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

Abstract

Recent data suggest that the parietal operculum acts as an integration center within a multimodal network, originating from different primary sensory and motor cortices and projecting to frontal, parietal and temporal cortical hubs, which in turn govern cognitive and motor functions. Thus, parietal operculum might also play a crucial role in the integrated control of voluntary movement and posture. As a first step to test this hypothesis, the Anticipatory Postural Adjustments (APAs) stabilizing the arm when the index-finger is briskly flexed were recorded, on the preferred side, in three groups of 10 healthy subjects, before, during and after CATHODAL or ANODAL transcranial Direct Current Stimulation (tDCS, 20 min at 2 mA) applied over the contralateral Parietal Operculum (coPO). Results were compared to those obtained in a SHAM group. In agreement with literature, in the SHAM group the activation of the prime mover Flexor Digitorum Superficialis was preceded by an inhibitory APA in Biceps Brachii and Anterior Deltoid, and almost simultaneous to an excitatory APA in Triceps Brachii. The same pattern was observed in both the CATHODAL and ANODAL groups, with no significant tDCS effects on APAs amplitude and timing. Index-finger kinematics were also unchanged. These negative results suggest that the coPO does not disturb the key network governing APAs in index-finger flexion. Since it has been well documented that such APAs share many features with those observed in trunk and limb muscles when performing several other movements, we suggest that coPO may not be crucial to the general APA control.

Dual-Hemisphere Transcranial Direct Current Stimulation on Parietal Operculum Does Not Affect the Programming of Intra-limb Anticipatory Postural Adjustments

“…In particular, Fujimoto et al (2017) reported that dh-tDCS over the POs, with the same 2 mA intensity used in the present study, actually produced a greater improvement in tactile orientation discrimination than the uni-hemisphere tDCS. Nevertheless, we did not observe any significant effect of dh-tDCS on amplitude or latency of intra-limb APAs associated with the index-finger flexion, in this way mimicking the results and confirming the conclusion of our previous work ( Marchese et al, 2019 ).…”

“…We focused on PO as an important hub able to integrate multisensory streams within the motor organization ( Milner et al, 2007 ; Sepulcre, 2014 ). Even though our recent work ( Marchese et al, 2019 ) demonstrated that anodal or cathodal tDCS limited to the PO contralateral to the moving finger (coPO) did not disturb the APAs, here, we bilaterally stimulated both POs with opposite currents (dh-tDCS) as this approach has been proved to produce stronger effects than the unilateral stimulation in several neuromodulation studies. Dh-tDCS has been described to be a proficient tool to improve cerebral functionality ( Vines et al, 2008 ) and to be more effective with respect to the uni-hemisphere approach.…”

“…Moreover, visual, somatosensory, and auditory functional streams, originating from different cerebral areas, converge in PO and are then headed to motor and premotor areas ( Felleman and Van Essen, 1991 ). We started by using anodal or cathodal tDCS to selectively modulate the excitability of the PO contralateral to the moving segment (coPO, Marchese et al, 2019 ), while assessing intra-limb APAs associated to brisk flexions of the index finger, according to the paradigm of Caronni and Cavallari (2009a) . Indeed, tDCS is known to modulate the cortical excitability by increasing or decreasing its activity, depending on the polarity.…”

Postural Control in Children with Cerebellar Ataxia

“…The onset of an excitatory or inhibitory EMG change was identified by a software algorithm, which searched the first time point in which the track fell above or below 2 SD of the reference signal (excitation or inhibition, respectively) and remained there for at least 50 ms. Whenever the criterion was met, the algorithm searched backward the point in which the signal started to deviate from the mean reference value [39]. No statistical analysis was performed on EMG timings because of the many cases in which no clear inhibitory or excitatory changes could be identified.…”

A Novel Viewpoint on the Anticipatory Postural Adjustments During Gait Initiation

“…The analysis aimed at highlighting APAs accompanying the first backward displacement of the CoP, which marks the onset of the afferent signals produced by the voluntary recruitment of the gait prime mover muscles. The data analysis approach replicated that used by Marchese et al (2019). In brief, the raw EMG data were high-pass filtered with a zero-phase shift sixth-order elliptic filter and a cut-off frequency of 50 Hz, to remove movement artifacts.…”