Transcutaneous Vagus Nerve Stimulation in Aphasia After Stroke

Aphasia is an acquired communication disorder, characterised by difficulties with the production and/or understanding of language. Stroke is the most common cause of aphasia which affects approximately 30% of stroke survivors. Many individuals are left with chronic deficits. Speech and Language Therapy (SLT) is the gold-standard treatment for aphasia but access to therapy is limited beyond the first few months of recovery. Individuals with chronic aphasia (>6 months) can benefit from SLT input. Computer-based SLT can lead to improvements in word-finding for people with aphasia, many years after stroke (Palmer et al., 2019). Improvements have not been found to translate to day-to-day conversation.

Vagus Nerve Stimulation (VNS) paired with upper limb rehabilitation has proved beneficial in chronic stroke. Transcutaneous Vagus Nerve Stimulation (tVNS) is a non-invasive technique which involves stimulating a branch of the vagus nerve through the skin of the ear, using a small earpiece. This technique is safe and has been approved for use in headache. The use of tVNS in chronic stroke is currently being explored, with promising findings when paired with upper limb rehabilitation exercises. To date, there are no published studies exploring the use of tVNS in chronic aphasia. Pairing tVNS with an SLT intervention may have the potential to promote language recovery in chronic stroke. An indication of study feasibility may support the development of a larger RCT to explore treatment efficacy.

This is a single centre, single blind, pilot randomised controlled trial. The primary aim is to explore the safety, tolerability and feasibility of self-directed computer-based SLT combined with tVNS, in individuals with chronic-stroke related aphasia. Secondary aims include exploring any indication of effect of the intervention on word-finding ability (trained words, generalisability to untrained words and conversation). Additionally, the study aims to explore potential mechanisms of action.

Participants will be asked to use the stimulation device alongside computer-based SLT, at home for 6 weeks. SLT training will include naming pictures of 30 personally relevant words, selected by the participant prior to the commencement of the intervention and uploaded onto the software. The SLT software (Step by Step) uses a self-guided errorless learning approach and will be completed on an ipad. The researcher will check-in with the participant each week to monitor any concerns, side effects and monitor engagement with the programme.

Potential participants will be recruited from Sheffield, using the NHS PHIND database. Accessible study invitations will be sent to potential participants. The Consent Support Tool will be used to ascertain the most appropriate way to provide study information. All participants will have capacity to consent to the study. Participants will be randomly allocated (SealedEnvelope Ltd) to an active or sham tVNS group, stratified according to language score. Participants will be blinded to group allocation.

The tVNS device will be applied to the ear (tragus or earlobe), depending on group allocation. The tVNS device (Nurosym/ Parasym II) is a UKCE marked device, indicated for off-label use in the current study. tVNS use is safe however it has been associated with mild and transitory side effects such as pain or irritation at the stimulation site, headache and nasopharyngitis (Redgrave et al 2018). Stimulation parameters are in line with previous studies:

• Pulse Width: 250µs
• Frequency: 25Hz
• Intensity: individual tolerability (below pain threshold)
• Duration: 45 minutes daily for 6 weeks

Language assessments will be taken at baseline, end of treatment (6 weeks) and at follow-up (12 weeks). To explore potential mechanisms, blood samples, heart rate variability (HRV) and pupillometry measures will be taken at baseline and end of treatment. The Functional near infrared spectroscopy (fNIRS; LUMO, Gowerlabs) will be used on a subset of participants to explore cortical activation in the frontal lobes in response to tVNS at baseline and end of treatment (6 weeks). Outcome measures will be undertaken by a trained member of the research team.

Inclusion criteria

• Supratentorial stroke at least 6 months prior to recruitment
• Aphasia (with word finding difficulties)
• Ability to engage in the programme (support can be provided for cognitive or receptive difficulties)
• Sufficient vision to engage in the computer-based SLT programme

Exclusion criteria

• Implanted devices (e.g. pacemaker) or implanted stimulation devices
• Currently receiving a programme of Speech and Language Therapy (SLT)
• Damage to the vagus nerve
• Symptomatic bradycardia/ 2nd or 3rd heart block
• Pregnancy
• Unable to speak English
• Severe deafness (despite using hear aids)