Voluntary Movement Takes Shape: The Link Between Movement Focusing and Sensory Input Gating

Abnormal motor surround inhibition associated with cortical and deep grey matter involvement in multiple sclerosis

OBJECTIVE

Motor surround inhibition (mSI) is a physiological mechanism that contributes to hand movement control by focusing voluntary movement. Growing evidence suggests that hand movement control is impaired in multiple sclerosis. The aim of the study was to evaluate mSI in MS and to investigate the brain structures involved in mSI in multiple sclerosis.

METHODS

We recruited 33 patients and 23 controls. To investigate mSI, we delivered transcranial magnetic single pulses during index finger flexion. Motor evoked potentials were recorded and first dorsal interosseous ("active muscle") and from the abductor digiti minimi ("surround muscle"). mSI was expressed as the ratio between Motor evoked potentials recorded from the surround muscle during movement and at rest. Participants underwent a magnetic resonance study.

RESULTS

Patients had impaired mSI as compared with controls. Magnetic resonance showed that basal ganglia had smaller volumes and higher mean diffusivity than controls. Impaired mSI correlated with primary motor cortex and basal ganglia involvement in multiple sclerosis.

CONCLUSION

Altered mSI in multiple sclerosis is related to cortical and subcortical grey matter involvement.

SIGNIFICANCE

Our study provides the first demonstration of a pathophysiological mechanism underlying hand movement control dysfunction in multiple sclerosis. mSI represents a new therapeutic target of multiple sclerosis rehabilitative approaches.

Somatosensory temporal discrimination threshold changes during motor learning

PURPOSE

Mechanisms underlying the somatosensory temporal discrimination threshold and its relationship with motor control have been reported; however, little is known regarding the change in temporal processing of tactile information during motor learning. We investigated the somatosensory temporal discrimination threshold changes during motor learning in a feedback-control task.

MATERIALS AND METHODS

We included 15 healthy individuals. The somatosensory temporal discrimination threshold was measured on the index finger. A 10-session coin rotation task was performed, with 2 min' training per session. The coin rotation scores were determined through tests (continuous coin rotation at 180° at maximum speed for 10 s). The coin rotation test score and the somatosensory temporal discrimination threshold were determined at baseline and after 5 and 10 sets of training, as follows: pre-test; training_5set (1 set × 5); post-test_5block; training_5set (1 set × 5); and post-test_10block. The coin rotation score and the somatosensory temporal discrimination threshold were compared between the tests. The latter was also compared between the right (the within-subject control) and left fingers.

RESULTS

The coin rotation score showed significant differences among all tests. In the somatosensory temporal discrimination threshold, there was a significant difference between the pre-test and post-test_5block values, pre-test and post-test_10block values of the left side and between the right and left sides in the post-test_5block and the post-test_10block values.

CONCLUSIONS

The somatosensory temporal discrimination threshold decreased along with task-performance progress following motor learning during a feedback-control task.

Botulinum Toxin Effects on Sensorimotor Integration in Focal Dystonias

(1) Background: In dystonia, the somatosensory temporal discrimination threshold (STDT) is abnormally increased at rest and higher and longer-lasting during movement execution in comparison with healthy subjects (HS), suggesting an abnormal sensorimotor integration. These abnormalities are thought to depend on abnormal proprioceptive input coming from dystonic muscles. Since Botulinum toxin-A (BT-A) reduces proprioceptive input in the injected muscles, our study investigated the effects of BT-A on STDT tested at rest and during voluntary movement execution in patients with focal dystonia. (2) Methods: We enrolled 35 patients with focal dystonia: 14 patients with cervical dystonia (CD), 11 patients with blepharospasm (BSP), and 10 patients with focal hand dystonia (FHD); and 12 age-matched HS. STDT tested by delivering paired stimuli was measured in all subjects at rest and during index finger abductions. (3) Results: Patients with dystonia had higher STDT values at rest and during movement execution than HS. While BT-A did not modify STDT at rest, it reduced the abnormal values of STDT during movement in CD and FHD patients, but not in BSP patients. (4) Conclusions: BT-A improved abnormal sensorimotor integration in CD and FHD, most likely by decreasing the overflow of proprioceptive signaling from muscle dystonic activity to the thalamus.

Deep grey matter involvement and altered sensory gating in multiple sclerosis

BACKGROUND

Somatosensory temporal discrimination threshold (STDT) is altered in multiple sclerosis (MS). In healthy subjects (HS), voluntary movement modulates the STDT through mechanisms of subcortical sensory gating.

OBJECTIVE

With neurophysiological and magnetic resonance imaging (MRI) techniques, we investigated sensory gating and sensorimotor integration in MS.

METHODS

We recruited 38 relapsing-remitting multiple sclerosis (RR-MS) patients with no-to-mild disability and 33 HS. We tested STDT at rest and during index finger abductions and recorded the movement kinematics. Participants underwent a 3T MRI protocol.

RESULTS

Patients exhibited higher STDT values and performed slower finger movements than HS. During voluntary movement, STDT values increased in both groups, albeit to a lesser extent in patients, while the mean angular velocity of finger movements decreased in patients alone. Patients had a smaller volume of the thalamus, pallidum and caudate nucleus, and displayed higher mean diffusivity in the putamen, pallidum and thalamus. STDT correlated with thalamic volume while mean angular velocity correlated with putaminal volume. Changes in mean angular velocity during sensorimotor integration inversely correlated with mean diffusivity in the thalamus and pallidum. Changes in STDT and velocity were associated with fatigue score.

CONCLUSION

Altered STDT and sensorimotor integration are related to structural damage in the thalamus and basal ganglia in MS and likely to affect motor performance.