Free will and neurosurgical resections of the supplementary motor area: a critical review

Abstract Background Research suggests that unconscious activity in the supplementary motor area (SMA) precedes not only certain simple motor actions but also the point at which we become aware of our intention to perform such actions. The extent to which these findings have implications for our understanding of the concepts of free will and personal responsibility has been subject of intense debate during the latest four decades. Methods This research is discussed in relation to effects of neurosurgical removal of the SMA in a narrative review. Results Removal of the SMA typically causes a transient inability to perform non-stimulus-driven, voluntary actions. This condition, known as the SMA syndrome, does not appear to be associated with a loss of sense of volition but with a profound disruption of executive function/cognitive control. Conclusions The role of the SMA may be to serve as a gateway between the corticospinal tract and systems for executive function. Such systems are typically seen as tools for conscious decisions. What is known about effects of SMA resections would thus seem to suggest a view that is compatible with concepts of personal responsibility. However, the philosophical question whether free will exists cannot be definitely resolved on the basis of these observations.

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The functional role of beta‐oscillations in the supplementary motor area during reaching and grasping after stroke: A question of structural damage to the corticospinal tract

Human Brain Mapping ◽

10.1002/hbm.24582 ◽

2019 ◽

Author(s):

Fanny Quandt ◽

Marlene Bönstrup ◽

Robert Schulz ◽

Jan E. Timmermann ◽

Maike Mund ◽

...

Keyword(s):

Structural Damage ◽

Functional Role ◽

Corticospinal Tract ◽

Supplementary Motor Area ◽

Motor Area ◽

Beta Oscillations

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Faculty Opinions recommendation of The role of the supplementary motor area (SMA) in word production.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1030406.371756 ◽

2006 ◽

Author(s):

Peter F MacNeilage

Keyword(s):

Supplementary Motor Area ◽

Word Production ◽

Motor Area

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Role of the supplementary motor area during reproduction of supra-second time intervals: An intracerebral EEG study

NeuroImage ◽

10.1016/j.neuroimage.2019.01.047 ◽

2019 ◽

Vol 191 ◽

pp. 403-420 ◽

Cited By ~ 1

Author(s):

Micha Pfeuty ◽

Vincent Monfort ◽

Madelyne Klein ◽

Julien Krieg ◽

Steffie Collé ◽

...

Keyword(s):

Supplementary Motor Area ◽

Motor Area ◽

Time Intervals ◽

Intracerebral Eeg

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Role of the Human Rostral Supplementary Motor Area and the Basal Ganglia in Motor Sequence Control: Investigations With H2 15O PET

Journal of Neurophysiology ◽

10.1152/jn.1998.79.2.1070 ◽

1998 ◽

Vol 79 (2) ◽

pp. 1070-1080 ◽

Cited By ~ 152

Author(s):

H. Boecker ◽

A. Dagher ◽

A. O. Ceballos-Baumann ◽

R. E. Passingham ◽

M. Samuel ◽

...

Keyword(s):

Basal Ganglia ◽

Primary Motor Cortex ◽

Supplementary Motor Area ◽

Motor Area ◽

Anterior Cingulate ◽

Central Control ◽

Motor Sequence ◽

Finger Movements ◽

Sequence Complexity

Boecker, H., A. Dagher, A. O. Ceballos-Baumann, R. E. Passingham, M. Samuel, K. J. Friston, J.-B. Poline, C. Dettmers, B. Conrad, and D. J. Brooks. Role of the human rostral supplementary motor area and the basal ganglia in motor sequence control: investigations with H2 15O PET. J. Neurophysiol. 79: 1070–1080, 1998. The aim of this study was to investigate the functional anatomy of distributed cortical and subcortical motor areas in the human brain that participate in the central control of overlearned complex sequential unimanual finger movements. On the basis of previous research in nonhuman primates, a principal involvement of basal ganglia (medial premotor loops) was predicted for central control of finger sequences performed automatically. In pertinent areas, a correlation of activation levels with the complexity of a motor sequence was hypothesized. H2 15O positron emission tomography (PET) was used in a group of seven healthy male volunteers [mean age 32.0 ± 10.4 yr] to determine brain regions where levels of regional cerebral blood flow (rCBF) correlated with graded complexity levels of five different key-press sequences. All sequences were overlearned before PET and involved key-presses of fingers II–V of the right hand. Movements of individual fingers were kept constant throughout all five conditions by external pacing at 1-Hz intervals. Positive correlations of rCBF with increasing sequence complexity were identified in the contralateral rostral supplementary motor area (pre-SMA) and the associated pallido-thalamic loop, as well as in right parietal area 7 and ipsilateral primary motor cortex (M1). In contrast, while rCBF in contralateral M1 and and extensive parts of caudal SMA was increased compared with rest during task performance, significant correlated increases of rCBF with sequence complexity were not observed. Inverse correlations of rCBF with increasing sequence complexity were identified in mesial prefrontal-, medial temporal-, and anterior cingulate areas. The findings provide further evidence in humans supporting the notion of a segregation of SMA into functionally distinct subcomponents: although pre-SMA was differentially activated depending on the complexity of a sequence of learned finger movements, such modulation was not detectable in caudal SMA (except the most antero-superior part), implicating a motor executive role. Our observations of complexity-correlated rCBF increases in anterior globus palllidus suggest a specific role for the basal ganglia in the process of sequence facilitation and control. They may act to filter and focus input from motor cortical areas as patterns of action become increasingly complex.

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