Neuroscience
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Sex differences in social cognitive ability are well established, including measures of Theory of Mind (ToM). The aim of this study was to investigate if sex mediates the effects of high-definition transcranial direct current stimulation (HD-tDCS) administered to a key hub of the social brain (i.e., the dorsomedial prefrontal cortex, dmPFC) on the Reading the Mind in the Eyes Test (RMET). Forty healthy young adults (18-35 years) were randomly allocated to receive either anodal or cathodal HD-tDCS in sham HD-tDCS controlled, double blind designs. ⋯ The current study is the first to show improved performance on the RMET after tDCS to the dmPFC in females only. The polarity-specific effects and use of focal HD-tDCS provide evidence for sex-dependent differences in dmPFC function in relation to the RMET. Future studies using tDCS to study or improve ToM, need to consider sex.
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Learning a motor task in one condition typically generalizes to another, although it is unclear why it generalizes substantially in certain situations, but only partially in other situations (e.g., across movement directions and motor effectors). Here, we demonstrate that generalization of motor learning across directions and effectors can be enhanced substantially by inducing use-dependent learning, that is, by having subjects experience motor actions associated with a desired trajectory repeatedly during reaching movements. In Experiments 1 and 2, healthy human adults adapted to a visuomotor rotation while concurrently experiencing repetitive passive movements guided by a robot. ⋯ This intervention resulted in increased motor-evoked potentials (MEPs) and decreased short-interval intracortical inhibition (SICI) in the rTMS group, but not in the sham group. These changes observed in the rTMS group were accompanied by enhanced generalization of visuomotor adaptation across the arms, which was not the case in the sham group. Collectively, these findings confirm the involvement of M1 in use-dependent learning, and suggest that use-dependent learning can contribute not only to motor learning, but also to motor generalization.
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Microstructural MRI basis of the cognitive functions in patients with Spinocerebellar ataxia type 2.
Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant neurodegenerative disease involving the cerebellum. The particular atrophy pattern results in some typical clinical features mainly including motor deficits. In addition, the presence of cognitive impairments, involving language, visuospatial and executive functions, has been also shown in SCA2 patients and it is now widely accepted as a feature of the disease. ⋯ In the present study, diffusion tensor imaging (DTI) based-tractography was performed to map the main cerebellar white matter (WM) bundles, such as Middle and Superior Cerebellar Peduncles, connecting cerebellum with higher order cerebral regions. Damage-related diffusivity measures were used to determine the pattern of pathological changes of cerebellar WM microstructure in patients affected by SCA2 and correlated with the patients' cognitive scores. Our results provide the first evidence that WM diffusivity is altered in the presence of the cerebellar cortical degeneration associated with SCA2 thus resulting in a cerebello-cerebral dysregulation that may account for the specificity of cognitive symptomatology observed in patients.
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We recently found that when monkeys performed an oculomotor version of the time production task, the trial-by-trial latency of self-timed saccades was negatively correlated with pupil diameter just before the delay period (Suzuki et al., 2016). Since pupil diameter has been shown to correlate with neuronal activity in the locus coeruleus, the level of noradrenaline (NA) in the brain might regulate the subjective passage of time. To examine this, we orally administered a selective noradrenaline reuptake inhibitor (reboxetine, 0.4-0.8 mg) when animals made a self-initiated memory-guided saccade >1 s following the appearance of a brief visual cue. ⋯ Because the changes in proportions and latencies of early impulsive saccades were comparable between conditions with and without drug administration, alteration of self-timing might not result from reduced impulsivity. We also assessed other behavioral parameters (saccade accuracy, velocity, and latency variance), but failed to find any drug effect except for the accuracy of visually triggered saccades in the high-dose condition, indicating that reboxetine specifically altered self-timing under our experimental conditions. Our results suggest that NA-related internal states may causally regulate temporal information processing in the brain.
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The calcium-binding protein, parvalbumin (PV), is highly expressed in thalamic reticular nucleus (TRN) GABAergic neurons, which receive input from the cerebral cortex and thalamus and send inhibitory output to the thalamic relay nucleus. Previous studies suggest that the TRN is involved in pain regulation as an important relay nucleus of the ascending pain pathway. However, little is known about its functional role in pain regulation and interconnectivity. ⋯ Furthermore, the anterodorsal and paratenial thalamic nucleus received innervation from PV-positive neurons in the TRNrd. They were specifically inhibited by GABA, which is released from local axonal endings of PV neurons. These findings indicate that activation of PV neurons in the TRNrd increases pain sensitivity in PV-Cre transgenic mice.