Stimulating Compassion UsingTranscutaneous Vagus Nerve Stimulation
Condition: Healthy Volunteers
Study type: Interventional

Summary: 
      This experimental proof-of-concept study in healthy volunteers investigates whether a
      specific form of self-relating, namely, self-compassion, can be controlled through
      non-invasive stimulation of the vagus nerve. The vagus nerve is part of the parasympathetic
      nervous system (the 'rest and digest' system) and its fibers are spread throughout the upper
      body, face, and neck, including a branch that innervates parts of the external ear (e.g. the
      tragus), close to the surface of the skin. This allows the 'auricular branch' of the vagus
      nerve to be readily stimulated electrically. Importantly, this can be achieved non-invasively
      using a transcutaneous vagus nerve stimulation (tVNS) device. The investigators will test the
      effects of tVNS alone and in combination with a meditation-like technique that is intended to
      increase participants' feelings of self-compassion (self-compassion imagery). In particular,
      the investigators will assess participants' experience of self-compassion and self-criticism,
      as well as other outcome measures, before and during stimulation, and again after they
      perform the self-compassionate imagery exercise. These effects will be compared to three
      other groups: one that receives tVNS along with a control (sham) imagery procedure, another
      that receives sham tVNS and self-compassion imagery, and a final group that receives sham
      tVNS and sham imagery. It is expected that the group that receives active tVNS and the
      self-compassion imagery exercise will experience the largest average increases in
      self-compassion and decreases in self-criticism. The findings of this study will help us
      better understand the role of the vagus nerve in complex cognitive-emotional experiences -
      like compassion - and may also motivate the development of bioelectronic stimulation methods
      that can be used alongside psychological techniques for improving self-compassion and
      reducing self-criticism, particularly among people with certain psychological disorders.
    

Detailed description: 
      The role of the vagus nerve in regulating cardiac, respiratory, and gut functioning via
      brainstem nuclei is well-established. More recently, its role has been examined in relation
      to the modulation of higher cognitive functions. Bodily signals (e.g. from the heart or gut)
      conveyed by vagal afferents could affect cognitive functioning via projections from the
      nucleus of the solitary tract (NTS) to the locus coeruleus and thence to widespread cortical
      areas through noradrenergic outputs. In addition, the NTS transmits sensory-visceral
      information to the central autonomic network, which includes higher brain areas (e.g.
      prefrontal cortex). Recent research suggests that vagus nerve activity is associated with a
      range of psychological functions including memory, executive function, and threat/fear
      processing. In addition, biobehavioral theories of vagal functioning, and emerging empirical
      evidence suggest a role for the vagus nerve in modulating social behavior as well as complex
      emotional states.

      A number of researchers have proposed a role for vagal nerve functioning in well-being, and
      particularly in generating or modulating feelings of 'safeness', contentedness, and
      relaxation that underlie complex social-affective-motivational states, such as compassion.
      Previous research has examined the effects of inducing compassionate feelings while measuring
      vagus nerve activity (via heart rate variability). However, to our knowledge, no published
      study has demonstrated an association between vagal activity and compassion by directly
      modulating the vagus nerve itself. Such studies have important theoretical implications but
      are also potentially valuable in the future development of interventions that employ tVNS or
      similar technology to augment psychological treatments that employ compassion-focused
      techniques (e.g. compassionate mind training; compassion-focused cognitive therapy;
      loving-kindness meditation-based treatments, etc.)

      The current experiment aims to determine if vagus nerve activation using tVNS is sufficient
      to generate positive affective states, especially compassion (specifically, self-reported
      self-compassion). Alternatively, tVNS may produce a permissive physiological context that
      facilitates compassionate responding. For example, tVNS may synergize the effects of a
      compassion-inducing behavioral intervention. To examine these possibilities, the
      investigators will test the separate and combined (interacting) effects of tVNS and a
      compassion-induction procedure (self-compassion mental imagery) compared to sham conditions,
      in a four-group factorial (2 x 2) design. Participants will be randomly assigned to (i)
      active tVNS + sham imagery, (ii) active tVNS + active self-compassion imagery, (iii)
      sham-tVNS + active self-compassion and (iv) sham-tVNS + sham imagery.

      In addition to examining the effects of stimulation and imagery conditions on
      self-compassion, the investigators will also test their effects on other types of positive
      affect, as well as self-criticism, which is an opposing form of self-representation to
      self-compassion. Self-criticism is a transdiagnostic psychological marker of psychopathology,
      and measures of self-criticism are sensitive to the effects of compassion-focused
      interventions , including brief self-compassion imagery, as will be used here. Vagal activity
      will be indexed using heart rate variability, and effects of stimulation and imagery will
      additionally be tested on attentional bias (e.g. first fixation, increased dwell time) to
      compassionate facial expressions.

      Participants attend two lab sessions (on Day 1 and 8) in which they will undergo either
      supervised active or sham tVNS and either the self-compassion or sham imagery exercise
      (delivered as standardized audio instructions), per their randomized condition. Assessments
      of heart rate variability, self-compassion, self-criticism, positive state affect, and state
      mindfulness will occur before stimulation, during stimulation, and after the imagery
      exercise. In addition, participants will complete the Day 1 stimulation procedure and imagery
      task on Days 2-7, guided via online audio and written instructions. This will allow us to
      test the effects of extended (daily) stimulation and imagery practice. Additional study
      details are available on the Open Science Framework (osf.io/k2dje).
    

Intervention name(s): Active transcutaneous vagus nerve stimulation; Active self-compassion imagery; Sham transcutaneous vagus nerve stimulation; Sham mental imagery
Intervention type(s): Device; Behavioral; Device; Behavioral
Intervention description(s): TVNS is a non-invasive counterpart to surgical methods for stimulating the vagus. For the active condition, stimulator electrodes deliver a mild electrical current to the tragus. Stimulation parameters: stimulation of left tragus via two gold-plated electrodes, attached by ear-clip. Waveform: rectangular, frequency: 20 Hz, pulse width: 0.2 ms, individually adjusted intensity based on participant's perceptual threshold.; Self-compassion imagery is both a meditative technique and a component of compassion-focused cognitive therapy. Here, self-compassionate imagery is delivered as standardized audio-recorded instructions.; TVNS is a non-invasive counterpart to surgical methods for stimulating the vagus. For the sham condition, stimulator electrodes deliver a mild electrical current to the earlobe. Stimulation parameters: stimulation of left earlobe via two gold-plated electrodes, attached by ear-clip. Waveform: rectangular, frequency: 20 Hz, pulse width: 0.2 ms, individually adjusted intensity based on participant's perceptual threshold.; Draw-a-face-in-imagination is the sham/ control imagery condition. Here, control imagery instructions are delivered as a standardized audio-recording, well-matched to self-compassion imagery for number of words, complexity of language, and duration of the audio instructions.
Other intervention name(s): Parasym tVNS device; Parasym tVNS device
Allocation: Randomized
Intervention model: Factorial Assignment
Intervention model description: Factorial 2 (sham stimulation v active stimulation) x 2 (sham v self-compassion imagery)
Masking: Single (Participant)
Primary purpose: Basic Science
Keywords: Vagus nerve; Neurostimulation; Transcutaneous vagus nerve stimulation; Mental imagery; Compassion; Meditation