Noninvasive brain stimulation and brain oscillations

Accelerated Transcutaneous Auricular Vagus Nerve Stimulation for Inpatient Depression and Anxiety: The iWAVE Open Label Pilot Trial

INTRODUCTION

Brain stimulation is not a common inpatient psychiatric treatment; however, there are an increasing number of neuromodulation treatments approved for psychiatric indications. Noninvasive techniques, such as transcutaneous auricular vagus nerve stimulation (taVNS), are promising and should be investigated in this novel setting. This study evaluates the safety and feasibility of taVNS on the inpatient psychiatric unit and preliminarily explores efficacy for comorbid depression and anxiety.

MATERIALS AND METHODS

Ten adult patients (five women, mean age ± SD, 35.60 ± 19.14 years) admitted to the inpatient psychiatric unit with comorbid depression and anxiety participated in this open-label safety and feasibility trial. Patients were randomized to receive one of two taVNS dosing approaches: 1) three taVNS sessions on three consecutive days (nine sessions total) (n = 5) or 2) nine taVNS sessions in one day (n = 5). Each day, we assessed depression, using the Patient Health Questionnaire (PHQ-9) and Beck Depression Inventory (BDI), and anxiety, using the Generalized Anxiety Disorder-7 (GAD-7) and Beck Anxiety Inventory (BAI).

RESULTS

Both taVNS dosing approaches were safe and feasible in this novel setting. There were no serious adverse events, and we observed a low rate of minor adverse effects, which was similar across treatment conditions. Regardless of condition, stimulation significantly reduced GAD-7 (mean reduction ± SD, -5.90 to 6.87, p < 0.05), BAI (-9.40 ± 10.52, p < 0.05), PHQ-9 (-6.00 ± 7.57, p < 0.05), and BDI (-11.00 ± 11.59, p < 0.05) final scores compared with baseline. There was not a significant difference in clinical response between treatment conditions.

DISCUSSION

In this open label study, taVNS significantly decreased depression and anxiety symptoms in patients admitted to the inpatient unit. The small sample size in this trial limited our ability to characterize patient characteristics that may drive response. However, our results suggest taVNS may be an effective adjunct to inpatient psychiatric treatment and should continue to be studied in this setting.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT05791383.

Combining non-invasive brain stimulation techniques and EEG markers analysis: an innovative approach to cognitive health in aging

In an era marked by a rapidly aging global population, delving into the intricate neurophysiological changes that accompany the aging process assumes paramount importance. This narrative review offers a comprehensive exploration of the intricate relationship between electromagnetic neuromodulation and electroencephalography (EEG) within the context of aging. Moreover, it showed the promising landscape of non-invasive neuromodulation techniques, encompassing established methodologies like transcranial magnetic stimulation (TMS) and transcranial direct and alternating current stimulation (tDCS/tACS). These modalities are analyzed for their potential to shape EEG marks in the aging population. These associations not only could broaden our understanding of the aging brain but could also suggest exciting scenarios for therapeutic interventions and cognitive enhancement among the elderly. Consequently, the comprehension of these mechanisms emerges as a critical key player for the development of precisely tailored interventions, aimed at mitigating age-associated cognitive decline and supporting robust brain health in the elderly.

Transcranial Magnetic Stimulation Across the Lifespan: Impact of Developmental and Degenerative Processes

Transcranial magnetic stimulation (TMS) has emerged as a pivotal noninvasive technique for investigating cortical excitability and plasticity across the lifespan, offering valuable insights into neurodevelopmental and neurodegenerative processes. In this review, we explore the impact of TMS applications on our understanding of normal development, healthy aging, neurodevelopmental disorders, and adult-onset neurodegenerative diseases. By presenting key developmental milestones and age-related changes in TMS measures, we provide a foundation for understanding the maturation of neurotransmitter systems and the trajectory of cognitive functions throughout the lifespan. Building on this foundation, the paper delves into the pathophysiology of neurodevelopmental disorders, including autism spectrum disorder, attention-deficit/hyperactivity disorder, Tourette syndrome, and adolescent depression. Highlighting recent findings on altered neurotransmitter circuits and dysfunctional cortical plasticity, we underscore the potential of TMS as a valuable tool for unraveling underlying mechanisms and informing future therapeutic interventions. We also review the emerging role of TMS in investigating and treating the most common adult-onset neurodegenerative disorders and late-onset depression. By outlining the therapeutic applications of noninvasive brain stimulation techniques in these disorders, we discuss the growing body of evidence supporting their use as therapeutic tools for symptom management and potentially slowing disease progression. The insights gained from TMS studies have advanced our understanding of the underlying mechanisms in both healthy and disease states, ultimately informing the development of more targeted diagnostic and therapeutic strategies for a wide range of neuropsychiatric conditions.

Slow-wave sleep dysfunction in mild parkinsonism is associated with excessive beta and reduced delta oscillations in motor cortex

Increasing evidence suggests slow-wave sleep (SWS) dysfunction in Parkinson's disease (PD) is associated with faster disease progression, cognitive impairment, and excessive daytime sleepiness. Beta oscillations (8-35 Hz) in the basal ganglia thalamocortical (BGTC) network are thought to play a role in the development of cardinal motor signs of PD. The role cortical beta oscillations play in SWS dysfunction in the early stage of parkinsonism is not understood, however. To address this question, we used a within-subject design in a nonhuman primate (NHP) model of PD to record local field potentials from the primary motor cortex (MC) during sleep across normal and mild parkinsonian states. The MC is a critical node in the BGTC network, exhibits pathological oscillations with depletion in dopamine tone, and displays high amplitude slow oscillations during SWS. The MC is therefore an appropriate recording site to understand the neurophysiology of SWS dysfunction in parkinsonism. We observed a reduction in SWS quantity (p = 0.027) in the parkinsonian state compared to normal. The cortical delta (0.5-3 Hz) power was reduced (p = 0.038) whereas beta (8-35 Hz) power was elevated (p = 0.001) during SWS in the parkinsonian state compared to normal. Furthermore, SWS quantity positively correlated with delta power (r = 0.43, p = 0.037) and negatively correlated with beta power (r = -0.65, p < 0.001). Our findings support excessive beta oscillations as a mechanism for SWS dysfunction in mild parkinsonism and could inform the development of neuromodulation therapies for enhancing SWS in people with PD.

Frequency-dependent tuning of the human vestibular "sixth sense" by transcranial oscillatory currents

OBJECTIVE

The vestibular cortex is a multisensory associative region that, in neuroimaging investigations, is activated by slow-frequency (1-2 Hz) galvanic stimulation of peripheral receptors. We aimed to directly activate the vestibular cortex with biophysically modeled transcranial oscillatory current stimulation (tACS) in the same frequency range.

METHODS

Thirty healthy subjects and one rare patient with chronic bilateral vestibular deafferentation underwent, in a randomized, double-blind, controlled trial, to tACS at slow (1 or 2 Hz) or higher (10 Hz) frequency and sham stimulations, over the Parieto-Insular Vestibular Cortex (PIVC), while standing on a stabilometric platform. Subjective symptoms of motion sickness were scored by Simulator Sickness Questionnaire and subjects' postural sways were monitored on the platform.

RESULTS

tACS at 1 and 2 Hz induced symptoms of motion sickness, oscillopsia and postural instability, that were supported by posturographic sway recordings. Both 10 Hz-tACS and sham stimulation on the vestibular cortex did not affect vestibular function. As these effects persisted in a rare patient with bilateral peripheral vestibular areflexia documented by the absence of the Vestibular-Ocular Reflex, the possibility of a current spread toward peripheral afferents is unlikely. Conversely, the 10 Hz-tACS significantly reduced his chronic vestibular symptoms in this patient.

CONCLUSIONS

Weak electrical oscillations in a frequency range corresponding to the physiological cortical activity of the vestibular system may generate motion sickness and postural sways, both in healthy subjects and in the case of bilateral vestibular deafferentation.

SIGNIFICANCE

This should be taken into account as a new side effect of tACS in future studies addressing cognitive functions. Higher frequencies of stimulation applied to the vestibular cortex may represent a new interventional option to reduce motion sickness in different scenarios.

Local and Distributed fMRI Changes Induced by 40 Hz Gamma tACS of the Bilateral Dorsolateral Prefrontal Cortex: A Pilot Study

Over the past few years, the possibility of modulating fast brain oscillatory activity in the gamma (γ) band through transcranial alternating current stimulation (tACS) has been discussed in the context of both cognitive enhancement and therapeutic scenarios. However, the effects of tACS targeting regions outside the motor cortex, as well as its spatial specificity, are still unclear. Here, we present a concurrent tACS-fMRI block design study to characterize the impact of 40 Hz tACS applied over the left and right dorsolateral prefrontal cortex (DLPFC) in healthy subjects. Results suggest an increase in blood oxygenation level-dependent (BOLD) activity in the targeted bilateral DLPFCs, as well as in surrounding brain areas affected by stimulation according to biophysical modeling, i.e., the premotor cortex and anterior cingulate cortex (ACC). However, off-target effects were also observed, primarily involving the visual cortices, with further effects on the supplementary motor areas (SMA), left subgenual cingulate, and right superior temporal gyrus. The specificity of 40 Hz tACS over bilateral DLPFC and the possibility for network-level effects should be considered in future studies, especially in the context of recently promoted gamma-induction therapeutic protocols for neurodegenerative disorders.

Dystonia, chorea, hemiballismus and other dyskinesias

Hyperkinesias are heterogeneous involuntary movements that significantly differ in terms of clinical and semeiological manifestations, including rhythm, regularity, speed, duration, and other factors that determine their appearance or suppression. Hyperkinesias are due to complex, variable, and largely undefined pathophysiological mechanisms that may involve different brain areas. In this chapter, we specifically focus on dystonia, chorea and hemiballismus, and other dyskinesias, specifically, levodopa-induced, tardive, and cranial dyskinesia. We address the role of neurophysiological studies aimed at explaining the pathophysiology of these conditions. We mainly refer to human studies using surface and invasive in-depth recordings, as well as spinal, brainstem, and transcortical reflexology and non-invasive brain stimulation techniques. We discuss the extent to which the neurophysiological abnormalities observed in hyperkinesias may be explained by pathophysiological models. We highlight the most relevant issues that deserve future research efforts. The potential role of neurophysiological assessment in the clinical context of hyperkinesia is also discussed.