Patrick Forbes and colleagues publish their work in Nature Communications!
Whether standing,
walking or driving, the vestibular system (i.e. our balance organ) provides
information to our brain about our orientation and movement in space. This
information is essential to our ability to orient, move and interact with our
environment. To study the vestibular system in isolation, researchers and
clinicians use galvanic vestibular stimulation (GVS), which delivers electrical
currents behind the ears to selectively activate the vestibular system. Despite
the growing popularity of GVS for the assessment and treatment of a wide range
of clinical disorders, including Parkinson’s disease, stroke, concussion and
even obesity, exactly how this non-invasive tool modulates vestibular signals remains
an open question.
In the new paper published in Nature Communications on April 23rd, Patrick Forbes (Erasmus MC), together
with colleagues from Johns Hopkins University and the University of British
Columbia, recorded the activity of vestibular neurons in monkeys during both
GVS and motion to reveal the neural substrate underpinning GVS-evoked
perceptual, ocular and postural responses. The authors show for the first time that
vestibular signals of both rotation and translation respond to the externally
delivered stimulus with constant GVS-evoked neuronal detection thresholds. This
resolves several conflicts regarding the neural mechanisms underlying GVS, and
rejects a prevailing assumption in the literature that neurons encoding
translation are preferentially activated during GVS. Instead, these results
demonstrate that all vestibular neurons transmit equivalent levels of
information to central vestibular pathways to detect GVS-evoked sensations of
self-motion. The
authors further demonstrate that neural response tuning to GVS differs markedly
from those produced during actual head motion. Using a simple model of
vestibular neural activity, the authors were able to explain the main trends
observed in GVS-evoked responses and identify future research directions to
address how detailed cellular channels contribute to neural responses.
Overall, these
findings provide key information for developing physiologically accurate models
of GVS activation of the vestibular system. Such models are essential for the advancement
and accurate application of this technique as a clinical tool in humans.
