Neuroscience
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Somatosensory inputs affect primary motor cortex (M1) excitability; however, the effect of movement-induced somatosensory inputs on M1 excitability is unknown. This study examined whether M1 excitability is modulated by somatosensory inputs with passive movement in 29 healthy subjects. Motor-evoked potentials (MEPs), elicited by transcranial magnetic stimulation (TMS) were recorded from the first dorsal interosseous (FDI) muscle (Experiment 1). ⋯ Passive movement was performed at two movement velocities (Experiment 3) or joint angles (Experiment 4). MEP facilitation was observed depending on the movement velocities or joint angles. These experiments demonstrated that somatosensory inputs induced by passive movements facilitated M1 excitability depending on the ISIs, passive movement velocity, and joint angle.
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Pregnancy is accompanied by complex biological adaptations, including extreme hormonal fluctuations. Moreover, changes on the endocrine level are accompanied by changes in cerebral anatomy, such as reductions in brain or gray matter volume. Since declining brain and tissue volumes are characteristic for normal aging, the question arises of whether such pregnancy-induced anatomical effects are permanent or transient. ⋯ Comparing the BrainAGE indices between both time points, female brains at late postpartum were estimated to be considerably younger than at early postpartum. On average, that difference was about five years (mean ± SD: 5.4 ± 2.4 years). These findings suggest a substantial restoration/rejuvenation effect after giving birth, which is evident already within the first couple of months.
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Action observation is known to enhance sensorimotor system activation, and such effect has been linked to neural priming and response facilitation mechanisms. This facilitation effect, however, has been primarily studied by focusing on high-level motor proficiency, whereas evidence on the effect of observing poorly performed actions is still lacking. We then devised a study to investigate neural correlates of the observation of suboptimal motor acts as mirrored by corticospinal activation (via transcranial magnetic stimulation (TMS), Experiment 1) and by modulation of cortical oscillatory activity (via electroencephalography (EEG), Experiment 2). 40 participants were presented with four randomly reiterated videos. ⋯ Analyses highlighted both increased corticospinal excitability and desynchronized alpha-beta oscillations during the observation of poorly performed motor acts performed by the mildly impaired MS patient. Further, we observed gradually increasing beta activity across videos reiterations, specifically for the minimally impaired patient's video. Reported findings corroborate the hypotheses that the action-observation network and the motor system might be involved in processes evoked in the attempt to understand and predict observed actions which do not belong to the onlookers' motor repertoire, reflecting in an increased sensorimotor activity.
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Cholinergic stimulation coupled with visual conditioning enhances the visual acuity and cortical responses in the primary visual cortex. To determine which cholinergic receptors are involved in these processes, qRT-PCR was used. Two modes of cholinergic enhancement were tested: a phasic increase of acetylcholine release by an electrical stimulation of the basal forebrain cholinergic nucleus projecting to the visual cortex, or a tonic pharmacological potentiation of the cholinergic transmission by the acetylcholine esterase inhibitor, donepezil. ⋯ A Kruskal-Wallis test showed a modulation of the expression in the visual cortex of m2, m3, m4, m5, α7, β4, NMDA and GAD65, but only β4 within the basal forebrain and none of these mRNA within the somatosensory cortex. The two modes of cholinergic enhancement induced different effects on mRNA expression, related to the number of visual conditioning sessions and receptor specificity. This study suggests that the combination of cholinergic enhancement and visual conditioning is specific to the visual cortex and varies between phasic or tonic manipulation of acetylcholine levels.
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Comparative Study
Masking Differentially Affects Envelope-following Responses in Young and Aged Animals.
Age-related hearing decline typically includes threshold shifts as well as reduced wave I auditory brainstem response (ABR) amplitudes due to cochlear synaptopathy/neuropathy, which may compromise precise coding of suprathreshold speech envelopes. This is supported by findings with older listeners, who have difficulties in envelope and speech processing, especially in noise. However, separating the effects of threshold elevation, synaptopathy, and degradation by noise on physiological representations may be difficult. ⋯ High-pass noise may affect EFR amplitudes in young animals more than aged by reducing the contributions of high-frequency-sensitive inputs. EFRs to SAM tones in modulated noise (NAM) suggest that neurons of young animals can synchronize to NAM at lower sound levels and maintain dual AM representations better than older animals. The overall results show that EFR amplitudes are strongly influenced by aging and the presence of a competing sound that likely reduces or shifts the pool of responsive neurons.