Neuroscience
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Cochlear neurons innervate the brainstem cochlear nucleus in a tonotopic fashion according to their sensitivity to different sound frequencies (known as the neuron's characteristic frequency). It is unclear whether these neurons with distinct characteristic frequencies use different strategies to innervate the cochlear nucleus. Here, we use genetic approaches to differentially label spiral ganglion neurons (SGNs) and their auditory nerve fibers (ANFs) that relay different characteristic frequencies in mice. ⋯ Moreover, similar to their peripheral projections, the central projections of ANFs show a gradient of development along the tonotopic axis, with outgrowth and branching of prospective high-frequency ANFs initiated about two days earlier than those of prospective low-frequency ANFs. The processes of synaptogenesis are similar between high- and low-frequency ANFs, but a higher proportion of low-frequency ANFs form smaller endbulb synaptic endings. These observations reveal the diversity of cellular mechanisms that auditory neurons that will become functionally distinct use to innervate their targets during tonotopic map formation.
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Previous research suggests that East Asians pay more attention than Caucasian Westerners to configural information in faces, while the latter group pays more attention to featural information. However, it is unclear whether this cultural variation in attention produces a different time course of the processing bias for configural and featural information. This was examined using event-related potentials in a spatial attention paradigm. ⋯ In contrast, Westerners exhibited a featural processing bias for own-race faces and a configural processing bias for other-race faces on P1 component, whereas a configural processing bias was observed on P2 component for both own- and other-race faces. These results demonstrate that there are important differences between East Asians and Westerners in their relative preferences for configural versus featural processing of own-race faces, but not other-race faces. The relative roles of configural and featural information processing for faces are thus dependent on both who is looking (the culture or race of the observer) and what they are looking at (the race of the face): Easterners enjoy an early global/configural processing bias and a late local/featural processing bias for own-race faces, while Westerners benefit from an early local/featural processing bias and a late global/configural processing bias for own-race faces; both of the groups have an early and late global/configural processing bias for other-race faces.
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As voluntary muscle fatigue increases, the perception of the effort required to produce a particular level of force also increases. This occurs because we produce greater neural outputs from the brain to compensate for the fatigue-induced loss of force. Muscle fatigue can also be generated following bouts of neuromuscular electrical stimulation (NMES), a technique widely used for rehabilitation and training purposes. ⋯ Contrary to voluntary muscle fatigue, the sense of effort decreased post-NMES in both tasks despite increased neural outputs to the elbow flexors of the fatigued indicator arm. This shows that the relationship between motor command magnitude and effort perception was completely modified by NMES. It is proposed that NMES alters the sensory structures responsible for effort signal integration.
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An animal's choice behavior is shaped by the outcome feedback from selected actions in a trial-and-error approach. Tonically active neurons (TANs), presumed cholinergic interneurons in the striatum, are thought to be involved in the learning and performance of reward-directed behaviors, but it remains unclear how TANs are involved in shaping reward-directed choice behaviors based on the outcome feedback. To this end, we recorded activity of TANs from the dorsal striatum of two macaque monkeys (Macaca fuscata; 1 male, 1 female) while they performed a multi-step choice task to obtain multiple rewards. ⋯ Moreover, the feedback responses of TANs were similarly observed in any search trials, without distinctions regarding the predicted probability of rewards and the location of chosen targets. Unambiguously, TANs detected reward and no-reward feedback specifically when the monkeys performed trial-and-error searches, in which the monkeys were learning the value of the targets and adjusting their subsequent choice behavior based on the reward and no-reward feedback. These results suggest that striatal cholinergic interneurons signal outcome feedback specifically during search behavior, in circumstances where the choice outcomes cannot be predicted with certainty by the animals.
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This study examined the processing of ambiguous morphemes in Chinese word recognition with a masked priming lexical decision task. Both behavioral and event-related potential (ERP) were recorded. All targets were bimorphemic compound words that contained ambiguous morphemes as the first morphemes. ⋯ These results have two implications to the processing of ambiguous morphemes during Chinese compound word recognition. First, the morpheme meanings could be activated rapidly. Second, the more frequently used dominant meanings could be activated more easily than the less frequently used subordinate meanings.