During a transforaminal lumbar interbody fusion a patient experienced acute intermittent bradycardia with manipulation of the intervertebral body space, followed by loss of somatosensory evoked potentials that did not recover. Postoperative evaluation revealed new bilateral lower extremity sensory and motor deficits. We postulate an afferent reflex arc to explain this and other reported instances of bradycardia and asystole during transforaminal lumbar interbody fusion surgery. Awareness of the association between bradycardia during lumbar spine surgery may alert anaesthetists, surgeons and neuromonitoring teams to impending neurological harm.