Neuroscience
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Adolescence is an important period for brain development. White matter growth is influenced by sex hormones such as testosterone, and the corpus callosum-the largest white matter structure in the human brain-may change structurally during the hormone-laden period of adolescence. Little is known about puberty's relationship to structural brain development, even though pubertal stage may better predict cognitive and behavioral maturity than chronological age. ⋯ Changing levels of circulating sex hormones during different phases of puberty likely contributed to the observed effects, and further research is clearly needed. Direct quantification of sex hormone levels and regional fiber connectivity-ideally using fiber tractography-will reveal whether hormones are the main drivers of callosal change during puberty. These callosal findings may lead to hypotheses regarding cortical changes during puberty, which may promote or result from changes in inter-hemispheric connectivity.
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Neonatal alcohol exposure impairs cognition and learning in adulthood and permanently damages the hippocampus. Wheel running (WR) improves hippocampus-associated learning and memory and increases the genesis and survival of newly generated neurons in the hippocampal dentate gyrus. WR significantly increases proliferation of newly generated dentate granule cells in alcohol-exposed (AE) and control rats on Postnatal Day (PD) 42 but only control rats show an increased number of surviving cells thirty days after WR (Helfer et al., 2009b). ⋯ Again, the WR/EC intervention reversed the deficit in conditioned fear to the context that was evident in the SH/SH condition. Post-weaning environmental manipulations promote cell survival and reverse learning deficits in rats that were exposed to alcohol during development. These manipulations may provide a basis for developing interventions that ameliorate learning impairments associated with human fetal alcohol spectrum disorders.
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Deliberation between possible options before making a decision is crucial to responding with an optimal choice. However, the neural mechanisms regulating this deliberative decision-making process are still unclear. Recent studies have proposed that the locus coeruleus-noradrenaline (LC-NA) system plays a role in attention, behavioral flexibility, and exploration, which contribute to the search for an optimal choice under uncertain situations. ⋯ In experiment 2, we inhibited LC-NA activity by injection of clonidine, an agonist of the alpha2 autoreceptor, during a decision-making task (1 vs. 3). The clonidine injection suppressed occurrence of VTE in the early phase of the task and subsequently impaired a valuable choice later in the task. These results suggest that the LC-NA system regulates the deliberative process during decision-making.
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Orbitofrontal reality filtering denotes a memory control mechanism necessary to keep thought and behavior in phase with reality. Its failure induces reality confusion as evident in confabulation and disorientation. In the present study, we explored the influence of orbitofrontal transcranial direct current stimulation (tDCS) on reality filtering. ⋯ Computational models predicted that this montage can produce polarity-specific current flow across the posterior medial orbitofrontal cortex (OFC). In agreement with our hypothesis, we found that cathodal tDCS over the frontal pole specifically impaired reality filtering in comparison to anodal and sham stimulation. This study shows that reality filtering, an orbitofrontal function, can be modulated with tDCS.
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Amygdala kindling is well known to increase unconditioned fear and anxiety. However, relatively little is known about whether this form of kindling causes functional changes within the neural circuitry that mediates fear learning and the retrieval of fear memories. To address this issue, we examined the effect of short- (i.e., 30 stimulations) and long-term (i.e., 99 stimulations) amygdala kindling in rats on trace and delay fear conditioning, which are aversive learning tasks that rely predominantly on the hippocampus and amygdala, respectively. ⋯ We also found that kindling-induced impairments in memory retrieval were accompanied by decreased Fos expression in several subregions of the hippocampus, parahippocampus, and amygdala. Interestingly, decreased freezing in the trace conditioning task was significantly correlated with dampened Fos expression in hippocampal and parahippocampal regions whereas decreased freezing in the delay conditioning task was significantly correlated with dampened Fos expression in hippocampal, parahippocampal, and amygdaloid circuits. Overall, these results suggest that amygdala kindling promotes functional changes in brain regions involved in specific types of fear learning and memory.