['To investigate whether functional specificity in different fascicles of the paraspinal muscles is associated with discrete organisation within the motor cortex.', 'In 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).', 'The 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.'] Are individual fascicles of the paraspinal muscles activated by discrete cortical networks in humans?