High-definition transcranial infraslow pink noise stimulation for chronic low back pain: protocol for a pilot, safety and feasibility randomised placebo-controlled trial

INTRODUCTION

Chronic low back pain (CLBP) is a common disabling health condition. Current treatments demonstrate modest effects, warranting newer therapies. Brain imaging demonstrates altered electrical activities in cortical areas responsible for pain modulation, emotional and sensory components of pain experience. Treatments targeting to change electrical activities of these key brain regions may produce clinical benefits. This pilot study aims to (1) evaluate feasibility, safety and acceptability of a novel neuromodulation technique, high-definition transcranial infraslow pink noise stimulation (HD-tIPNS), in people with CLBP, (2) explore the trend of effect of HD-tIPNS on pain and function, and (3) derive treatment estimates to support sample size calculation for a fully powered trial should trends of effectiveness be present.

METHODS AND ANALYSIS

A pilot, triple-blinded randomised two-arm placebo-controlled parallel trial. Participants (n=40) with CLBP will be randomised to either sham stimulation or HD-tIPNS (targeting somatosensory cortex and dorsal and pregenual anterior cingulate cortex). Primary outcomes include feasibility and safety measures, and clinical outcomes of pain (Brief Pain Inventory) and disability (Roland-Morris disability questionnaire). Secondary measures include clinical, psychological, quantitative sensory testing and electroencephalography collected at baseline, immediately postintervention, and at 1-week, 1-month and 3 months postintervention. All data will be analysed descriptively. A nested qualitative study will assess participants perceptions about acceptability of intervention and analysed thematically.

ETHICS AND DISSEMINATION

Ethical approval has been obtained from Health and Disability Ethics Committee (Ref:20/NTB/67). Findings will be reported to regulatory and funding bodies, presented at conferences, and published in a scientific journal.

TRIAL REGISTRATION NUMBER

ACTRN12620000505909p.

Pain and the Triple Network Model

Acute pain is a physiological response that causes an unpleasant sensory and emotional experience in the presence of actual or potential tissue injury. Anatomically and symptomatically, chronic pathological pain can be divided into three distinct but interconnected pathways, a lateral “painfulness” pathway, a medial “suffering” pathway and a descending pain inhibitory circuit. Pain (fullness) can exist without suffering and suffering can exist without pain (fullness). The triple network model is offering a generic unifying framework that may be used to understand a variety of neuropsychiatric illnesses. It claims that brain disorders are caused by aberrant interactions within and between three cardinal brain networks: the self-representational default mode network, the behavioral relevance encoding salience network and the goal oriented central executive network. A painful stimulus usually leads to a negative cognitive, emotional, and autonomic response, phenomenologically expressed as pain related suffering, processed by the medial pathway. This anatomically overlaps with the salience network, which encodes behavioral relevance of the painful stimuli and the central sympathetic control network. When pain lasts longer than the healing time and becomes chronic, the pain- associated somatosensory cortex activity may become functionally connected to the self-representational default mode network, i.e., it becomes an intrinsic part of the self-percept. This is most likely an evolutionary adaptation to save energy, by separating pain from sympathetic energy-consuming action. By interacting with the frontoparietal central executive network, this can eventually lead to functional impairment. In conclusion, the three well-known pain pathways can be combined into the triple network model explaining the whole range of pain related co-morbidities. This paves the path for the creation of new customized and personalized treatment methods.

Predisposition to domain-wide maladaptive changes in predictive coding in auditory phantom perception

Tinnitus is hypothesised to be a predictive coding problem. Previous research indicates lower sensitivity to prediction errors (PEs) in tinnitus patients while processing auditory deviants corresponding to tinnitus-specific stimuli. However, based on research with patients with hallucinations and no psychosis we hypothesise tinnitus patients may be more sensitive to PEs produced by auditory stimuli that are not related to tinnitus characteristics. Specifically in patients with minimal to no hearing loss, we hypothesise a more top-down subtype of tinnitus that may be driven by maladaptive changes in an auditory predictive coding network. To test this, we use an auditory oddball paradigm with omission of global and local deviants, a measure that is previously shown to empirically characterise hierarchical prediction errors (PEs). We observe: (1) increased predictions characterised by increased pre-stimulus response and increased alpha connectivity between the parahippocampus, dorsal anterior cingulate cortex and parahippocampus, pregenual anterior cingulate cortex and posterior cingulate cortex; (2) increased PEs characterised by increased P300 amplitude and gamma activity and increased theta connectivity between auditory cortices, parahippocampus and dorsal anterior cingulate cortex in the tinnitus group; (3) increased overall feed-forward connectivity in theta from the auditory cortex and parahippocampus to the dorsal anterior cingulate cortex; (4) correlations of pre-stimulus theta activity to tinnitus loudness and alpha activity to tinnitus distress. These results provide empirical evidence of maladaptive changes in a hierarchical predictive coding network in a subgroup of tinnitus patients with minimal to no hearing loss. The changes in pre-stimulus activity and connectivity to non-tinnitus specific stimuli suggest that tinnitus patients not only produce strong predictions about upcoming stimuli but also may be predisposed to stimulus a-specific PEs in the auditory domain. Correlations with tinnitus-related characteristics may be a biomarker for maladaptive changes in auditory predictive coding.

Baseline delayed verbal recall predicts response to high definition transcranial direct current stimulation targeting the superior medial frontal cortex

Anodal high definition transcranial direct current stimulation (HD-tDCS) targeting the pre-supplementary motor area/dorsal anterior cingulate cortex (pre-SMA/dACC) has recently been shown to improve verbal retrieval deficits in veterans with chronic traumatic brain injury (TBI) (Motes et al., 2020), but predictors of treatment response are unclear. We hypothesized that baseline delayed verbal recall, a sensitive measure for post-TBI chronic cognitive decline, would predict therapeutic effects of HD-tDCS targeting the pre-SMA/dACC for verbal retrieval deficits. Standardized verbal retrieval measures were administered at baseline, immediately after and 8 weeks after treatment completion. We applied mixed generalized linear modeling as a post-hoc subgroup analysis to the verbal retrieval scores that showed significant improvement in Motes at el. (2020) to examine effects of active stimulation across the groups with baseline-intact delayed recall (N = 10) and baseline-impaired delayed recall (N = 8), compared to sham (N = 7). Individuals with impaired baseline delayed recall showed significant improvement (compared to baseline) in both category fluency and color-word inhibition/switch, while individuals with intact delayed recall showed significant improvement only in color-word inhibition/switch. Baseline delayed verbal recall may therefore be considered as a predictor for future electromodulation studies targeting frontal structures to treat TBI-related verbal deficits.

Is the posterior cingulate cortex an on-off switch for tinnitus?: A comparison between hearing loss subjects with and without tinnitus

As the human brain works in a Bayesian manner to minimize uncertainty toward external stimuli, the deafferented brain may generate tinnitus in an attempt to fill in missing auditory information, e.g. due to hearing loss. However, not everybody with hearing loss develops tinnitus. Understanding the differences between people with hearing loss who develop tinnitus versus those who do not offers a unique opportunity to unravel critical brain areas involved in the generation of a phantom sound. In this study, we compared resting-state quantitative electroencephalography between hearing loss patients with (HL-T) and without tinnitus (HL-NT) to identify cortical oscillatory signatures that may reveal prerequisites for the selective development of tinnitus in subjects with hearing loss. We enrolled 65 subjects with HL-NT and 65 subjects with HL-T whose tinnitus handicap inventory scores were <16 (grade 1) to minimize the bias induced by distress-induced cortical activity changes. Subjects in the HL-T and HL-NT groups were matched in terms of the bilateral hearing threshold (0.25-8 kHz) using nearest neighbor method. Compared to the HL-NT group, the HL-T group showed significantly higher activity in the right parahippocampus for the beta 1 frequency band, in the left inferior parietal lobule (IPL) for the beta 2 frequency band, and in the right IPL for the beta 3- and gamma frequency bands. Functional connectivity analyses revealed that the HL-T group had significantly higher connectivity than the HL-NT group between both parahippocampal gyri and the right IPL for the delta frequency band, and between the left posterior cingulate cortex (PCC) and right IPL for the beta 2 frequency band. These results suggest that tinnitus may be perceived only if auditory memory stored in the parahippocampus is actively linked to the IPL-based "circuit breaker" system and the circuit breaker signal is connected to the PCC-based default mode network (DMN). Thus, when the circuit breaker system regards tinnitus secondary to peripheral deafferentation as a salient event and then the DMN regards tinnitus as a norm, subjects with hearing loss may consciously perceive tinnitus. The results of this study further refine the recently proposed Bayesian model and decipher the neurobiological mechanism of the selective development of tinnitus in subjects with hearing loss.

The anatomy of pain and suffering in the brain and its clinical implications

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Chronic pain, with a prevalence of 20-30 % is the major cause of human suffering worldwide, because effective, specific and safe therapies have yet to be developed. It is unevenly distributed among sexes, with women experiencing more pain and suffering. Chronic pain can be anatomically and phenomenologically dissected into three separable but interacting pathways, a lateral 'painfulness' pathway, a medial 'suffering' pathway and a descending pain inhibitory pathway. One may have pain(fullness) without suffering and suffering without pain(fullness). Pain sensation leads to suffering via a cognitive, emotional and autonomic processing, and is expressed as anger, fear, frustration, anxiety and depression. The medial pathway overlaps with the salience and stress networks, explaining that behavioural relevance or meaning determines the suffering associated with painfulness. Genetic and epigenetic influences trigger chronic neuroinflammatory changes which are involved in transitioning from acute to chronic pain. Based on the concept of the Bayesian brain, pain (and suffering) can be regarded as the consequence of an imbalance between the two ascending and the descending pain inhibitory pathways under control of the reward system. The therapeutic clinical implications of this simple pain model are obvious. After categorizing the working mechanisms of each of the available treatments (pain killers, psychopharmacology, psychotherapy, neuromodulation, psychosurgery, spinal cord stimulation) to 1 or more of the 3 pathways, a rational combination can be proposed of activating the descending pain inhibitory pathway in combination with inhibition of the medial and lateral pathway, so as to rebalance the pain (and suffering) pathways.

Sex Differences in Locus Coeruleus: A Heuristic Approach That May Explain the Increased Risk of Alzheimer's Disease in Females

This article aims to reevaluate our approach to female vulnerability to Alzheimer's disease (AD) and put forth a new hypothesis considering how sex differences in the locus coeruleus-noradrenaline (LC-NA) structure and function could account for why females are more likely to develop AD. We specifically focus our attention on locus coeruleus (LC) morphology, the paucity of estrogens, neuroinflammation, blood-brain barrier permeability, apolipoprotein ɛ4 polymorphism (APOEɛ4), and cognitive reserve. The role of the LC-NA system and sex differences are two of the most rapidly emerging topics in AD research. Current literature either investigates the LC due to it being one of the first brain areas to develop AD pathology or acknowledges the neuroprotective effects of estrogens and how the loss of these female hormones have the capacity to contribute to the sex differences seen in AD; however, existing research has neglected to concurrently examine these two rationales and therefore leaving our hypothesis undetermined. Collectively, this article should assist in alleviating current challenges surrounding female AD by providing thought-provoking connections into the interrelationship between the disruption of the female LC-NA system, the decline of estrogens, and AD vulnerability. It is therefore likely that treatment for this heterogeneous disease may need to be distinctly developed for females and males separately, and may require a precision medicine approach.

Case Report: Improving Verbal Retrieval Deficits With High Definition Transcranial Direct Current Stimulation Targeting the Pre-Supplementary Motor Area in a Patient With Chronic Traumatic Brain Injury

We report a patient who has cognitive sequalae including verbal retrieval deficits after severe traumatic brain injury (TBI). The cortico-caudate-thalamic circuit involving the pre-Supplementary Motor Area (pre-SMA) has been proposed to underlie verbal retrieval functions. We hypothesized that High Definition-transcranial Direct Current Stimulation (HD-tDCS) targeting the pre-SMA would selectively modulate this circuit to remediate verbal retrieval deficits. After the patient underwent 10 sessions of 20 min of 1 mA HD-tDCS targeting the pre-SMA, we documented significant improvements for verbal fluency and naming, and for working memory and executive function tasks that involve the frontal lobes. The effects persisted for up to 14 weeks after completion of HD-tDCS treatment. We also demonstrated normalization of the event-related potentials suggesting modulation of the underlying neural circuit. Our study implicates that region-specific non-invasive brain stimulation, such as HD-tDCS, serves as a potential individualized therapeutic tool to treat cognitive deficits by inducing longer-lasting neuroplasticity even in the chronic phase of TBI.

The balance between Bayesian inference and default mode determines the generation of tinnitus from decreased auditory input: A volume entropy-based study

Along with phantom pain, tinnitus, a phantom auditory perception occurring in the absence of an external acoustic stimulus, is one of the most representative phantom perceptions that develops in subjects with decreased peripheral sensory input. Although tinnitus is closely associated with peripheral hearing loss (HL), it remains unclear why only some individuals with HL develop tinnitus. In this study, we investigated the differences between 65 HL with tinnitus (HL‐T) and 104 HL with no tinnitus (HL‐NT) using a resting‐state electroencephalography data‐based volume entropy model of the brain network, by comparing the afferent node capacities, that quantify the contribution of each node to the spread of information, of all Brodmann areas. While the HL‐T group showed increased information flow in areas involved in Bayesian inference (the left orbitofrontal cortex, the left subgenual anterior cingulate cortex, and the left ventrolateral prefrontal cortex) and auditory memory storage (the right hippocampus/parahippocampus), the HL‐NT group showed increased afferent node capacity in hub areas of the default mode network (DMN; the right posterior cingulate cortex and the right medial temporal gyrus). These results suggest that the balance of activity between the Bayesian inferential network (updating missing auditory information by retrieving auditory memories from the hippocampus/parahippocampus) and DMN (maintaining the “silent status quo”) determines whether phantom auditory perception occurs in a brain with decreased peripheral auditory input.

The limited effect of neural stimulation on visual attention and social cognition in individuals with schizophrenia

BACKGROUND

Research demonstrates a relationship between faulty visual attention and poorer social cognition in schizophrenia. One potential explanatory model suggests abnormal neuromodulation in specific neural networks may result in reduced attention to socially important cues, leading to poorer understanding of another's emotional state or intentions.

OBJECTIVE

The current study experimentally manipulated neural networks using tDCS to examine this potential causal mechanism. The primary aim was to determine whether stimulation to the right temporoparietal junction (rTPJ) improves visual attention, and secondary aims were to determine whether 1) stimulation improves social cognitive performance and 2) visual attention moderates this improved performance.

METHOD

Using a double-blind crossover design, 69 individuals with schizophrenia underwent both active and sham stimulation to either the rTPJ of the ventral attention network (n = 36) or the dorsomedial prefrontal cortex of the social brain network (dmPFC; n = 33). Following stimulation, participants completed tasks assessing emotion recognition and mentalizing. Concurrent eye tracking assessed visual attention, measuring proportion of time spent attending to areas of interest.

RESULTS

For emotion recognition, stimulation failed to impact either visual attention or social cognitive task accuracy. Similarly, neurostimulation failed to affect visual attention on the mentalizing task. However, exploratory analyses demonstrated that mentalizing accuracy significantly improved after stimulation to the active comparator, dmPFC, with no improvement after stimulation to rTPJ.

CONCLUSION

Results demonstrate limited effect of a single stimulation session on visual attention and emotion recognition accuracy but provide initial support for an alternate neural mechanism for mentalizing, highlighting the importance of executive functions over visual attention.

Preliminary evidence for the efficacy of single-session transcranial direct current stimulation to the ventrolateral prefrontal cortex for reducing subclinical paranoia in healthy individuals

OBJECTIVES

Paranoia manifests similarly in subclinical and clinical populations and is related to distress and impairment. Previous work links paranoia to amygdala hyperactivity and reduced activation of the ventrolateral prefrontal cortex (VLPFC), a region thought to regulate amygdala activity.

METHODS

This study aimed to reduce subclinical paranoia in 40 undergraduates by increasing activity of the VLPFC via single-session transcranial Direct Current Stimulation (tDCS). A double-blind, crossover (active vs. sham stimulation) design was used.

RESULTS

Paranoia significantly decreased after active stimulation (d_z  = 0.51) but not sham (d_z  = 0.19), suggesting that tDCS of VLPFC was associated with mean-level reductions in paranoia.

CONCLUSION

These findings demonstrate preliminary support for the role of single-session active stimulation to the VLPFC for reducing subclinical paranoia in healthy individuals.

PRACTITIONER POINTS

In both clinical and subclinical populations, paranoia is related to distress and poorer functional outcomes. Paranoia has been linked to overactivation of the amygdala, a brain region responsible for detecting salience and threat, and reduced activation of the ventrolateral prefrontal cortex (VLPFC), a region thought to modulate and regulate amygdala activity. In this study, transcranial direct current stimulation (tDCS) of the VLPFC reduced self-reported paranoia in healthy undergraduate students. tDCS may be a promising intervention for reducing paranoia in subclinical and clinical populations. Effects were relatively small and require replication with larger subclinical samples and with clinical samples.

The future of neuromodulation: smart neuromodulation

Introduction: The International Neuromodulation Society defines neuromodulation as the alteration of nerve activity through targeted delivery of a stimulus, such as electrical stimulation or chemical agents, to specific neurological sites in the body.Areas covered: In the near future (<5 years) increasingly complex implantable neuromodulation systems will enter the market. These devices are capable of closed-loop stimulation and the delivery of novel stimulation designs, pushing the need for upgradability. But what about the near-to-far future, meaning 5-10 years from now?Expert opinion: We propose that neuromodulation in the near to far future (5-10 years) will involve integration of adaptive network neuromodulation with predictive artificial intelligence, automatically adjusted by brain and external sensors, and controlled via cloud-based applications. The components will be introduced in a phased approach, culminating in a fully autonomous brain-stimulator-cloud interface. This may, in the long future (>10 years), lead to the brain of the future, a brain with integrated artificial intelligence.

Impaired posterior cingulate cortex-parahippocampus connectivity is associated with episodic memory retrieval problems in amnestic mild cognitive impairment

Episodic memory retention and retrieval decline are the most common impairments observed in amnestic mild cognitive impairment (aMCI) patients who progress to Alzheimer's disease (AD). Clinical electroencephalography research shows that patients with dementia due to AD exhibit a slowing of neural electrical activity in the parietal cortex. Memory research has further suggested that successful memory performance is associated with changes in a posterior cingulate-parahippocampal cortical network together with increased θ-γ oscillatory coupling, where θ oscillations act as carrier waves for γ oscillations, which contain the actual information. However, the neurophysiological link between the memory research and clinical studies investigating aMCI and AD is lacking. In this study, we look at brain activity in aMCI and how it relates to memory performance. We demonstrate decreased γ power in the posterior cingulate cortex and the left and right parahippocampus in aMCI patients in comparison to control participants. This goes together with reduced θ coherence between the posterior cingulate cortex and parahippocampus associated with altered memory performance aMCI patients in comparison to control participants. In addition, comparing patients with aMCI to control participants reveals an effect for θ-γ coupling for the posterior cingulate cortex, and the left and right parahippocampus. Taken together, our results show that parahippocampus and posterior cingulate cortex interact via θ-γ coupling, which is associated with memory recollection and is altered in aMCI patients, offering a potential candidate mechanism for memory decline in aMCI.

Structural correlates of the audiological and emotional components of chronic tinnitus

The objective is to investigate white matter tracts, more specifically the arcuate fasciculus and acoustic radiation, in tinnitus and assess their relationship with distress, loudness and hearing loss. DTI images were acquired for 58 tinnitus patients and 65 control subjects. Deterministic tractography was first performed to visualize the arcuate fasciculus and acoustic radiation tracts bilaterally and to calculate tract density, fractional anisotropy, radial diffusivity, and axial diffusivity for tinnitus and control subjects. Tinnitus patients had a significantly reduced tract density compared to controls in both tracts of interest. They also exhibited increased axial diffusivity in the left acoustic radiation, as well as increased radial diffusivity in the left arcuate fasciculus, and both the left and right acoustic radiation. Furthermore, they exhibited decreased fractional anisotropy in the left arcuate fasciculus, as well as the left and right acoustic radiation tracts. Partial correlation analysis showed: (1) a negative correlation between arcuate fasciculus tract density and tinnitus distress, (2) a negative correlation between acoustic radiation tract density and hearing loss, (3) a negative correlation between acoustic radiation tract density and loudness, (4) a positive correlation between left arcuate fasciculus and tinnitus distress for radial diffusivity, (5) a negative correlation between left arcuate fasciculus and tinnitus distress for fractional anisotropy, (6) a positive correlation between left and right acoustic radiation and hearing loss for radial diffusivity, (7) No correlation between any of the white matter characteristics and tinnitus loudness. Structural alterations in the acoustic radiation and arcuate fasciculus correlate with hearing loss and distress in tinnitus but not tinnitus loudness showing that loudness is a more functional correlate of the disorder which does not manifest structurally.

Chronic pain as a brain imbalance between pain input and pain suppression

Chronic pain is pain that persists beyond the expected period of healing. The subjective experience of chronic pain results from pathological brain network interactions, rather than from persisting physiological sensory input of nociceptors. We hypothesize that pain is an imbalance between pain evoking dorsal anterior cingulate cortex and somatosensory cortex and pain suppression (i.e. pregenual anterior cingulate cortex). This imbalance can be measured objectively by current density ratios between pain input and pain inhibition. A balance between areas involved in pain input and pain suppression requires communication, which can be objectively identified by connectivity measures, both functional and effective connectivity. In patients with chronic neuropathic pain, electroencephalography is performed with source localization demonstrating that pain is reflected by an abnormal ratio between the dorsal anterior cingulate cortex, somatosensory cortex and pregenual anterior cingulate cortex. Functional connectivity demonstrates decreased communication between these areas, and effective connectivity puts the culprit at the dorsal anterior cingulate cortex, suggesting that the problem is related to abnormal behavioral relevance attached to the pain. In conclusion, chronic pain can be considered as an imbalance between pain input and pain suppression.

The BDNF Val66Met polymorphism regulates vulnerability to chronic stress and phantom perception

Auditory phantom percepts, such as tinnitus, are a heterogeneous condition with great interindividual variations regarding both the percept itself and its concomitants. Tinnitus causes a considerable amount of distress, with as many as 25% of affected people reporting that it interferes with their daily lives. Although previous research gives an idea about the neural correlates of tinnitus-related distress, it cannot explain why some tinnitus patients develop distress and while others are not bothered by their tinnitus. BDNF Val⁶⁶Met polymorphism (rs6265) is a known risk factor for affective disorders due to its common frequency and established functionality. To elucidate, we explore the neural activation pattern of tinnitus associated with the BDNF Val⁶⁶Met polymorphism using electrophysiological data to assess activity and connectivity changes. A total of 110 participants (55 tinnitus and 55 matched control subjects) were included. In this study, we validate that the BDNF Val⁶⁶Met polymorphism plays an important role in the susceptibility to the clinical manifestation of tinnitus-related distress. We demonstrate that Val/Met carriers have increased alpha power in the subgenual anterior cingulate cortex that correlates with distress levels. Furthermore, distress mediates the relationship between BDNF Val⁶⁶Met polymorphism and tinnitus loudness. In other words, for Val/Met carriers, the subgenual anterior cingulate cortex sends distress-related information to the parahippocampus, which likely integrates the loudness and distress of the tinnitus percept.

Identification of selection and inhibition components in a Go/NoGo task from EEG spectra using a machine learning classifier

INTRODUCTION

Prior Go/NoGo studies have localized specific regions and EEG spectra for which traditional approaches have distinguished between Go and NoGo conditions. A more detailed characterization of the spatial distribution and timing of the synchronization of frequency bands would contribute substantially to the clarification of neural mechanisms that underlie performance of the Go/NoGo task.

METHODS

The present study used a machine learning approach to learn the features that distinguish between ERSPs involved in selection and inhibition in a Go/NoGo task. A single-layer neural network classifier was used to predict task conditions for each subject to characterize ERSPs associated with Go versus NoGo trials.

RESULTS

The final classifier accurately identified individual task conditions at an overall rate of 92%, estimated by fivefold cross-validation. The detailed accounting of EEG time-frequency patterns localized to brain regions (i.e., thalamus, pre-SMA, orbitofrontal cortex, and superior parietal cortex) corroborates and also elaborates upon previous findings from fMRI and EEG studies, and expands the information about EEG power changes in multiple frequency bands (i.e., primarily theta power increase, alpha decreases, and beta increases and decreases) within these regions underlying the selection and inhibition processes engaged in the Go and NoGo trials.

CONCLUSION

This time-frequency-based classifier extends previous spatiotemporal findings and provides information about neural mechanisms underlying selection and inhibition processes engaged in Go and NoGo trials, respectively. This neural network classifier can be used to assess time-frequency patterns from an individual subject and thus may offer insight into therapeutic uses of neuromodulation in neural dysfunction.

Associations between Hypertension, Treatment, and Cognitive Function in the Irish Longitudinal Study on Ageing

Epidemiological studies have produced conflicting results regarding the associations between the use of different hypertensive drugs and cognition. Data from the Irish Longitudinal Study on Ageing (TILDA), a nationwide prospective longitudinal study of adults aged 50 or more years, was used to explore the associations between hypertensive status, categories of antihypertensive and cognitive function controlling for age, education, and other demographic and lifestyle factors. The study sample included 8173 participants. ANCOVAs and multivariate regressions were used to assess the cross-sectional and longitudinal associations between cognitive function and hypertension status and the different categories of hypertensive medication. Hypertension was not associated with decline in global cognitive and executive functions and were fully explained by age and education. Different hypertensive medications were not associated with cognitive function. Consistent with previous studies, changes in cognition can largely be explained by age and education. The use of antihypertensive medications is neither harmful nor protective for cognition.

The peripheral effect of direct current stimulation on brain circuits involving memory

An ongoing debate surrounding transcranial direct current stimulation (tDCS) of the scalp is whether it modulates brain activity both directly and in a regionally constrained manner enough to positively affect symptoms in patients with neurological disorders. One alternative explanation is that direct current stimulation affects neural circuits mainly indirectly, i.e., via peripheral nerves. Here, we report that noninvasive direct current stimulation indirectly affects neural circuits via peripheral nerves. In a series of studies, we show that direct current stimulation can cause activation of the greater occipital nerve (ON-tDCS) and augments memory via the ascending fibers of the occipital nerve to the locus coeruleus, promoting noradrenaline release. This noradrenergic pathway plays a key role in driving hippocampal activity by modifying functional connectivity supporting the consolidation of a memory event.

Paradoxical relationship between distress and functional network topology in phantom sound perception

Distress is a domain-general symptom that accompanies several disorders, including tinnitus. Based on previous studies, we know that distress is encoded by changes in functional connectivity between cortical and subcortical regions. However, how distress relates to large-scale brain networks is not yet clear. In the current study, we investigate the relationship between distress and the efficiency of a network by examining its topological properties using resting state fMRI collected from 90 chronic tinnitus patients. The present results indicate that distress negatively correlates with path length and positively correlates with clustering coefficient, small-worldness, and efficiency of information transfer. Specifically, path analysis showed that the relationship between distress and efficiency is significantly mediated by the resilience of the feeder connections and the centrality of the rich-club connections. In other words, the higher the network efficiency, the lower the resilience of the feeder connections and the centrality of the rich-club connections, which in turn reflects in higher distress in tinnitus patients. This indicates a reorganization of the network towards a paradoxically more efficient topology in patients with high distress, potentially explaining their increased rumination on the tinnitus percept itself.

Bimodal neuromodulation combining sound and tongue stimulation reduces tinnitus symptoms in a large randomized clinical study

Tinnitus is a phantom auditory perception coded in the brain that can be bothersome or debilitating, affecting 10 to 15% of the population. Currently, there is no clinically recommended drug or device treatment for this major health condition. Animal research has revealed that sound paired with electrical somatosensory stimulation can drive extensive plasticity within the brain for tinnitus treatment. To investigate this bimodal neuromodulation approach in humans, we evaluated a noninvasive device that delivers sound to the ears and electrical stimulation to the tongue in a randomized, double-blinded, exploratory study that enrolled 326 adults with chronic subjective tinnitus. Participants were randomized into three parallel arms with different stimulation settings. Clinical outcomes were evaluated over a 12-week treatment period and a 12-month posttreatment phase. For the primary endpoints, participants achieved a statistically significant reduction in tinnitus symptom severity at the end of treatment based on two commonly used outcome measures, Tinnitus Handicap Inventory (Cohen’s d effect size: −0.87 to −0.92 across arms; P < 0.001) and Tinnitus Functional Index (−0.77 to −0.87; P < 0.001). Therapeutic improvements continued for 12 months after treatment for specific bimodal stimulation settings, which had not previously been demonstrated in a large cohort for a tinnitus intervention. The treatment also achieved high compliance and satisfaction rates with no treatment-related serious adverse events. These positive therapeutic and long-term results motivate further clinical trials toward establishing bimodal neuromodulation as a clinically recommended device treatment for tinnitus.