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

The interaction effect of high social support and resilience on functional connectivity using seed-based resting-state assessed by 7-Tesla ultra-high field MRI

Recent resilience research has increasingly emphasized the importance of focusing on investigating the protective factors in mentally healthy populations, complementing the traditional focus on psychopathology. Social support has emerged as a crucial element within the complex interplay of individual and socio-environmental factors that shape resilience. However, the neural underpinnings of the relationship between social support and resilience, particularly in healthy subjects, remain largely unexplored. With advances in neuroimaging techniques, such as ultra-high field MRI at 7T and beyond, researchers can more effectively investigate the neural mechanisms underlying these factors. Thus, our study employed ultra-high field rs-fMRI to explore how social support moderates the relationship between psychological resilience and functional connectivity in a healthy cohort. We hypothesized that enhanced social support would amplify resilience-associated connectivity within neural circuits essential for emotional regulation, cognitive processing, and adaptive problem-solving, signifying a synergistic interaction where strong social networks bolster the neural underpinnings of resilience. (n = 30). Through seed-based functional connectivity analyses and interaction analysis, we aimed to uncover the neural correlates at the interplay of social support and resilience. Our findings indicate that perceived social support significantly (p<0.001) alters functional connectivity in the right and left FP, PCC, and left hippocampus, affirming the pivotal roles of these regions in the brain's resilience network. Moreover, we identified significant moderation effects of social support across various brain regions, each showing unique connectivity patterns. Specifically, the right FP demonstrated a significant interaction effect where high social support levels were linked to increased connectivity with regions involved in socio-cognitive processing, while low social support showed opposite effects. Similar patterns by social support levels were observed in the left FP, with connectivity changes in clusters associated with emotional regulation and cognitive functions. The PCC's connectivity was distinctly influenced by support levels, elucidating its role in emotional and social cognition. Interestingly, the connectivity of the left hippocampus was not significantly impacted by social support levels, indicating a unique pattern within this region. These insights highlight the importance of high social support levels in enhancing the neural foundations of resilience and fostering adaptive neurological responses to environmental challenges.

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

Evidence shows that the postural and focal components within the voluntary motor command are functionally unique. In 2015, we reported that the supplementary motor area (SMA) processes Anticipatory Postural Adjustments (APAs) separately from the command to focal muscles, so we are still searching for a hierarchically higher area able to process both components. Among these, the parietal operculum (PO) seemed to be a good candidate, as it is a hub integrating both sensory and motor streams. However, in 2019, we reported that transcranial Direct Current Stimulation (tDCS), applied with an active electrode on the PO contralateral to the moving segment vs. a larger reference electrode on the opposite forehead, did not affect intra-limb APAs associated to brisk flexions of the index-finger. Nevertheless, literature reports that two active electrodes of opposite polarities, one on each PO (dual-hemisphere, dh-tDCS), elicit stronger effects than the "active vs. reference" arrangement. Thus, in the present study, the same intra-limb APAs were recorded before, during and after dh-tDCS on PO. Twenty right-handed subjects were tested, 10 for each polarity: anode on the left vs. cathode on the right, and vice versa. Again, dh-tDCS was ineffective on APA amplitude and timing, as well as on prime mover recruitment and index-finger kinematics. These results confirm the conclusion that PO does not take part in intra-limb APA control. Therefore, our search for an area in which the motor command to prime mover and postural muscles are still processed together will have to address other structures.

Disrupted hypothalamic functional connectivity related to cognitive impairment after diffuse axonal injury

This study aims to investigate whether there is imaging evidence of disrupted hypothalamic functional connectivity (FC) in patients with diffuse axonal injury (DAI) and relationships with cognitive impairment.Resting-state functional magnetic resonance imaging (fMRI) data were acquired from acute patients with diagnosed DAI (n = 30) and healthy controls (HC) (n = 30). We first assessed hypothalamic FC with seed-based analysis. Furthermore, the lateral and medial hypothalamic seed was selected to show distinct functional connectivity in DAI. In addition, partial correlation was used to measure the clinical associations with the altered hypothalamic FC in DAI patients.Compared with HC, DAI group showed significantly increased hypothalamic FC with superior temporal gyrus, and the regions around the operculum. Furthermore, there was a significant negative correlation between the connectivity coefficient of hypothalamus to right and left superior temporal gyrus and the disability rating scale scores in DAI group. When the seed regions were divided into lateral and medial hypothalamus, except for increased connectivity of medial hypothalamus (P < .01 with correction), we more observed that decreased left lateral hypothalamic connectivity was positively correlated with mini-mental state examination (MMSE) scores.Our results suggest that there are alterations of hypothalamic FC in DAI and offer further understanding of clinical symptoms including related cognitive impairment.

A Novel Viewpoint on the Anticipatory Postural Adjustments During Gait Initiation

Anticipatory postural adjustments (APAs) are the coordinated muscular activities that precede the voluntary movements to counteract the associated postural perturbations. Many studies about gait initiation call APAs those activities that precede the heel-off of the leading foot, thus taking heel-off as the onset of voluntary movement. In particular, leg muscles drive the center of pressure (CoP) both laterally, to shift the body weight over the trailing foot and backward, to create a disequilibrium torque pushing forward the center of mass (CoM). However, since subjects want to propel their body rather than lift their foot, the onset of gait should be the CoM displacement, which starts with the backward CoP shift. If so, the leg muscles driving such a shift are the prime movers. Moreover, since the disequilibrium torque is mechanically equivalent to a forward force acting at the pelvis level, APAs should be required to link the body segments to the pelvis: distributing such concentrated force throughout the body would make all segments move homogeneously. In the aim of testing this hypothesis, we analyzed gait initiation in 15 right-footed healthy subjects, searching for activities in trunk muscles that precede the onset of the backward CoP shift. Subjects stood on a force plate for about 10 s and then started walking at their natural speed. A minimum of 10 trials were collected. A force plate measured the CoP position while wireless probes recorded the electromyographic activities. Recordings ascertained that at gait onset APAs develop in trunk muscles. On the right side, Rectus Abdominis and Obliquus Abdominis were activated in 11 and 13 subjects, respectively, starting on average 33 and 54 ms before the CoP shift; Erector Spinae (ES) at L2 and T3 levels was instead inhibited (9 and 7 subjects, 104 and 120 ms). On the contralateral side, the same muscles showed excitatory APAs (abdominals in 11 and 12 subjects, 27 and 82 ms; ES in 10 and 7 subjects, 75 and 32 ms). The results of this study provide a novel framework for distinguishing postural from voluntary actions, which may be relevant for the diagnosis and rehabilitation of gait disorders.

Functional plasticity in lateral hypothalamus and its prediction of cognitive impairment in patients with diffuse axonal injury: evidence from a resting-state functional connectivity study

OBJECTIVE

Diffuse axonal injury (DAI) is a common pathological process after traumatic brain injury, which may cause survivors severe functional disorders, including cognitive impairment and physical disability. Recent literature indicated lateral hypothalamus and medial hypothalamus damage during DAI. Thus, we aim to investigate whether there is imaging evidence of hypothalamic injury in patients with DAI and its clinical association.

METHODS

Twenty-four patients with diagnosed DAI and 26 age and sex-matched healthy controls underwent resting-state functional MRI. We assessed the lateral hypothalamus and medial hypothalamus functional connectivity with seed-based analysis in DAI. Furthermore, a partial correlation was used to measure its clinical association. The prediction of the severity of DAI from the altered lateral hypothalamus and medial hypothalamus connectivity was conducted using a general linear model.

RESULTS

Compared with healthy control, the DAI group showed significantly decreased lateral hypothalamus functional connectivity with the basal ganglia and cingulate gyrus, which was positively correlated with mini-mental state examination scores (Bonferroni correction at P < 0.0125). Importantly, this disrupted functional connectivity can be used to predict the patients' cognitive state reliably (P = 0.006; P = 0.009, respectively) in DAI. Moreover, we also observed increased connectivity of medial hypothalamus with the superior temporal gyrus and the regions around the operculum. Furthermore, there was a trend of negative correlation between the medial hypothalamus functional connectivity changes to the right superior temporal gyrus and the disability rating scale scores in the DAI group.

CONCLUSION

Our results suggest that there are alterations of medial hypothalamus and lateral hypothalamus connectivity in DAI and further understand its clinical symptoms, including related cognitive impairment.

Postural Control in Children with Cerebellar Ataxia

Controlling posture, i.e., governing the ensemble of involuntary muscular activities that manage body equilibrium, represents a demanding function in which the cerebellum plays a key role. Postural activities are particularly important during gait initiation when passing from quiet standing to locomotion. Indeed, several studies used such motor task for evaluating pathological conditions, including cerebellar disorders. The linkage between cerebellum maturation and the development of postural control has received less attention. Therefore, we evaluated postural control during quiet standing and gait initiation in children affected by a slow progressive generalized cerebellar atrophy (SlowP) or non-progressive vermian hypoplasia (Joubert syndrome, NonP), compared to that of healthy children (H). Despite the similar clinical evaluation of motor impairments in NonP and SlowP, only SlowP showed a less stable quiet standing and a shorter and slower first step than H. Moreover, a descriptive analysis of lower limb and back muscle activities suggested a more severe timing disruption in SlowP. Such differences might stem from the extent of cerebellar damage. However, literature reports that during childhood, neural plasticity of intact brain areas could compensate for cerebellar agenesis. We thus proposed that the difference might stem from disease progression, which contrasts the consolidation of compensatory strategies.