Amygdalar and hippocampal theta rhythm synchronization during fear memory retrieval

The amygdalohippocampal circuit plays a pivotal role in Pavlovian fear memory. We simultaneously recorded electrical activity in the lateral amygdala (LA) and the CA1 area of the hippocampus in freely behaving fear-conditioned mice. Patterns of activity were related to fear behavior evoked by conditioned and indifferent sensory stimuli and contexts. Rhythmically synchronized activity at theta frequencies increased between the LA and the CA1 after fear conditioning and became significant during confrontation with conditioned fear stimuli and expression of freezing behavior. Synchronization of theta activities in the amygdalohippocampal network represents a neuronal correlate of conditioned fear, apt to improve neuronal communication during memory retrieval.     

Retention in immediate memory estimated without retrieval

Report of the missing member of a set depends upon retention of the other members presented. Such a missing scan reveals greater retention than does a digit span and, unlike the digit span, better retention of later than earlier presentations.     

利用Google搜索引擎进行农业信息检索和信息分析的实践

本文根据笔者使用Coogle搜索引擎的实践,介绍了利用Coogle搜索引擎进行农业信息检索和农业信息分析的几种方法,给出了具体的例子,并对利用搜索引擎进行品种相关信息检索作了特别的介绍.     

Marihuana and memory: acquisition or retrieval?

Two experiments were conducted to determine the means by which marihuana affects human memory. The results of these studies indicated that marihuana did not affect retrieval of information in memory when the method of free recall was used, but did affect recognition processes such that subjects were less able to discriminate between items that had been presented previously and items that had not appeared a short time before. With respect to initial learning, marihuana was shown to affect acquisition processes involved in the storage of information.     

Operant conditioning of cortical unit activity

The activity of single neurons in precentral cortex of unanesthetized monkeys (Macaca mulatta) was conditioned by reinforcing high rates of neuronal discharge with delivery of a food pellet. Auditory or visual feedback of unit firing rates was usually provided in addition to food reinforcement. After several training sessions, monkeys could increase the activity of newly isolated cells by 50 to 500 percent above rates before reinforcement.     

Protein kinase C overactivity impairs prefrontal cortical regulation of working memory

The prefrontal cortex is a higher brain region that regulates thought, behavior, and emotion using representational knowledge, operations often referred to as working memory. We tested the influence of protein kinase C (PKC) intracellular signaling on prefrontal cortical cognitive function and showed that high levels of PKC activity in prefrontal cortex, as seen for example during stress exposure, markedly impair behavioral and electrophysiological measures of working memory. These data suggest that excessive PKC activation can disrupt prefrontal cortical regulation of behavior and thought, possibly contributing to signs of prefrontal cortical dysfunction such as distractibility, impaired judgment, impulsivity, and thought disorder.     

Neuron activity related to short-term memory

Nerve cells in the monkey's prefrontal cortex and nucleus medialis dorsalis of the thalamus show changes of firing frequency associated with the performance of a delayed response test. Most cells increase firing during the cue presentation period or at the beginning of the ensuing delay; spike discharge highler than that in intertrial periods is present in some cells throughout the delay. These changes are interpreted as suggestive evidence of a role of frontothalamic circuits in the attentive process involved in short-term memory     

Breakdown of cortical effective connectivity during sleep

When we fall asleep, consciousness fades yet the brain remains active. Why is this so? To investigate whether changes in cortical information transmission play a role, we used transcranial magnetic stimulation together with high-density electroencephalography and asked how the activation of one cortical area (the premotor area) is transmitted to the rest of the brain. During quiet wakefulness, an initial response (approximately 15 milliseconds) at the stimulation site was followed by a sequence of waves that moved to connected cortical areas several centimeters away. During non-rapid eye movement sleep, the initial response was stronger but was rapidly extinguished and did not propagate beyond the stimulation site. Thus, the fading of consciousness during certain stages of sleep may be related to a breakdown in cortical effective connectivity.     

Neural readout from memory during generalization

Eight cats with implanted electrodes were trained to obtain food on presentation of one flicker frequency and to avoid shock on presentation of a second flicker frequency. A third flicker frequency, midway between the first and the second, was then presented. Differential generalization ensued, in which either the food response or the avoidance response was performed. Average evoked potentials from generalization trials with different outcomes were significantly different. The wave shape elicited by the stimulus for generalization closely resembled the usual response to the appropriate signal for the behavior which was displayed. This constitutes evidence for release of a neural process representing previous experience. The release of this process begins about 35 milliseconds after stimulation.     

Layer-specific somatosensory cortical activation during active tactile discrimination

Ensemble neuronal activity was recorded in each layer of the whisker area of the primary somatosensory cortex (SI) while rats performed a whisker-dependent tactile discrimination task. Comparison of this activity with SI activity evoked by similar passive whisker stimulation revealed fundamental differences in tactile signal processing during active and passive stimulation. Moreover, significant layer-specific functional differences in SI activity were observed during active discrimination. These differences could not be explained solely by variations in ascending thalamocortical input to SI. Instead, these results suggest that top-down influences during active discrimination may alter the overall functional nature of SI as well as layer-specific mechanisms of tactile processing.     

Early tagging of cortical networks is required for the formation of enduring associative memory

Although formation and stabilization of long-lasting associative memories are thought to require time-dependent coordinated hippocampal-cortical interactions, the underlying mechanisms remain unclear. Here, we present evidence that neurons in the rat cortex must undergo a "tagging process" upon encoding to ensure the progressive hippocampal-driven rewiring of cortical networks that support remote memory storage. This process was AMPA- and N-methyl-D-aspartate receptor-dependent, information-specific, and capable of modulating remote memory persistence by affecting the temporal dynamics of hippocampal-cortical interactions. Post-learning reinforcement of the tagging process via time-limited epigenetic modifications resulted in improved remote memory retrieval. Thus, early tagging of cortical networks is a crucial neurobiological process for remote memory formation whose functional properties fit the requirements imposed by the extended time scale of systems-level memory consolidation.     

Dynamics of the hippocampus during encoding and retrieval of face-name pairs

The medial temporal lobe (MTL) is critical in forming new memories, but how subregions within the MTL carry out encoding and retrieval processes in humans is unknown. Using new high-resolution functional magnetic resonance imaging (fMRI) acquisition and analysis methods, we identified mnemonic properties of different subregions within the hippocampal circuitry as human subjects learned to associate names with faces. The cornu ammonis (CA) fields 2 and 3 and the dentate gyrus were active relative to baseline only during encoding, and this activity decreased as associations were learned. Activity in the subiculum showed the same temporal decline, but primarily during retrieval. Our results demonstrate that subdivisions within the hippocampus make distinct contributions to new memory formation.     

Intracellular potentials of cortical neurons during focal epileptogenic discharges

Focal electroencephalographic discharges in lesions of cortex induced by freezing are associated with prolonged membrane depolarizations and hyperpolarizations in neurons located at various depths in the lesion sites. Transmembrane potential changes have properties similar to those of postsynaptic potentials. The temporal relationship between intracellular potentials and paroxysmal discharges indicates that the latter are extracellularly recorded summations of synchronously developing depolarizations and hyperpolarizations in complex synaptic organizations of neurons.     

Odor cues during slow-wave sleep prompt declarative memory consolidation

Sleep facilitates memory consolidation. A widely held model assumes that this is because newly encoded memories undergo covert reactivation during sleep. We cued new memories in humans during sleep by presenting an odor that had been presented as context during prior learning, and so showed that reactivation indeed causes memory consolidation during sleep. Re-exposure to the odor during slow-wave sleep (SWS) improved the retention of hippocampus-dependent declarative memories but not of hippocampus-independent procedural memories. Odor re-exposure was ineffective during rapid eye movement sleep or wakefulness or when the odor had been omitted during prior learning. Concurring with these findings, functional magnetic resonance imaging revealed significant hippocampal activation in response to odor re-exposure during SWS.     

Lhx2 selector activity specifies cortical identity and suppresses hippocampal organizer fate

The earliest step in creating the cerebral cortex is the specification of neuroepithelium to a cortical fate. Using mouse genetic mosaics and timed inactivations, we demonstrated that Lhx2 acts as a classic selector gene and essential intrinsic determinant of cortical identity. Lhx2 selector activity is restricted to an early critical period when stem cells comprise the cortical neuroepithelium, where it acts cell-autonomously to specify cortical identity and suppress alternative fates in a spatially dependent manner. Laterally, Lhx2 null cells adopt antihem identity, whereas medially they become cortical hem cells, which can induce and organize ectopic hippocampal fields. In addition to providing functional evidence for Lhx2 selector activity, these findings show that the cortical hem is a hippocampal organizer.     

Amino acid incorporation into rat brain proteins during spreading cortical depression

Unilateral spreading cortical depression was elicited by applying potassium chloride solutions to the dura of conscious, freely moving rats. Incorporation of (3)H-leucine into soluble cortical proteins was decreased in the depressed hemisphere relative to the control side, while soluble brainstem proteins from both sides had the same specific activity. Various subfractions of soluble cortical proteins were affected to equal degrees.