Beatrice P. De Koninck

Introduction Therapeutic interventions for disorders of consciousness lack consistency; evidence supports non-invasive brain stimulation, but few studies assess neuromodulation in acute-to-subacute brain-injured patients. This study aims to validate the feasibility and assess the effect of a multi-session transcranial alternating current stimulation (tACS) intervention in subacute brain-injured patients on recovery of consciousness, related brain oscillations and brain network dynamics. Methods and analyses The study is comprised of two phases: a validation phase (n=12) and a randomised controlled trial (n=138). Both phases will be conducted in medically stable brain-injured adult patients (traumatic brain injury and hypoxic-ischaemic encephalopathy), with a Glasgow Coma Scale score ≤12 after continuous sedation withdrawal. Recruitment will occur at the intensive care unit of a Level 1 Trauma Centre in Montreal, Quebec, Canada. The intervention includes a 20 min 10 Hz tACS at 1 mA intensity or a sham session over parieto-occipital cortical sites, repeated over five consecutive days. The current’s frequency targets alpha brain oscillations (8–13 Hz), known to be associated with consciousness. Resting-state electroencephalogram (EEG) will be recorded four times daily for five consecutive days: pre and post-intervention, at 60 and 120 min post-tACS. Two additional recordings will be included: 24 hours and 1-week post-protocol. Multimodal measures (blood samples, pupillometry, behavioural consciousness assessments (Coma Recovery Scale-revised), actigraphy measures) will be acquired from baseline up to 1 week after the stimulation. EEG signal analysis will focus on the alpha bandwidth (8–13 Hz) using spectral and functional network analyses. Phone assessments at 3, 6 and 12 months post-tACS, will measure long-term functional recovery, quality of life and caregivers’ burden. Ethics and dissemination Ethical approval for this study has been granted by the Research Ethics Board of the CIUSSS du Nord-de-l’Île-de-Montréal (Project ID 2021–2279). The findings of this two-phase study will be submitted for publication in a peer-reviewed academic journal and submitted for presentation at conferences. The trial’s results will be published on a public trial registry database (ClinicalTrials.gov). Trial registration number NCT05833568.

Transcranial alternating current stimulation, a non-invasive brain stimulation technique, has been used to increase alpha (8–12 Hz) power, the latter being associated with various brain functions and states. Heterogeneity among stimulation parameters across studies makes it difficult to implement reliable transcranial alternating current stimulation protocols, explaining the absence of consensus on optimal stimulation parameters to modulate the alpha rhythm. This project documents the differential impact of controlling for key transcranial alternating current stimulation parameters, namely the intensity, the frequency and the stimulation site (anterior versus posterior). Phase 1:20 healthy participants underwent 4 different stimulation conditions. In each experimental condition, stimulation via 2 electrodes was delivered for 20 min. Stimulation conditions were administered at PO7-PO8 or F3-F4 at individual’s alpha frequency, or at individual’s theta frequency or sham. Stimulation intensity was set according to each participant’s comfort following a standardized unpleasantness scale (≤ 40 out of 100) and could not exceed 6 mA. All conditions were counterbalanced. Phase 2: participants who tolerated higher intensity of stimulation (4–6 mA) underwent alpha-frequency stimulation applied over PO7–PO8 at 1 mA to investigate within-subject modulation of stimulation response according to stimulation intensity. Whether set over posterior or anterior cortical sites, alpha-frequency stimulation showed greater increase in alpha power relative to stimulation at theta frequency and sham stimulation. Posterior alpha-frequency stimulation showed a greater increase in alpha power relative to the adjacent frequency bands over frontal and occipito-parietal brain areas. Low intensity (1 mA) posterior alpha stimulation showed a similar increase in alpha power than at high (4–6 mA) intensity when measured immediately after stimulation. However, when tested at 60 min or 120 min, low intensity stimulation was associated with significantly superior alpha power increase relative to high intensity stimulation. This study shows that posterior individual’s alpha frequency stimulation at higher intensities is well tolerated but fails to increase stimulation aftereffects recorded within 2 h of stimulation on brain oscillations of the corresponding frequency band. In sharp contrast, stimulating at 1 mA (regardless of phosphene generation or sensory perception) effectively and selectively modulates alpha power within that 2-h time window, thus validating that it as a reliable stimulus intensity for future studies. This study also shows that posterior alpha-frequency stimulation preferentially modulates endogenous brain oscillations of the corresponding frequency band. Moreover, our data suggest that posterior alpha-frequency transcranial alternating current stimulation is a reliable and precise non-invasive brain stimulation technique for persistent modulation of both frontal and occipito-parietal alpha power.

Dentists stand in an optimal position to prevent and manage patients suffering from chronic orofacial pain (OFP) disorders, such as temporomandibular disorders, burning mouth syndrome, trigeminal neuralgia, persistent idiopathic dentoalveolar pain, among others. However, there are consistent reports highlighting a lack of knowledge and confidence in diagnosing and treating OFP among dental students, recent graduates, and trained dentists, which leads to misdiagnosis, unnecessary costs, delay in appropriate care and possible harm to patients. Education in OFP is necessary to improve the quality of general dental care and reduce individual and societal burden of chronic pain through prevention and improved quality of life for OFP patients. Our aims are to emphasize the goals of OFP education, to identify barriers for its implementation, and to suggest possible avenues to improve OFP education in general, postgraduate, and continuing dental education levels, including proposed minimum OFP competencies for all dentists. Moreover, patient perspectives are also incorporated, including a testimony from a person with OFP. General dentists, OFP experts, educators, researchers, patients, and policy makers need to combine efforts in order to successfully address the urgent need for quality OFP education.

Although empathy is an indispensable competence to social adaptation throughout the lifespan, it has been mostly studied with subjective, questionnaire-based measures in the context of healthy aging. Electroencephalography (EEG) provides an objective measure to investigate underlying neurophysiological processes related to empathy through mu rhythm. The current study used empathy-related mu rhythm during the observation of emotional facial expressions (EFE) in addition to the Empathy Quotient questionnaire in order to explore age-related changes of empathy across sexes. A total of 65 participants, including 33 young adults and 32 seniors, took part in this study. They were instructed to observe as well as to try experiencing emotional facial expressions (joy, fear, neutral) depicted on short video clips during which continuous EEG was recorded. They also completed the Empathy Quotient (EQ) questionnaire. Young adults reacted more strongly to emotional EFEs. Seniors perceived themselves as less empathic and exhibited an equivalent neurophysiological response to emotional and neutral stimuli. A significant sex effect in favour of females was found on mu rhythm modulation. Mu rhythm appears to be an age and sex sensitive neurophysiological marker linked to empathy and could therefore serve as an objective measure of empathy.