Disrupt of Intra-Limb APA Pattern in Parkinsonian Patients Performing Index-Finger Flexion

Abstract

Voluntary movements induce postural perturbations which are counteracted by anticipatory postural adjustments (APAs). These actions are known to build up long fixation chains toward available support points (inter-limb APAs), so as to grant whole body equilibrium. Moreover, recent studies highlighted that APAs also build-up short fixation chains, within the same limb where a distal segment is moved (intra-limb APAs), aimed at stabilizing the proximal segments. The neural structures generating intra-limb APAs still need investigations; the present study aims to compare focal movement kinematics and intra-limb APA latencies and pattern between healthy subjects and parkinsonian patients, assuming the latter as a model of basal ganglia dysfunction. Intra-limb APAs that stabilize the arm when the index-finger is briskly flexed were recorded in 13 parkinsonian patients and in 10 age-matched healthy subjects. Index-finger movement was smaller in parkinsonian patients vs. healthy subjects (p = 0.01) and more delayed with respect to the onset of the prime mover flexor digitorum superficialis (FDS, p < 0.0001). In agreement with the literature, in all healthy subjects the FDS activation was preceded by an inhibitory intra-limb APA in biceps brachii (BB) and anterior deltoid (AD), and almost simultaneous to an excitatory intra-limb APA in triceps brachii (TB). In parkinsonian patients, no significant differences were found for TB and AD intra-limb APA timings, however only four patients showed an inhibitory intra-limb APA in BB, while other four did not show any BB intra-limb APAs and five actually developed a BB excitation. The frequency of occurrence of normal sign, lacking, and inverted BB APAs was different in healthy vs. parkinsonian participants (p = 0.0016). The observed alterations in index-finger kinematics and intra-limb APA pattern in parkinsonian patients suggest that basal ganglia, in addition to shaping the focal movement, may also contribute to intra-limb APA control.

Postural Control in Children with Cerebellar Ataxia

“…This aspect agreed with the general view that assigns to the cerebellum the role of a "timing-machine" [41][42][43][44][45] and leaves the pattern selection to other brain structures, like the basal ganglia. Such a perspective has been confirmed also for what regards APAs in adults [46,47].…”

Transcranial Direct Current Stimulation on Parietal Operculum Contralateral to the Moving Limb Does Not Affect the Programming of Intra-Limb Anticipatory Postural Adjustments

“…The present study belongs to a broad line of research oriented to investigate how the APA control is organized. In fact, several studies showed the role of sensory and motor areas, including the primary and supplementary motor cortices, as well as subcortical structures like basal ganglia, cerebellum and spinal cord (Viallet et al, 1992; Palmer et al, 1994; Petersen et al, 2009; Bolzoni et al, 2012, 2015, 2018; Ng et al, 2013; Bruttini et al, 2015). Although it is still not well established whether the command for recruiting the prime mover muscles and that governing the postural muscles are separately processed or have a common origin, we provided evidence that a functionally unique motor command should drive both the prime mover and the muscles of the intra-limb APAs chain (Bruttini et al, 2014).…”

Overview of the Cerebellar Function in Anticipatory Postural Adjustments and of the Compensatory Mechanisms Developing in Neural Dysfunctions

“…Schmitz et al (2005) [56] reported the involvement of Sensorimotor Areas, using functional Magnetic Resonance Imaging, while Schepens et al (2004) [57] reported that the Pontomedullary Reticular Formation, a site of integration of signals from both cortical and subcortical structures, is able to mediate APAs in time and magnitude, to optimize motor control of posture and movement in the cat. Moreover, basal ganglia have been reported to contribute to APA control (Figure 1); in particular, a disruption in intra-limb APAs associated with the index finger flexion [58] and an impairment in inter-limb APAs during a bimanual load-lifting task [59] have been found in patients with Parkinson's disease. Cortices, as well as about the motor goal from SMA and Premotor Cortices.…”

“…Therefore, this work supports the hypothesis that the cerebellum plays a key role also during human development, in particular, in building up internal models of gait initiation timings. Moreover, considering that the APA pattern was not affected by cerebellar dysfunction, pattern selection is a functional skill which may be attributed to other brain structures, like the basal ganglia [58].…”