102,048 research outputs found
Theta–gamma coupling as a ubiquitous brain mechanism: implications for memory, attention, dreaming, imagination, and consciousness
No full textBrain rhythms are known to play a relevant role in many cognitive functions. In particular, coupling between theta and gamma oscillations was first observed in the hippocampus, where it is assumed to implement a code for organizing multiple items in memory. More recent advances, however, demonstrate that this mechanism is ubiquitously present in the brain and plays a role not only in working memory but also in episodic and semantic memory, attention, emotion, dreaming, and imagination. Furthermore, altered mental states and neurological disorders show profound alterations in the theta–gamma code. In this review, which summarizes the most recent experimental and theoretical evidence, we suggest that the substantial capacity to integrate information characteristic of the theta–gamma entrainment is fundamental for implementing many conscious cognitive processes
Modeling the contribution of theta-gamma coupling to sequential memory, imagination, and dreaming
No full textGamma oscillations nested in a theta rhythm are observed in the hippocampus, where are assumed to play a role in sequential episodic memory, i.e., memorization and retrieval of events that unfold in time. In this work, we present an original neurocomputational model based on neural masses, which simulates the encoding of sequences of events in the hippocampus and subsequent retrieval by exploiting the theta-gamma code. The model is based on a three-layer structure in which individual Units oscillate with a gamma rhythm and code for individual features of an episode. The first layer (working memory in the prefrontal cortex) maintains a cue in memory until a new signal is presented. The second layer (CA3 cells) implements an auto-associative memory, exploiting excitatory and inhibitory plastic synapses to recover an entire episode from a single feature. Units in this layer are disinhibited by a theta rhythm from an external source (septum or Papez circuit). The third layer (CA1 cells) implements a hetero-associative net with the previous layer, able to recover a sequence of episodes from the first one. During an encoding phase, simulating high-acetylcholine levels, the network is trained with Hebbian (synchronizing) and anti-Hebbian (desynchronizing) rules. During retrieval (low-acetylcholine), the network can correctly recover sequences from an initial cue using gamma oscillations nested inside the theta rhythm. Moreover, in high noise, the network isolated from the environment simulates a mind-wandering condition, randomly replicating previous sequences. Interestingly, in a state simulating sleep, with increased noise and reduced synapses, the network can “dream” by creatively combining sequences, exploiting features shared by different episodes. Finally, an irrational behavior (erroneous superimposition of features in various episodes, like “delusion”) occurs after pathological-like reduction in fast inhibitory synapses. The model can represent a straightforward and innovative tool to help mechanistically understand the theta-gamma code in different mental states
A model of working memory for encoding multiple items and ordered sequences exploiting the theta-gamma code
No full textRecent experimental evidence suggests that oscillatory activity plays a pivotal role in the maintenance of information in working memory, both in rodents and humans. In particular, cross-frequency coupling between theta and gamma oscillations has been suggested as a core mechanism for multi-item memory. The aim of this work is to present an original neural network model, based on oscillating neural masses, to investigate mechanisms at the basis of working memory in different conditions. We show that this model, with different synapse values, can be used to address different problems, such as the reconstruction of an item from partial information, the maintenance of multiple items simultaneously in memory, without any sequential order, and the reconstruction of an ordered sequence starting from an initial cue. The model consists of four interconnected layers; synapses are trained using Hebbian and anti-Hebbian mechanisms, in order to synchronize features in the same items, and desynchronize features in different items. Simulations show that the trained network is able to desynchronize up to nine items without a fixed order using the gamma rhythm. Moreover, the network can replicate a sequence of items using a gamma rhythm nested inside a theta rhythm. The reduction in some parameters, mainly concerning the strength of GABAergic synapses, induce memory alterations which mimic neurological deficits. Finally, the network, isolated from the external environment ("imagination phase") and stimulated with high uniform noise, can randomly recover sequences previously learned, and link them together by exploiting the similarity among items
Il cimitero ebraico di Lugo
No full textIl volume fornisce il testo ebraico annotato e una versione italiana degli epitaffi incisi sulle lapidi conservate nell'attuale cimitero ebraico di Lugo, in cui si trovano sia le stele ivi trasportate dal vecchio cimitero verso il 1877 sia quelle posate successivamente. Le ampie introduzioni sulla presenza ebraica a Lugo, sulla storia del suo cimitero, sull'epitaffio come genere letterario e fonte storica e sulle moltissime fonti prodotte dagli ebrei lughesi mostrano come nel Sei-Settecento Lugo fosse uno dei centri più fecondi e importanti della cultura ebraica in Italia. Situata nel Ducato di Ferrara, la cittadina divenne di grande importanza come centro ebraico dopo che nel 1639 papa Urbano VIII ordinò a tutti gli ebrei del ducato di concentrarsi nei ghetti di Ferrara, Lugo e Cento. Anche se vantava una presenza ebraica precedente, con questo decreto papale il centro romagnolo vide un aumento esponenziale della sua popolazione ebraica, che raggiunse oltre seicento persone, pari al dieci per cento di tutti gli abitanti. Già nel tardo Cinquecento, ma specialmente durante l'età barocca, gli epitaffi divennero vere e proprie poesie in rima e ritmo, che, arricchite da citazioni bibliche e rabbiniche, costituiscono sia pregievoli documenti letterari che interessanti fonti storiche: essi forniscono preziose informazioni su personaggi noti e meno noti e sulle loro reciproche relazioni parentali. Durante lo studio delle epigrafi è stato possibile identificare la lapide di Dawid Semu'el Del Vecchio, illustre rabbino lughese che nel 1807 partecipò al Grand Sanhedrin, convocato a Parigi da Napoelone, nonché quelle di suo suocero e di altre personalità. Di grandissimo interesse per completare la ricostruzione storica si è dimostrata l'integrazione dei dati contenuti negli epitaffi con quelli contenuti nel registro dei morti della comunità di Lugo, documento che copre un arco di quasi due secoli e che oggi è conservato a New York. Un sedicesimo di immagini a colori e un indice dei nomi in ebraico e in italiano arricchiscono e rendono agevole la consultazione del volume, che nelle appendici presenta anche due cippi funerari ebraici del Cinquecento conservati a Ravenna, uno scoperto nella vicina Bagnacavallo, e due note in memoria di alcuni membri delle famiglie ebraiche lughesi Sinigaglia e Marach. Grazie alla ricomposizione delle tessere di questo affascinante mosaico, si apre al lettore uno spettacolare squarcio sulla vita e la cultura di una comunità ebraica nell'Italia settentrionale dei secoli XVII-XIX
Push-push X band GaInP/GaAs VCO with a fully monolithic microstrip resonator
No full textIn this paper the design of a VCO using GaInP/GaAs HBT technology is presented. The VCO is designed to be a part of a PDH point to point radio system. To achieve low phase noise performances GaInP/GaAs HBT technology and push-push topology have been chosen. The MMIC includes predistorters to emphasize the second harmonic, f/sub 0//2 prescalers for PLL locking and buffer amplifiers. A fully monolithic microstrip resonator is coupled with integrated varactors to achieve the specified tuning bandwidth. Phase noise, bandwidth and power measurements will also be presente
Surveillance of infections in an intensive care and rianimation department: results of 689 patients.
No full textChanges in brain rhythms and connectivity tracking fear acquisition and reversal
No full textFear conditioning is used to investigate the neural bases of threat and anxiety, and to understand their flexible modifications when the environment changes. This study aims to examine the temporal evolution of brain rhythms using electroencephalographic signals recorded in healthy volunteers during a protocol of Pavlovian fear conditioning and reversal. Power changes and Granger connectivity in theta, alpha, and gamma bands are investigated from neuroelectrical activity reconstructed on the cortex. Results show a significant increase in theta power in the left (contralateral to electrical shock) portion of the midcingulate cortex during fear acquisition, and a significant decrease in alpha power in a broad network over the left posterior-frontal and parietal cortex. These changes occur since the initial trials for theta power, but require more trials (3/4) to develop for alpha, and are also present during reversal, despite being less pronounced. In both bands, relevant changes in connectivity are mainly evident in the last block of reversal, just when power differences attenuate. No significant changes in the gamma band were detected. We conclude that the increased theta rhythm in the cingulate cortex subserves fear acquisition and is transmitted to other cortical regions via increased functional connectivity allowing a fast theta synchronization, whereas the decrease in alpha power can represent a partial activation of motor and somatosensory areas contralateral to the shock side in the presence of a dangerous stimulus. In addition, connectivity changes at the end of reversal may reflect long-term alterations in synapses necessary to reverse the previously acquired contingencies
Evolutionary Implications of Environmental Toxicant Exposure
No full textHomo sapiens have been exposed to various toxins and harmful compounds that change according to various phases of human evolution. Population genetics studies showed that such exposures lead to adaptive genetic changes; while observing present exposures to different toxicants, the first molecular mechanism that confers plasticity is epigenetic remodeling and, in particular, DNA methylation variation, a molecular mechanism proposed for medium-term adaptation. A large amount of scientific literature from clinical and medical studies revealed the high impact of such exposure on human biology; thus, in this review, we examine and infer the impact that different environmental toxicants may have in shaping human evolution. We first describe how environmental toxicants shape natural human variation in terms of genetic and epigenetic diversity, and then we describe how DNA methylation may influence mutation rate and, thus, genetic variability. We describe the impact of these substances on biological fitness in terms of reproduction and survival, and in conclusion, we focus on their effect on brain evolution and physiology
Trattamento mini-invasivo nella sostituzione monocompartimentale di ginocchio: rewiew della letteratura
No full texttrattamento mini-invasivo nella sostituzione monocompartimentale di ginocchio: rewiew della letteratur
C Band DROs Using Microwave Bipolar Devices
No full textA silicon self-aligned-emitter bipolar process
from STMicroelectronics for very high efficiency handsets
power applications has been used to build two Dielectric
Resonator Oscillators. Despite this technology addresses the
mobile telephony frequency range at 1.8GHz, the oscillators
generate a stable reference at 6GHz and 7.5GHz with good
phase noise performance. A low frequency noise model has
been identified and implemented in a Gummel Poon BJT
nonlinear model. A design technique to optimize stability
and phase noise performances has been used. The DROs
exhibit phase noise of -116dBc/Hz and -107dBc/Hz at 10KHz
offset from the carrier at 6GHz and 7.5GHz, respectively
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