Local sleep and learning

Human sleep is a global state whose functions remain unclear. During much of sleep, cortical neurons undergo slow oscillations in membrane potential, which appear in electroencephalograms as slow wave activity (SWA) of <4 Hz. The amount of SWA is homeostatically regulated, increasing after wakefulness and returning to baseline during sleep. It has been suggested that SWA homeostasis may reflect synaptic changes underlying a cellular need for sleep. If this were so, inducing local synaptic changes should induce local SWA changes, and these should benefit neural function. Here we show that sleep homeostasis indeed has a local component, which can be triggered by a learning task involving specific brain regions. Furthermore, we show that the local increase in SWA after learning correlates with improved performance of the task after sleep. Thus, sleep homeostasis can be induced on a local level and can benefit performance.     

Consolidation during sleep of perceptual learning of spoken language

Memory consolidation resulting from sleep has been seen broadly: in verbal list learning, spatial learning, and skill acquisition in visual and motor tasks. These tasks do not generalize across spatial locations or motor sequences, or to different stimuli in the same location. Although episodic rote learning constitutes a large part of any organism's learning, generalization is a hallmark of adaptive behaviour. In speech, the same phoneme often has different acoustic patterns depending on context. Training on a small set of words improves performance on novel words using the same phonemes but with different acoustic patterns, demonstrating perceptual generalization. Here we show a role of sleep in the consolidation of a naturalistic spoken-language learning task that produces generalization of phonological categories across different acoustic patterns. Recognition performance immediately after training showed a significant improvement that subsequently degraded over the span of a day's retention interval, but completely recovered following sleep. Thus, sleep facilitates the recovery and subsequent retention of material learned opportunistically at any time throughout the day. Performance recovery indicates that representations and mappings associated with generalization are refined and stabilized during sleep.     

Boosting slow oscillations during sleep potentiates memory

There is compelling evidence that sleep contributes to the long-term consolidation of new memories. This function of sleep has been linked to slow (<1 Hz) potential oscillations, which predominantly arise from the prefrontal neocortex and characterize slow wave sleep. However, oscillations in brain potentials are commonly considered to be mere epiphenomena that reflect synchronized activity arising from neuronal networks, which links the membrane and synaptic processes of these neurons in time. Whether brain potentials and their extracellular equivalent have any physiological meaning per se is unclear, but can easily be investigated by inducing the extracellular oscillating potential fields of interest. Here we show that inducing slow oscillation-like potential fields by transcranial application of oscillating potentials (0.75 Hz) during early nocturnal non-rapid-eye-movement sleep, that is, a period of emerging slow wave sleep, enhances the retention of hippocampus-dependent declarative memories in healthy humans. The slowly oscillating potential stimulation induced an immediate increase in slow wave sleep, endogenous cortical slow oscillations and slow spindle activity in the frontal cortex. Brain stimulation with oscillations at 5 Hz--another frequency band that normally predominates during rapid-eye-movement sleep--decreased slow oscillations and left declarative memory unchanged. Our findings indicate that endogenous slow potential oscillations have a causal role in the sleep-associated consolidation of memory, and that this role is enhanced by field effects in cortical extracellular space.     

Human theta oscillations exhibit task dependence during virtual maze navigation.

Theta oscillations (electroencephalographic activity with a frequency of 4-8 Hz) have long been implicated in spatial navigation in rodents; however, the role of theta oscillators in human spatial navigation has not been explored. Here we describe subdural recordings from epileptic patients learning to navigate computer-generated mazes. Visual inspection of the raw intracranial signal revealed striking episodes of high-amplitude slow-wave oscillations at a number of areas of the cortex, including temporal cortex. Spectral analysis showed that these oscillations were in the theta band. These episodes of theta activity, which typically last several cycles, are dependent on task characteristics. Theta oscillations occur more frequently in more complex mazes; they are also more frequent during recall trials than during learning trials.     

去势对成年雄性斑胸草雀HVC-RA突触可塑性的影响

应用在体电生理方法研究了去势前后成年雄性斑胸草雀发声运动通路中HVC-RA 突触的可塑性变化,进一步探讨雄激素在调节鸣唱行为中的作用和机制.结果表明:低频刺激可引起 HVC-RA突触群体峰电位幅度的短时程抑制(Short-term depression, STD),高频刺激可引起群体峰电位幅度的长时程抑制(Long-term depression, LTD).而去势后30 d,鸣曲稳定时再给予同样的条件刺激,发现无论低频或高频刺激,HVC-RA 突触的短时程抑制和长时程抑制现象同时消失.研究结果显示:鸣曲稳定性可能依赖于HVC-RA通路的突触可塑性,雄激素在维持鸣曲稳定过程中发挥重要作用.     

Decrystallization of adult birdsong by perturbation of auditory feedback.

Young birds learn to sing by using auditory feedback to compare their own vocalizations to a memorized or innate song pattern; if they are deafened as juveniles, they will not develop normal songs. The completion of song development is called crystallization. After this stage, song shows little variation in its temporal or spectral properties. However, the mechanisms underlying this stability are largely unknown. Here we present evidence that auditory feedback is actively used in adulthood to maintain the stability of song structure. We found that perturbing auditory feedback during singing in adult zebra finches caused their song to deteriorate slowly. This 'decrystallization' consisted of a marked loss of the spectral and temporal stereotypy seen in crystallized song, including stuttering, creation, deletion and distortion of song syllables. After normal feedback was restored, these deviations gradually disappeared and the original song was recovered. Thus, adult birds that do not learn new songs nevertheless retain a significant amount of plasticity in the brain.     

Projection neurons within a vocal motor pathway are born during song learning in zebra finches

Many birds learn song during a restricted 'sensitive' period. Juveniles memorize a song model, and then learn the pattern of muscle contractions necessary to reproduce the song. Of the neural changes accompanying avian song learning, perhaps the most remarkable is the production of new neurons which are inserted into the hyperstriatum ventralis pars caudalis (HVc), a region critical for song production. We report here that in young male zebra finches many of the new neurons incorporated into the HVc innervate the robust nucleus of the archistriatum (RA) which projects to motor neurons controlling the vocal musculature. Furthermore, far fewer of these new neurons are incorporated into the HVc of either adult males that are beyond the sensitive learning period, or young females (who do not develop song). Thus, a major portion of the vocal motor pathway is actually created during song learning. This may enable early sensory experience and vocal practice to not only modify existing neuronal circuits, but also shape the insertion and initial synaptic contacts of neurons controlling adult song.     

Contributions of an avian basal ganglia-forebrain circuit to real-time modulation of song

Cortical-basal ganglia circuits have a critical role in motor control and motor learning. In songbirds, the anterior forebrain pathway (AFP) is a basal ganglia-forebrain circuit required for song learning and adult vocal plasticity but not for production of learned song. Here, we investigate functional contributions of this circuit to the control of song, a complex, learned motor skill. We test the hypothesis that neural activity in the AFP of adult birds can direct moment-by-moment changes in the primary motor areas responsible for generating song. We show that song-triggered microstimulation in the output nucleus of the AFP induces acute and specific changes in learned parameters of song. Moreover, under both natural and experimental conditions, variability in the pattern of AFP activity is associated with variability in song structure. Finally, lesions of the output nucleus of the AFP prevent naturally occurring modulation of song variability. These findings demonstrate a previously unappreciated capacity of the AFP to direct real-time changes in song. More generally, they suggest that frontal cortical and basal ganglia areas may contribute to motor learning by biasing motor output towards desired targets or by introducing stochastic variability required for reinforcement learning.     

Altered brain response to verbal learning following sleep deprivation

The effects of sleep deprivation on the neural substrates of cognition are poorly understood. Here we used functional magnetic resonance imaging to measure the effects of 35 hours of sleep deprivation on cerebral activation during verbal learning in normal young volunteers. On the basis of a previous hypothesis, we predicted that the prefrontal cortex (PFC) would be less responsive to cognitive demands following sleep deprivation. Contrary to our expectations, however, the PFC was more responsive after one night of sleep deprivation than after normal sleep. Increased subjective sleepiness in sleep-deprived subjects correlated significantly with activation of the PFC. The temporal lobe was activated after normal sleep but not after sleep deprivation; in contrast, the parietal lobes were not activated after normal sleep but were activated after sleep deprivation. Although sleep deprivation significantly impaired free recall compared with the rested state, better free recall in sleep-deprived subjects was associated with greater parietal lobe activation. These findings show that there are dynamic, compensatory changes in cerebral activation during verbal learning after sleep deprivation and implicate the PFC and parietal lobes in this compensation.     

Female visual displays affect the development of male song in the cowbird

The role of social stimulation in avian vocal learning is well documented. The separate contribution of social, as opposed to vocal, stimulation has been difficult to address, however, because in almost all cases both tutor and pupil sing. The opportunity to isolate such effects arose in cowbirds (Molothrus ater ater) after discovering that males housed with non-singing female cowbirds made vocal changes which related directly to the female preferences for native song. Here we report how females communicate with males about songs. We describe a visual display by females, a wing stroke, that is elicited by specific vocalizations. The songs that trigger wing strokes are in turn highly effective releasers of copulatory postures, and thus this previously unnoticed female display has biological significance. The data not only provide the first evidence of the tutorial role of male-female interactions during song ontogeny, they also clearly implicate visual stimulation in song learning, a process that has until now been assumed to be affected only by auditory information.     

The role of sex steroids in the acquisition and production of birdsong

Male birdsong is generally regarded as a secondary sexual characteristic under the control of gonadal steroids. Song typically waxes and wanes with the seasonal cycle of testicular growth and regression and decreases after adult castration. Testosterone therapy reinstates song, induces it in females, augments it in intact males, and spring testosterone profiles correlate with seasonal song production. Thus, testosterone has been viewed as a major factor in song acquisition and production acting either directly, or after aromatization within the brain. We show here, however, that song learning and early phases of the development of singing both take place in castrated male birds with no significant levels of testosterone in their blood plasma. Testosterone seems to be required for song crystallization, however. Oestradiol was unexpectedly still present after castration, evidently from a non-testicular source, throughout the period of male song acquisition.     

英文歌曲教学与英语口语的提高

将音乐引入课堂,运用正确的方法来学唱英文歌曲,有助于激发学生的学习英语的兴趣,增强学好英语的信心,提供练习英语口语的机会。     

Species-typical songs in white-crowned sparrows tutored with only phrase pairs

Modern theories of learned vocal behaviours, such as human speech and singing in songbirds, posit that acoustic communication signals are reproduced from memory, using auditory feedback. The nature of these memories, however, is unclear. Here we propose and test a model for how complex song structure can emerge from sparse sequence information acquired during tutoring. In this conceptual model, a population of combination-sensitive (phrase-pair) detectors is shaped by early exposure to song and serves as the minimal representation of the template necessary for generating complete song. As predicted by the model, birds that were tutored with only pairs of normally adjacent song phrases were able to assemble full songs in which phrases were placed in the correct order; birds that were tutored with reverse-ordered phrase pairs sang songs with reversed phrase order. Birds that were tutored with all song phrases, but presented singly, failed to produce normal, full songs. These findings provide the first evidence for a minimal requirement of sequence information in the acoustic model that can give rise to correct song structure.     

鸣禽鸣啭系统的可塑性及长时程增强研究

鸣禽的鸣唱控制系统已成为研究神经系统与学习、行为和发育相关的一个重要模型.鸣禽的鸣啭表现出一种复杂的学习过程.鸣禽学习鸣啭的过程可以分为两个阶段.在感觉学习期,幼鸟必须听到成鸟的鸣啭,并形成鸣啭模板记忆;在感觉运动学习期,鸣禽通过听觉反馈与模板匹配逐步建立稳定的鸣啭.该文对近年来鸣禽鸣啭学习过程中的新生神经元及长时程增强研究进展进行综述.     

鸣禽鸣啭学习研究进展

禽的鸣啭表现出一种复杂的学习过程，鸣禽学习鸣啭的过程可以分为两个阶段．在感觉学习期，幼鸟必须听到成鸟的鸣啭，并形成鸣啭模板记忆；在感觉运动学习期，鸣禽通过听觉反馈与模板匹配逐步建立稳定的鸣啭．对近年来鸣禽鸣啭学习过程的研究进展进行综述．     

Interruption of a basal ganglia-forebrain circuit prevents plasticity of learned vocalizations

Birdsong, like speech, is a learned vocal behaviour that relies greatly on hearing; in both songbirds and humans the removal of auditory feedback by deafening leads to a gradual deterioration of adult vocal production. Here we investigate the neural mechanisms that contribute to the processing of auditory feedback during the maintenance of song in adult zebra finches. We show that the deleterious effects on song production that normally follow deafening can be prevented by a second insult to the nervous system--the lesion of a basal ganglia-forebrain circuit. The results suggest that the removal of auditory feedback leads to the generation of an instructive signal that actively drives non-adaptive changes in song; they also suggest that this instructive signal is generated within (or conveyed through) the basal ganglia-forebrain pathway. Our findings provide evidence that cortical-basal ganglia circuits may participate in the evaluation of sensory feedback during calibration of motor performance, and demonstrate that damage to such circuits can have little effect on previously learned behaviour while conspicuously disrupting the capacity to adaptively modify that behaviour.     

An ultra-sparse code underlies the generation of neural sequences in a songbird

Sequences of motor activity are encoded in many vertebrate brains by complex spatio-temporal patterns of neural activity; however, the neural circuit mechanisms underlying the generation of these pre-motor patterns are poorly understood. In songbirds, one prominent site of pre-motor activity is the forebrain robust nucleus of the archistriatum (RA), which generates stereotyped sequences of spike bursts during song and recapitulates these sequences during sleep. We show that the stereotyped sequences in RA are driven from nucleus HVC (high vocal centre), the principal pre-motor input to RA. Recordings of identified HVC neurons in sleeping and singing birds show that individual HVC neurons projecting onto RA neurons produce bursts sparsely, at a single, precise time during the RA sequence. These HVC neurons burst sequentially with respect to one another. We suggest that at each time in the RA sequence, the ensemble of active RA neurons is driven by a subpopulation of RA-projecting HVC neurons that is active only at that time. As a population, these HVC neurons may form an explicit representation of time in the sequence. Such a sparse representation, a temporal analogue of the 'grandmother cell' concept for object recognition, eliminates the problem of temporal interference during sequence generation and learning attributed to more distributed representations.     

河南省公共服务与经济发展协调性动态评价

通过构建公共服务与经济发展协调性评价指标体系,借助熵权TOPSIS法,对河南省2000—2010年的公共服务供给与经济发展协调性进行量化动态评价.结果表明:河南省11年间公共服务供给与经济发展协调等级总体较低,处于"较不协调"和"一般协调"水平,与理想最优的协调状态还有较大差距;公共服务与经济发展协调状态呈U型波动,各年之间的改善系数并未出现持续递增趋势,河南省公共服务与经济发展协调状态存在"恶化"的风险,需要密切关注.最后提出相应对策建议.     

Stress response genes protect against lethal effects of sleep deprivation in Drosophila

Sleep is controlled by two processes: a homeostatic drive that increases during waking and dissipates during sleep, and a circadian pacemaker that controls its timing. Although these two systems can operate independently, recent studies indicate a more intimate relationship. To study the interaction between homeostatic and circadian processes in Drosophila, we examined homeostasis in the canonical loss-of-function clock mutants period (per(01)), timeless (tim(01)), clock (Clk(jrk)) and cycle (cyc(01)). cyc(01) mutants showed a disproportionately large sleep rebound and died after 10 hours of sleep deprivation, although they were more resistant than other clock mutants to various stressors. Unlike other clock mutants, cyc(01) flies showed a reduced expression of heat-shock genes after sleep loss. However, activating heat-shock genes before sleep deprivation rescued cyc(01) flies from its lethal effects. Consistent with the protective effect of heat-shock genes, was the observation that flies carrying a mutation for the heat-shock protein Hsp83 (Hsp83(08445)) showed exaggerated homeostatic response and died after sleep deprivation. These data represent the first step in identifying the molecular mechanisms that constitute the sleep homeostat.     

Sleep inspires insight

Insight denotes a mental restructuring that leads to a sudden gain of explicit knowledge allowing qualitatively changed behaviour. Anecdotal reports on scientific discovery suggest that pivotal insights can be gained through sleep. Sleep consolidates recent memories and, concomitantly, could allow insight by changing their representational structure. Here we show a facilitating role of sleep in a process of insight. Subjects performed a cognitive task requiring the learning of stimulus-response sequences, in which they improved gradually by increasing response speed across task blocks. However, they could also improve abruptly after gaining insight into a hidden abstract rule underlying all sequences. Initial training establishing a task representation was followed by 8 h of nocturnal sleep, nocturnal wakefulness, or daytime wakefulness. At subsequent retesting, more than twice as many subjects gained insight into the hidden rule after sleep as after wakefulness, regardless of time of day. Sleep did not enhance insight in the absence of initial training. A characteristic antecedent of sleep-related insight was revealed in a slowing of reaction times across sleep. We conclude that sleep, by restructuring new memory representations, facilitates extraction of explicit knowledge and insightful behaviour.