Motor recruitment during pain anticipation similar to experiencing actual pain
MedWire News: Similar alteration of motor recruitment strategies occurs when anticipating pain to when experiencing pain, shows research.
"It is generally accepted that changes in activity of muscle during painful noxious stimuli is mediated by inputs from nociceptor afferents onto motoneurones in the spinal cord… The alternative view is that modulation of motoneurone discharge properties may be mediated by descending inputs," write study authors, Kylie Tucker (University of Queensland, Brisbane, Australia) and colleagues.
The researchers aimed to resolve this by investigating a pain condition that only has descending components: the anticipation of pain.
Nine participants were asked to perform contraction tasks while experiencing 5 minutes of pain induced in the patella fat pad by hypertonic saline injection. The same tasks were also completed when the patients were anticipating painful electrical stimulation of the patella fat pad; the patients were told that they would receive electrical stimulation at random intervals during the contractions, which occurred without further warning. The participants maintained their contraction level until two 5-second periods with no painful stimulus had passed.
The participants were asked to record their experience of pain on the visual analog scale where 0 represents 'no pain' and 10 is the 'worst pain imaginable.' The discharge properties of motoneurones were determined via evaluation of motor unit action potential morphology.
A control study was also conducted where the participants completed the contraction tasks and were told that no further pain would be induced and they did not experience any further pain.
The researchers found that the discharge rate of motor units decreased significantly during pain and during anticipation compared with the control contractions. The motoneurone changes in both pain and anticipation involved reduced discharge in one population of motor units and increased discharge in another population.
They also report that the changes in motor unit discharge with either pain or anticipation do not return to their original states immediately once stimuli have ceased.
"We argue that changes in motor control are likely to involve top-down mechanisms and do not simply involve direct nociceptive input to the motoneurone pool," write Tucker et al.
They say their study, published in the journal Pain, provides important information considering rehabilitation for patients with musculoskeletal conditions.
By Chloe McIvor