Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale
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Comparative Study
Information and force level interact in regulating force output during two and three digit grip configurations.
The experiment examined the force fluctuations during two and three digit grip configurations to investigate the relationship between task performance and inter-digit individuation as a function of force level and visual information intermittency rate over approximately 100-fold range (0.21-20 Hz). Subjects grasped an object with either the index finger (two digit grip) or the index and middle finger (three digit grip) opposing the thumb and produced isometric force to match a low and high total force level target. Force accuracy was lower at the large visual intermittency conditions and the higher force level. ⋯ Linear regression between the measures of task performance and inter-digit individuation yielded a significant negative relationship that was only present in the two digit grip when visual feedback rate was 1.67 Hz or lower and in the three digit grip when the feedback rate was 10 Hz or lower. The greater biomechanical degrees of freedom in the three digit grip configuration enable the subject to use, more effectively, visual information feedback at faster timescales in maximizing task performance by increasing digit independence. The shift from visual to nonvisual dominated motor control processes is dependent on the interaction of informational and biomechanical degrees of freedom.
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The lateral prefrontal cortex (LPFC) is important in cognitive control. During the delay period of a working memory (WM) task, primate LPFC neurons show sustained activity that is related to retaining task-relevant cognitive information in WM. However, it has not yet been determined whether LPFC delay neurons are concerned exclusively with the cognitive control of WM task performance. ⋯ Spatial WM-related neurons were more likely to be involved in reward expectancy than in omission-of-reward expectancy. In addition, LPFC delay neurons observed during the delayed response task were not concerned exclusively with the cognitive control of task performance; some were related to reward/omission-of-reward expectancy but not to WM, and many showed more memory-related activity for preferred rewards than for less-desirable rewards. Since employing a more preferred reward induced better task performance in the monkeys, as well as enhanced WM-related neuronal activity in the LPFC, the principal function of the LPFC appears to be the integration of cognitive and motivational operations in guiding the organism to obtain a reward more effectively.
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In Parkinson's disease (PD), the striatal dopamine depletion and the following overactivation of the indirect pathway of the basal ganglia leads to very early disinhibition of the subthalamic nucleus (STN) that may contribute to the progression of PD by glutamatergic overstimulation of the dopaminergic neurons in the substantia nigra. Adenosine A2A antagonism has been demonstrated to attenuate the overactivity of the striatopallidal pathway. To investigate whether neuroprotection exerted by the A2A antagonist 8-(3-chlorostyryl)caffeine (CSC) correlates with a diminution of the striatopallidal pathway activity, we have examined the changes in the mRNA encoding for enkephalin, dynorphin, and adenosine A2A receptors by in situ hybridization induced by subacute systemic pretreatment with CSC in rats with striatal 6-hydroxydopamine(6-OHDA) administration. ⋯ Vehicle-treated group received a solution of dimethyl sulfoxide. CSC pretreatment partially attenuated the decrease in nigral tyrosine hydroxylase immunoreactivity induced by 6-OHDA, whereas no modification of the increase in preproenkephalin mRNA expression in the dorsolateral striatum was observed. The neuroprotective effect of the adenosine A2A antagonist CSC in striatal 6-OHDA-lesioned rats does not result from a normalization of the increase in striatal PPE mRNA expression in the DL striatum, suggesting that other different mechanisms may be involved.
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The increasing therapeutic use of transcranial magnetic stimulation (TMS) in disorders of cortical excitability raises the need for reliable stimulus variables. Stimulation of cortical motor areas influences motor programming and execution. We investigated the effects of TMS delivered over various cortical motor areas during the reaction time (RT) on the execution of sequential rapid arm movements in healthy subjects. ⋯ TMS-induced changes in the kinematics of a sequential arm movement depend closely on the timing of TMS interference, the scalp site stimulated, and the intensity (and number) of stimuli delivered. Late TMS interference inhibits, whereas early interference facilitates, motor performance. The cortical motor region most sensitive to TMS-induced inhibition is that below the scalp site for M1-FDI. In contrast, TMS-induced facilitation has no strict topographic organization. Particularly for MT (although inhibitory and facilitatory effects both depend on stimulation at high intensities) intensity is less crucial than timing of interference and scalp site.
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When standing and balancing on a continuously and predictably moving platform, body equilibrium relies on both anticipatory control and proprioceptive feedback. We have vibrated different postural muscles of the body to assess any effect of confounding the proprioceptive input on balance during such unstable conditions. Low and high platform oscillation frequencies were used, because different strategies are used to withstand the two perturbations. ⋯ The results were (a) the head A-P oscillation was smaller with EO than EC, under both quiet stance and dynamic conditions; (b) vibration of tibialis and triceps surae, but not of other muscles, slightly increased head and body A-P oscillation with EC under dynamic conditions; (c) at 0.2 Hz but not at 0.6 Hz, for all visual and vibration conditions, there was a significant association between head and feet; (d) at 0.2 Hz, EC, neck muscle vibration increased this association, whereas vibration of the other muscles induced a major time delay in the oscillation of head compared with feet; (e) vibration of either neck or tibialis induced forward body leaning, while vibration of either triceps surae or biceps femoris induced backward leaning, with both EO and EC, under both static and dynamic conditions; (f) the head A-P oscillation, however, under dynamic conditions was not dependent on body leaning. The relatively scarce effects of proprioceptive disturbance on head stabilization and multijoint coordination (in spite of effects on body orientation similar to those observed during stance) speak for a major role of anticipatory control in the dynamic equilibrium task. However, the significant vibration-induced time delay in segments' coordination at low translation frequency, EC, suggests that the normally patterned Ia input promotes continuous adjustments of the feed-forward control mode.