Parameters of cortical excitability were evaluated at rest and at six points in time during the preparation of a simple finger movement. Patients with Gilles de la Tourette syndrome displayed significantly reduced short-interval intracortical inhibition at rest, while no differences were apparent for unconditioned motor evoked potential

or intracortical facilitation. During the premovement phase, significant differences between groups were seen for single pulse motor evoked potential amplitudes and short-interval intracortical inhibition. Short-interval intracortical inhibition was reduced in the early phase of movement Angiogenesis inhibitor preparation (similar to rest) followed by a transition towards more inhibition. Subsequently modulation of short-interval intracortical inhibition was comparable to controls, while corticospinal recruitment was reduced in later phases of movement preparation.

The present data support the hypothesis of motorcortical disinhibition in Gilles de la Tourette signaling pathway syndrome at rest. During performance of a motor task, patients start from an abnormally disinhibited level of short-interval intracortical inhibition early during movement preparation with subsequent modulation of inhibitory activity similar to healthy controls. We hypothesize that while at rest, abnormal subcortical inputs from aberrant striato-thalamic afferents target the motor cortex, during motor performance, motor cortical excitability most likely underlies top-down control from higher motor areas and prefrontal cortex, which override these abnormal subcortical inputs to guarantee adequate behavioural performance.”
“Tanaka H, Sejnowski TJ. Computing reaching dynamics in motor cortex with Cartesian selleck compound spatial coordinates. J Neurophysiol 109: 1182-1201, 2013. First published October 31, 2012; doi:10.1152/jn.00279.2012.-How neurons in the primary motor cortex control arm movements is not yet understood. Here we show that the equations of motion governing reaching simplify when expressed in spatial coordinates. In this fixed reference frame, joint torques are the sums

of vector cross products between the spatial positions of limb segments and their spatial accelerations and velocities. The consequences that follow from this model explain many properties of neurons in the motor cortex, including directional broad, cosinelike tuning, nonuniformly distributed preferred directions dependent on the workspace, and the rotation of the population vector during arm movements. Remarkably, the torques can be directly computed as a linearly weighted sum of responses from cortical motoneurons, and the muscle tensions can be obtained as rectified linear sums of the joint torques. This allows the required muscle tensions to be computed rapidly from a trajectory in space with a feedforward network model.