P01 Cold-water immersion of a single limb increases motor cortex excitability for the opposite limb
Delahunty ET and Kavanagh JJ
Menzies Health Institute Queensland, Griffith University, Gold Coast, Queensland, Australia
A body of evidence indicates that strong voluntary contractions can elicit unintended motor activity in the opposite limb. However, it is unknown if acute changes of sensory input for one limb can alter motor activity on the opposite side of the body. The current study examined if immersing a single upper limb in very cold water (4 degrees Celsius) affected motor cortex circuitry for the opposite non-immersed limb. We hypothesised that intense pain evoked by cold stimuli would increase excitability in ipsilateral primary motor cortex.
Eight healthy subjects (22.1 ± 2.7 yr) participated in the experiment. Standard paired-pulse TMS protocols were used to assess motor cortex circuitry associated with the non-immersed limb. Resting motor threshold, short interval intracortical inhibition (SICI), long interval intracortical inhibition (LICI), and intracortical facilitation (ICF) were assessed for the extensor carpi radialis brevis muscle in the non-immersed limb.
Visual analogue scales confirmed that significant changes in pain and temperature occurred due to the intervention. Although resting motor threshold and LICI was unaltered, SICI was significantly reduced (p = 0.02), ICF was significantly increased (p < 0.01), and background EMG was significantly increased (p = 0.04) for the non-immersed limb during the intervention.
The presence of a localised painful stimulus on one side of the body affected cortical circuits responsible for activating muscles on the opposite side of the body. While separate mechanisms may regulate SICI and ICF, the overall effect of intense pain was an increase in motor cortex excitability of the ipsilateral hemisphere.