Individual fascicles of the paraspinal muscles are activated by discrete cortical networks in humans

ObjectiveTo investigate whether functional specificity in different fascicles of the paraspinal muscles is associated with discrete organisation within the motor cortex.MethodsIn 11 healthy volunteers, electromyographic (EMG) activity was recorded bilaterally using fine-wire intramuscular electrodes from the short and deep fibres of multifidus (DM) at L4, and the longer and more superficial fibres of longissimus erector spinae (LES) at L4 and L1. Surface electrodes were also placed over the right LES at L4 and L1. Organisation at the motor cortex associated with motor excitation was investigated using transcranial magnetic stimulation (TMS).ResultsThe results showed that motor cortical representation for DM was located posteriorly to that for LES. TMS maps from surface recordings of LES showed two optimal sites, which were located in proximity to the sites for DM and LES from intramuscular recordings.ConclusionDifferent fascicles of the paraspinal muscles are organised and thus could be controlled by discrete neuronal networks within the motor cortex. Further, TMS mapping from surface recordings of paraspinal muscles may be confounded by cross-talk from multiple underlying fascicles.SignificanceDiscrete organisation at the motor cortex appears consistent with differential activation of different fascicles of the paraspinal muscles with function.

► Discrete organisation at the motor cortex is present for different fascicles of the paraspinal muscles.
► This was only observed using selective intramuscular recordings of myoelectric activity.
► Discrete organisation of different fascicles of the paraspinal muscles is consistent with its differential control during functional tasks.