Caudate infarcts and hemorrhages

Cerebellum drives functional dysfunctions in restless leg syndrome

OBJECTIVE

Restless legs syndrome (RLS) has serious effects on patients' sleep quality, physical and mental health. However, the pathophysiological mechanisms of RLS remain unclear. This study utilized both static and dynamic functional activity and connectivity analyses approaches as well as effective connectivity analysis to reveal the neurophysiological basis of RLS.

METHODS

The resting-state functional MRI (rs-fMRI) data from 32 patients with RLS and 33 age-, and gender-matched healthy control (HC) were collected. Dynamic and static amplitude of low frequency fluctuation (ALFF), functional connectivity (FC), and Granger causality analysis (GCA) were employed to reveal the abnormal functional activities and couplings in patients with RLS.

RESULTS

RLS patients showed over-activities in left parahippocampus and right cerebellum, hyper-connectivities of right cerebellum with left basal ganglia, left postcentral gyrus and right precentral gyrus, and enhanced effective connectivity from right cerebellum to left postcentral gyrus compared to HC.

CONCLUSIONS

Abnormal cerebellum-basal ganglia-sensorimotor cortex circuit may be the underlying neuropathological basis of RLS. Our findings highlight the important role of right cerebellum in the onset of RLS and suggest right cerebellum may be a potential target for precision therapy.

Connectomic insight into unique stroke patient recovery after rTMS treatment

An improved understanding of the neuroplastic potential of the brain has allowed advancements in neuromodulatory treatments for acute stroke patients. However, there remains a poor understanding of individual differences in treatment-induced recovery. Individualized information on connectivity disturbances may help predict differences in treatment response and recovery phenotypes. We studied the medical data of 22 ischemic stroke patients who received MRI scans and started repetitive transcranial magnetic stimulation (rTMS) treatment on the same day. The functional and motor outcomes were assessed at admission day, 1 day after treatment, 30 days after treatment, and 90 days after treatment using four validated standardized stroke outcome scales. Each patient underwent detailed baseline connectivity analyses to identify structural and functional connectivity disturbances. An unsupervised machine learning (ML) agglomerative hierarchical clustering method was utilized to group patients according to outcomes at four-time points to identify individual phenotypes in recovery trajectory. Differences in connectivity features were examined between individual clusters. Patients were a median age of 64, 50% female, and had a median hospital length of stay of 9.5 days. A significant improvement between all time points was demonstrated post treatment in three of four validated stroke scales utilized. ML-based analyses identified distinct clusters representing unique patient trajectories for each scale. Quantitative differences were found to exist in structural and functional connectivity analyses of the motor network and subcortical structures between individual clusters which could explain these unique trajectories on the Barthel Index (BI) scale but not on other stroke scales. This study demonstrates for the first time the feasibility of using individualized connectivity analyses in differentiating unique phenotypes in rTMS treatment responses and recovery. This personalized connectomic approach may be utilized in the future to better understand patient recovery trajectories with neuromodulatory treatment.

Dynamics of phase oscillator networks with synaptic weight and structural plasticity

We study the dynamics of Kuramoto oscillator networks with two distinct adaptation processes, one varying the coupling strengths and the other altering the network structure. Such systems model certain networks of oscillatory neurons where the neuronal dynamics, synaptic weights, and network structure interact with and shape each other. We model synaptic weight adaptation with spike-timing-dependent plasticity (STDP) that runs on a longer time scale than neuronal spiking. Structural changes that include addition and elimination of contacts occur at yet a longer time scale than the weight adaptations. First, we study the steady-state dynamics of Kuramoto networks that are bistable and can settle in synchronized or desynchronized states. To compare the impact of adding structural plasticity, we contrast the network with only STDP to one with a combination of STDP and structural plasticity. We show that the inclusion of structural plasticity optimizes the synchronized state of a network by allowing for synchronization with fewer links than a network with STDP alone. With non-identical units in the network, the addition of structural plasticity leads to the emergence of correlations between the oscillators' natural frequencies and node degrees. In the desynchronized regime, the structural plasticity decreases the number of contacts, leading to a sparse network. In this way, adding structural plasticity strengthens both synchronized and desynchronized states of a network. Second, we use desynchronizing coordinated reset stimulation and synchronizing periodic stimulation to induce desynchronized and synchronized states, respectively. Our findings indicate that a network with a combination of STDP and structural plasticity may require stronger and longer stimulation to switch between the states than a network with STDP only.

Transcranial electric and acoustic stimulation for tinnitus: study protocol for a randomized double-blind controlled trial assessing the influence of combined transcranial random noise and acoustic stimulation on tinnitus loudness and distress

Background

Tinnitus is the result of aberrant neuronal activity. As a novel treatment form, neuromodulation is used to modify neuronal activity of brain areas involved in tinnitus generation. Among the different forms of electric stimulation, transcranial random noise stimulation (tRNS) has been shown to be a promising treatment option for tinnitus. In addition, recent studies indicate that the reduction in tinnitus can be more pronounced when different modalities of stimulation techniques are combined (“bimodal stimulation”). TRNS can be used in combination with acoustic stimulation (AS), a further treatment option recognized in the literature. The aim of the proposed study is to investigate whether simultaneous tRNS and AS improve levels of tinnitus loudness and distress.

Methods

The intervention consists of bilateral high-definition tRNS (HD-tRNS) over the auditory cortex combined with the application of AS which is studied in a crossover design. The visits will be performed in 26 sessions. There will be 20 treatment sessions, divided into two blocks: active and sham HD-tRNS. Within the blocks, the interventions are divided into group A: HD-tRNS and AS, and group B: HD-tRNS alone. Furthermore, in addition to the assessments directly following the intervention sessions, there will be six extra sessions performed subsequently at the end of each block, after a period of some days (follow-ups 1 and 2) and a month after the last intervention (C). Primary outcome measures are analog scales for evaluation of subjective tinnitus loudness and distress, and the audiological measurement of minimum masking level (MML). Secondary outcome measures are brain activity as measured by electroencephalography and standardized questionnaires for evaluating tinnitus distress and severity.

Discussion

To the best of our knowledge, this is the first study which uses HD-tRNS combined with AS for tinnitus treatment. The crossover design permits the comparison between HD-tRNS active vs. sham and with vs. without AS. Thus, it will be possible to evaluate the efficacy of the combined approach to HD-tRNS alone. In addition, the use of different objective and subjective evaluations for tinnitus enable more reliable and valid results.

Trial registration

Swiss Ethics Committee (BASEC-Nr. 2020-02027); Swiss Federal Complementary Database (kofam.ch: SNCTP000004051); and ClinicalTrials.gov (clinicaltrials.gov: NCT04551404).

Stroke-related restless legs syndrome: Clinical and anatomo-functional characterization of an emerging entity

BACKGROUND AND PURPOSE

Stroke-related restless legs syndrome (sRLS) secondary to ischemic lesions is an emerging entity and an interesting condition, but there are limited available data to help us further understand its underlying pathways. In this study, we characterized sRLS clinically, neuroanatomically and functionally.

METHODS

Consecutive patients hospitalized in the Stroke Unit of the University Hospital of Strasbourg were assessed clinically and electrophysiologically for sRLS characteristics. They underwent brain magnetic resonance imaging for the neuroanatomical study of involved structures, and received functional evaluations with ¹⁸ F-FDG (2-deoxy-2-[fluorine-18]fluoro-D-glucose) positron emission tomography (PET) for glucose consumption, ¹²³ I-FP-CIT ([123]I-2beta-carbometoxy-3beta-[4-iodophenyl]-N-[3-fluoropropyl]nortropane) single-photon emission computed tomography for dopamine reuptake and PET with ¹⁸ F-FDOPA ((3,4-dihydroxy-6-[18]F-fluoro-l-phenylalanine) for presynaptic dopaminergic synthesis.

RESULTS

Sixteen patients with sRLS, eight women and eight men, aged 41-81 years, were included. The clinical characteristics of sRLS and idiopathic RLS were similar. Most patients presented with bilateral and symmetric de novo RLS. Eight patients had infarction in the lenticulostriate area (middle cerebral artery and internal carotid arteria). The body of the caudate nucleus was most commonly affected. Seven patients had sRLS secondary to ventral brainstem infarction (perforating branches of the basilar arteria) affecting the pons in six patients and the medulla oblongata in one patient. Both the corticospinal tract and the cortico-pontocerebellar fibres were lesioned in all patients with brainstem stroke. One patient had infarction in the left posterior cerebellar vermis and occipital area (posterior cerebral artery and superior cerebellar artery). Isotopic explorations showed a significantly increased dopaminergic tone in the striatum ipsilateral to lenticulostriate infarction. Dopamine fixation was normal in patients with stroke outside of the lenticulostriate area.

CONCLUSIONS

Clinicians should be aware of the characteristics of sRLS for the appropriate diagnosis and treatment of this condition.

Bimodal Auditory Electrical Stimulation for the Treatment of Tinnitus: Preclinical and Clinical Studies

Tinnitus, or the phantom perception of sound, arises from pathological neural activity. Neurophysiological research has shown increased spontaneous firing rates and synchronization along the auditory pathway correlate strongly with behavioral measures of tinnitus. Auditory neurons are plastic, enabling external stimuli to be utilized to elicit long-term changes to spontaneous firing and synchrony. Pathological plasticity can thus be reversed using bimodal auditory plus nonauditory stimulation to reduce tinnitus. This chapter discusses preclinical and clinical evidence for efficacy of bimodal stimulation treatments of tinnitus, with highlights on sham-controlled, double-blinded clinical trials. The results from these studies have shown some efficacy in reducing the severity of tinnitus, based on subjective and objective outcome measures including tinnitus questionnaires and psychophysical tinnitus measurements. While results of some studies have been positive, the degree of benefit and the populations that respond to treatment vary across the studies. Directions and implications of future studies are discussed.

The state of the art of sound therapy for subjective tinnitus in adults

Background:

Sound therapy is a clinically common method of tinnitus management. Various forms of sound therapy have been developed, but there are controversies regarding the selection criteria and the efficacy of different forms of sound therapy in the clinic. Our goal was to review the types and forms of sound therapy and our understanding of how the different characteristics of tinnitus patients influence their curative effects so as to provide a reference for personalized choice of tinnitus sound therapy.

Method:

Using an established methodological framework, a search of six databases including PubMed identified 43 records that met our inclusion criteria. The search strategy used the following key words: tinnitus AND (acoustic OR sound OR music) AND (treatment OR therapy OR management OR intervention OR measure).

Results:

There are various forms of sound therapy, and most of them show positive therapeutic effects. The effect of customized sound therapy is generally better than that of non-customized sound therapy, and patients with more severe initial tinnitus respond better to sound therapy.

Conclusion:

Sound therapy can effectively suppress tinnitus, at least in some patients. However, there is a lack of randomized controlled trials to identify effective management strategies. Further studies are needed to identify the most effective form of sound therapy for individualized therapy, and large, multicenter, long-term follow-up studies are still needed in order to develop more effective and targeted sound-therapy protocols. In addition, it is necessary to analyze the characteristics of individual tinnitus patients and to unify the assessment criteria of tinnitus.

Comparing Glioblastoma Surgery Decisions Between Teams Using Brain Maps of Tumor Locations, Biopsies, and Resections

Purpose

The aim of glioblastoma surgery is to maximize the extent of resection while preserving functional integrity, which depends on the location within the brain. A standard to compare these decisions is lacking. We present a volumetric voxel-wise method for direct comparison between two multidisciplinary teams of glioblastoma surgery decisions throughout the brain.

Methods

Adults undergoing first-time glioblastoma surgery from 2012 to 2013 performed by two neuro-oncologic teams were included. Patients had had a diagnostic biopsy or resection. Preoperative tumors and postoperative residues were segmented on magnetic resonance imaging in three dimensions and registered to standard brain space. Voxel-wise probability maps of tumor location, biopsy, and resection were constructed for each team to compare patient referral bias, indication variation, and treatment variation. To evaluate the quality of care, subgroups of differentially resected brain regions were analyzed for survival and functional outcome.

Results

One team included 101 patients, and the other included 174; 91 tumors were biopsied, and 181 were resected. Patient characteristics were largely comparable between teams. Distributions of tumor locations were dissimilar, suggesting referral bias. Distributions of biopsies were similar, suggesting absence of indication variation. Differentially resected regions were identified in the anterior limb of the right internal capsule and the right caudate nucleus, indicating treatment variation. Patients with (n = 12) and without (n = 6) surgical removal in these regions had similar overall survival and similar permanent neurologic deficits.

Conclusion

Probability maps of tumor location, biopsy, and resection provide additional information that can inform surgical decision making across multidisciplinary teams for patients with glioblastoma.

Sense and Sensibility: A Review of the Behavioral Neuroscience of Tinnitus Sound Therapy and a New Typology

Tinnitus Sound Therapy is not a single strategy. It consists of many different sound types, targeting many different mechanisms. Therapies that use sound to cover, reduce attention to, or facilitate habituation of tinnitus are among the most common tinnitus treatment paradigms. Recent history has seen a proliferation of sound therapies, but they have each been criticized for having limited empirical support. In this review, Sound Therapy's modern history will be described, and a typology will be introduced and discussed in light of current behavioral neuroscience research. It will be argued that contributing factors to the limited evidence for the efficacy of Sound Therapy are its diversity, plural modes of action, and absence of a clear typology. Despite gaps in understanding the efficacy of sound's effects on tinnitus, there is compelling evidence for its multiple, but related, neurophysiological mechanisms. Evidence suggests that sound may reduce tinnitus through its presence, context, reaction, and potentially adaptation. This review provides insights into the neurocognitive basis of these tinnitus Sound Therapy modes. It concludes that a unifying classification is needed to secure and advance arguments in favor of Sound Therapy.

Locomotion and eating behavior changes in Yucatan minipigs after unilateral radio-induced ablation of the caudate nucleus

The functional roles of the Caudate nucleus (Cd) are well known. Selective Cd lesions can be found in neurological disorders. However, little is known about the dynamics of the behavioral changes during progressive Cd ablation. Current stereotactic radiosurgery technologies allow the progressive ablation of a brain region with limited adverse effects in surrounding normal tissues. This could be of high interest for the study of the modified behavioral functions in relation with the degree of impairment of the brain structures. Using hypofractionated stereotactic radiotherapy combined with synchrotron microbeam radiation, we investigated, during one year after irradiation, the effects of unilateral radio-ablation of the right Cd on the behavior of Yucatan minipigs. The right Cd was irradiated to a minimal dose of 35.5 Gy delivered in three fractions. MRI-based morphological brain integrity and behavioral functions, i.e. locomotion, motivation/hedonism were assessed. We detected a progressive radio-necrosis leading to a quasi-total ablation one year after irradiation, with an additional alteration of surrounding areas. Transitory changes in the motivation/hedonism were firstly detected, then on locomotion, suggesting the influence of different compensatory mechanisms depending on the functions related to Cd and possibly some surrounding areas. We concluded that early behavioral changes related to eating functions are relevant markers for the early detection of ongoing lesions occurring in Cd-related neurological disorders.

Acoustic coordinated reset therapy for tinnitus with perceptually relevant frequency spacing and levels

Acoustic coordinated reset (CR) therapy based on neuromodulation and neuroplasticity principles has been proposed for the treatment of tonal tinnitus. The original therapy involved periodic delivery of randomly ordered sequences of four low-level tones centered around the frequency of a tone that matched the tinnitus pitch, f_T, with fixed ratios relative to f_T and delivered several hours/day over several weeks. Here we transform the original CR tone selection method to a more perceptually-relevant equivalent rectangular bandwidth (ERB) frequency scale, the ERB_N-number scale. Specifically, we provide a mathematical model that enables calculation of CR tones that accounts for f_T- and hearing loss-related ERB widening and ERB overlaps and gaps of CR tone alignments. Further, the model ensures symmetric CR tone alignments based on modelling studies that indicate the effect is optimal if the CR stimuli are symmetrically spaced relative to the tinnitus-related population of abnormally synchronized cortical neurons to activate the adjacent sub-populations. We also present experimentally testable ERB-based CR tone alignment strategies and explain how to use the ERB-based model in experiments, clinical studies, other types of tinnitus sound treatment such as tailor-made notch music training and limitations of our approach.

Detection and characterization of small infarcts in the caudate nucleus on 7 Tesla MRI: The SMART-MR study

Small infarcts are among the key imaging features of cerebral small vessel disease (CSVD), but remain largely undetected on conventional MRI. We aimed to evaluate (1) imaging criteria for the detection of small infarcts in the caudate nucleus on 7T MRI, (2) intra- and inter-rater agreement, (3) frequency and (4) detection rate on 7T versus 1.5T MRI. In 90 patients (68 ± 8 years) with a history of vascular disease from the SMART-MR study, we defined 7T imaging criteria for cavitated and non-cavitated small infarcts in the caudate nucleus. In a separate set of 23 patients from the SMART study, intra-rater and inter-rater agreement was excellent for presence, number, and individual locations (Kappa's, ICCs, and Dice similarity coefficients ranged from 0.85 to 1.00). In the 90 patients, 21 infarcts (20 cavitated) in 12 patients were detected on 7T (13%) compared to 7 infarcts in 6 patients on 1.5T (7%). In conclusion, we established reproducible imaging criteria for the detection of small infarcts in the caudate nucleus on 7T MRI and showed that 7T MRI allows for a higher detection rate than conventional 1.5T MRI. These imaging criteria can be used in future studies to provide new insights into the pathophysiology of CSVD.

Delay-Induced Multistability and Loop Formation in Neuronal Networks with Spike-Timing-Dependent Plasticity

Spike-timing-dependent plasticity (STDP) adjusts synaptic strengths according to the precise timing of pre- and postsynaptic spike pairs. Theoretical and computational studies have revealed that STDP may contribute to the emergence of a variety of structural and dynamical states in plastic neuronal populations. In this manuscript, we show that by incorporating dendritic and axonal propagation delays in recurrent networks of oscillatory neurons, the asymptotic connectivity displays multistability, where different structures emerge depending on the initial distribution of the synaptic strengths. In particular, we show that the standard deviation of the initial distribution of synaptic weights, besides its mean, determines the main properties of the emergent structural connectivity such as the mean final synaptic weight, the number of two-neuron loops and the symmetry of the final structure. We also show that the firing rates of the neurons affect the evolution of the network, and a more symmetric configuration of the synapses emerges at higher firing rates. We justify the network results based on a two-neuron framework and show how the results translate to large recurrent networks.

Bilateral caudate nucleus infarcts: A case report of a rare complication following endoscopic resection of a tuberculum sellae meningioma

Background:

We present a rare complication of bilateral caudate infarcts and necrosed nasoseptal flaps after endoscopic transsphenoidal resection of tuberculum sellae meningioma. This case highlights the importance of early and accurate diagnosis and treatment of a postoperative cerebrospinal fluid (CSF) leak and associated bacterial meningitis, and reviews any existing guidelines regarding its management.

Case Description:

A 54-year-old otherwise healthy man presented with progressive bitemporal hemianopsia. Magnetic resonance imaging of the head revealed a large, homogeneously enhancing sellar and suprasellar mass consistent with a meningioma. An endoscopic endonasal transsphenoidal approach was performed to resect the tuberculum sellae meningioma. The patient developed basal bacterial meningitis secondary to a CSF leak, requiring repair on two separate occasions. At the time of both repairs, there was evidence of necrosis of the nasoseptal flaps used for the repairs. Soon after the diagnosis of meningitis, the patient developed bilateral caudate infarcts.

Conclusion:

This report discusses the possible underlying etiologies for the bilateral caudate infarcts and necrosed flaps including bacterial meningitis with associated local vasospasm of nearby vessels resulting in infarction. This case emphasizes the importance of concise management of postendoscopic CSF leak and discusses the guidelines regarding antimicrobial therapy and the management of lumbar drains.

Advances in closed-loop deep brain stimulation devices

BACKGROUND

Millions of patients around the world are affected by neurological and psychiatric disorders. Deep brain stimulation (DBS) is a device-based therapy that could have fewer side-effects and higher efficiencies in drug-resistant patients compared to other therapeutic options such as pharmacological approaches. Thus far, several efforts have been made to incorporate a feedback loop into DBS devices to make them operate in a closed-loop manner.

METHODS

This paper presents a comprehensive investigation into the existing research-based and commercial closed-loop DBS devices. It describes a brief history of closed-loop DBS techniques, biomarkers and algorithms used for closing the feedback loop, components of the current research-based and commercial closed-loop DBS devices, and advancements and challenges in this field of research. This review also includes a comparison of the closed-loop DBS devices and provides the future directions of this area of research.

RESULTS

Although we are in the early stages of the closed-loop DBS approach, there have been fruitful efforts in design and development of closed-loop DBS devices. To date, only one commercial closed-loop DBS device has been manufactured. However, this system does not have an intelligent and patient dependent control algorithm. A closed-loop DBS device requires a control algorithm to learn and optimize the stimulation parameters according to the brain clinical state.

CONCLUSIONS

The promising clinical effects of open-loop DBS have been demonstrated, indicating DBS as a pioneer technology and treatment option to serve neurological patients. However, like other commercial devices, DBS needs to be automated and modernized.

Research of cerebral activation in Uygur-speaking and Chinese-speaking participants during verb generation task with functional magnetic resonance imaging

The aims are to investigate and compare the activated cerebral regions of Uygur-speaking and Chinese-speaking participants during verb generation task.A total of 31 cases of Uygur and 28 cases of Han healthy volunteers were enrolled. They were requested to take verb generation tasks. Blood oxygenation level-dependent functional magnetic resonance imaging (BOLD-fMRI) was performed. The fMRI images were collected and activated brain regions were analyzed.In Chinese-speaking participants, the main activated cerebral regions were as follows: the left caudate nucleus, the left occipital gyrus, the left fusiform gyrus, bilateral supplementary motor area (BA8/ 6), the left BA32, left precuneus, the left superior parietal lobule, the left inferior parietal lobule (BA7), the left angular gyrus, the right side of the central gyrus (BA9), the left inferior frontal gyrus triangular section, the right pars opercularis gyri frontalis inferiorista, and bilateral cerebellum. In Uygur-speaking subjects, the main activated cerebral regions included left precentral gyrus (BA9 region), inferior frontal gyrus of left opercular part, inferior frontal gyrus of left triangle part, and left cerebellum. Left caudate nucleus, left orbital frontal gyrus, right caudate nucleus, and bilateral anterior cingulate gyrus (BA32 region) of Chinese group were significantly activated compared with Uygur group. By contrast, Uygur group showed no region that was more activated than Chinese group.The present study demonstrates that activated brain regions in verb generation tasks are different between Uygur and Chinese languages. Processing of Uygur characters is mainly in the left hemisphere of the brain, while the processing of Chinese characters needs more participation by the right hemisphere of the brain.

Closed-loop deep brain stimulation by pulsatile delayed feedback with increased gap between pulse phases

Computationally it was shown that desynchronizing delayed feedback stimulation methods are effective closed-loop techniques for the control of synchronization in ensembles of interacting oscillators. We here computationally design stimulation signals for electrical stimulation of neuronal tissue that preserve the desynchronizing delayed feedback characteristics and comply with mandatory charge deposit-related safety requirements. For this, the amplitude of the high-frequency (HF) train of biphasic charge-balanced pulses used by the standard HF deep brain stimulation (DBS) is modulated by the smooth feedback signals. In this way we combine the desynchronizing delayed feedback approach with the HF DBS technique. We show that such a pulsatile delayed feedback stimulation can effectively and robustly desynchronize a network of model neurons comprising subthalamic nucleus and globus pallidus external and suggest this approach for desynchronizing closed-loop DBS. Intriguingly, an interphase gap introduced between the recharging phases of the charge-balanced biphasic pulses can significantly improve the stimulation-induced desynchronization and reduce the amount of the administered stimulation. In view of the recent experimental and clinical studies indicating a superiority of the closed-loop DBS to open-loop HF DBS, our results may contribute to a further development of effective stimulation methods for the treatment of neurological disorders characterized by abnormal neuronal synchronization.

Dendritic and Axonal Propagation Delays Determine Emergent Structures of Neuronal Networks with Plastic Synapses

Spike-timing-dependent plasticity (STDP) modifies synaptic strengths based on the relative timing of pre- and postsynaptic spikes. The temporal order of spikes turned out to be crucial. We here take into account how propagation delays, composed of dendritic and axonal delay times, may affect the temporal order of spikes. In a minimal setting, characterized by neglecting dendritic and axonal propagation delays, STDP eliminates bidirectional connections between two coupled neurons and turns them into unidirectional connections. In this paper, however, we show that depending on the dendritic and axonal propagation delays, the temporal order of spikes at the synapses can be different from those in the cell bodies and, consequently, qualitatively different connectivity patterns emerge. In particular, we show that for a system of two coupled oscillatory neurons, bidirectional synapses can be preserved and potentiated. Intriguingly, this finding also translates to large networks of type-II phase oscillators and, hence, crucially impacts on the overall hierarchical connectivity patterns of oscillatory neuronal networks.

Noise-enhanced coupling between two oscillators with long-term plasticity

Spike timing-dependent plasticity is a fundamental adaptation mechanism of the nervous system. It induces structural changes of synaptic connectivity by regulation of coupling strengths between individual cells depending on their spiking behavior. As a biophysical process its functioning is constantly subjected to natural fluctuations. We study theoretically the influence of noise on a microscopic level by considering only two coupled neurons. Adopting a phase description for the neurons we derive a two-dimensional system which describes the averaged dynamics of the coupling strengths. We show that a multistability of several coupling configurations is possible, where some configurations are not found in systems without noise. Intriguingly, it is possible that a strong bidirectional coupling, which is not present in the noise-free situation, can be stabilized by the noise. This means that increased noise, which is normally expected to desynchronize the neurons, can be the reason for an antagonistic response of the system, which organizes itself into a state of stronger coupling and counteracts the impact of noise. This mechanism, as well as a high potential for multistability, is also demonstrated numerically for a coupled pair of Hodgkin-Huxley neurons.

Maladaptive plasticity in tinnitus--triggers, mechanisms and treatment

Tinnitus is a phantom auditory sensation that reduces quality of life for millions of people worldwide, and for which there is no medical cure. Most cases of tinnitus are associated with hearing loss caused by ageing or noise exposure. Exposure to loud recreational sound is common among the young, and this group are at increasing risk of developing tinnitus. Head or neck injuries can also trigger the development of tinnitus, as altered somatosensory input can affect auditory pathways and lead to tinnitus or modulate its intensity. Emotional and attentional state could be involved in the development and maintenance of tinnitus via top-down mechanisms. Thus, military personnel in combat are particularly at risk owing to combined risk factors (hearing loss, somatosensory system disturbances and emotional stress). Animal model studies have identified tinnitus-associated neural changes that commence at the cochlear nucleus and extend to the auditory cortex and other brain regions. Maladaptive neural plasticity seems to underlie these changes: it results in increased spontaneous firing rates and synchrony among neurons in central auditory structures, possibly generating the phantom percept. This Review highlights the links between animal and human studies, and discusses several therapeutic approaches that have been developed to target the neuroplastic changes underlying tinnitus.

Graph theoretical analysis of brain connectivity in phantom sound perception

Tinnitus is a phantom sound commonly thought of to be produced by the brain related to auditory deafferentation. The current study applies concepts from graph theory to investigate the differences in lagged phase functional connectivity using the average resting state EEG of 311 tinnitus patients and 256 healthy controls. The primary finding of the study was a significant increase in connectivity in beta and gamma oscillations and a significant reduction in connectivity in the lower frequencies for the tinnitus group. There also seems to be parallel processing of long-distance information between delta, theta, alpha1 and gamma frequency bands that is significantly stronger in the tinnitus group. While the network reorganizes into a more regular topology in the low frequency carrier oscillations, development of a more random topology is witnessed in the high frequency oscillations. In summary, tinnitus can be regarded as a maladaptive ‘disconnection’ syndrome, which tries to both stabilize into a regular topology and broadcast the presence of a deafferentation-based bottom-up prediction error as a result of a top-down prediction.

A Systematic Review of Eligibility and Outcomes in Tinnitus Trials

Objective

To analyze existing tinnitus treatment trials with regard to eligibility criteria, outcome measures, study quality, and external validity and to recognize the effect of patient demographics, symptom duration, severity, and otologic comorbidity on research findings to help practitioners apply them to patient encounters.

Data Sources

Systematic literature search conducted by an information specialist for development of the American Academy of Otolaryngology—Head and Neck Surgery Foundation’s tinnitus clinical practice guideline.

Review Methods

Articles were assessed for eligibility with the PRISMA protocol (Preferred Reporting Items for Systematic Reviews and Meta-analyses) and data extracted by 2 independent investigators. Studies were assessed for methodological quality, inclusion and exclusion criteria, patient demographics, and outcome measures.

Results

A total of 147 randomized trials met inclusion criteria. Nearly all studies took place in a specialist setting. More than 50% did not explicitly define tinnitus, and 44% used a subjective severity threshold, such as “severely disturbing.” Fifty-four percent required symptom duration of at least 6 months for study eligibility, and up to 33% excluded patients with “organic” hearing loss or otologic conditions. Mean age was 52.2 years, and median follow-up was 3 months. Only 20% had a low risk of bias.

Conclusion

Randomized trials of tinnitus interventions are most applicable to older adults with tinnitus lasting ≥6 months who are evaluated in specialty settings. High risk of bias, short follow-up, and outcome reporting raise concerns about the validity of findings and may influence how clinicians apply trial results to individual patients and establish treatment expectations, thus demonstrating the need for further quality research in this field.

Regional distribution of synaptic markers and APP correlate with distinct clinicopathological features in sporadic and familial Alzheimer's disease

Recent studies suggest that subcortical structures, including striatum, are vulnerable to amyloid-β accumulation and other neuropathological features in familial Alzheimer's disease due to autosomal dominant mutations. We explored differences between familial and sporadic Alzheimer's disease that might shed light on their respective pathogenic mechanisms. To this end, we analysed 12 brain regions, including neocortical, limbic and subcortical areas, from post-mortem brains of familial Alzheimer's disease (n = 10; age at death: 50.0 ± 8.6 years) with mutations in amyloid precursor protein (APP) or presenilin 1 (PSEN1), sporadic Alzheimer's disease (n = 19; age at death: 84.7 ± 7.8 years), neurologically normal elderly without amyloid-β accumulation (normal ageing; n = 13, age at death: 82.9 ± 10.8 years) and neurologically normal elderly with extensive cortical amyloid-β deposits (pathological ageing; n = 15; age at death: 92.7 ± 5.9 years). The levels of amyloid-β₄₀, amyloid-β₄₂, APP, apolipoprotein E, the synaptic marker PSD95 (now known as DLG4), the astrocyte marker GFAP, other molecules related to amyloid-β metabolism, and tau were determined by enzyme-linked immunosorbent assays. We observed that familial Alzheimer's disease had disproportionate amyloid-β₄₂ accumulation in subcortical areas compared with sporadic Alzheimer's disease, whereas sporadic Alzheimer's disease had disproportionate amyloid-β₄₂ accumulation in cortical areas compared to familial Alzheimer's disease. Compared with normal ageing, the levels of several proteins involved in amyloid-β metabolism were significantly altered in both sporadic and familial Alzheimer's disease; however, such changes were not present in pathological ageing. Among molecules related to amyloid-β metabolism, the regional distribution of PSD95 strongly correlated with the regional pattern of amyloid-β₄₂ accumulation in sporadic Alzheimer's disease and pathological ageing, whereas the regional distribution of APP as well as β-C-terminal fragment of APP were strongly associated with the regional pattern of amyloid-β₄₂ accumulation in familial Alzheimer's disease. Apolipoprotein E and GFAP showed negative regional association with amyloid-β (especially amyloid-β₄₀) accumulation in both sporadic and familial Alzheimer's disease. Familial Alzheimer's disease had greater striatal tau pathology than sporadic Alzheimer's disease. In a retrospective medical record review, atypical signs and symptoms were more frequent in familial Alzheimer's disease compared with sporadic Alzheimer's disease. These results suggest that disproportionate amyloid-β₄₂ accumulation in cortical areas in sporadic Alzheimer's disease may be mediated by synaptic processes, whereas disproportionate amyloid-β₄₂ accumulation in subcortical areas in familial Alzheimer's disease may be driven by APP and its processing. Region-specific amyloid-β₄₂ accumulation might account for differences in the relative amounts of tau pathology and clinical symptoms in familial and sporadic Alzheimer's disease.

Functional roles of the thalamus for language capacities

Early biological concepts of language were predominantly corticocentric, but over the last decades biolinguistic research, equipped with new technical possibilities, has drastically changed this view. To date, connectionist models, conceiving linguistic skills as corticobasal network activities, dominate our understanding of the neural basis of language. However, beyond the notion of an involvement of the thalamus and, in most cases also, the basal ganglia (BG) in linguistic operations, specific functions of the respective depth structures mostly remain rather controversial. In this review, some of these issues shall be discussed, particularly the functional configuration of basal network components and the language specificity of subcortical supporting activity. Arguments will be provided for a primarily cortico-thalamic language network. In this view, the thalamus does not engage in proper linguistic operations, but rather acts as a central monitor for language-specific cortical activities, supported by the BG in both perceptual and productive language execution.