Cranial Nerve Stimulation and Neuromodulation Techniques:
Non-Invasive Techniques:
a) Transcranial Magnetic Stimulation (TMS): TMS is a non-invasive method
that uses magnetic fields to modulate the activity of specific brain
regions. In PD, TMS has been applied to various motor and non-motor
cortical areas, showing promising results in improving motor symptoms,
cognition, and mood [20]. Repetitive TMS (rTMS) has been the most
commonly used protocol, with high-frequency rTMS targeting the primary
motor cortex and supplementary motor area to enhance cortical
excitability and promote neuroplasticity [21].
b) Transcranial Direct Current Stimulation (tDCS): tDCS is another
non-invasive neuromodulation technique that delivers weak direct
currents to the scalp, modulating cortical excitability and inducing
lasting changes in synaptic efficacy [22]. Several studies have
investigated the effects of tDCS on motor and non-motor symptoms in PD
patients, demonstrating improvements in gait, balance, and cognitive
function [23]. The most common approach involves anodal tDCS over
the primary motor cortex, although other cortical targets and montages
have been explored [24].
Minimally Invasive Techniques:
a) Vagus Nerve Stimulation (VNS): VNS is a well-established treatment
for drug-resistant epilepsy and depression, and its potential benefits
in PD have been increasingly investigated [25]. VNS involves the
implantation of a pulse generator subcutaneously in the chest, with a
connecting lead placed around the left vagus nerve in the neck. The
device delivers electrical stimulation to the nerve, modulating the
activity of various brainstem nuclei and cortical areas implicated in PD
pathophysiology [26]. Preliminary studies have suggested that VNS
may improve motor and non-motor symptoms, with a favorable safety
profile [27].
b) Trigeminal Nerve Stimulation (TNS): TNS is a novel neuromodulation
technique that targets the trigeminal nerve, the largest of the cranial
nerves, which innervates various brain regions implicated in PD,
including the basal ganglia and thalamus [28]. TNS can be applied
externally (eTNS) using adhesive electrodes placed on the forehead or
invasively (iTNS) with an implanted device. Early studies have reported
encouraging results on motor symptoms, sleep, and cognition in PD
patients, although more extensive research is needed to confirm its
efficacy and safety [29].
In summary, the emerging cranial nerve stimulation and neuromodulation
techniques offer promising alternatives to traditional pharmacological
and surgical treatments for PD. These innovative approaches hold the
potential to address the limitations of current therapies, providing
more targeted, less invasive, and better-tolerated options for patients
with this debilitating disorder [30].