Emotions arise from activations of specialized neuronal populations in several parts of the cerebral cortex, notably the anterior cingulate, insula, ventromedial prefrontal, and subcortical structures, such as the amygdala, ventral striatum, putamen, caudate nucleus, and ventral tegmental area. Feelings are conscious, emotional experiences of these activations that contribute to neuronal networks mediating thoughts, language, and behavior, thus enhancing the ability to predict, learn, and reappraise stimuli and situations in the environment based on previous experiences. Contemporary theories of emotion converge around the key role of the amygdala as the central subcortical emotional brain structure that constantly evaluates and integrates a variety of sensory information from the surroundings and assigns them appropriate values of emotional dimensions, such as valence, intensity, and approachability. The amygdala participates in the regulation of autonomic and endocrine functions, decision-making and adaptations of instinctive and motivational behaviors to changes in the environment through implicit associative learning, changes in short- and long-term synaptic plasticity, and activation of the fight-or-flight response via efferent projections from its central nucleus to cortical and subcortical structures.

Little is known about the development of the human entorhinal cortex (EC), a major hub in a widespread network for learning and memory, spatial navigation, high‐order processing of object information, multimodal integration, attention and awareness, emotion, motivation, and perception of time. We analyzed a series of 20 fetal and two adult human brains using Nissl stain, acetylcholinesterase (AChE) histochemistry, and immunocytochemistry for myelin basic protein (MBP), neuronal nuclei antigen (NeuN), a pan‐axonal neurofilament marker, and synaptophysin, as well as postmortem 3T MRI. In comparison with other parts of the cerebral cortex, the cytoarchitectural differentiation of the EC begins remarkably early, in the 10th week of gestation (w.g.). The differentiation occurs in a superficial magnocellular layer in the deep part of the marginal zone, accompanied by cortical plate (CP) condensation and multilayering of the deep part of CP. These processes last until the 13–14th w.g. At 14 w.g., the superficial lamina dissecans (LD) is visible, which divides the CP into the lamina principalis externa (LPE) and interna (LPI). Simultaneously, the rostral LPE separates into vertical cell‐dense islands, whereas in the LPI, the deep LD emerges as a clear acellular layer. In the 16th w.g., the LPE remodels into vertical cell‐dense and cell‐sparse zones with a caudorostral gradient. At 20 w.g., NeuN immunoreactivity is most pronounced in the islands of layer II cells, whereas migration and differentiation inside‐out gradients are seen simultaneously in both the upper (LPE) and the lower (LPI) pyramidal layers. At this stage, the EC adopts for the first time an adult‐like cytoarchitectural organization, the superficial LD becomes discernible by 3T MRI, MBP‐expressing oligodendrocytes first appear in the fimbria and the perforant path (PP) penetrates the subiculum to reach its molecular layer and travels along through the Cornu Ammonis fields to reach the suprapyramidal blade of the dentate gyrus, whereas the entorhinal‐dentate branch perforates the hippocampal sulcus about 2–3 weeks later. The first AChE reactivity appears as longitudinal stripes at 23 w.g. in layers I and II of the rostrolateral EC and then also as AChE‐positive in‐growing fibers in islands of superficial layer III and layer II neurons. At 40 w.g., myelination of the PP starts as patchy MBP‐immunoreactive oligodendrocytes and their processes. Our results refute the possibility of an inside‐out pattern of the EC development and support the key role of layer II prospective stellate cells in the EC lamination. As the early cytoarchitectural differentiation of the EC is paralleled by the neurochemical development, these developmental milestones in EC structure and connectivity have implications for understanding its normal function, including its puzzling modular organization and potential contribution to consciousness content (awareness), as well as for its insufficiently explored deficits in developmental, psychiatric, and degenerative brain disorders.

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In everyday clinical practice, there is an ongoing debate about the nature of major depressive disorder (MDD) in patients with borderline personality disorder (BPD). The underlying research does not give us a clear distinction between those 2 entities, although depression is among the most frequent comorbid diagnosis in borderline personality patients. The notion that depression can be a distinct disorder but also a symptom in other psychopathologies led our team to try and delineate those 2 entities using 146 EEG recordings and machine learning. The utilized algorithms, developed solely for this purpose, could not differentiate those 2 entities, meaning that patients suffering from MDD did not have significantly different EEG in terms of patients diagnosed with MDD and BPD respecting the given data and methods used. By increasing the data set and the spatiotemporal specificity, one could have a more sensitive diagnostic approach when using EEG recordings. To our knowledge, this is the first study that used EEG recordings and advanced machine learning techniques and further confirmed the close interrelationship between those 2 entities.

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