Top-down control of vestibular inputs by the dorsolateral prefrontal cortex

Overlaps of fMRI activation patterns of the anxiety-emotional and the vestibular-sensory networks

Clinical and meta-analytic imaging data suggest a considerable overlap between vestibular-sensory and anxiety-emotional processing networks. We therefore examined functional MRI activation using galvanic vestibular stimulation (GVS) and a fear conditioning paradigm in the same 28 healthy individuals. This study was to proof the effects of both stimulations in the same individual whereas our earlier meta-analytical analysis compared groups of participants who had received only one or the other stimulation. In the actual study we further assessed subjective experience (expectancy ratings, questionnaires) and autonomic arousal (skin conductance response; SCR). Activation patterns during vestibular stimulation confirmed previous findings showing highest fMRI-activation in the parieto-insular vestibular cortex. Fear conditioning activated the anterior insula, secondary somatosensory cortex (S2) and thalamus. A conjunction of fMRI-activation maps for both stimulation paradigms revealed bilateral anterior and posterior insula, dorsolateral prefrontal cortex and S2 as well as cerebellar hemisphere fMRI-activation. Regression analyses showed a high positive association of left anterior insular activation during the fear extinction period with trait anxiety. The vestibular intensity during GVS was positively associated with right ventro-lateral prefrontal cortex (PFC) fMRI-activation. This is compatible with the earlier hypothesized top-down regulation of vestibular perception which involves the PFC beneficial for suppression of unusual vestibular excitation or vertigo related to vestibular disorders.

Phantom earthquake syndrome presenting with chronic dizziness after an earthquake: A case report

RATIONALE

Phantom earthquake syndrome is a rare condition seen in earthquake survivors characterized by false sense of earthquake-like motion (phantom earthquake sensations) with vegetative and motor symptoms, even though there was not any recorded earthquake by available earthquake registry. Here, we report first documented case of phantom earthquake syndrome in Turkey following the Maraş, Turkey 2023 earthquake which had presented with persistent dizziness following earthquake despite 3-month course of betahistine dihydrochloride therapy and was successfully treated with vestibular rehabilitation, lifestyle modifications and vitamin D supplementation.

PATIENT CONCERNS

A 44-year-old female patient was referred to our Family Medicine General Check-Up Clinic with complaints of persistent general weakness, diffuse body aches, and dizziness lasting over the previous 6 months following the Maraş, Turkey 2023 earthquake in spite of 3 months course of medical therapy.

DIAGNOSES

The patient's dizziness was independent of recorded aftershocks and was characterized by sensations of ground movement and earthquake-like vibrations, resulting in functional impairment due to anxiety. Comprehensive physical examination, including neurological, ophthalmological, and otoscopic evaluations, revealed no abnormalities. Laboratory studies indicated marginally elevated LDL cholesterol and triglycerides, along with slightly reduced vitamin D and thyroid-stimulating hormone levels. Cranial and cervical MRI, as well as carotid artery Doppler ultrasonography, yielded normal findings. These findings align with phantom earthquake syndrome.

INTERVENTIONS

Initial management by a neurologist with a 3-month course of betahistine dihydrochloride (2 × 24 mg) did not improve our patient's symptoms. Upon the fact the patient's earthquake experience which the patient mentioned for the first time on further history-taking along with her laboratory and imaging findings, betahistine dihydrochloride was discontinued and a treatment plan which is focusing on symptomatic relief with exercise and vestibular rehabilitation, along with vitamin D supplementation was initiated.

OUTCOMES

After 1 month, the patient's symptoms subsided and her biochemical and hematological parameters were within normal ranges with exercise and vestibular rehabilitation, along with vitamin D supplementation.

LESSONS

This case contributes to diagnose phantom earthquake syndrome as a psychosomatic response to disaster which highlights the significance of further history-taking and non-pharmacological treatments like exercise and vestibular rehabilitation for alleviating symptoms.

rTMS-induced neuroimaging changes measured with structural and functional MRI in autism

Introduction

Autism Spectrum Disorder (ASD) is a complex neurodevelopmental condition characterized by deficits in social communication, repetitive behaviors, and restricted interests. Despite increasing prevalence, effective therapeutic interventions remain limited. Repetitive transcranial magnetic stimulation (rTMS) has emerged as a promising non-invasive neuromodulation technique; however, its neural mechanisms and clinical efficacy in children with ASD require further investigation.

Methods

This study enrolled 14 children diagnosed with ASD to undergo a structured rTMS intervention. Neuroimaging data-including voxel-based morphometry (VBM) and resting-state functional connectivity (FC)-as well as behavioral assessments were collected before and after the intervention to evaluate changes in brain structure, function, and symptomatology.

Results

Post-intervention analyses revealed significant increases in gray matter volume (GMV) in the cerebellar Vermis, Caudate nucleus, and Postcentral gyrus. Additionally, enhanced functional connectivity was observed between the Fusiform gyrus, Temporal cortex, Frontal cortex, and Precuneus. Correlation analyses indicated that these neuroimaging changes were significantly associated with improvements in behavioral scores.

Discussion

These findings suggest that rTMS may exert therapeutic effects in children with ASD by modulating cerebellar development and cognitive control networks. The observed structural and functional brain changes support the potential utility of rTMS as a neuromodulatory intervention for ASD. Further studies with larger cohorts are needed to confirm these preliminary results and elucidate the mechanisms underlying rTMS-induced symptom improvement.

Electrical stimulation of the dorsolateral prefrontal cortex inhibits vestibular signalling in humans: A BOLD fMRI study

BACKGROUND

Low-frequency sinusoidal galvanic vestibular stimulation (sGVS) can induce perceptions of sway and nausea through entraining vestibular afferent firing to the sinusoidal stimulus. As recently shown, concurrent dorsolateral prefrontal cortex (dlPFC) stimulation via transcranial alternating current stimulation (tACS) greatly attenuates these vestibular perceptions.

OBJECTIVE

Given that both vestibular afferents and dlPFC efferents project to the insular cortex, it was reasoned that the insula is the most likely area for the top-down inhibitory interaction to take place.

METHODS

To identify the sites of this interaction, blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) was collected whilst simultaneously delivering sinusoidal electrical stimulation (±2 mA, 0.2 Hz, 60 cycles) to 20 participants. These stimuli were randomly applied as follows: (i) bilateral sGVS alone via the mastoid processes; (ii) tACS of the dlPFC alone at electroencephalogram site F4; and (iii) sGVS and tACS together.

RESULTS

Altered BOLD signal-intensity patterns were identified in the parieto-insular vestibular cortex and thalamus when comparing both sGVS and dlPFC stimulation to concurrent stimulation. Within the brainstem, signal-intensity increased in the inferior olivary nucleus and decreased in the nucleus of the solitary tract during concurrent stimulation, when analysed relative to single stimuli. Because concurrent stimulation elicited different activation patterns in each of these regions compared to the single stimuli, they were considered to be key for the interaction.

CONCLUSION

Given the role each plays in dlPFC and vestibular pathways, the inhibitory function exerted by the dlPFC on vestibular processing likely involves ongoing modulation of one or several of these cortical or subcortical areas.

Dual-Task Effect on Center of Pressure Oscillations and Prefrontal Cortex Activation Between Young and Older Adults

Purpose: This study aimed to investigate the dual-task effect on conventional center of pressure (CoP) outcomes, CoP oscillations, and prefrontal cortex (PFC) activation between young and older adults. Methods: Fourteen healthy older adults (age: 66.25 ± 3.43 years) and another fourteen gender-matched young adults (age: 19.80 ± 0.75 years) participated in this study. Participants completed single-task and dual-task standing trials in a fixed order. The displacement of CoP and PFC activation were recorded using a Force plate and a functional near-infrared spectroscopy system, respectively. Two-way MANOVAs were used to examine the group and task effects. Additionally, the Pearson correlation analyses were used to investigate the relationship between CoP oscillations and PFC activation. Results: Our results showed a worse balance performance, greater CoP oscillations of 0-0.1 (11.03 ± 8.24 vs. 23.20 ± 12.54 cm2) and 0.1-0.5 (13.62 ± 9.30 vs. 30.00 ± 23.12 cm2) Hz in the medial-lateral direction and higher right (dorsomedial: -0.0003 ± 0.021 vs. 0.021 ± 0.021 & ventrolateral: 0.0087 ± 0.047 vs. 0.025 ± 0.045 mol/ml) and left (dorsomedial: 0.0033 ± 0.024 vs. 0.020 ± 0.025 & ventrolateral: 0.0060 ± 0.037 vs. 0.034 ± 0.037 mol/ml) PFC activation in response to a secondary cognitive task in older adults (p < .05). Older adults also showed significant positive correlations between CoP oscillations in the anterior-posterior direction and PFC activation under the single-task standing. Conclusion: These results suggest that older adults presented a loss of postural automaticity contributing to cognitive dysfunction. Moreover, heightened CoP oscillations at 0-0.5 Hz in response to a secondary cognitive task could provide evidence of a loss of automaticity, which might be associated with a greater reliance on the sensory inputs.

Non-additive effects of electrical stimulation of the dorsolateral prefrontal cortex and the vestibular system on muscle sympathetic nerve activity in humans

Sinusoidal galvanic vestibular stimulation (sGVS) induces robust modulation of muscle sympathetic nerve activity (MSNA) alongside perceptions of side-to-side movement, sometimes with an accompanying feeling of nausea. We recently showed that transcranial alternating current stimulation (tACS) of the dorsolateral prefrontal cortex (dlPFC) also modulates MSNA, but does not generate any perceptions. Here, we tested the hypothesis that when the two stimuli are given concurrently, the modulation of MSNA would be additive. MSNA was recorded from 11 awake participants via a tungsten microelectrode inserted percutaneously into the right common peroneal nerve at the fibular head. Sinusoidal stimuli (± 2 mA, 0.08 Hz, 100 cycles) were applied in randomised order as follows: (i) tACS of the dlPFC at electroencephalogram (EEG) site F4 and referenced to the nasion; (ii) bilateral sGVS applied to the vestibular apparatuses via the mastoid processes; and (iii) tACS and sGVS together. Previously obtained data from 12 participants supplemented the data for stimulation protocols (i) and (ii). Cross-correlation analysis revealed that each stimulation protocol caused significant modulation of MSNA (modulation index (paired data): 35.2 ± 19.4% for sGVS; 27.8 ± 15.2% for tACS), but there were no additive effects when tACS and sGVS were delivered concurrently (32.1 ± 18.5%). This implies that the vestibulosympathetic reflexes are attenuated with concurrent dlPFC stimulation. These results suggest that the dlPFC is capable of blocking the processing of vestibular inputs through the brainstem and, hence, the generation of vestibulosympathetic reflexes.

Localization of Vestibular Cortex Using Electrical Cortical Stimulation: A Systematic Literature Review

The vestibular system plays a fundamental role in body orientation, posture control, and spatial and body motion perception, as well as in gaze and eye movements. We aimed to review the current knowledge regarding the location of the cortical and subcortical areas, implicated in the processing of vestibular stimuli. The search was performed in PubMed and Scopus. We focused on studies reporting on vestibular manifestations after electrical cortical stimulation. A total of 16 studies were finally included. Two main types of vestibular responses were elicited, including vertigo and perception of body movement. The latter could be either rotatory or translational. Electrical stimulation of the temporal structures elicited mainly vertigo, while stimulation of the parietal lobe was associated with perceptions of body movement. Stimulation of the occipital lobe produced vertigo with visual manifestations. There was evidence that the vestibular responses became more robust with increasing current intensity. Low-frequency stimulation proved to be more effective than high-frequency in eliciting vestibular responses. Numerous non-vestibular responses were recorded after stimulation of the vestibular cortex, including somatosensory, viscero-sensory, and emotional manifestations. Newer imaging modalities such as functional MRI (fMRI), Positron Emission Tomography (PET), SPECT, and near infra-red spectroscopy (NIRS) can provide useful information regarding localization of the vestibular cortex.