197,233 research outputs found
Theta–gamma coupling as a ubiquitous brain mechanism: implications for memory, attention, dreaming, imagination, and consciousness
Get PDFBrain 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
Get PDFGamma 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
Models and methods to study Schwann cells
Get PDFSchwann cells (SCs) are fundamental components of the peripheral nervous system (PNS) of all vertebrates and play essential roles in development, maintenance, function, and regeneration of peripheral nerves. There are distinct populations of SCs including: (1) myelinating SCs that ensheath axons by a specialized plasma membrane, called myelin, which enhances the conduction of electric impulses; (2) non-myelinating SCs, including Remak SCs, which wrap bundles of multiple axons of small caliber, and perysinaptic SCs (PSCs), associated with motor axon terminals at the neuromuscular junction (NMJ). All types of SCs contribute to PNS regeneration through striking morphological and functional changes in response to nerve injury, are affected in peripheral neuropathies and show abnormalities and a diminished plasticity during aging. Therefore, methodological approaches to study and manipulate SCs in physiological and pathophysiological conditions are crucial to expand the present knowledge on SC biology and to devise new therapeutic strategies to counteract neurodegenerative conditions and age-derived denervation. We present here an updated overview of traditional and emerging methodologies for the study of SCs for scientists approaching this research field
A model of working memory for encoding multiple items and ordered sequences exploiting the theta-gamma code
Get PDFRecent 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
The role of the single interchains disulfide bond in tetanus and botulinum neurotoxins and the development of antitetanus and antibotulism drugs
Get PDFA large number of bacterial toxins consist of active and cell binding protomers linked by an interchain disulfide bridge. The largest family of such disulfide-bridged exotoxins is that of the clostridial neurotoxins that consist of two chains and comprise the tetanus neurotoxins causing tetanus and the botulinum neurotoxins causing botulism. Reduction of the interchain disulfide abolishes toxicity, and we discuss the experiments that revealed the role of this structural element in neuronal intoxication. The redox couple thioredoxin reductase-thioredoxin (TrxR-Trx) was identified as the responsible for reduction of this disulfide occurring on the cytosolic surface of synaptic vesicles. We then discuss the very relevant finding that drugs that inhibit TrxR-Trx also prevent botulism. On this basis, we propose that ebselen and PX-12, two TrxR-Trx specific drugs previously used in clinical trials in humans, satisfy all the requirements for clinical tests aiming at evaluating their capacity to effectively counteract human and animal botulism arising from intestinal toxaemias such as infant botulism
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
C Band DROs Using Microwave Bipolar Devices
Get PDFA 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
Tetanus and tetanus neurotoxin: From peripheral uptake to central nervous tissue targets
Get PDFTetanus is a deadly but preventable disease caused by a protein neurotoxin produced by Clostridium tetani. Spores of C. tetani may contaminate a necrotic wound and germinate into a vegetative bacterium that releases a toxin, termed tetanus neurotoxin (TeNT). TeNT enters the general circulation, binds to peripheral motor neurons and sensory neurons, and is transported retroaxonally to the spinal cord. It then enters inhibitory interneurons and blocks the release of glycine or GABA causing a spastic paralysis. This review attempts to correlate the metalloprotease activity of TeNT and its trafficking and localization into the vertebrate body to the nature and sequence of appearance of the symptoms of tetanus. (Figure presented.)
C Band DROs Using Microwave Bipolar Devices: Nonlinear Design Technique and Noise Model for Phase Noise Prediction
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 respectively. A low frequency noise model has been identified and implemented in a Gummel Poon 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 respectively
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