Functions
Penfield and Welch in 1951 first described SMA in the monkey brain and the human brain as a representation of the body on the medial wall of the hemisphere. Woolsey and colleagues in 1952 confirmed SMA in the monkey brain, describing it as a rough somatotopic map with the legs in a posterior location and the face in an anterior location. The representations of different body parts were found to overlap extensively. Stimulation of many sites evoked bilateral movements and sometimes movements of all four limbs. This overlapping somatotopic map in SMA was confirmed by many others.
Four main hypotheses have been proposed for the function of SMA: the control of postural stability during stance or walking, coordinating temporal sequences of actions, bimanual coordination, and the initiation of internally generated as opposed to stimulus driven movement. The data, however, tend not to support an exclusive role of SMA in any one of these functions. Indeed, SMA is demonstrably active during non-sequential, unimanual, and stimulus-cued movements.
SMA in the monkey brain may emphasize locomotion, especially complex locomotion such as climbing or leaping. This suggestion was based on studies in which stimulation on a behaviorally relevant time scale evoked complex, full body movements that resembled climbing or leaping. This hypothesis is consistent with previous hypotheses, including the involvement of SMA in postural stabilization, in internally generated movements, in bimanual coordination, and in the planning of movement sequences, because all of these functions are heavily recruited in complex locomotion. The locomotion hypothesis is an example of interpreting the motor cortex in terms of the underlying behavioral repertoire from which abstract control functions emerge, an approach emphasized by Graziano and colleagues.
Read more about this topic: Supplementary Motor Area
Famous quotes containing the word functions:
“One of the most highly valued functions of used parents these days is to be the villains of their children’s lives, the people the child blames for any shortcomings or disappointments. But if your identity comes from your parents’ failings, then you remain forever a member of the child generation, stuck and unable to move on to an adulthood in which you identify yourself in terms of what you do, not what has been done to you.”
—Frank Pittman (20th century)
“The English masses are lovable: they are kind, decent, tolerant, practical and not stupid. The tragedy is that there are too many of them, and that they are aimless, having outgrown the servile functions for which they were encouraged to multiply. One day these huge crowds will have to seize power because there will be nothing else for them to do, and yet they neither demand power nor are ready to make use of it; they will learn only to be bored in a new way.”
—Cyril Connolly (1903–1974)
“Those things which now most engage the attention of men, as politics and the daily routine, are, it is true, vital functions of human society, but should be unconsciously performed, like the corresponding functions of the physical body.”
—Henry David Thoreau (1817–1862)