Ehrsson, H. H. (2001). Neural correlates of skilled movement: Functional mapping of the human brain with fMRI and PET. Stockholm, Sweden: Departments of Woman and Child Health and Neuroscience Karolinska Institute.

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Humans have unique abilities to perform certain types of skilled voluntary movements. This set of investigations studied the neural substrates of: (i) fine digit actions, in particular the control of fingertip forces during manipulation, (ii) the coordination of voluntary movements of different limbs, and (iii) the neural correlates of the kinesthetic perception and imagery of limb movements. Functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) were used to measure the blood oxygenation level dependent contrast and regional cerebral blood flow as indexes of neuronal activity.

In a series of functional magnetic resonance imaging experiments, the active cortical areas associated with the control of fingertip forces and production of hand postures with independent movements of the digits were investigated. In the fingertip force experiments, Ss used the right index finger and thumb to apply forces to a fixed object. These precision-grip tasks consistently activated a set of bilateral fronto-parietal areas including the primary motor cortex, the non-primary motor areas, and the posterior parietal cortex. It was found that the control of small grip forces during precision grips is dependent more on non-primary fronto-parietal areas than when the force is excessively large or when a power grip is used between all digits and the palm. Specifically, the bilateral ventral premotor cortex, area 44, supramarginal cortex and the right intraparietal cortex were involved in the control of small precision grip forces. Furthermore, areas in the left posterior parietal cortex were involved in the control of lift forces for object displacement whereas the right posterior intraparietal cortex appeared to support the coordination of grip-lift forces during precision grips. The primary motor cortex was particularly active during forceful gripping, but also when holding an object close to the slip point requiring very precise force control. The supplementary motor area, cingulate motor area, and left supramarginal cortex were also active in this latter task. The control of independent movements of the digits during the production of hand postures involves the supplementary motor area, the bilateral dorsal premotor cortex, postcentral cortex, cerebellum, and the left anterior intraparietal cortex. It was concluded that fine digit actions in humans depend on a network of bilateral front-parietal areas that are active in a task-dependent manner.

The brain regions controlling coordinated movements of limbs were examined. It was concluded that coordinated movements of two limbs are controlled by the areas that control isolated movements of the same limbs. Also, two natural patterns of bimanual temporal coordination were supported by distinct regions: the left anterior cerebellar lobe (and caudal cingulate motor area and precuneus), and were associated with synchronous finger tapping, whilst alternating finger tapping strongly engaged bilateral front-parieto-temporal areas. The medial cerebellum was strongly activated in polyrhythmic tasks. These observations supported the hypothesis that different brain regions support temporal and spatial inter-limb coordination.

The neural correlates of the kinesthetic perception and imagery of limb movement were examined. When Ss experienced an illusory limb movement elicited by vibration stimuli (~80 Hz) applied to the skin over the tendon of a muscle, the contralateral primary motor cortex, primary somatosensory cortex, supplementary motor area, and cingulate motor area were active. When Ss imagined that they were executing movements of their fingers, toes, and tongue, some of the corresponding gross somatotopical zones of the frontal motor areas were recruited. Thus, the frontal motor areas were seen to be involved in the kinesthetic perception and imagery of limb movement, in addition to the execution of action.

Implication. For quite some time, the brain has been represented as a map of areas of motor movements associated with parts of the body. Recent studies, as represented by this series of investigations, have now mapped the functional aspects of movements leading to a better understanding of how the brain functions in movements of different types. This new level of description complexity not only demonstrates the marvelous attributes of the brain but it also demonstrates the ability of complex human movements to be represented by the involvement of discrete sections of the brain in unique patterns of activation. The acceptance of movements being singularly represented and activated by real and imagined movements (the "simulation hypothesis") is unequivocally supported by observable and measurable brain functions.

Within sporting specialties, such as pitching or cricket bowling, there still are defined various skills (e.g., types of pitch thrown). There are implications from brain-pattern research for understanding the needs for training multi-skilled specialist athletes. In pitching, when a power pitch (e.g., a fastball) is thrown different control areas of the brain will be stimulated to those that would be stimulated when a precision/control pitch (e.g., a curveball) is delivered. If those differences are not practiced and overlearned as well as discriminated effectively, there will be no performance improvement. No amount of assumed cross-training activities, such as long-tossing, will improve the pattern recognition, refinement, or emergence of the fine skills that are supposed to be the mark of a good pitcher. Only specific exact patterned practice will be conducive to performance improvement. The current trend to not train specifically for pitching and to not do any appreciable volume of repetitions of desired movements, could be asserted as the reason why modern pitchers cannot throw equivalent numbers of innings in a season, balls in a game, and complete games that were thrown by many pitchers up until the mid-1980's.

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