During my PhD studies, I have dealt with several aspects of the relationship between posture and voluntary movement. In particular, the main subject of my work has been to analyze the functional role of the Anticipatory Postural Adjustments (APAs) within the motor act and how these are programmed by the central nervous system.
In the past literature, it has been described that APAs are unconscious muscular activities aimed to maintain the equilibrium of the whole body (Massion 1992). The role of the APAs has been first disclosed in movements involving relatively large masses, such as an upper-limb flexion (see for a review, Bouisset and Do 2008). In this case, the shoulder flexion may displace the projection of the center of mass to ground, eventually causing an imbalance of the whole body. Therefore, in order to counteract such a perturbation, the recruitment of the prime mover (Anterior Deltoid) is normally preceded by a specific pattern of EMG activities, defined as APAs, developing in the lower limbs, the hips and the trunk. This inter-limb APA chain is thus able to induce a forward displacement which prevents the backward perturbation caused by the focal movement.
More recently, Caronni and Cavallari (2009a) demonstrated that an APA chain also develop for very simple movements such as a finger flexion, in which small masses are involved and in which the whole-body equilibrium is not threatened. Indeed, the index-finger flexion, performed with the hand prone, has been found being preceded by an excitatory burst in Triceps Brachii, while Biceps Brachii and Anterior Deltoid showed a concomitant inhibition. This APA pattern, shaped in the primary motor cortex (Caronni and Cavallari 2009b), contrasts the flexion of elbow and shoulder induced by the upward perturbation that the index-finger flexion causes on the metacarpo-phalangeal joint.
Caronni and Cavallari papers (2009a, b) contributed to arise three questions: i) do inter-limb and intra-limb APAs share similar control mechanisms? If yes, ii) what is the functional role of intra-limb APAs, since it is hard to keep considering intra-limb APAs simply as a counter-perturbation aiming to maintain the whole-body equilibrium and iii) does the prime mover recruitment and its associated postural adjustments result from two different central commands, as classically proposed (Babinski 1899; Hess 1943; Cordo and Nashner 1982; Brown and Frank 1987) or are they both controlled by a unique motor command, as suggested by more recent evidences (Aruin and Latash 1995; Petersen et al. 2009; Caronni and Cavallari 2009b; Leonard et al. 2011)?
Aim of the present thesis is to shed further light on these questions with the specific target of investigating a possible role of APAs in refining movement accuracy and demonstrating the oneness of the motor command for both anticipatory postural adjustments (APAs) and prime mover recruitment. Thus, I will illustrate: i) the key role of a properly-tailored APA chain on prime mover recruitment in refining movement accuracy, ii) the superposition of the neural network responsible for controlling the voluntary movement and the APAs, focusing on Supplementary Motor Area and Cerebellum, iii) the disruption of both the postural chain and the prime mover recruitment after a period of immobilization and iv) the APAs adaptation to the intended movement, i.e. the expected perturbation. These observations have been already published or are at this moment submitted to publication.
The thesis has been divided in four sections: 1) the Introduction, which includes a review on the existing literature on inter- and intra-limb APAs, and explains my working hypothesis; 2) the Experimental Procedure, which describes how data were collected and analyzed.; 3) the collection of the original papers, and finally 4) the Conclusion, in which I will explain the interpretation of the present results and develop possible conclusions, with special regards on the relationship between postural and prime mover command
