the medial wall of the frontal lobe, anterior to the leg area of the primary motor cortex and dorsal to the cingulate sulcus, with gross anatomy described in classical atlases such as those by Broca, Penfield, and Brodmann who delineated adjacent cytoarchitectonic fields including areas 6 and 8. Cytoarchitectural and tractographic studies from institutions like Harvard Medical School, Johns Hopkins Hospital, and the Karolinska Institute subdivide it into a pre-SMA and a more caudal SMA-proper, consistent with parcellations in the Human Connectome Project and the work of Ralph Adolphs and Marcus Raichle. Surgical maps from neurosurgeons such as Wilder Penfield and Santiago Ramón y Cajal–in historical context–inform localization used by centers like Mayo Clinic and Cleveland Clinic during resections involving the medial frontal lobe. Vascular supply is primarily from branches of the anterior cerebral artery and venous drainage connects with superior sagittal sinus territories studied by teams at Massachusetts General Hospital and Guy's Hospital.

Function

Functional roles are drawn from lesion studies, stimulation mapping, and neuroimaging by groups at University College London, Stanford University, University of Oxford, and University of Cambridge. The area contributes to internally generated movement initiation described in classic reports by Vittorio Benussi and modern analyses by John R. Keenan and H. Branch Coslett, and to temporal sequencing examined by researchers at Columbia University and University of Pennsylvania. Its role in bimanual coordination and motor sequence learning has been tested in experiments associated with laboratories from Donders Institute and Max Planck Society. Contributions to speech and vocalization link it functionally to regions implicated in language such as those studied by Noam Chomsky-influenced cognitive neuroscience groups and clinical teams at Mount Sinai Hospital and Guy's and St Thomas' NHS Foundation Trust. Cognitive control aspects have been integrated into models by investigators at Princeton University, University of California, Berkeley, and New York University.

Connectivity

Anatomical and functional connectivity has been demonstrated between the SMA and primary motor cortex, dorsal and ventral premotor areas, anterior cingulate cortex, posterior parietal cortex, and prefrontal cortex in tract-tracing and diffusion tensor imaging studies conducted at MIT, University of Toronto, and University of Pittsburgh. Subcortical loops involve dense reciprocal projections with the basal ganglia, including the putamen and globus pallidus examined by researchers at Cold Spring Harbor Laboratory and Salk Institute, and cerebellar pathways through the thalamus mapped by teams at ETH Zurich and University of California, San Diego. Thalamic relays such as the ventrolateral and ventroanterior nuclei were characterized in classical neuroanatomy texts from John Fulton and modern atlases used at Yale School of Medicine. Electrophysiological coherence and resting-state correlations have been reported in large cohorts from the Human Connectome Project and multicenter consortia including researchers at UCLA and Karolinska Institute.

Clinical significance

Lesions, seizures, or surgical interruption produce deficits described across case series from centers like Hospital for Sick Children (Toronto), Royal Melbourne Hospital, and Birmingham Children's Hospital. Clinical syndromes include akinetic mutism documented by teams at Massachusetts General Hospital and Mayo Clinic, supplementary motor area syndrome with transient contralateral akinesia and speech arrest noted in operative series by Wilder Penfield-related protocols and more recent neurosurgical groups at Stanford Health Care and UCSF Medical Center, and focal seizures originating in the medial frontal lobe reported by epilepsy centers at Cleveland Clinic Foundation and Johns Hopkins Hospital. Parkinsonian and dystonic manifestations implicating SMA dysfunction were explored by movement disorder clinics at National Institutes of Health and University College London Hospitals. Rehabilitation approaches and neuromodulation, including transcranial magnetic stimulation and deep brain stimulation trials, have been pursued by teams at Karolinska University Hospital, Mount Sinai, and Oxford University Hospitals.

Neurophysiology and imaging studies

Intraoperative stimulation and microelectrode recordings from centers such as UCLA Medical Center, Royal London Hospital, and Beijing Tiantan Hospital reveal movement-related preparatory potentials and Bereitschaftspotential components originally described by researchers like Kornhuber and Deecke. Functional MRI, PET, and magnetoencephalography studies from laboratories at University of Michigan, McGill University, and Imperial College London show SMA activation during self-initiated movements, imagined movements, speech tasks, and motor sequencing paradigms. Resting-state and task-based network analyses by the Human Connectome Project, ENIGMA Consortium, and groups at Cold Spring Harbor Laboratory demonstrate SMA participation in distributed motor-control networks and alterations in disorders studied at Massachusetts General Hospital and Johns Hopkins.

Category:Neuroanatomy