[Objective]

To analyze the brain activity of patients with low back pain using functional magnetic resonance imaging (fMRI).

[Subjects and Methods] The study involved 11 patients (6 men and 5 women, mean age: 60.0 years) with low back pain that persisted for more than 3 months [numerical pain rating scale (NPRS) score ≥ 5: low back pain group] and 14 individuals (7 men and 7 women, mean age: 50.1 years) without low back pain (control group). Using audio triggers, fMRI was performed while the subjects were asked questions both related to low back pain (pain condition) and not related to low back pain (neutral condition), and their brain activity was measured.

A questionnaire survey using the Pain Catastrophizing Scale (PCS) was conducted for all the subjects. Based on the fMRI data, the brain activity (β values) was calculated using analytical software, SPM and MarsBaR.

Evaluation items comprised the activated brain areas and the β values of those areas.

The β values obtained for the control and low back pain groups in three conditions—neutral, pain, and pain–neutral (P–N) conditions—were compared.

[Results] In both the control and low back pain groups, the posterior insula cortex and the superior and transverse temporal gyri were activated. Meanwhile, the left amygdala was activated only in the low back pain group. Thus, the control and low back pain groups were compared in terms of the β values of the left amygdala. In the neutral condition, the β value of the control group was 0.041 ± 0.332 and that of the low back pain group was −0.047 ± 0.279; no significant differences were observed (P = 0.78). Similarly, with the β value of −0.030 ± 0.358 and −0.007 ± 0.337 in the control and low back pain groups, respectively, no significant differences were noted in the pain condition. In the P–N condition, however, the β value was −0.071 ± 0.161 and 0.040 ± 0.149 in the control and low back pain groups, respectively; therefore, the low back pain group exhibited a significantly higher value (P = 0.04).

Assuming that catastrophic thinking might be associated with the activation of the amygdala, the low back pain group was divided into two subgroups—the N subgroup with PCS score < 30 (n = 8) and the P subgroup with PCS score ≥ 30 (n = 3. The brain activities were then analyzed for these two subgroups and the control group. However, when compared in terms of the β values obtained for the left amygdala in the neutral, pain, and P–N conditions, no significant differences were observed between the control group and the N and P subgroups.

[Conclusion]

These results suggest the possibility that patients with chronic low back pain are susceptible to the activation of negative emotions regarding low back pain regardless of the presence/absence of catastrophic thinking.