Can transcutaneous vagus nerve stimulation (tVNS) modulation of heart rate variability reduce aggression by adults with developmental or acquired brain injury? A study with people with intellectual (learning) disabilities, autism or acquired brain injury.
Type of research:
Acceptability and feasibility study using a single case design
Background & Scientific Rationale:
Repeated aggressive behaviours are frequent in people with the cognitive, social and emotional problems associated with developmental conditions (e.g. intellectual disabilities (IDs), autism) and acquired brain injuries (ABI), affecting an estimated 10-15% of adults with IDs, 35% with ABI, and up to 60% with autism. The consequences are severe, both for victims and the person themselves: they include breakdowns in relationships with care-givers and/or living arrangements and employment, contact with the criminal justice system and/or admission to (often costly out-of-area) in-patient services. Current interventions remain very limited. Pharmacological treatment is normally ineffective in the absence of an underlying mental health need, and behavioural/cognitive behavioural treatments are also often of limited benefit.
Recent research has started to describe and test the potential role of disturbed autonomic nervous system activity on the brain and subsequently on behaviour1. There is preliminary evidence that heart-rate variability (HRV; a measure of autonomic nervous system functioning), can be experimentally modulated, with increased HRV2 affecting brain responses to negative emotional stimuli, leading to improvements in both mood and behaviour. Unfortunately, almost all existing empirical studies have lacked ecological validity, and moreover, have very rarely involved people with developmental or acquired disorders. The findings may not, therefore, be relevant to the development of treatments that may improve the lives of the service users with whom we are concerned and their potential victims.
Since people with a range of developmental or acquired brain injuries are at increased risk of engaging in aggressive behaviours, the study aimed to investigate whether there is a scientific model that could explain this shared occurrence and inform the development of a potential transdiagnostic intervention. We seeked to address two questions:
- Is the use of transcutaneous (external) vagal nerve stimulation (tVNS) acceptable to, and feasible in, adults with intellectual disabilities, acquired brain injury, or autism who also have aggressive outbursts and who live in the community?
- In everyday life, are increases in average HRV associated with reductions in the frequency and severity of aggressive outbursts?
Developing our previous work, the proposed methods involved:
Design: using a well-established means of assessing feasibility and effectiveness, a single-case study with three conditions: (i) baseline observations; (ii) sham tVNS stimulation with intermittent heart-rate recording using a wearable monitor; and (iii) active stimulation with the same device, also for three separate one-hour periods a day and again with intermittent heart-rate recording. Baseline lasted at least five and up to eight weeks or 15 aggressive episodes, whichever was shorter, with transition from baseline to sham randomly jittered within a two-week window. For each participant, the duration of subsequent conditions was similar to baseline. In sham, participants only noticed aural sensory stimulation when the device was switched on; in the active condition they noticed this stimulation for three hours a day but they were not told the reason for the difference until the end of their participation.
Participants: Clinically stable adults aged 18-55 years, with capacity to consent to participation, who engaged at least three times a week in aggressive behaviours with a negative impact on their lives, recruited from community-based clinical services for people with IDs, neurorehabilitation, or autism without intellectual disabilities. Based on an estimated retention rate of 50%, we recruited a total of twelve participants: four in each of the study groups. NRES ethical approval was sought.
Measures: Included (i) heart rate using Intelesens’ ‘zensor’ technology in 24 hour blocks during sham and active conditions, with data stored on an integral SD card for subsequent off-line analysis. HRV was determined from the intervals between beats and the average determined for each participant for brief (15 min.) and prolonged (24 hr.) intervals; (ii) the frequency and severity of aggressive behaviours, through daily behavioural electronic diaries, tailored to individuals’ and completed by participants and/or care-givers throughout all conditions, and the Challenging Behaviour Interview; (iii) mood, using established scales; (iv) cognition: intellectual functioning at the start of the study; executive functioning , and hostility bias at start and end of study; (iv) feasibility and acceptability was investigated through retention and adherence rates and semi-structured interviews with participants and their care-givers.
Data analysis: Qu. 1: Semi-structured interviews and adherence rates; Qu. 2: Differences between conditions was analysed separately in each individual using the non-overlap all pairs (NAP) statistical method.
Key findings and outputs:
1. Acceptability and feasibility data for this intervention in adults with intellectual disabilities, autism or acquired brain injury;
2. Piloted data on potential effects of tVNS on aggressive behaviour in the three clinical conditions;
3. Preliminary evidence as to whether modulating HRV changes perception of, and ANS response to, potential threat, with an estimation of associated effect sizes.
Findings were presented to participants and care-givers; written up for submission to a peer-reviewed academic journal and disseminated through conference presentations and appropriate websites; and formed the basis of an application for grant-funding for the development of an intervention that we intended subsequently to be investigated through a clinical trial.
A joint application with an existing group using tVNS (led by Tony Holland) has received funding from Cambridgeshire and Peterborough NHS Foundation Trust (CPFT) R&D Strategic Funding to develop a programme of research on the impact of vagal nerve stimulation on aggression. An NRES application to extend our recruitment sites has been submitted.
For further information on this project, contact Howard Ring, Principal Investigator, firstname.lastname@example.org