Neuroscience
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The vestibular system of the inner ear contains Type I and Type II hair cells (HCs) generated from sensory progenitor cells; however, little is known about how the HC subtypes are formed. Sox2 (encoding SRY-box 2) is expressed in Type II, but not in Type I, HCs. The present study aimed to investigate the role of SOX2 in cell fate determination in Type I vs. ⋯ These results demonstrate that SOX2 plays a critical role in the determination of Type II vs. Type I HC fate. The results suggested that Sox2 is a potential target for generating Type I HCs, which may be important for regenerative strategies for balance disorders.
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This study compared the effects of fatigue on corticospinal responsiveness in the upper- and lower-limb muscles of the same participants. Seven healthy males performed a 2-min maximal voluntary isometric contraction of the elbow flexors or knee extensors on four separate days. Electromyographic responses were elicited by nerve stimulation (maximal M-wave) in all sessions and by transcranial magnetic stimulation (motor-evoked potential; silent period) and spinal tract stimulation (cervicomedullary or thoracic motor-evoked potentials; silent period) in one session each per limb. ⋯ Sustained maximal contractions elicit different neurophysiological adjustments in upper- and lower-limb muscles. Specifically, motoneuronal excitability was reduced in biceps brachii, but not in rectus femoris, and this reduction required greater compensatory adjustments from the motor cortex. Therefore, changes in cortical and spinal excitability during sustained maximal exercise are likely specific to the muscle performing the task.
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The production of new neurons and their incorporation into preexisting neuronal circuits occur throughout adulthood in the olfactory bulb and the hippocampal dentate gyrus of the mammalian brain. To determine whether the adult-born neurons are engaged in the acquisition and retrieval of olfactory associative memory, we developed and validated a single-trial olfactory fear conditioning protocol in mice which allows to detect activation of newborn neurons during a specific episode of memory acquisition. Using c-Fos mapping of neuronal activity, we then examined the activation of new and preexisting neurons during training and testing sessions. ⋯ Activation of neurons in the dentate gyrus during memory retrieval was observed mainly in the suprapyramidal blade. In the olfactory bulb, 1.6-2.7% of newborn GCs marked with thymidine analogues (2, 4, and 6 weeks old) expressed c-Fos during memory retrieval, while in the dentate gyrus no newborn neurons were found among the c-Fos-positive cells. These data are consistent with the hypothesis that adult-born GCs of the olfactory bulb are less involved in odor-cued associative fear memory than in odor-cued operant behavior memory.
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We explore whether near infrared light can change patterns of resting (task-negative) and/or evoked (task-positive; eg finger-tapping) brain activity in normal, young human subjects using fMRI (functional magnetic resonance imaging). To this end, we used a vielight transcranial device (810 nm) and compared the scans in subjects after active- and sham-light sessions. Our fMRI results showed that, while light had no effect on cerebral blood flow and global resting state brain activity (task-negative), there were clear differences between the active- and sham-light sessions in the patterns of evoked brain activity after finger-tapping (task-positive). ⋯ In summary, our fMRI findings indicated that transcranially applied light did have a major impact on brain activity in normal subjects, but only when the brain region was itself functionally active, when undertaking a particular task. We suggest that these light-induced changes, particularly those in parietal association cortex, were associated with attention and novelty, and served to deactivate the so-called default mode network. Our results lay the template for our planned fMRI explorations into the effects of light in both Alzheimer's and Parkinson's disease patients.
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Although the neural basis underlying visuospatial reasoning has been widely explored by neuroimaging techniques, the brain activation patterns during naturalistic visuospatial reasoning such as tangram remains unclear. In this study, the directional functional connectivity of fronto-parietal networks during the tangram task was carefully inspected by using combined functional near-infrared spectroscopy (fNIRS) and conditional Granger causality analysis (GCA). Meanwhile, the causal networks during the traditional spatial reasoning task were also characterized to exhibit the differences with those during the tangram task. ⋯ Further correlation analyses showed that the behavioral performance in the spatial reasoning rather than the tangram task manifested the relationship with the connectivity between the frontal and parietal cortex. Our findings demonstrate that the tangram task measures a different aspect of the visuospatial reasoning ability which requires more trial-and-error strategies and creative thinking rather than inductive reasoning. In particular, the frontal cortex is mostly involved in tangram puzzle-solving, whereas the interaction between frontal and parietal cortices is regulated by the hands-on experience during the tangram task.