Is There a Future for Non-invasive Brain Stimulation as a Therapeutic Tool?

Several techniques and protocols of non-invasive transcranial brain stimulation (NIBS), including transcranial magnetic and electrical stimuli, have been developed in the past decades. These techniques can induce long lasting changes in cortical excitability by promoting synaptic plasticity and thus may represent a therapeutic option in neuropsychiatric disorders. On the other hand, despite these techniques have become popular, the fragility and variability of the after effects are the major challenges that non-invasive transcranial brain stimulation currentlyfaces. Several factors may account for such a variability such as biological variations, measurement reproducibility, and the neuronal state of the stimulated area. One possible strategy, to reduce this variability is to monitor the neuronal state in real time using EEG and trigger TMS pulses only at pre-defined state. In addition, another strategy under study is to use the spaced application of multiple NIBS protocols within a session to improve the reliability and extend the duration of NIBS effects. Further studies, although time consuming, are required for improving the so far limited effect sizes of NIBS protocols for treatment of neurological or psychiatric disorders

Endogenous orientation of visual attention in auditory space

Visuospatial attention is asymmetrically distributed with a leftward bias (i.e. pseudoneglect), while evidence for asymmetries in auditory spatial attention is still controversial. In the present study, we investigated putative asymmetries in the distribution of auditory spatial attention and the influence that visual information might have on its deployment. A modified version of the Posner task (i.e. the visuo-audio spatial task [VAST]) was used to investigate spatial processing of auditory targets when endogenous orientation of spatial attention was mediated by visual cues in healthy adults. A line bisection task (LBT) was also administered to assess the presence of a leftward bias in deployment of visuospatial attention. Overall, participants showed rightward and leftward biases in the VAST and the LBT, respectively. In the VAST, sound localization was enhanced by visual cues. Altogether, these findings support the existence of a facilitation effect for auditory targets originating from the right side of space and provide new evidence for crossmodal links in endogenous spatial attention between vision and audition

Structural connectivity‐based topography of the human globus pallidus: Implications for therapeutic targeting in movement disorders

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Consensus Paper: Probing Homeostatic Plasticity of Human Cortex With Non-invasive Transcranial Brain Stimulation

AbstractHomeostatic plasticity is thought to stabilize neural activity around a set point within a physiologically reasonable dynamic range. Over the last ten years, a wide range of non-invasive transcranial brain stimulation (NTBS) techniques have been used to probe homeostatic control of cortical plasticity in the intact human brain. Here, we review different NTBS approaches to study homeostatic plasticity on a systems level and relate the findings to both, physiological evidence from in vitro studies and to a theoretical framework of homeostatic function. We highlight differences between homeostatic and other non-homeostatic forms of plasticity and we examine the contribution of sleep in restoring synaptic homeostasis. Finally, we discuss the growing number of studies showing that abnormal homeostatic plasticity may be associated to a range of neuropsychiatric diseases

Post-traumatic olfactory dysfunction: a scoping review of assessment and rehabilitation approaches

Post-traumatic Olfactory Dysfunction (PTOD) consists of a complete or partial loss of olfactory function that may occur after a traumatic brain injury (TBI). PTOD may be linked to some neuropsychiatric features, such as social, cognitive and executive dysfunction, as well as behavioral symptoms, especially when TBI involves the orbito-frontal cortex. The diagnosis of PTOD is based on medical history and clinical data and it is supported by psychometric tests (i.e., subjective tools) as well as electrophysiological and neuroimaging measures (i.e., objective methods). The assessment methods allow monitoring the changes in olfactory function over time and help to establish the right therapeutic and rehabilitative approach. In this context, the use of the olfactory training (OT), which is a non-pharmacological and non-invasive treatment option, could promote olfactory function through top-down (central) and bottom-up (peripheral) processes. To better manage patients with TBI, PTOD should be detected early and properly treated using the various therapeutic rehabilitative possibilities, both conventional and advanced, also taking into consideration the emerging neuromodulation approach

Non-Invasive Brain Stimulation for the Modulation of Aggressive Behavior—A Systematic Review of Randomized Sham-Controlled Studies

Intro: Aggressive behavior represents a significant public health issue, with relevant social, political, and security implications. Non-invasive brain stimulation (NIBS) techniques may modulate aggressive behavior through stimulation of the prefrontal cortex. Aims: To review research on the effectiveness of NIBS to alter aggression, discuss the main findings and potential limitations, consider the specifics of the techniques and protocols employed, and discuss clinical implications. Methods: A systematic review of the literature available in the PubMed database was carried out, and 17 randomized sham-controlled studies investigating the effectiveness of NIBS techniques on aggression were included. Exclusion criteria included reviews, meta-analyses, and articles not referring to the subject of interest or not addressing cognitive and emotional modulation aims. Conclusions: The reviewed data provide promising evidence for the beneficial effects of tDCS, conventional rTMS, and cTBS on aggression in healthy adults, forensic, and clinical samples. The specific stimulation target is a key factor for the success of stimulation on aggression modulation. rTMS and cTBS showed opposite effects on aggression compared with tDCS. However, due to the heterogeneity of stimulation protocols, experimental designs, and samples, we cannot exclude other factors that may play a confounding role

Practice changes beta power at rest and its modulation during movement in healthy subjects but not in patients with Parkinson\u27s disease

Abstract Background PD (Parkinson\u27s disease) is characterized by impairments in cortical plasticity, in beta frequency at rest and in beta power modulation during movement (i.e., event‐related ERS [synchronization] and ERD [desynchronization]). Recent results with experimental protocols inducing long‐term potentiation in healthy subjects suggest that cortical plasticity phenomena might be reflected by changes of beta power recorded with EEG during rest. Here, we determined whether motor practice produces changes in beta power at rest and during movements in both healthy subjects and patients with PD. We hypothesized that such changes would be reduced in PD. Methods We thus recorded EEG in patients with PD and age‐matched controls before, during and after a 40‐minute reaching task. We determined posttask changes of beta power at rest and assessed the progressive changes of beta ERD and ERS during the task over frontal and sensorimotor regions. Results We found that beta ERS and ERD changed significantly with practice in controls but not in PD. In PD compared to controls, beta power at rest was greater over frontal sensors but posttask changes, like those during movements, were far less evident. In both groups, kinematic characteristics improved with practice; however, there was no correlation between such improvements and the changes in beta power. Conclusions We conclude that prolonged practice in a motor task produces use‐dependent modifications that are reflected in changes of beta power at rest and during movement. In PD, such changes are significantly reduced; such a reduction might represent, at least partially, impairment of cortical plasticity

Constrained spherical deconvolution provides evidence of extensive subcortical direct cerebellumbasal ganglia connections in human brain

Traditionally, the basal ganglia (BG) are thought to play a major role in the selection and inhibition of motor commands, while the cerebellum plays a role in tuning and reshaping on-going movement. In the past, the connections between the cerebellum and the cerebral cortex have been considered to be anatomically and functionally distinct from those linking the BG with the cerebral cortex. Evidences from recent anatomical experiments, using retrograde transneuronal transport of rabies virus in macaques, have challenged this old perspective demonstrating disynaptic subcortical pathways that directly link the cerebellum with the BG. Since the application of these techniques to the human brain remains elusive, due to the invasive nature of such methods, whether and to what extent these specific connections between the BG and cerebellum exist in the human brain remains unclear. However, recent developments in Diffusion Magnetic Resonance Imaging (dMRI) and diffusion tractography may allow for non-invasive and in vivo studies of the anatomical substrate of basal ganglia systems. Indeed, in our previous paper we studied the basal ganglia connectome providing strong evidences of a direct connection from cortex to Globus Pallidum (GPe and GPi) [1]. Thirteen normal subjects with no history of any overt neurological and/or psychiatric disorders were examined to test the hypotheses that substantial interactions, at least on the level shown in animal studies, also exist in the human brain. We demonstrated that it is feasible to disclose these cerebellar-subcortical connections by using constrained spherical deconvolution (CSD), an innovative approach which allows a reliable reconstruction of small- and long-fiber pathways, with subvoxel resolution in brain regions with multiple fiber orientations [2]. In particular we found evidences of subthalamic-cerebellar, dentate-thalamo-striatal, dentate-rubral-thalamic, dentate-rubral-pallidal and dentate-nigral connections. In addition to these connections, we found a direct cerebellar-dentate-pallidal connection never reported in literature to our knowledge; we identified and isolated two well-distinct tracts presenting an ipsilateral and contralateral component, converging mainly on the antero-medial part of the globus pallidus

Sensory Abnormalities in Focal Hand Dystonia and Non-Invasive Brain Stimulation

It has been proposed that synchronous and convergent afferent input arising from repetitive motor tasks may play an important role in driving the maladaptive cortical plasticity seen in focal hand dystonia (FHD).This hypothesis receives support from several sources. First, it has been reported that in subjects with FHD, paired associative stimulation produces an abnormal increase in corticospinal excitability, which was not confined to stimulated muscles. These findings provide support for the role of excessive plasticity in FHD. Second, the genetic contribution to the dystonias is increasingly recognized indicating that repetitive, stereotyped afferent inputs may lead to late-onset dystonia, such as FHD, more rapidly in genetically susceptible individuals. It can be postulated, according to the two factor hypothesis that dystonia is triggered and maintained by the concurrence of environmental factors such as repetitive training and subtle abnormal mechanisms of plasticity within somatosensory loop. In the present review, we examine the contribution of sensory-motor integration in the pathophysiology of primary dystonia. In addition, we will discuss the role of non-invasive brain stimulation as therapeutic approach in FHD