2. To understand the neurophysiological mechanisms of paediatric PCS and assess any resultant effects of treatment with melatonin. Methods: A case-controlled study within the RCT, using functional MRI and Transcranial Magnetic Stimulation to investigate the neurophysiological properties of paediatric mTBI before and after treatment; Treatment groups from the RCT will be compared with two control groups: i) normal controls and ii) asymptomatic mTBI children.