Effects of altered sensory input from the neck on cerebellar function, body schema and sensorimotor integration

Abstract

Neck muscles have a high density of muscle spindle afferents and their input is critical for formulating the perception of head position relative to the body. Chronic alterations in afferent input from the neck may be studied in individuals with subclinical neck pain (SCNP), defined as non-severe recurrent neck pain lasting at least three months in the past year and testable on pain-free days so as to explore altered-afferent-input effects on cerebellar processing, upper extremity function and spatial awareness in the absence of pain. The first study tested participants with SCNP using transcranial magnetic stimulation to activate the cerebellar-thalamic-cortical circuit and produce cerebellar inhibition (CBI). SCNP participants were randomized to receive cervical manipulation or passive head movement (PHM), following which all participants completed a motor acquisition task. Healthy controls and SCNP participants who received manipulation showed significantly less CBI and improved motor performance whereas the SCNP group who received PHM showed no changes to CBI. The second study tested SCNP participants on upper extremity dart throwing. Three sets of ten darts were thrown at a slow-to-normal speed and three sets of ten darts were thrown at a fast speed. Compared to healthy participants, SCNP participants showed significantly greater elbow and forearm variability in motor selection, greater peak acceleration velocity of shoulder flexion-extension movement, and greater peak deceleration velocity of wrist movement. The third study looked at whether SCNP also impacted spatial awareness beyond an egocentric frame of reference, by measuring the response time to recognize objects which were rotated relative to their usual orientation. The SCNP group showed slower mental rotation at baseline and a smaller improvement when measured after four weeks (8.6%) in comparison to the healthy group (16.1%). These studies provide compelling evidence that chronic alterations in sensory input from the neck influences cerebellar integration leading to changes to upper extremity movement and spatial awareness of object orientation.