Supplementary motor area structure and function: Review and hypotheses

Abstract

Though its existence has been known for well over 30 years, only recently has the supplementary motor area (SMA) and its role in the cortical organization of movement come to be examined in detail by neuroscientists. Evidence from a wide variety of investigational perspectives is reviewed in an attempt to synthesize a conceptual framework for understanding SMA function. It is suggested that the SMA has an important role to play in the intentional process whereby internal context influences the elaboration of action. It may be viewed as phylogenetically older motor cortex, derived from anterior cingulate periarchicortical limbic cortex, which, as a key part of a medial premotor system, is crucial in the "programming" and fluent execution of extended action sequences which are "projectional" in that they rely on model-based prediction. This medial system can be distinguished from a lateral premotor system postulated to have evolved over phylogeny from a different neural source. An anatomico-physiologic model of the medial premotor system is proposed which embodies the principles of cyclicity and reentrance in the process of selecting those neural components to become active in conjunction with the performance of a particular action. The postulated dynamic action of this model in the microgenesis of a discrete action is outlined. It is concluded that although there is a great deal to be learned about the SMA, a convergence of current evidence can be identified. Such evidence suggests that the SMA plays an important role in the development of the intention-to-act and the specification and elaboration of action through its mediation between medial limbic cortex and primary motor cortex.

fMRI study of bimanual coordination

“…There is considerable agreement in the literature that the SMA is involved when sequences are voluntary/self-initiated [6,21,26,32,41]. The self-initiation role can also be related to the`intentionality' aspect of motor function that is guided by the SMA, a role anticipated by Goldberg [17]. Summarizing these observations, it appears that our task did involve all of these elements, but, of course, it is not at all obvious which of the elements is of cardinal importance.…”

Context-Switching and Responsiveness to Real Relevance

“…The plausible and broadly accepted hypothesis for UB is that at the neural level the (lateral premotor) 13 system that generates stimulus-driven or externally-driven motor control has been disinhibited as a result of a lesion of the (medial premotor) system that generates internally-driven motor control (Goldberg, 1985, Archibald et al, 2001, Boccardi et al, 2002, Eslinger, 2002. Due to this lesion of the medial network, the patients' capacity for endogeneously-driven behavior is reduced (Eslinger, 2002).…”

Central nervous system control of the laryngeal muscles in humans

“…Concurrent physiological measures were made to confirm that the five subjects could emphasize inspiration with passive expiration and emphasize expiration with passive inspiration. Both the inspiration and expiration tasks involved increased activity in a high region of the primary motor strip (M1) representing the diaphragmatic, thoracic and abdominal muscles, the SMA thought to be involved in pre-programmed motor movements (Goldberg, 1985) and the right PM area. The major difference between cerebral activation for inspiration and expiration, however, was the greater activation during expiration in the lower part of the primary sensorimotor cortex, the region responsible for laryngeal muscle control (LX) (Fig.…”