A Proposed Neurologic Pathway for Scalp Acupuncture: Trigeminal Nerve–Meninges–Cerebrospinal Fluid–Contacting Neurons–Brain

Scalp acupuncture represents a specialized modality of acupuncture that emerged as an independent system in the 1970s, combining knowledge from modern neuroanatomy with principles of traditional Chinese medicine. This pioneering experimental study proposes a specific neurologic pathway to explain the therapeutic mechanisms of scalp acupuncture, an area that has remained poorly understood scientifically. The researchers used 25 Sprague-Dawley rats to investigate the connections between scalp acupoints and brain structures, focusing specifically on the role of the trigeminal nerve as a mediator of these responses. The methodology involved two main experiments: observation of plasma extravasation using Evans Blue dye and measurement of cerebral blood flow through laser perfusion imaging.

In the first experiment, electrical stimulation of the trigeminal nerve induced visible plasma extravasation both in the facial skin and in the dura mater, demonstrating a direct neurologic connection between the cranial surface and the meninges. This phenomenon, known as neurogenic inflammation, occurs through axonal reflexes and dorsal root reflexes, in which stimulation of one nerve branch can antidromically activate other branches of the same axon. The second experiment compared the effects of electroacupuncture at GB-15 (Toulinqi), located on the scalp and innervated by the supraorbital nerve, with the effects at ST-36 (Zusanli), located on the leg. The results showed that stimulation of GB-15 produced a significant increase in cerebral blood flow during and after treatment, while ST-36 showed no similar effects.

This difference suggests that scalp acupuncture has distinct and potentially more effective mechanisms of action for influencing brain function. The findings led the researchers to propose a specific neurologic pathway termed 'trigeminal nerve–meninges–cerebrospinal fluid–contacting neurons–brain.' This pathway represents a possible shortcut for cerebral functional regulation, in which scalp acupoints, innervated by the trigeminal nerve, can influence the meninges through neural reflexes. The meninges, in turn, interact with specialized neurons that contact the cerebrospinal fluid, creating a communication bridge with the brain parenchyma. Cerebrospinal fluid–contacting neurons (CSF-cNs) are specialized cells found in various brain regions, including nuclei of the hypothalamus, thalamus, and brainstem.

These neurons send dendritic projections into the cerebral ventricles and central canal, functioning as chemoreceptors that can detect and respond to changes in cerebrospinal fluid composition. Previous studies have indicated that CSF-cNs are involved in pain modulation and in the transduction of headache-related signals. The clinical implications of this study are significant for the practice of scalp acupuncture. The identification of a specific neural pathway provides a scientific basis for the use of this technique in the treatment of brain diseases, including stroke sequelae, dementia, epilepsy, and motor disorders.

The demonstration that scalp acupuncture can increase cerebral blood flow more effectively than body acupuncture suggests unique therapeutic mechanisms that justify its specialized clinical application.