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].