Neuroscience
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The velocity of impact between an object and the human head is a critical factor influencing brain injury outcomes but has not been explored in any detail in animal models. Here we provide a comprehensive overview of the interplay between impact velocity and injury severity in a well-established weight-drop impact acceleration (WDIA) model of diffuse brain injury in rodents. ⋯ There were impact velocity-dependent reductions in sensorimotor performance and in cortical depth-related depression of sensory cortex responses; however axonal injury (demonstrated by immunohistochemistry for β-amyloid precursor protein and neurofilament heavy-chain) was discernible only at the highest impact velocity. We conclude that the WDIA model is capable of producing graded axonal injury in a repeatable manner, and as such will prove useful in the study of the biomechanics, pathophysiology and potential treatment of diffuse axonal injury.
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Cortical sensory representations can be reorganized by sensory exposure in an epoch of early development. The adaptive role of this type of plasticity for natural sounds in sensory development is, however, unclear. We have reared rats in a naturalistic, complex acoustic environment and examined their auditory representations. ⋯ A comparison of population-temporal responses to the experienced complex sounds revealed that cortical responses to different renderings of the same song motif were more similar, indicating that the cortical neurons became less sensitive to natural acoustic variations associated with stimulus context and sound renderings. By contrast, cortical responses to sounds of different motifs became more distinctive, suggesting that cortical neurons were tuned to the defining features of the experienced sounds. These effects lead to emergent "categorical" representations of the experienced sounds, which presumably facilitate their recognition.
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Pretend play, emerging at about 18 months, and explicit false belief (FB) understanding, arising around 4 years, constitute two pivotal milestones in the development of a Theory of Mind since both involve the ability to separate real from non-real content. The developmental lag has evoked vivid discussion with respect to whether or not pretense (PT) involves a metarepresentational understanding similar to FB. However, in children PT and FB have not yet been contrasted on a neural level to reveal whether they are subserved by the same neurocognitive mechanism. ⋯ Given the differences in latency, polarity, and topography, PT and FB seem to rely on distinct neural substrates in children. The early negative frontal slow wave indicates that for PT reasoning children may use simple mentalizing processes such as intention processing, whereas the late positive slow-wave shows that for FB children may engage in metarepresentational processing. Therefore, the present findings seem to substantiate theoretical accounts postulating simple mentalistic reasoning for PT in children.
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In many day-to-day situations humans manifest a marked tendency to hold the head vertical while performing sensori-motor actions. For instance, when performing coordinated whole-body motor tasks, such as skiing, gymnastics or simply walking, and even when driving a car, human subjects will strive to keep the head aligned with the gravito-inertial vector. Until now, this phenomenon has been thought of as a means to limit variations of sensory signals emanating from the eyes and inner ears. ⋯ In this situation, the CNS might reconstruct the orientation of the target in kinesthetic space or reconstruct the orientation of the hand in visual space, or both. By having subjects tilt the head during target acquisition or during movement execution, we show a greater propensity to perform the sensory reconstruction that can be achieved when the head is held upright. These results suggest that the reason humans tend to keep their head upright may also have to do with how the brain manipulates and stores spatial information between reference frames and between sensory modalities, rather than only being tied to the specific problem of stabilizing visual and vestibular inputs.
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The cortical area located in the lateral portion of the posteromedial suprasylvian sulcus (PMLS) is considered a key area for motion processing. It receives major projections from areas 17 and 18 but also from the lateral posterior-pulvinar complex where neurons exhibit, for the most part, complex receptive fields (RF). Based on these inputs, complex-like RFs would be expected for PMLS neurons and results from hand-plot mapping support this idea. ⋯ The data show that the direction index is positively correlated with subfield size difference and negatively correlated with spatial subfield overlap. Modulation index is negatively correlated with the degree of temporal subfield activity overlap. We conclude that first-order RF structures are important functional factors that shape PMLS neurons response characteristics.