Global collaboration is the cornerstone of scientific advancement. Frontiers in Neuroscience has organized a series of special edition Research Topics, with the goal of highlighting the latest advancements in the Neural Circuits field across the globe, showcasing the academic excellence and high-quality work of internationally recognized researchers. This collection aims to shed light on the recent progress made across the entire breadth of the field and reflect on outstanding questions being addressed by researchers across Central and South America. Please note, contributions to the collection are by invitation only however, please contact the Editorial Office if you are interested in submitting a manuscript. Authors must be from Central and South America or currently working in the region.

Bioquímica e Farmacologia, Universidade Federal do Espírito Santo

University of Chile

Pontificia Universidad Católica de Chile

Frontiers in Neural Circuits

Global Excellence in Neural Circuits: Central and South America

The nervous system comprises two cell types: neurons and glia. Individually or collectively, these cells form interconnected systems with different levels of complexity&#x2014;neural circuits&#x2014;that build the perception of the external world and guide the decisions made by each species. From this simplistic perspective, one may ask: how do these cells contribute to different behaviors and how does the environment influence them? To address these questions, we can begin with the notion proposed by Hippocrates that in order to properly study the mind, one must first study the brain.The organization of the brain shows how this group of cells forms an intricate and well-orchestrated circuitry. The neuropil (or neuropile) is a fundamental form of cellular organization in the brain, in which a dense network of dendrites, axonal terminals, and glial processes connect in a precise and finely coordinated manner. Therefore, comprehending how information flows in a specific circuit is essential for understanding its function.The in-depth understanding of neural circuits began with cellular studies conducted by Camillo Golgi and Santiago Ramon Y. Cajal, progressing to the breakthrough in neurophysiology with the publication of the book &#x201c;Integrative action of the nervous system&#x201d; by Sir Charles Scott Sherrington that coined the term synapse. Currently, gene manipulations in specific cell groups, coupled to optogenetics tools, enable the evaluation of how cells within a specific circuitry contribute to precise behaviors. For instance, studies examine the persistent chemical and or/physical changes that occur in the nervous system&#x2014;engrams&#x2014;in response to learned experiences and how these engrams are involved in the encoding, consolidation, and retrieval of a particular memory. Therefore, modern neuroscience aims to understand how different neural circuits are interconnected and integrate within the brain, employing comprehensive maps known as connectomics.The aim of the present editorial is to present two studies on different neural circuities in humans and animals conducted in South America. Manuscripts include one original research study and one review.<a href="https://doi.org/10.3389/fncir.2023.1301962">Donoso-San Martín et al.</a> evaluated possible alterations in the corticofugal pathways in patients with tinnitus during a cross-modal attention task. The authors presented evidence that chronic tinnitus sufferers exhibit a high prevalence of neuropsychiatric conditions along with attention impairment. To test their hypothesis, the authors submitted 28 participants (14 subjects with tinnitus and 14 subjects comprising the control group) to an auditory and visual selective task using simultaneous electroencephalogram (EEG) and distortion-product otoacoustic emissions (DPOAE) recording. They proposed that this attentional paradigm, along with the aforementioned integrated recording methods, may detect possible alterations in the cerebral cortex to cochlea neural network. Although the study is limited by the small number of subjects, the authors found a significant decrease in the DPOAE oscillatory amplitude during the visual attention period, compared to the auditory period in both tinnitus and control groups. Although between-subject statistical analysis (tinnitus vs. control) was not significant, the study suggested that, in tinnitus patients, the top-down infrasonic low-frequency cochlear oscillatory activity in the delta and theta bands is preserved.<a href="https://doi.org/10.3389/fncir.2024.1286111">Negrón-Oyarzo et al.</a> put forward a well-documented review on the importance of prefrontal cortex (PFC) activity, along with other important brain structures, in influencing cognitive control of behavior in normal aging and pathological mental conditions. The authors presented a large body of evidence indicating that cognitive control of behavior is directed toward goal achievement and requires the coordination of several simultaneous neural processes affected by the environment. As environmental conditions constantly change, this continuous inconstance enables animals to respond in an “elastic way”, that is, with behavioral flexibility.Initially, to address the importance of the neural network under PFC coordination, the authors compiled several studies in rodents showing that the medial-PFC (mPFC) is a &#x201c;functional homolog&#x201d; to the human PFC, despite not sharing anatomical features with the primate PFC. In fact, based on cortical folding, rodents are lissencephalic and primates are gyrencephalic species. However, transcriptomic studies showed that rodents and primates exhibit similarities in laminar-gene expression, cell density, and local and large-scale connectivity. Moreover, rodents and primates are social animals, and from a behavioral perspective both species required several cognitive strategies supported by the PFC for goal-directed adaptation.In the second part of the review article, the authors presented the neurophysiological basis of how the PFC contributes to the implementation of cognitive control of behavior. Relying on the neuronal assembly hypothesis, they argue that a small set of neurons fire synchronously during a behavioral task (e.g., the hippocampal place cells that fire specifically when the animal is at a certain location) and the synchronized neuronal spiking in the mPFC (oscillatory frequencies) seems to support cognitive operations. The amplitude and frequency of oscillations depend on the identity and neural composition of neurons in the cerebral space. Thus, different oscillatory frequencies reflect the synchronized recruitment of different levels of neural populations: large-scale neuronal populations exhibit low-frequency oscillations and local neural populations present high-frequency oscillations. As an example, the authors remarked that the mPFC exhibit theta oscillations (6&#x2013;12 Hz) as the most prominent low-frequency oscillatory activity during locomotion and high cognitive demands.Finally, in the third part of the review, the authors explore how impairments of the mPFC lead to dysfunctional activity in normal aging and mental illnesses such as mood disorders and schizophrenia. The aging of populations is rapidly accelerating worldwide. Aging is a natural process accompanied by a decline in cognitive abilities, and although it differs from pathological brain disorders, both processes share pivotal alterations in the mPFC. The authors present studies conducted in rodent models of aging and mental illness that support a robust relationship between aberrant oscillatory activity in the mPFC and the impaired cognitive control of behavior observed in elderly people and mental illness patients. The current pharmacotherapy for cognitive decline (in both normal and pathological mental conditions) is debatable, prompting the authors to propose that new studies should focus on the re-establishment of prefrontal neural activity patterns, and that rodents are suitable for pre-clinical trials.In summary, having a collection of works about neural circuits developed by researchers from South America comprises and important source of information to inspire neuroscientists abroad.CM-S: Writing &#x2013; original draft.The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Editorial: Global excellence in neural circuits: Central and South America

Cognitive control of behavior is crucial for well-being, as allows subject to adapt to changing environments in a goal-directed way. Changes in cognitive control of behavior is observed during cognitive decline in elderly and in pathological mental conditions. Therefore, the recovery of cognitive control may provide a reliable preventive and therapeutic strategy. However, its neural basis is not completely understood. Cognitive control is supported by the prefrontal cortex, structure that integrates relevant information for the appropriate organization of behavior. At neurophysiological level, it is suggested that cognitive control is supported by local and large-scale synchronization of oscillatory activity patterns and neural spiking activity between the prefrontal cortex and distributed neural networks. In this review, we focus mainly on rodent models approaching the neuronal origin of these prefrontal patterns, and the cognitive and behavioral relevance of its coordination with distributed brain systems. We also examine the relationship between cognitive control and neural activity patterns in the prefrontal cortex, and its role in normal cognitive decline and pathological mental conditions. Finally, based on these body of evidence, we propose a common mechanism that may underlie the impaired cognitive control of behavior.

Cognitive control of behavior is crucial for well-being, as allows subject to adapt to changing environments in a goal-directed way. Changes in cognitive control of behavior is observed during cognitive decline in elderly and in pathological mental conditions. Therefore, the recovery of cognitive control may provide a reliable preventive and therapeutic strategy. However, its neural basis is not completely understood. Cognitive control is supported by the prefrontal cortex, structure that integrates relevant information for the appropriate organization of behavior. At neurophysiological level, it is suggested that cognitive control is supported by local and large-scale synchronization of oscillatory activity patterns and neural spiking activity between the prefrontal cortex and distributed neural networks. In this review, we focus mainly on rodent models approaching the neuronal origin of these prefrontal patterns, and the cognitive and behavioral relevance of its coordination with distributed brain systems. We also examine the relationship between cognitive control and neural activity patterns in the prefrontal cortex, and its role in normal cognitive decline and pathological mental conditions. Finally, based on these body of evidence, we propose a common mechanism that may underlie the impaired cognitive control of behavior.

Large-scale coupling of prefrontal activity patterns as a mechanism for cognitive control in health and disease: evidence from rodent models

IntroductionThe mechanisms underlying tinnitus perception are still under research. One of the proposed hypotheses involves an alteration in top-down processing of auditory activity. Low-frequency oscillations in the delta and theta bands have been recently described in brain and cochlear infrasonic signals during selective attention paradigms in normal hearing controls. Here, we propose that the top-down oscillatory activity observed in brain and cochlear signals during auditory and visual selective attention in normal subjects, is altered in tinnitus patients, reflecting an abnormal functioning of the corticofugal pathways that connect brain circuits with the cochlear receptor.</sec>MethodsTo test this hypothesis, we used a behavioral task that alternates between auditory and visual top-down attention while we simultaneously measured electroencephalogram (EEG) and distortion-product otoacoustic emissions (DPOAE) signals in 14 tinnitus and 14 control subjects.</sec>ResultsWe found oscillatory activity in the delta and theta bands in cortical and cochlear channels in control and tinnitus patients. There were significant decreases in the DPOAE oscillatory amplitude during the visual attention period as compared to the auditory attention period in tinnitus and control groups. We did not find significant differences when using a between-subjects statistical approach comparing tinnitus and control groups. On the other hand, we found a significant cluster in the delta band in tinnitus when using within-group statistics to compare the difference between auditory and visual DPOAE oscillatory power.</sec>ConclusionThese results confirm the presence of top-down infrasonic low-frequency cochlear oscillatory activity in the delta and theta bands in tinnitus patients, showing that the corticofugal suppression of cochlear oscillations during visual and auditory attention in tinnitus patients is preserved.</sec>

Introduction: The mechanisms underlying tinnitus perception are still under research. One of the proposed hypotheses involves an alteration in top-down processing of auditory activity. Low-frequency oscillations in the delta and theta bands have been recently described in brain and cochlear infrasonic signals during selective attention paradigms in normal hearing controls. Here, we propose that the top-down oscillatory activity observed in brain and cochlear signals during auditory and visual selective attention in normal subjects, is altered in tinnitus patients, reflecting an abnormal functioning of the corticofugal pathways that connect brain circuits with the cochlear receptor.Methods: To test this hypothesis, we used a behavioral task that alternates between auditory and visual top-down attention while we simultaneously measured electroencephalogram (EEG) and distortion-product otoacoustic emissions (DPOAE) signals in 14 tinnitus and 14 control subjects.Results: We found oscillatory activity in the delta and theta bands in cortical and cochlear channels in control and tinnitus patients. There were significant decreases in the DPOAE oscillatory amplitude during the visual attention period as compared to the auditory attention period in tinnitus and control groups. We did not find significant differences when using a between-subjects statistical approach comparing tinnitus and control groups. On the other hand, we found a significant cluster in the delta band in tinnitus when using within-group statistics to compare the difference between auditory and visual DPOAE oscillatory power.Conclusion: These results confirm the presence of top-down infrasonic low-frequency cochlear oscillatory activity in the delta and theta bands in tinnitus patients, showing that the corticofugal suppression of cochlear oscillations during visual and auditory attention in tinnitus patients is preserved.

The corticofugal oscillatory modulation of the cochlear receptor during auditory and visual attention is preserved in tinnitus

While external stimulation can reliably trigger neuronal activity, cerebral processes can operate independently from the environment. In this study, we conceptualize autogenous cerebral processes (ACPs) as intrinsic operations of the brain that exist on multiple scales and can influence or shape stimulus responses, behavior, homeostasis, and the physiological state of an organism. We further propose that the field should consider exploring to what extent perception, arousal, behavior, or movement, as well as other cognitive functions previously investigated mainly regarding their stimulus–response dynamics, are ACP-driven.

While external stimulation can reliably trigger neuronal activity, cerebral processes can operate independently from the environment. In this study, we conceptualize autogenous cerebral processes (ACPs) as intrinsic operations of the brain that exist on multiple scales and can influence or shape stimulus responses, behavior, homeostasis, and the physiological state of an organism. We further propose that the field should consider exploring to what extent perception, arousal, behavior, or movement, as well as other cognitive functions previously investigated mainly regarding their stimulus–response dynamics, are ACP-driven.

Autogenous cerebral processes: an invitation to look at the brain from inside out

Animal motor behaviors require the coordination of different body segments. Thus the activity of the networks that control each segment, which are distributed along the nerve cord, should be adequately matched in time. This temporal organization may depend on signals originated in the brain, the periphery or other segments. Here we evaluate the role of intersegmental interactions. Because of the relatively regular anatomy of leeches, the study of intersegmental coordination in these animals restricts the analysis to interactions among iterated units. We focused on crawling, a rhythmic locomotive behavior through which leeches move on solid ground. The motor pattern was studied ex vivo, in isolated ganglia and chains of three ganglia, and in vivo. Fictive crawling ex vivo (crawling) displayed rhythmic characteristics similar to those observed in vivo. Within the three-ganglion chains the motor output presented an anterior-posterior order, revealing the existence of a coordination mechanism that occurred in the absence of brain or peripheral signals. An experimental perturbation that reversibly abolished the motor pattern in isolated ganglia produced only a marginal effect on the motor activity recorded in three-ganglion chains. Therefore, the segmental central pattern generators present in each ganglion of the chain lost the autonomy observed in isolated ganglia, and constituted a global network that reduced the degrees of freedom of the system. However, the intersegmental phase lag in the three-ganglion chains was markedly longer than in vivo. This work suggests that intersegmental interactions operate as a backbone of correlated motor activity, but additional signals are required to enhance and speed coordination in the animal.

Animal motor behaviors require the coordination of different body segments. Thus the activity of the networks that control each segment, which are distributed along the nerve cord, should be adequately matched in time. This temporal organization may depend on signals originated in the brain, the periphery or other segments. Here we evaluate the role of intersegmental interactions. Because of the relatively regular anatomy of leeches, the study of intersegmental coordination in these animals restricts the analysis to interactions among iterated units. We focused on crawling, a rhythmic locomotive behavior through which leeches move on solid ground. The motor pattern was studied ex vivo, in isolated ganglia and chains of three ganglia, and in vivo. Fictive crawling ex vivo (crawling) displayed rhythmic characteristics similar to those observed in vivo. Within the three-ganglion chains the motor output presented an anterior-posterior order, revealing the existence of a coordination mechanism that occurred in the absence of brain or peripheral signals. An experimental perturbation that reversibly abolished the motor pattern in isolated ganglia produced only a marginal effect on the motor activity recorded in three-ganglion chains. Therefore, the segmental central pattern generators present in each ganglion of the chain lost the autonomy observed in isolated ganglia, and constituted a global network that reduced the degrees of freedom of the system. However, the intersegmental phase lag in the three-ganglion chains was markedly longer than in vivo. This work suggests that intersegmental interactions operate as a backbone of correlated motor activity, but additional signals are required to enhance and speed coordination in the animal.