Methods: The dual peripheral nerve stimulation somatosensory evoked potential (SEP) ratio technique was used in 11 subjects before and after a 20-minute typing task and again when the typing task was preceded with cervical spine manipulation. Somatosensory evoked potentials were recorded after median and ulnar nerve stimulation at the wrist (1 millisecond square wave pulse, 2.47 Hz, 1× motor threshold). The SEP ratios were calculated for the N9, N11, N13, P14-18, N20-P25, and P22-N30 peak complexes from SEP amplitudes obtained from simultaneous median and ulnar (MU) stimulation divided by the arithmetic sum of SEPs obtained from individual stimulation of the median (M) and ulnar (U) nerves.
Results: There was a significant increase in the MU/M+U ratio for both cortical (ie, N20-P25 and P22-N30) SEP components after the 20-minute repetitive contraction task. This did not occur when the motor training task was preceded with spinal manipulation. Instead, there was a significant decrease in the MU/M+U ratio for the cortical P22-N30 SEP component. The ratio changes appear to be due to changes in the ability to suppress the dual input as concurrent changes in the MU amplitudes were observed.
Discussion: This study suggests that cervical spine manipulation not only alters cortical integration of dual somatosensory input but also alters the way the central nervous system responds to subsequent motor training tasks.
Conclusion: These findings may help to clarify the mechanisms responsible for the effective relief of pain and restoration of functional ability documented after spinal manipulation and the mechanism involved in the initiation of overuse injuries.[ACC-RAC Award Winning Paper]
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