Motor Cortex Excitability After Vagus Nerve Stimulation in Major Depression

Abstract

Recent data suggest that inhibitory pathways may be involved in the pathophysiology of depression and in the mode of action of some antidepressant interventions. The aim of the present study was to test whether vagus nerve stimulation (VNS) can affect motor cortex excitability. Measures of motor cortical excitability were probed by using single-pulse and paired-pulse transcranial magnetic stimulation at baseline, after 10 weeks of left VNS, and additionally, in an on-off paradigm in 10 patients with treatment-resistant unipolar depression. Ten weeks of VNS was associated with a selective and pronounced increase in intracortical inhibition, whereas no changes occurred in the on-off paradigm. These results suggest that VNS is capable of changing motor cortical excitability in patients with depression.

Efficacy of vagus nerve stimulation in the treatment of depression

“…Considering the clinical effects of anticonvulsants, the anticonvulsive effects of ECT measured in neuroimaging and neurophysiological approaches, there is good evidence that the GABA system may play a role in the mode of action of different antidepressant interventions, especially in ECT. In line with this, data from studies using VNS indicate that this neurotransmitter system may play a role, for example, by downregulating overactive brain regions such as the cingulate cortex (e.g., inhibitory effects on a neurophysiological level) [52,53].…”

“…Several groups [40][41][42][43] Our own previous work showed increased intracortical inhibition in ten unipolar MDD patients after 10 weeks of VNS [44], although not as an acute effect, while in epilepsy patients an acute effect could be shown [45]. These differential results might be due to comedication with antidepressants and anticonvulsants, respectively, or it could be caused by the application of different stimulation parameters in the studies.…”

“…In rats, repeated ECT leads to an increase in GABA release and concentration. Several anticonvulsant properties such as increased seizure threshold and slow-wave activation in postictal EEG also imply a general involvement of inhibitory pathways [52,53]. These findings led to the assumption that the anticonvulsant effect of VNS and ECT might be responsible for the antidepressant effect of these treatments.…”

Resting motor threshold changes in vagus nerve stimulation‐treated patients during on/off‐stimulation conditions

“…As shown in recently published studies, however, rMT does not appear to be a static variable and changes in motor cortex excitability are implicated, similar to previous results. 3,6,7 The present results suggest that VNS affects the motor cortex by increasing motor excitability, thereby reducing rMT. This reduction should be discussed as a significant indicator of increased responsiveness of the frontal and motor cortex due to VNS.…”

Therapeutic Options for Treatment-Resistant Depression

“…[90] Beyond this general description, the mechanism of action for VNS as treatment for affective disorders is still only partially understood. Neuroimaging studies showed changes in cerebral blood flow, [91] enhanced firing rates in select brainstem nuclei, [92] changes in cerebral oxygenation levels [93] and changes in motor cortical excitability [94] in patients with depression treated with VNS. It has also been reported that VNS can interfere with the retrieval memory of negative information, which might counteract the over-representation of negative thoughts and memories in depressed patients.…”