Figure 1.

Relation between tonic and phasic LC discharge (blue curve) and proposed effects of t-VNS treatment. Under normal conditions (left), a moderate range of tonic activity (indicated by green lines) allows for an optimal level of phasic activity in response to salient stimuli. Under constant stress (middle), LC tonic activity is thought to shift from moderate to high tonic discharge (solid red lines) which in turn impairs phasic discharge, presumably facilitating neuroinflammatory processes and contributing to neurodegeneration. t-VNS treatment (right) is proposed to restore tonic discharge to a moderate range, thus enabling an optimal level of phasic discharge, and presumably inhibiting neuroinflammatory/neurodegenerative processes by neuroprotective effects of NE.