What happens in the brains of both the patient and the chiropractor during chiropractic care?

Participants in the intervention group will receive chiropractic care (Single session), including spinal adjustments performed by a registered chiropractor. A registered chiropractor will assess the entire spine, and both sacroiliac joints will be assessed for vertebral subluxation by a registered chiropractor with at least five years of clinical experience. The clinical indicators that will be used to assess the function of the spine before spinal adjustment intervention include assessing for joint tenderness to palpation manually palpating for a restricted intersegmental range of motion, assessing for palpable asymmetric intervertebral muscle tension, and any abnormal or blocked joint play and end-feel of the joints. Chiropractors use these biomechanical characteristics as clinical indicators of spinal dysfunction and vertebral subluxation. All spinal adjustments carried out in this study will be high-velocity, low-amplitude thrusts to the spine or pelvic joints, a standard adjusting technique used by chiropractors. The mechanical properties of chiropractic adjustment have been investigated; and although the actual force applied to the patient's spine depends on the chiropractor, the patient, and the spinal location of the subluxation, the general shape of the force-time history of spinal adjustments is very consistent and the duration of the thrust is always less than 200 milliseconds. The whole assessment and intervention will take around 45 minutes. EEG: EEG will be recorded before, during, and after the intervention session using a portable 64-channel, research-grade system (gel-based cap with active electrodes). Two separate EEG units will be used for the participants and the chiropractors, with caps appropriately sized for each wearer. A trained EEG researcher will apply, check impedances, and monitor the recording throughout, under the oversight of the study’s lead. The anticipated EEG monitoring duration during intervention is ~10-15 minutes per session, with continuous artifact monitoring and standard safety/hygiene procedures followed. Materials: Before enrolment, participants will receive a Participant Information Sheet and Consent Form (and a brief pre-visit guidance sheet), while treating chiropractors will use a standardized procedure checklist and case-report form aligned with the study rubric. Setting: All sessions will be delivered at the New Zealand College of Chiropractic (NZCC) Chiropractic Centre (Auckland). Adherence/fidelity: Because this is a single-session intervention, adherence will be defined as attendance and completion of the visit; this will be verified via clinic scheduling logs and a signed clinician checklist documenting each protocol step, with any deviations recorded in the case-report form.