Distinct neural ensemble response statistics are associated with recognition and discrimination of natural sound textures

The perception of sound textures, a class of natural sounds defined by statistical sound structure such as fire, wind, and rain, has been proposed to arise through the integration of time-averaged summary statistics. Where and how the auditory system might encode these summary statistics to create internal representations of these stationary sounds, however, is unknown. Here, using natural textures and synthetic variants with reduced statistics, we show that summary statistics modulate the correlations between frequency organized neuron ensembles in the awake rabbit inferior colliculus (IC). These neural ensemble correlation statistics capture high-order sound structure and allow for accurate neural decoding in a single trial recognition task with evidence accumulation times approaching 1 s. In contrast, the average activity across the neural ensemble (neural spectrum) provides a fast (tens of milliseconds) and salient signal that contributes primarily to texture discrimination. Intriguingly, perceptual studies in human listeners reveal analogous trends: the sound spectrum is integrated quickly and serves as a salient discrimination cue while high-order sound statistics are integrated slowly and contribute substantially more toward recognition. The findings suggest statistical sound cues such as the sound spectrum and correlation structure are represented by distinct response statistics in auditory midbrain ensembles, and that these neural response statistics may have dissociable roles and time scales for the recognition and discrimination of natural sounds.

What makes a sound natural, and what are the neural codes that support recognition and discrimination of real-world natural sounds? Although it is known that the early auditory system decomposes sounds along fundamental acoustic dimensions such as intensity and frequency, the higher-level neural computations that mediate natural sound recognition are poorly understood. This general lack of understanding is in part attributed to the structural complexity of natural sounds, which is difficult to study with traditional auditory test stimuli, such as tones, noise, or modulated sequences. Such stimuli can reveal details of the neural representation for relatively low-level acoustic cues, yet they don’t capture the rich and diverse statistical structure of natural sounds. Thus, they cannot reveal many of the computations associated with higher-level sound properties that facilitate auditory tasks such as natural sound recognition or discrimination. A class of stationary natural sounds termed textures, such as the random sounds emanating from a running stream, a crowded restaurant, or a chorus of birds, have been proposed as alternative natural stimuli which allow for manipulating high-level acoustic structure (1). Texture sounds are composed of spatially and temporally distributed acoustic elements that are collectively perceived as a single source and are defined by their statistical features. Identification of these natural sounds has been proposed to be mediated through the integration of time-averaged summary statistics, which account for high-level structures such as the sparsity and time-frequency correlation structure found in many natural sounds (1–3). Using a generative model of the auditory system to measure summary statistics from natural texture sounds, it is possible to synthesize highly realistic synthetic auditory textures (1). This suggests that high-order statistical cues are perceptually salient and that the brain might extract these statistical features to build internal representations of sounds.Although neural activity throughout the auditory pathway is sensitive to a variety of statistical cues such as the sound contrast, modulation power spectrum, and correlation structure (4–12), how sound summary statistics contribute toward basic auditory tasks such as recognition and discrimination of sounds is poorly understood. Furthermore, it is unclear where along the auditory pathway summary statistics are represented and how they are reflected in neural activity. The inferior colliculus (IC) is one candidate midlevel structure for representing such summary statistics. As the principal midbrain auditory nucleus, the IC receives highly convergent brainstem inputs with varied sound selectivities. Neurons in the IC are selective over most of the perceptually relevant range of sound modulations and neural activity is strongly driven by multiple high-order sound statistics (4–7, 10). In previous work, we showed the correlation statistics of natural sounds are highly informative about stimulus identity and they appear to be represented in the correlation statistics of auditory midbrain neuron ensembles (4). Correlations between neurons have also been proposed as mechanisms for pitch identification (13) and sound localization (14). This broadly supports the hypotheses that high-order sound statistics are reflected in the response statistics of neural ensembles and that these neural response statistics could potentially subserve basic auditory tasks.Here using natural and synthetic texture sounds, we test the hypothesis that statistical structure in natural texture sounds modulates the response statistics of neural ensembles in the IC of unanesthetized rabbits, and that distinct neural response statistics have the potential to contribute toward sound recognition and discrimination behaviors. By comparing the performance of neural decoders with human texture perception, we find that place rate representation of sounds (neural spectrum) accumulates evidence about the sounds on relatively fast time scales (tens of milliseconds) exhibiting decoding trends that mirror those seen for human texture discrimination. High-order statistical sound cues, by comparison, are reflected in the correlation statistics of neural ensembles, which require substantially longer evidence accumulation times (>500 ms) and follow trends that mirror those measured for human texture recognition. Collectively, the findings suggest that spectrum cues and accompanying place rate representation (neural spectrum) may contribute surprisingly little toward the recognition of auditory textures. Instead, high-order statistical sound structure is reflected in the distributed patterns of correlated activity across IC neural ensembles and such neural response structure has the potential to contribute toward the recognition of natural auditory textures.     

Orientation selectivity and noise correlation in awake monkey area V1 are modulated by the γ cycle

Gamma-band synchronization adjusts the timing of excitatory and inhibitory inputs to a neuron. Neurons in the visual cortex are selective for stimulus orientation because of dynamic interactions between excitatory and inhibitory inputs. We hypothesized that these interactions and hence also orientation selectivity vary during the gamma cycle. We determined for each spike its phase relative to the gamma cycle. As a function of gamma phase, we then determined spike rates and their orientation selectivity. Orientation selectivity was modulated by gamma phase. The firing rate of spiking activity that occurred close to a neuron's mean gamma phase of firing was most orientation selective. This stimulus-selective signal could best be conveyed to postsynaptic neurons if it were not corrupted by noise correlations. Noise correlations between firing rates were modulated by gamma phase such that they were not statistically detectable for the spiking activity occurring close to a neuron's mean gamma phase of firing. Thus, gamma-band synchronization produces spiking activity that carries maximal stimulus selectivity and minimal noise correlation in its firing rate, and at the same time synchronizes this spiking activity for maximal impact on postsynaptic targets.     

Sex and hemispheric differences in facial invariants extraction

This present study investigates sex differences in hemispheric cooperation during a facial identity matching task. The method used was a divided visual field paradigm in which the probe face was neutral or expressive and the target face was always neutral. Probe and target faces were presented both unilaterally and sequentially. A total of 28 right-handed women and 32 right-handed men participated in this study. The results confirm the women's advantage in face recognition and reveal symmetrical interhemispheric cooperation in women only. In men, processing time was faster when the probe face appeared in the left visual field—and encoded by the right hemisphere—and the target in the right visual field—projected to the left hemisphere—compared to the reverse direction. Interestingly, the data also show that women were not influenced by the expression of the probe face when matching identity, whereas men were always faster when the probe face was neutral, like the target, than when it was expressive. These results are discussed in light of Bruce and Young's (1986) model, and in terms of view-dependent and view-independent processes.     

Designing trauma registry system using a logical framework approach

While trauma registries provide the mechanisms to collect comprehensive, timely and accurate data related to the injuries and evaluate trauma care systems, they have not been established in most developing countries. On the other hand, in complex projects that have large aims, a logical framework approach （LFA） can help summarize and describe the multiple branches of the project systematically, and elucidate the main goals, extensive objectives, activities and expected outcomes. Therefore a LFA can be used to design and guide trauma registry project management, to integrate the cultural, clinical and capacity variations among countries; and to ensure early alignment of the project＇s design and evaluation.     

Multisensory integration across exteroceptive and interoceptive domains modulates self-experience in the rubber-hand illusion

Identifying with a body is central to being a conscious self. The now classic “rubber hand illusion” demonstrates that the experience of body-ownership can be modulated by manipulating the timing of exteroceptive (visual and tactile) body-related feedback. Moreover, the strength of this modulation is related to individual differences in sensitivity to internal bodily signals (interoception). However the interaction of exteroceptive and interoceptive signals in determining the experience of body-ownership within an individual remains poorly understood. Here, we demonstrate that this depends on the online integration of exteroceptive and interoceptive signals by implementing an innovative “cardiac rubber hand illusion” that combined computer-generated augmented-reality with feedback of interoceptive (cardiac) information. We show that both subjective and objective measures of virtual-hand ownership are enhanced by cardio-visual feedback in-time with the actual heartbeat, as compared to asynchronous feedback. We further show that these measures correlate with individual differences in interoceptive sensitivity, and are also modulated by the integration of proprioceptive signals instantiated using real-time visual remapping of finger movements to the virtual hand. Our results demonstrate that interoceptive signals directly influence the experience of body ownership via multisensory integration, and they lend support to models of conscious selfhood based on interoceptive predictive coding.     

64排螺旋CT与选择性冠状动脉造影评价急性冠状动脉综合征患者易损斑块形态、成分及大小的价值对比研究

目的 探讨64排螺旋CT评价急性冠状动脉综合征(ACS)患者易损斑块形态、成分及大小的价值.方法 65例冠心病患者(其中ACS组32例,稳定性心绞痛组33例)行64排螺旋CT冠状动脉成像及选择性冠状动脉造影.对ACS组及稳定性心绞痛组的管腔狭窄程度、斑块最低密度值、钙化形态(点状钙化或大钙化)及斑块大小进行评价.计算64排MDCT对ACS易损斑块诊断的敏感性、特异性、阳性预测值、阴性预测值.采用SPSS 13.0统计软件进行ACS组与SAP两组之间特征的差异描述和分析,定性变量用卡方检验,定量变量采用两独立样本t检验,P ＜0.05为差异有显著性.结果 两组之间管腔的狭窄程度无差别.ACS组斑块的最低密度CT值[(39±78)HU]低于稳定性心绞痛组斑块的最低密度CT值[(103±114)HU],两组比较差异有统计学意义(P＜0.05,t=0.315).斑块的总体积两组比较无差异,软斑块体积比例＞40％的例数,ACS组较稳定性心绞痛组大,差异不具有统计学意义(P＞0.05).点状钙化在ACS组更频繁而稳定性心绞痛组大钙化更为常见,两组比较差异均有统计学意义(P＜0.01,t=0.221).斑块最小密度CT值＜35 HU的比例在ACS组较SAP组更频繁(P＜0.01,t=0.161).同时存在点状钙化及斑块最小CT值＜35 HU这两个特征对ACS诊断显示很高的阳性预测值,而缺少这两个特征阴性预测值很高.结论 ACS易损斑块CT特征包括:斑块低密度、点状钙化、软斑块体积所占比例较大的特点.冠状动脉粥样斑块同时具有CT值＜35 HU、点状钙化特征高度提示斑块的易损性.     

Use-dependent control of presynaptic calcium signalling at central synapses

Voltage-gated Ca(2+) channels activated by action potentials evoke Ca(2+) entry into presynaptic terminals thus briefly distorting the resting Ca(2+) concentration. When this happens, a number of processes are initiated to re-establish the Ca(2+) equilibrium. During the post-spike period, the increased Ca(2+) concentration could enhance the presynaptic Ca(2+) signalling. Some of the mechanisms contributing to presynaptic Ca(2+) dynamics involve endogenous Ca(2+) buffers, Ca(2+) stores, mitochondria, the sodium-calcium exchanger, extraterminal Ca(2+) depletion and presynaptic receptors. Additionally, subthreshold presynaptic depolarization has been proposed to have an effect on release of neurotransmitters through a mechanism involving changes in resting Ca(2+). Direct evidence for the role of any of these participants in shaping the presynaptic Ca(2+) dynamics comes from direct recordings of giant presynaptic terminals and from fluorescent Ca(2+) imaging of axonal boutons. Here, some of this evidence is presented and discussed.     

Developmental changes in odor-evoked activity in rat piriform cortex

In adult rats, odor-evoked Fos protein expression is found in rostrocaudally-oriented bands of cells in anterior piriform cortex (APC), likely indicating functionally distinct subregions, while activated cells in posterior piriform cortex (PPC) lack apparent spatial organization. To determine whether these patterns are present during early postnatal life, and whether they change during development, Fos expression was assessed following acute exposure to single aliphatic acid odors in developing rats beginning at postnatal day 3 (P3). In the olfactory bulb, Fos-immunoreactive cells were present in the granule cell, mitral cell and glomerular layers at the earliest ages examined. Cells immunopositive for Fos were clustered in areas previously reported as active in response to these odors. In piriform cortex, activation in layers II/III shared some features with that seen in the adult; in APC, rostro-caudally oriented bands of Fos-positive cells alternated with bands relatively free of label, while labeled cells were found dispersed throughout PPC. However, in P3-P7 animals, Fos-positive cells in APC were found in a central rostro-caudally oriented band that was flanked by two bands relatively free of Fos-positive cells. This contrasted with the adult pattern, a central cell-poor band flanked by cell-rich bands, which was observed beginning at P10. These results suggest that subregions of APC visualized by odor-evoked Fos expression are active and functionally distinct shortly after birth. Changes in activity within these subregions during early postnatal development coincide with a shift toward adult-like olfactory learning behavior in the second postnatal week, and may play a role in this behavioral shift.