Neuroscience
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We used the behavioral task and theoretical construct of the countermanding paradigm to test whether there is any difference between the inhibitory control of the finger, wrist, and arm. Participants were instructed (primary task) to respond to a directional go signal presented at the fovea by pressing a button with either their index or middle fingers, moving a joystick with their wrists, or reaching to a stimulus on a touch screen with their arms. They were also instructed (secondary task) to withhold their responses when a stop signal was presented on 25% of trials. ⋯ By modeling each participant's inhibition function, we estimated that the time needed to inhibit a commanded movement was about 240 ms, a variable that did not differ significantly between the three limb segments. Moreover, we found that the best-fit model of each segment's inhibition function could fit equally well the inhibition functions obtained with the other two segments. These results provide evidence that the upper limb segments share a common inhibitory control, which may facilitate the regulation of neuronal activity within the distributed motor cortical representations and thus simplify the voluntary control of multi-segmental movements.
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Maternal separation (MS) has been used to model the causal relationship between early life stress and the later stress-over-reactivity and affective disorders. Arginine vasopressin (AVP) is among several factors reported to be abnormal. The role of AVP on anxiety is still unclear. ⋯ Volumes of AVP-PVN and AVP-SON measured at PND75 had marked increases as well as AVP plasma concentration at 12h of water deprivation (WD). MS rats demonstrated a high conditioned anxious state under VCT paradigm whereas no difference was found under EPM. These data demonstrate direct relationships between enhanced AVP neuronal activation and a potentiated vasopressin system, and this latter one with high conditioned anxiety in MS male rats.
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Functional effect of short-term immobilization: kinematic changes and recovery on reaching-to-grasp.
Although previous investigations agree in showing significant cortical modifications related to short-term limb immobilization, little is known about the functional changes induced by non-use. To address this issue, we studied the kinematic effect of 10h of hand immobilization. In order to prevent any movement, right handed healthy participants wore on their dominant hand a soft bandage. ⋯ The present findings show firstly that the transport phase of the reaching-to-grasp task was affected by a temporary reduction of sensory and motor information. Secondly, a trial-by-trial recovery of the immobilization-related changes, likely driven by the sensory inputs and motor outputs associated to the repetition of the movement has been observed. All together these results confirm a fundamental role of a continuous stream of sensorimotor signals in maintaining motor efficiency and in driving recovery process.
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Basal ganglia are a network of interconnected nuclei, involved in motor control, goal-directed behaviors and procedural learning. Basal ganglia process information from the cerebral cortex through three main pathways. The striatum is the input nucleus of the direct (cortico-striato-nigral) and indirect (cortico-striato-pallido-subthalamo-nigral) pathways while the subthalamic nucleus (STN) is the input structure of the hyperdirect (cortico-subthalamo-nigral) pathway. ⋯ STN stimulations evoked monosynaptic glutamatergic events in SNr neurons with a mean latency of 2.5 ms and a mean amplitude of 116 pA. This brain slice also preserved a part of the direct and indirect pathways such as the cortico-striatal connection. This novel slice configuration containing the hyperdirect pathway is a useful tool to better understand the transmission and plasticity in this pathway and hence the physiology and the pathophysiology of basal ganglia.
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The striatum is particularly vulnerable to mitochondrial dysfunction and this problem is linked to pathology created by environmental neurotoxins, stimulants like amphetamine, and metabolic disease and ischemia. We studied the course of recovery following a single systemic injection of the mitochondrial complex II inhibitor 3-nitropropionic acid (3-NP) and found 3-NP caused lasting changes in motor behavior that were associated with altered activity-dependent plasticity at corticostriatal synapses in Fischer 344 rats. The changes in synapse behavior varied with the time after exposure to the 3-NP injection. ⋯ Thereafter, the likelihood and degree of inducing D2 DA receptor dependent long-term depression (LTD) gradually increased, relative to saline controls, peaking at 1 month after the 3-NP exposure. NMDA receptor binding did not change over the same post 3-NP time points. These data indicate even brief exposure to 3-NP can have lasting behavioral effects mediated by changes in the way DA and glutamate synapses interact.