Neuroimaging cortical proprioceptive processing with evoked movements

Motor function such as a person grasping an apple depends on functional motor efference. Motor efference means downstream neural, electrochemical signalling, where the motor regions of the brain send neural signals via the spinal cord for the appropriate muscles to contract and relax. Often overlooked aspect of motor function, however, is the sensory afference, where the feedback from the sensory organs is processed in the brain to plan and correct movement. Sensory afference includes proprioception which is the position, force and movement sense of the body. Signals from the proprioceptors residing mainly in the muscles inform the brain about the positional configuration of the body to initiate and adjust appropriate movements. Cortical proprioception is mainly processed in the somatosensory cortices. Cortical proprioception can be studied with neuroimaging methods in conjunction with evoked (passive) movements. Behavioral methods can also be used to study proprioception. This thesis consists of three publications (PI–PIII) studying cortical proprioception using functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) with evoked movements of the index fingers and ankles. The evoked movements stimulating the proprioceptors were produced with pneumatic devices. First (PI) and second publications (PII) studied how varying kinematic parameters such as movement frequency and range of evoked index finger movements affected cortical proprioceptive responses in fMRI and MEG. The third publication (PIII) examined how cortical proprioceptive processing differed between adolescents with and without cerebral palsy and how these differences related to sensorimotor performance (i.e. motor and sensory abilities). Movement frequency ≥ 3 Hz and range ≥ 5 mm of the index finger elicited strongest cortical proprioceptive responses in fMRI (PI). In contrast, movement range did not have an effect on cortical proprioceptive response strength in MEG (PII). Adolescents with CP had stronger cortical proprioceptive responses of the somatosensory cortices in their more affected hemisphere to index finger stimulation compared to adolescents without CP (PIII). Moreover, worse sensorimotor performance was associated with stronger cortical proprioceptive responses regardless whether the participant had CP or not (PIII). These studies demonstrate that using evoked movements with neuroimaging is a viable tool to study cortical proprioception. The effect of kinematic stimulation parameters on cortical proprioceptive processing can be studied using evoked movements. Neuroimaging with evoked movements also revealed that proprioceptive processing differs between adolescents with and without CP and these differences are associated with sensorimotor performance or motor ability (PIII). Sensory afference in general and cortical proprioception in particular is a critical part of motor function and should be studied further with neuroimaging and evoked movements.