The Deceptively Simple N170 Reflects Network Information Processing Mechanisms Involving Visual Feature Coding and Transfer Across Hemispheres

A key to understanding visual cognition is to determine where, when and how brain responses reflect the processing of the specific visual features that modulate categorization behavior - the what. The N170 is the earliest Event-Related Potential (ERP) that preferentially responds to faces. Here, we demonstrate that a paradigmatic shift is necessary to interpret the N170 as the product of an information processing network that dynamically codes and transfers face features across hemispheres, rather than as a local stimulus-driven event. Reverse-correlation methods coupled with information-theoretic analyses revealed that visibility of the eyes influences face detection behavior. The N170 initially reflects coding of the behaviorally relevant eye contra-lateral to the sensor, followed by a causal communication of the other eye from the other hemisphere. These findings demonstrate that the deceptively simple N170 ERP hides a complex network information processing mechanism involving initial coding and subsequent cross-hemispheric transfer of visual features

The Regulation of Brain Nucleoside Utilization

The homeostatic regulation of intracellular purine and pyrimidine pools has long been studied at the level of de novo nucleotide synthesis. However, brain maintains the proper qualitative and quantitative nucleotide balance by salvaging preformed nucleosides, imported from blood stream, rather than by de novo synthesis from simple precursors. The main salvage enzymes are the nucleoside-kinases, catalyzing the ATP mediated phosphorylation of nucleosides in their 5’-position. Salvaged nucleoside-monophosphates are then either further phosphorylated, or converted back to nucleosides by a set of 5’-nucleotidases. This poses the following problem: why are nucleosides produced from nucleosidemonophosphates, to be converted back to the same compounds at the expense of ATP? As discussed in this article, the quantitative and qualitative intracellular balance of brain purine and pyrimidine compounds is maintained i) by the intracellular interplay between the rates of nucleoside-kinases and 5’-nucleotidases, ii) by the relative rates of the inward and outward nucleoside transport through equilibrative and concentrative transport systems, iii) by the metabolic cross-talk between extracellularly exported nucleoside-triphosphate breakdown and the intracellular process of nucleoside-triphosphate salvage synthesis

Purine and Pyrimidine Salvage in Whole Rat Brain. Utilization of ATP-derived Ribose-1-Phosphate and 5-Phosphoribosyl-1-pyrophosphate Generated in Experiments with Dialyzed Cell-free Extracts

The object of this work stems from our previous studies on the mechanisms responsible of ribose-1-phosphate- and 5-phosphoribosyl-1-pyrophosphate-mediated nucleobase salvage and 5-fluorouracil activation in rat brain (Mascia, L., Cappiello M., Cherri, S., and Ipata, P. L. (2000) Biochim. Biophys. Acta 1474, 70-74; Mascia, L., Cotrufo, T., Cappiello, M., and Ipata, P. L. (1999) Biochim. Biophys. Acta 1472, 93-98). Here we show that when ATP at "physiological concentration" is added to dialyzed extracts of rat brain in the presence of natural nucleobases or 5-fluorouracil, adenine-, hypoxanthine-, guanine-, uracil-, and 5-fluorouracil-ribonucleotides are synthesized. The molecular mechanism of this peculiar nueleotide synthesis relies on the capacity of rat brain to salvage purine and pyrimidine bases by deriving ribose-1-phosphate and 5-phosphoribosyl-1-pyrophosphate from ATP even in the absence of added pentose or pentose phosphates. The levels of the two sugar phosphates formed are compatible with those of synthesized nucleotides. We propose that the ATP-mediated 5-phosphoribosyl-1-pyrophosphate synthesis occurs through the action of purine nucleoside phosphorylase, phosphopentomutase, and 5-phosphoribosyl-1-pyrophosphate synthetase. Furthering our previous observations on the effect of ATP in the 5-phosphoribosyl-1-pyrophosphate-mediated 5-fluorouracil activation in rat liver (Mascia, L., and Ipata, P. L. (2001) Biochem. Pharmacol. 62, 213-218), we now show that the ratio [5-phosphoribosyl-1-pyrophosphate]/[ATP] plays a major role in modulating adenine salvage in rat brain. On the basis of our in vitro results, we suggest that massive ATP degradation, as it occurs in brain during ischemia, might lead to an increase of the intracellular 5-phosphoribosyl-1-pyrophosphate and ribose-1-phosphate pools, to be utilized for nucleotide resynthesis during reperfusion

El nuevo rol de las administraciones aduaneras: una buena ley como base del "customs compliance"

En los últimos años se ha avanzado en la “globalización” de la producción mundial no sólo por la consideración supranacional de los mercados, sino por el flujo de inversiones extranjeras y las estrategias de las empresas multinacionales. De hecho, las innovaciones en materia de transportes, comunicaciones y telecomunicaciones, junto con una creciente difusión tecnológica, están conduciendo a una segmentación de los procesos de producción – la denominada “partición de la cadena de valor” – que posibilita localizar las distintas partes del proceso de producción en diferentes países, en función de los requerimientos de cada una de las etapas de dicho proceso

El nuevo rol de las administraciones aduaneras: una buena ley como base del "customs compliance"

En los últimos años se ha avanzado en la “globalización” de la producción mundial no sólo por la consideración supranacional de los mercados, sino por el flujo de inversiones extranjeras y las estrategias de las empresas multinacionales. De hecho, las innovaciones en materia de transportes, comunicaciones y telecomunicaciones, junto con una creciente difusión tecnológica, están conduciendo a una segmentación de los procesos de producción – la denominada “partición de la cadena de valor” – que posibilita localizar las distintas partes del proceso de producción en diferentes países, en función de los requerimientos de cada una de las etapas de dicho proceso

A competitive integration model of exogenous and endogenous eye movements

We present a model of the eye movement system in which the programming of an eye movement is the result of the competitive integration of information in the superior colliculi (SC). This brain area receives input from occipital cortex, the frontal eye fields, and the dorsolateral prefrontal cortex, on the basis of which it computes the location of the next saccadic target. Two critical assumptions in the model are that cortical inputs are not only excitatory, but can also inhibit saccades to specific locations, and that the SC continue to influence the trajectory of a saccade while it is being executed. With these assumptions, we account for many neurophysiological and behavioral findings from eye movement research. Interactions within the saccade map are shown to account for effects of distractors on saccadic reaction time (SRT) and saccade trajectory, including the global effect and oculomotor capture. In addition, the model accounts for express saccades, the gap effect, saccadic reaction times for antisaccades, and recorded responses from neurons in the SC and frontal eye fields in these tasks. © The Author(s) 2010