The measurements of the similarity of dynamic brain functional network / 生物医学工程学杂志

Brain functional network changes over time along with the process of brain development, disease, and aging. However, most of the available measurements for evaluation of the difference (or similarity) between the individual brain functional networks are for charactering static networks, which do not work with the dynamic characteristics of the brain networks that typically involve a long-span and large-scale evolution over the time. The current study proposes an index for measuring the similarity of dynamic brain networks, named as dynamic network similarity (DNS). It measures the similarity by combining the "evolutional" and "structural" properties of the dynamic network. Four sets of simulated dynamic networks with different evolutional and structural properties (varying amplitude of changes, trend of changes, distribution of connectivity strength, range of connectivity strength) were generated to validate the performance of DNS. In addition, real world imaging datasets, acquired from 13 stroke patients who were treated by transcranial direct current stimulation (tDCS), were used to further validate the proposed method and compared with the traditional similarity measurements that were developed for static network similarity. The results showed that DNS was significantly correlated with the varying amplitude of changes, trend of changes, distribution of connectivity strength and range of connectivity strength of the dynamic networks. DNS was able to appropriately measure the significant similarity of the dynamics of network changes over the time for the patients before and after the tDCS treatments. However, the traditional methods failed, which showed significantly differences between the data before and after the tDCS treatments. The experiment results demonstrate that DNS may robustly measure the similarity of evolutional and structural properties of dynamic networks. The new method appears to be superior to the traditional methods in that the new one is capable of assessing the temporal similarity of dynamic functional imaging data.

Evaluation of thymic lymphocyte loss of broiler using Digital Analysis of the Lymphoid Depletion System (ADDL) / Avaliação de perda de linfócitos do timo em frangos usando análise digital do sistema de depleção linfóide (ADDL)

The thymus is a lymphoid organ and usually evaluated for the degree of lymphocyte loss with subjective histological techniques. This study aimed to adapt and to apply of the digital analysis of the lymphoid depletion system (ADDL) in the thymus in order to obtain a more accurate analysis. Glucocorticoid was used to induce immunosuppression in 55 broilers at 21 days of age; other 15 broilers were the control group. After euthanasia of the broilers, postmortem examination was made. Both thymic chains were collected and six lobes were selected for histological examination of the degree of lymphocyte depletion (scores 1 to 5) and for submission to all stages of processing by the ADDL system. The artificial constructed neural networks (ANN) obtained 94.03% of correct classifications. In conclusion, it was possible to adopt objective criteria to evaluate thymic lymphoid depletion with the ADDL system.(AU)

O timo é um órgão linfóide, que é normalmente avaliado para o grau de perda de linfócitos a partir de técnicas histológicas subjetivas. Este trabalho teve como objetivo a adaptação e aplicação do sistema de análise digital de depleção linfóide (ADDL) para o timo, a fim de tornar sua análise mais acurada. Glicocorticóides foram utilizados a fim de induzir imunossupressão em 55 aves de 21 dias de idade. Outras 15 aves formaram o grupo controle. Posteriormente, para cada um dos aves, realizou-se a eutanásia e necropsia. Ambas as cadeias do timo foram coletadas e foram selecionadas seis lóbulos para processamento histológico, análise quanto ao grau de depleção linfocitária (escores de 1-5) e submissão a todas as fases do processamento pelo sistema ADDL. Observou-se que a rede neural artificial (RNA) construída obteve 94,03% de classificações corretas. Em conclusão, foi possível adotar critérios objetivos para avaliar a depleção linfóide tímica utilizando o sistema ADDL.(AU)

Morphometric analysis of feedforward pathways from the primary somatosensory area (S1) of rats

We used biotinylated dextran amine (BDA) to anterogradely label individual axons projecting from primary somatosensory cortex (S1) to four different cortical areas in rats. A major goal was to determine whether axon terminals in these target areas shared morphometric similarities based on the shape of individual terminal arbors and the density of two bouton types: en passant (Bp) and terminaux (Bt). Evidence from tridimensional reconstructions of isolated axon terminal fragments (n=111) did support a degree of morphological heterogeneity establishing two broad groups of axon terminals. Morphological parameters associated with the complexity of terminal arbors and the proportion of beaded Bp vs stalked Bt were found to differ significantly in these two groups following a discriminant function statistical analysis across axon fragments. Interestingly, both groups occurred in all four target areas, possibly consistent with a commonality of presynaptic processing of tactile information. These findings lay the ground for additional work aiming to investigate synaptic function at the single bouton level and see how this might be associated with emerging properties in postsynaptic targets.

Las enfermedades ¿son solo padecimientos?: biomedicina, formas de atención "paralelas" y proyectos de poder / Is disease merely illness?: Biomedicine, "parallel" forms of care and power

Partiendo de la propuesta de Giovanni Berlinguer, de que los procesos de salud/enfermedad constituyen algunos de los principales espías de las contradicciones de un sistema, se describen en primer lugar algunos casos ocurridos en contextos capitalistas centrales y periféricos, así como en Estados denominados "socialistas reales", que permiten observar dicho papel. En segundo lugar, observamos los procesos y sobre todo las interpretaciones que se han desarrollado en América Latina y especialmente en México respecto del papel atribuido a la medicina tradicional en la identidad y pertenencia de los pueblos originarios, y que subrayan la incompatibilidad de las cosmovisiones indígenas con la biomedicina, analizando algunos proyectos que se impulsaron en términos de salud intercultural, y que concluyeron en su mayoría en fracasos, tanto desde el punto de vista de la salud, como político. Se subraya el contenido y la perspectiva casi exclusivamente ideológicos de dichos proyectos, y su poca relación con la realidad de los pueblos originarios. Por último, se trata de ver si la trayectoria de estas concepciones y programas de salud expresan y explican el notable repliegue que sufren desde hace casi diez años la mayoría de los movimientos étnicos en América Latina.

Following Giovanni Berlinguer's proposal that health/disease processes are one of the primary spies into the contradictions of a system, this article describes cases that occurred in central and peripheral capitalist contexts as well as in the so-called "real socialist" States that allow such a role to be seen. Secondly, we observe the processes and above all the interpretations developed in Latin America and especially Mexico regarding the role attributed to traditional medicine in the identity and sense of belonging of indigenous peoples, which emphasize the incompatibility of indigenous worldviews with biomedicine. To do so we analyze projects that were carried out under the notion of intercultural health, which in large part resulted in failure both in health and political terms. The almost entirely ideological content and perspective of these projects is highlighted, as is the scant relationship they hold with the reality of indigenous people. Lastly, the impact and role that the advance of these conceptualizations and health programs might have had in the disengagement experienced over the last nearly ten years in the ethnic movements of Latin America is considered.

Sensory evaluation of dairy supplements enriched with reduced iron, ferrous sulfate or ferrous fumarate / Evaluación sensorial de suplementos lácteos enriquecidos con hierro reducido, sulfato ferroso o fumarato ferroso

Objective. To determine the degree of liking of the Oportunidades programme dietary supplements (DS) -purees and beverages- added with different iron salts (IS): reduced iron (RI), ferrous sulphate (FS) or ferrous fumarate (FF) during 24 weeks of storage. Materials and methods. The DS were evaluated through a hedonic scale for aroma, flavour and colour attributes; at time zero and every eight weeks, each panel member evaluated three DS with same flavour and presentation but different IS. Seventy women participated as panel members. Results. The chocolate and banana DS exhibited a change in preference by colour and flavour due to storage. DS with FS or RI showed the least preference by flavour and colour in the context of the three IS considered. The chocolate and neutral DS enriched with FS changed their colour and flavour. Conclusion. DS were, in general, well-liked; nonetheless, for purees enriched with FS and for beverages enriched with RI, the less-liked attributes were colour and flavour.

Objetivo. Determinar el nivel de agrado de los suplementos alimenticios (SA) (papillas y bebidas) del Programa Oportunidades, adicionados con diferentes sales de hierro (SH): hierro reducido (HR), sulfato ferroso (SF) o fumarato ferroso (FF), durante 24 semanas de almacenamiento. Material y métodos. Se evaluaron mediante una escala hedónica los atributos olor, sabor y color; a tiempo cero y cada ocho semanas, cada juez evaluó tres suplementos, mismo sabor, presentación y diferente SH. Participaron 70 mujeres. Resultados. Los SA sabor chocolate y plátano presentaron modificación del agrado por color y sabor durante el almacenamiento. Los SA con SF o HR presentaron el menor agrado para sabor y olor por efecto de las SH. En los SA sabor chocolate y natural adicionados con SF se afectó el color y el sabor. Conclusión. Los SA en general presentaron agrado; sin embargo, en las papillas adicionadas con SF y las bebidas con HR los atributos limitantes fueron color y sabor.

Bases neurobiológicas de la conciencia: aspectos neuroanatómicos, cognitivos y evolutivos / Neurobiological basis of consciousness: neuroanatomical, cognitive and evolutionary aspects

La investigación sobre la conciencia desde una perspectiva neurobiológica constituye uno de los temas más controvertidos en el amplio dominio de las neurociencias. Tradicionalmente, la conciencia ha sido entendida como la experiencia subjetiva y privada que surge de la actividad de neuronas múltiples y que incluye nuestros pensamientos, recuerdos y lo imaginado. A menudo se hace la distinción entre una conciencia intransitiva, que alude a un estado de vigilancia opuesto al estado de coma clínico, y una transitiva, que se refiere al acceso consciente de diferentes piezas de información. Evolutivamente, al entender la conciencia como el resultado de habilidades cognitivas complejas, es posible plantear que ella se encuentra distribuida en la filogenia incluso más allá de los mamíferos sociales. A partir de la relación entre conciencia y cognición, dos teorías han sido ampliamente difundidas y debatidas: la del núcleo dinámico y la del espacio de trabajo global. La primera relaciona la experiencia consciente con circuitos tálamo-corticales recurrentes, mientras que la segunda considera vastas redes neuronales parieto-temporales y prefrontales como base para el acceso consciente. Se ha postulado que la conciencia depende de la actividad de una red neural por defecto. Aún más, la conciencia humana representaría una corriente narrativa cuya historia ha sido modulada por la interacción social.

Research about consciousness from a neurobiological perspective is one of the most controversial issues in the broad domain of neuroscience. Traditionally, consciousness has been defined as subjective and private experience that arises from multiple neuronal activities and it includes our thoughts, memories and imaging. Usually, it has been made a distinction between intransitive consciousness that refers to a vigilance state opposite to clinical coma and transitive consciousness conceived as a conscious access to different pieces of information. From an evolutionary perspective, consciousness may be conceived as the result of complex cognitive skills leading to claim that it is distributed in phylogeny even beyond social mammals. From the relationship between consciousness and cognition, two theories have been widely discussed: the Dynamic Core and the Global Workspace. The first relates conscious experience to recurrent thalamo cortical circuits, while the second considers parietotemporal and prefrontal large neural networks as the basis for conscious access. It has been suggested that human consciousness depends on a default network. Furthermore, human consciousness could represent a narrative stream of reflective thought that is critical for the control of actions and is encultured by social interaction.

Inferência do tempo de atividade neural a partir do efeito BOLD em ressonância magnética funcional / Inference of neural activity time from BOLD effect in functional magnetic resonance imaging

A inferência do curso temporal da atividade neural a partir do efeito BOLD é um importante problema, ainda em aberto. A forma da curva BOLD não reflete diretamente as características temporais da atividade eletrofisiológica dos neurônios. Nessa tese, é introduzido o conceito de tempo de processamento neural (TPN) como um dos parâmetros do modelo biofísico da função de resposta hemodinâmica (HRF). O objetivo da introdução desse conceito é obter estimativas mais acuradas da duração da atividade neural a partir do efeito BOLD, que possui auto grau de nãolinearidade. Duas formas de estimar os parâmetros do modelo do efeito BOLD foram desenvolvidas. A validade e aplicabilidade do conceito de TPN e das rotinas de estimação foram avaliadas por simulações computacionais e análise de séries temporais experimentais. Os resultados das simulações e da aplicação foram comparados com medidas da forma da HRF. O experimento analisado consistiu em um paradigma de tomada de decisão na presença de distratores emocionais. Esperase que o TPN em áreas sensoriais primárias seja equivalente ao tempo de apresentação de estímulos. Por outro lado, o TPN em áreas relacionadas com a tomada de decisão deve ser menor que a duração dos estímulos. Além disso, o TPN deve depender da condição experimental em áreas relacionadas ao controle de distratores emocionais. Como predito, o valores estimados do TPN no giro fusiforme foram equivalentes à duração dos estímulos e o TPN no giro do cíngulo dorsal variou com a presença de distrator emocional. Observou-se ainda lateralidade do TPN no córtex pré-frontal dorsolateral. As medidas da forma da HRF obtidas por um método convencional não dectectaram as variações observadas no TPN.

The extraction of information about neural activity dynamics related to the BOLD signal is a challenging task. The temporal evolution of the BOLD signal does not directly reflect the temporal characteristics of electrical activity of neurons. In this work, we introduce the concept of neural processing time (NPT) as a parameter of the biophysical model of the hemodynamic response function (HRF). Through this new concept we aim to infer more accurately the duration of neuronal response from the highly nonlinear BOLD effect. We describe two routines to estimate the parameters of the HRF model. The face validity and applicability of the concept of NPT and the estimation procedures are evaluated through simulations and analysis of experimental time series. The results of both simulation and application were compared with summary measures of HRF shape. We analysed an experiment based on a decision-making paradigm with simultaneous emotional distracters. We hypothesize that the NPT in primary sensory areas is approximately the stimulus presentation duration. On the other hand, the NPT in brain areas related to decisionmaking processes should be less than the stimulus duration. Moreover, in areas related to processing of an emotional distracter, the NPT should depend on the experimental condition. As predicted, the NPT in fusiform gyrus is close to the stimulus duration and the NPT in dorsal anterior cingulate gyrus depends on the presence of an emotional distracter. Interestingly, the estimated NPTs in the dorsolateral prefrontal cortex indicate functional laterality of this region. The analysis using standard measures of HRF did not detect the variations observed in our method (NPT).

Learning about brain physiology and complexity from the study of the epilepsies

The brain is a complex system, which produces emergent properties such as those associated with activity-dependent plasticity in processes of learning and memory. Therefore, understanding the integrated structures and functions of the brain is well beyond the scope of either superficial or extremely reductionistic approaches. Although a combination of zoom-in and zoom-out strategies is desirable when the brain is studied, constructing the appropriate interfaces to connect all levels of analysis is one of the most difficult challenges of contemporary neuroscience. Is it possible to build appropriate models of brain function and dysfunctions with computational tools? Among the best-known brain dysfunctions, epilepsies are neurological syndromes that reach a variety of networks, from widespread anatomical brain circuits to local molecular environments. One logical question would be: are those complex brain networks always producing maladaptive emergent properties compatible with epileptogenic substrates? The present review will deal with this question and will try to answer it by illustrating several points from the literature and from our laboratory data, with examples at the behavioral, electrophysiological, cellular and molecular levels. We conclude that, because the brain is a complex system compatible with the production of emergent properties, including plasticity, its functions should be approached using an integrated view. Concepts such as brain networks, graphics theory, neuroinformatics, and e-neuroscience are discussed as new transdisciplinary approaches dealing with the continuous growth of information about brain physiology and its dysfunctions. The epilepsies are discussed as neurobiological models of complex systems displaying maladaptive plasticity.

Numerical exploration of the influence of neural noise on the psychometric function at low stimulation intensity levels.

The relationship between stimulus intensity and the probability of detecting the presence of the stimulus is described by the psychometrical function.The probabilistic nature of this relationship is based on the stochastic behaviour of sensory neural channels and sensory networks involved in perceptual processing (Kiang 1968). This study tries to establish a continuum of variability across different levels of integration in the central nervous system. Once the opening and closing times of ionic channels was simulated, a threshold to the collective behaviour of voltage-gated ionic channels was imposed in order to generate the spike train of a single neuron. Afterwards,the trains of spikes of different neurons were added up,simulating the activity of a sensory nerve. By adding the activity due to the stimulus to the spontaneous neural behaviour,the psychometric function was simulated using a thresholding approach.The results can replicate the stochastic resonance phenomenon, but also open up the possibility that attentional phenomena can be mediated not only by increasing neural activity (bursting or oscillatory),but also by increasing noise at the neural level.

Engagement of multifocal neural circuits during recall of autobiographical happy events

Happy emotional states have not been extensively explored in functional magnetic resonance imaging studies using autobiographic recall paradigms. We investigated the brain circuitry engaged during induction of happiness by standardized script-driven autobiographical recall in 11 healthy subjects (6 males), aged 32.4 ± 7.2 years, without physical or psychiatric disorders, selected according to their ability to vividly recall personal experiences. Blood oxygen level-dependent (BOLD) changes were recorded during auditory presentation of personal scripts of happiness, neutral content and negative emotional content (irritability). The same uniform structure was used for the cueing narratives of both emotionally salient and neutral conditions, in order to decrease the variability of findings. In the happiness relative to the neutral condition, there was an increased BOLD signal in the left dorsal prefrontal cortex and anterior insula, thalamus bilaterally, left hypothalamus, left anterior cingulate gyrus, and midportions of the left middle temporal gyrus (P < 0.05, corrected for multiple comparisons). Relative to the irritability condition, the happiness condition showed increased activity in the left insula, thalamus and hypothalamus, and in anterior and midportions of the inferior and middle temporal gyri bilaterally (P < 0.05, corrected), varying in size between 13 and 64 voxels. Findings of happiness-related increased activity in prefrontal and subcortical regions extend the results of previous functional imaging studies of autobiographical recall. The BOLD signal changes identified reflect general aspects of emotional processing, emotional control, and the processing of sensory and bodily signals associated with internally generated feelings of happiness. These results reinforce the notion that happiness induction engages a wide network of brain regions.

Emergência e conexionismo como hipóteses suplementares ao Entwurf einer Psychologie de Freud / Emergency and connectionism like supplementary hypothesis in Freud Entwurf einer Psychology

O artigo aborda a arquitetura do aparelho nervoso, apresentada por Freud no Entwurf einer Psychologie, notadamente sua proposição de três sistemas neuronais distintos – j, y e w. Demonstra como Freud ficou insatisfeito com suas próprias explicações ontológicas para a estrutura apresentada e propõe que existe uma compatibilidade entre as abordagens da emergência e do conexionismo e a postulação freudiana.

The paper work with Freud’s proposal for an architecture of the nervous system, in his book Entwurf einer Psychologie, giving emphasis to his distinction among three systems of neurons – j, y e w. It seeks to show how Freud was not completely sure about his own ontological explanations for the proposed structure and try to show that there is compatibility between Freud’s work and the emergence and connectionism perspectives.

Neurobiología y neurocomputación de los sistemas cerebrales de orientación espacial: parte 2 / Neurobiology and Neurocomputation of brain systems for spatial orientation. Part two

El hipocampo es una de las áreas más modelizadas en el sistema nervioso central. Las razones son a la vez filogenéticas, funcionales y arquitectónicas. Filogenéticamente es una de las áreas cerebrales más antiguas (arquicortex) y que hapasado por una fuerza importante de selección en diversas especies casi sin variaciones anatómicas. Funcionalmente está involucrado en dos aspectos de interés computacional: orientación espacial y tareas de navegación, por una parte, e intervención en la memoria episódica, por la otra. Incluso se estiman los trabajos pioneros de Marr en los que considera al hipocampo como un circuito interviniente en las formas más simples de memoria y hace una modelización de este, como los trabajos de inicio a la neurocomputación. Posteriormente se han hecho numerosos modelos. Uno de los circuitos más estudiados corresponde a las relaciones entre la corteza entorrinal medial (MEC) y la formación del hipocampo. En particular se han estudiado los mapas cognitivos espaciales relacionados con las tareas de orientación y navegación. El hipocampo posee una población de neuronas piramidales, las place cells (PC), que tienen la particularidad de disparar sus impulsos en determinadas localizaciones en el espacio (place fields). Recientemente se ha observado que la principal aferencia a las PC proviene de la MEC a través de las denominadas grid cells (GC). Estas células poseen un patrón de disparo que dibuja en el espacio una grilla hexagonal compuesta de triángulos equiláteros correspondientes a las zonas de disparo. Una hipótesis en boga es la de la MEC actuando como un área de integración de información sensorial que será transmitida a las PC.

Networks in Cognitive Systems and Biomedicine: Cerebral Processes, Models and Mathematical Tools Design

Convergence of clinical, empirical, methodological and theoretical approaches aimed at understanding the relation between brain function and cognition, is by now standard in most if not all academic programs in the area of Cognitive Science. This confederation of disciplines is one of the liveliest domains of inquiry and discussion into some of the most fundamental -and historically resilient- questions human beings have posed themselves. The contributions gathered in this special issue of Biological Research, directly inspired by the ongoing work at the Instituto de Sistemas Complejos de Valparaiso and the December 2006 CONICYT-INSERM-SFI workshop "Networks in Cognitive Systems / Trends and Challenge in Biomedicine: From Cerebral Process to Mathematical Tools Design", Chile, represent an explicit invitation to the reader to dive deeper into this fascinating terrain.

Dynamical Complexity in Cognitive Neural Networks

In the last twenty years an important effort in brain sciences, especially in cognitive science, has been the development of mathematical tool that can deal with the complexity of extensive recordings corresponding to the neuronal activity obtained from hundreds of neurons. We discuss here along with some historical issues, advantages and limitations of Artificial Neural Networks (ANN) that can help to understand how simple brain circuits work and whether ANN can be helpful to understand brain neural complexity.

Dynamic Causal Models and Autopoietic Systems

Dynamic Causal Modelling (DCM) and the theory of autopoietic systems are two important conceptual frameworks. In this review, we suggest that they can be combined to answer important questions about self-organising systems like the brain. DCM has been developed recently by the neuroimaging community to explain, using biophysical models, the non-invasive brain imaging data are caused by neural processes. It allows one to ask mechanistic questions about the implementation of cerebral processes. In DCM the parameters of biophysical models are estimated from measured data and the evidence for each model is evaluated. This enables one to test different functional hypotheses (i.e., models) for a given data set. Autopoiesis and related formal theories of biological systems as autonomous machines represent a body of concepts with many successful applications. However, autopoiesis has remained largely theoretical and has not penetrated the empiricism of cognitive neuroscience. In this review, we try to show the connections that exist between DCM and autopoiesis. In particular, we propose a simple modification to standard formulations of DCM that includes autonomous processes. The idea is to exploit the machinery of the system identification of DCMs in neuroimaging to test the face validity of the autopoietic theory applied to neural subsystems. We illustrate the theoretical concepts and their implications for interpreting electroencephalographic signals acquired during amygdala stimulation in an epileptic patient. The results suggest that DCM represents a relevant biophysical approach to brain functional organisation, with a potential that is yet to be fully evaluated.

A construçäo da atençäo a partir da memória / Building attention from memory

Os processos que levam à seleçäo de certas categorias de informaçäo para processamento preferencial, que caracterizam a atençäo, dependem näo apenas da história prévia do sistema selecionador, isto é, suas memórias, como também de expectativas geradas com base em memórias sobre regularidades passadas e planos de açäo. Defende-se neste trabalho que a associaçäo conceitual envolvendo memória e atençäo é vantajosa pois permite oferecer explicaçöes parcimoniosas sobre diversos fenômeros revelados em estudos sobre atençäo, além de gerar previsöes testáveis sobre os efeitos da experiência prévia no desempenho em testes de atençäo. Apresenta-se aqui um modelo sobre a influência de memórias (representadas por vias facilitadas no sistema nervoso) na atividade da rede nervosa e nos processos atencionais durante o desempenho de determinados tipos de tarefas

Theoretical approaches to holistic biological features: Pattern formation, neural networks and the brain-mind relation.

The topic of this article is the relation between bottom-up and top-down, reductionist and holistic approaches to the solution of basic biological problems. While there is no doubt that the laws of physics apply to all events in space and time, including the domains of life, understanding biology depends not only on elucidating the role of the molecules involved, but, to an increasing extent, on systems theoretical approaches in diverse fields of the life sciences. Examples discussed in this article are the generation of spatial patterns in development by the interplay of autocatalysis and lateral inhibition; the evolution of integrating capabilities of the human brain, such as cognition-based empathy; and both neurobiological and epistemological aspects of scientific theories of consciousness and the mind.

Beyond maps: a dynamic view of the somatosensory system

Current theories on how tactile information is processed by the mammalian somatosensory system are based primarily on data obtained in studies in which the physiological properties of single neurons were characterized, one at a time, in behaving or anesthetized animals. Yet, the central nervous system relies on the concurrent activation of large populations of neurons to process the variety of sensory stimuli that contribute to normal tactile perception. The recent introduction of electrophysiological methods for chronic and simultaneous recordings of the extracellular activity of large numbers of single neurons per animal has allowed us to investigate, for the first time, how populations of neurons, located at multiple processing stages of the somatosensory system, interact following passive and active tactile stimulation. The rat trigeminal somatosensory system was used as a model for this investigation. Our results revealed the existence of highly dynamic and distributed representations of tactile information, not only in the somatosensory cortex, but also in the thalamus and even in the brainstem. In these structures, we identified broadly tuned neurons with multiwhisker receptive fields (RFs). In the thalamus, a large percentage of neurons exhibited shifts in the spatial domain of their RFs as a function of post-stimulus time. During these shifts, the center of the neuron's RF moved across the whisker pad from caudal to rostral whiskers, but not in the opposite direction, suggesting that these spatiotemporal RFs may encode directional information. Further studies revealed that somatosensory representations were maintained by dynamic interactions between multiple convergent afferents, since they could be altered in a matter of seconds by reversible sensory deprivations. Overall, these results suggest that the rat somatosensory system relies on both spatial and temporal interactions between populations of cortical and subcortical neurons to process multiple attributes of tactile stimuli.

Linear analysis of auto-organization in Hebbian neural networks

The self-organization of neurotopies where neural connections follow Hebbian dynamics is framed in terms of linear operator theory. A general and exact equation describing the time evolution of the overall synaptic strength connecting two neural laminae is derived. This linear matricial equation, which is similar to the equations used to describe oscillating systems in physics, is modified by the introduction of non-linear terms, in order to capture self-organizing (or auto-organizing) processes. The behavior of a simple and small system, that contains a non-linearity that mimics a metabolic constraint, is analyzed by computer simulations. The emergence of a simple ®order® (or degree of organization) in this low-dimensionality model system is discussed

Bases neurobiológicas de la agresión: implicaciones farmacoterapéuticas / The neurobiological bases of aggression: the pharmacotherapeutic implications

The aim of this paper is to attempt a classification of aggressive behavior based on neurobiological mechanisms and to shed some light on the pharmacological treatment of this condition. Drugs that enhance serotonin transmission are indicated in conditions related to decreased serotonergic transmission. Dopamine blockers are useful in the acute control of aggression and the violence displayed by schizophrenic patients. Clozapine probably has an anti-aggressive effect independent of its antipsychotic action. Noradrenergic agents have been shown effective in chronic aggression of organic brain syndromes. Gabaergic drugs are effective in acute aggression and in organic brain syndromes