Combined Effects of Green Light and Transcranial Direct Current Stimulation in Migraine Patients.

Migraine is a common and debilitating neurological disorder, defined as "an episodic headache associated with certain features, such as sensitivity to light, sound, or movement", classified by headache frequency, with chronic migraine (CM), defined as 15 or more headache days a month for three or more months while episodic migraine (EM), is defined as occurring on fewer than 15 headache days per month.

It is also known as a common relapsing headache disease with a huge socioeconomic burden, characterized by a headache lasting 4 - 72 hours when untreated, which tends to be unilateral, pulsating, and of moderate to severe pain intensity.

According to the Global Burden of Disease (GBD) study, headache disorders are among the most prevalent and disabling conditions worldwide, with estimated 1-year prevalence of migraine (22.5%) in Pakistan, considerably higher than the global 1-year prevalence of 15%.

In the international classification of headache disorders 3rd Edition (ICHD-3), migraines may be diagnosed with aura or without aura. Migraine with aura is a complex neurological manifesting clinically as visual, somatosensory, speech or motor symptoms that precedes the headache phase. Migraine without aura is a recurrent headache disorder with specific features like unilateral, pulsating pain, nausea, and light/sound sensitivity, lasting between 4 and 72 hours.

The Graham and Wolff proposed the vascular theory for migraines, which stated that the serotonin released from the platelets in blood vessels to be the causal molecule. Because serotonin has constrictive effects on blood vessels, local cerebral blood flow is decreased, and this was thought to cause the auras that occur in migraines. After the reuptake or metabolism of this serotonin, the constricted blood vessels dilate, inducing the pain of the migraine headache.

The primary cause of migraines is the activation of the cervical complex of the trigeminal nucleus and trigeminal nerve. This activation of the trigeminal nerve results in neurogenic inflammation, including CGRP release from the C-fibers of the trigeminal ganglion and peripheral trigeminal nerve terminal. CGRP receptors are located in larger neurons and thicker fibers, which correspond to the Aδ-fibers of the trigeminal nerve. A δ-fibers are myelinated nociceptive nerves; thus, stimulation of Aδ-fiber CGRP receptors causes sharp severe headaches. The activation of the trigeminovascular system, mostly pertaining to the peripheral nervous system, is the key event of migraine pain generation.

The treatment options comprise such as lifestyle modifications, behavioral therapy, medication such as nonsteroidal anti-inflammatory drugs (NSAIDs), beta blockers, calcium channel blockers, antiepileptic drugs or antibodies against calcitonin gene-related peptide (CGRP) or its receptor, and neuromodulation. Neuromodulation can be defined as an intervention that potentiates or inhibits the transmission of a nerve impulse but is not the actual means of transmission itself.

One of the non-invasive neuromodulation technique is used in migraine patients .i.e., transcranial direct current stimulation (tDCS), tDCS is a promising method for migraine treatment delivering a low-intensity current through the scalp by means of electrodes to modulate the state of polarization of the cerebral cortex; depending on the polarity of the electrical stimulation, tDCS can be either anodal(excitatory) or cathodal(inhibitory). Neuromodulation by tDCS is thought to follow Hebbian Theory ("neurons that fire together, wire together"). If presynaptic and postsynaptic neurons are both active, the result is synaptic strengthening; if one or both are inactive, no change occurs. The literature reported significant reduction in migraine days when applying tDCS to the occipital cortex, primary motor cortex, or the dorsolateral prefrontal cortex. The advantages of tDCS treatment are its relatively low cost compared to other neuro-stimulation methods, safety and generally mild side effects.

Reports suggested that exposure to lights of different wavelengths can affect nociception in rodents. For example, exposure to a green light emitting diode (GLED) resulted in anti-nociception in naïve rats and anti-hyperalgesia in rats with neuropathic pain that was dependent on engagement of the visual system. Also exploratory studies demonstrated that isolated exposure to green light may reduce the intensity and duration of migraine attacks.

The rationale for this study is to evaluate whether combining tDCS with green light exposure provides synergistic benefits in reducing migraine frequency, intensity, and improving the overall quality of life for patients suffering from migraine. This dual approach may enhance therapeutic outcomes by targeting both the neural mechanisms underlying migraine attacks through neuromodulation (tDCS) and alleviating visual discomfort via green light.

The proposed study seeks to address a gap in current migraine treatment by exploring the potential of a non-pharmacological, combinatory intervention that could offer a more effective, lasting solution for migraine management. Given the growing interest in non-pharmacological treatments for migraine and the promise of both tDCS and green light exposure, this research will hold significant potential for advancing migraine care and providing new treatment options for patients who prefer or require alternatives to conventional medications.