Is the Organization of the Primary Motor Cortex in Low Back Pain Related to Pain, Movement, and/or Sensation?

AIM/BACKGROUND: Primary motor cortex (M1) organization differs between individuals with and without chronic low back pain (CLBP), in parallel with motor and sensory impairments. This study investigated whether movement behaviour and tactile/pain sensation are related to M1 organisation in CLBP.

METHODS: Transcranial magnetic stimulation (TMS) was used to map the M1 representation of the erector spinae and multifidus muscles in 20 participants with and without CLBP. Cortical organisation was quantified by: map volume; center of gravity (CoG); number of peaks; and primary and secondary peak location. Movement behaviour was assessed as the ability to dissociate lumbar from thorax motion and sensory function as two-point discrimination, pressure pain thresholds, and pain intensity (visual analogue scale).

RESULTS: People with CLBP showed more anterior location of the CoG than controls. Map peaks were more numerous in CLBP participants who performed the movement task good than those with poor performance. In CLBP, smaller map volume correlated with greater pain during the movement task. Movement behaviour was not linearly correlated with M1 features.

CONCLUSIONS: This study confirms that M1 maps differ between people with and without CLBP, but these changes are variable within the CLBP group and are not related to motor and sensory features in a simple manner.