A study published in the Journal of Manipulative and Physiological Therapeutics in October 2014 used functional magnetic resonance imaging (fMRI) to evaluate how the brain reacts to spinal manipulation used by chiropractors. Brain scans revealed that spinal manipulation and other types of manual therapy have an immediate effect on functional connectivity between regions of the brain that are responsible for processing pain.
Previous research has established a connection between neurophysical changes in regional brain communication and manual therapy. Many patients seek chiropractic care for pain relief, and multiple studies testify that chiropractic treatment relieves pain in neck pain patients, lower back pain patients, and others.
This study, conducted by researchers at the University of Florida, suggests that increases in functional connectivity or brain communication after manual therapy underlie pain relief.

Functional Connectivity and Pain Processing

Functional connectivity (FC) is defined as communication between regions of the brain, and in the case of this study, refers to communication between the pain-processing regions of the brain.
There are several areas of the brain associated with processing and modulating pain, including the thalamus, primary and secondary somatosensory, cingulate, and insular cortices. These regions are referred to together as the pain processing network. Activity in the PPN is part of pain recognition, but it also includes the interaction between the PPN and other areas of the brain.

Study Methodology

The researchers recruited participants, 24 of whom (17 men and 7 women) completed exercises designed to induce lower back pain. They were separated into three groups, each of which was treated with one form of manual therapy — either spinal manipulation, therapeutic touch, or spinal mobilization.
Participants were measured for pain intensity, sensitivity, and underwent an fMRI 48 hours after the pain-inducing protocol. They were randomized to one of the three treatment groups and then received the same measurements after treatment. All manual and manipulative therapies were administered by a physical therapist or chiropractor, using a standardized set of techniques.
Before and after undergoing their assigned treatment, participants were measured for changes in functional connectivity (FC) between regions of the brain that process and respond to pain. Functional MRIs revealed changes in FC between several regions of the brain after treatment. Several of these changes in connectivity between brain regions were shared among patients from all three of the treatment groups.

Manual Therapy, Functional Connectivity, and Pain Relief

Manual therapy consists of a variety of physical rehabilitation techniques, including spinal manipulation, spinal mobilization, therapeutic touch, tissue massage, and other techniques. According to the American Chiropractic Association, manual therapies are the most common treatment administered by chiropractors.
Researchers examined activity in the pain processing network and also how it reacted with other areas of the brain after treatment. Results found clinically significant changes in functional connectivity between several areas of the brain that appeared to be directly related to manual therapy.
Changes were also recorded in pain intensity and pain sensitivity. All three groups reported similar changes in pain intensity, but no changes were found in pain sensitivity.
These results may indicate that after manual therapy, functional changes are an underlying mechanism of pain relief.

More Research Needed

This study is unique because it includes more precise measurement than previous studies, including fMRIs of patients in a resting state before treatment.
Due to a lack of a control group that received no treatment — as well as the relatively small sample size — more research is needed to confirm the association between manual therapy and increased functional connectivity. It also suggests a future study on the effects and changes of MT on patients with chronic pain, since these results are only applicable to patients with acute pain.