Abstract
For vision, audition and tactile sense, the optimal stimulus frequency for fMRI is somewhat known. For proprioception, i.e., the “movement sense”, however, the optimal frequency is unknown. We studied the effect of passive-finger-movement frequency on proprioceptive fMRI responses using a novel pneumatic-movement actuator. Eleven healthy right-handed volunteers participated in the study. The movement actuator passively moved the participant’s right index finger at frequencies of 0.3, 1, 3, 6, 9, or 12 Hz in a blocked design. A functional localizer was used to define regions-of-interest in SI and SII cortices. In addition, effect of movement range on the fMRI responses was tested in a separate session with 1, 3, 5, and 7 mm movement ranges at a fixed 2 Hz frequency. In primary somatosensory (SI) cortex, the responses were stronger at 3 Hz than at 0.3 Hz (p < 0.001) or 1 Hz (p < 0.05), and at ≥6 Hz than 0.3 Hz (p < 0.001 for frequencies ≥ 6 Hz). In secondary somatosensory (SII) cortex, all movements, except at 0.3 Hz, elicited significant responses of similar strength. In addition, 6, 9, and 12-Hz movements elicited a significant offset response in both SI and SII cortices (p < 0.001–0.05). SI cortex required a total stimulation duration of 4 min to elicit significant activations at the group-level whereas for SII cortex 1 min 20 s was sufficient. Increase in the movement range led to stronger responses in SI cortex, but not in SII cortex. Movements above 3 Hz elicited the strongest SI cortex responses, and increase in the movement range enhanced the response strength. We thus recommend that movements at 3–6 Hz with a movement range of 5 mm or higher to be used in future studies of proprioception. Our results are in-line with previous fMRI and PET studies using tactile or median nerve stimulation at different stimulation frequencies.
Highlights
The term proprioception, i.e., the position and movement sense of the body, was first introduced by Sherrington (1907), who described proprioceptors as: “In muscular receptivity we see the body itself acting as a stimulus to its own receptors—the proprioceptors”
In SII cortex, the response strength did not differ between the frequencies (p = 0.39, χ2 = 5.2, DF = 5; Figure 2B)
We found that increase in the total movement range enhanced the response strength in SI cortex, but not in SII cortex
Summary
The term proprioception, i.e., the position and movement sense of the body, was first introduced by Sherrington (1907), who described proprioceptors as: “In muscular receptivity we see the body itself acting as a stimulus to its own receptors—the proprioceptors” (for a review, see Proske and Gandevia, 2012). Proprioceptors are located in muscles and joints and are sensitive to changes. Muscle spindles are sensitive to changes in the length and stretch of the muscle, and GTOs are monitoring tension produced by the muscle (Moore, 1984; for a review, see Proske and Gandevia, 2012). It is not surprising that many motor disorders, such as cerebral palsy and Parkinson’s disease, are accompanied with deficits in proprioception (Zia et al, 2000; for a review see Konczak et al, 2009). Despite its relevance to motor control and motor disorders, proprioceptive processing in the human brain is still inadequately understood
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