The neural networks underlying endogenous auditory covert orienting and reorienting

Auditory information communicated through vocalizations, music, or sounds in the environment is commonly used to orient and direct attention to different locations in extrapersonal space. The neural networks subserving attention to auditory space remain poorly understood in comparison to our knowledge about attention in the visual system. The present study investigated whether a parietal-prefrontal right-hemisphere network controls endogenous orienting and reorienting of attention to the location of sounds just as it does for visual-spatial information. Seventeen healthy adults underwent event-related functional magnetic resonance imaging (FMRI) while performing an endogenous auditory orienting task, in which peripheral cues correctly (valid) or incorrectly (invalid) specified the location of a forthcoming sound. The results showed that a right precuneus and bilateral temporal-frontal network mediated the reorienting of auditory attention at both short and long stimulus onset asynchronies (SOAs). In contrast, the more automatic stage of auditory reorienting at the shorter SOA was associated with activation in a bilateral inferior parietal-frontal oculomotor network. These findings suggest that the reorienting of auditory attention is generally supported by a similar inferior parietal-frontal network as visual attention, but in both hemispheres. However, peripheral auditory cues also appear to elicit an automatic orienting response to the spatial location of a sound followed by a period of reduced processing of information that occurs in the same location later in time.     

Generators of the intracranial P50 response in auditory sensory gating

Clarification of the cortical mechanisms underlying auditory sensory gating may advance our understanding of brain dysfunctions associated with schizophrenia. To this end, data from nine epilepsy patients who participated in an auditory paired-click paradigm during pre-surgical evaluation and had grids of electrodes covering temporal and frontal lobe were analyzed. A distributed source localization approach was applied to the intracranial P50 response and the Gating Difference Wave obtained by subtracting the response to the second stimuli from the response to the first stimuli. Source reconstruction of the P50 showed that the main generators of the response were localized in the temporal lobes. The analysis also suggested that the maximum neuronal activity contributing to the amplitude reduction in the P50 time range (phenomenon of auditory sensory gating) is localized at the frontal lobe. Present findings suggest that while the temporal lobe is the main generator of the P50 component, the frontal lobe seems to be a substantial contributor to the process of sensory gating as observed from scalp recordings.     

首发精神分裂症患者听感觉门控P50及认知功能的相关性研究

目的 探讨首发精神分裂症患者听感觉门控P50与威斯康星卡片分类测验之间的相关性.方法 采用配对听觉条件、测试刺激范式及威斯康星卡片分类测验对51名首发精神分裂症患者和51名健康常人进行检测,并进行相关性分析.结果 患者组听感觉门控P50抑制明显高于对照组(P<0.01);威斯康星卡片分类测验结果显示,患者组完成分类数和正确分类数显著低于对照组,而错误数和持续错误数显著高于对照组(P<0.01);患者组听感觉门控P50抑制与威斯康星卡片分类测验指标间无相关性.结论 首发精神分裂症患者存在认知功能损害与额叶功能缺陷,反映出可能存在不同的神经发生机制.     

Evoked and induced oscillatory activity contributes to abnormal auditory sensory gating in schizophrenia

The ratio of magnetoencephalogram-recorded brain responses occurring 50ms after paired clicks (S2-evoked M50/S1-evoked M50) serves as a measure of sensory gating. An abnormally large ratio is commonly found in schizophrenia. Whether this abnormality indicates impaired gating is debated. Using event-related oscillations the present study sought to elucidate processes contributing to the phenomenon of altered M50 gating ratio. Schizophrenia inpatients (n=50) showed the expected large M50 gating ratio relative to 48 healthy controls, which correlated with less induced frontally generated activity in the 10-15Hz frequency band starting 200ms before the onset of S2. Patients also produced smaller alpha (8-12Hz) and gamma (60-80Hz) responses to S1. Results suggest that the deviant gating ratio in schizophrenia is a consequence of a complex alteration in the processing of incoming information that cannot be attributed to impaired gating alone.     

首发精神分裂症听觉感觉门控异常的功能磁共振研究

目的通过功能磁共振成像(fMRI)技术探讨首发精神分裂症听觉感觉门控异常与脑功能异常激活之间的关系,为该病的临床研究提供更多客观依据。方法选择2011年6月至2012年6月精神科收治的15例首发精神分裂症患者作为研究组,同时选取年龄、性别、受教育程度相匹配的15例志愿者作为正常对照组,两组均进行脑功能磁共振成像,采用多声音刺激和单声音刺激比较的范式,比较两组患者感觉听觉门控的异常。结果研究组听觉感觉门控脑激活在右侧海马、右侧丘脑区明显低于正常对照组,差异有统计学意义(P<0.05)。结论首发精神分裂症患者的听觉门控异常可能与大脑海马、丘脑等功能激活异常有关。     

A comparison of neural circuits underlying auditory and visual object categorization

Knowledge about environmental objects derives from representations of multiple object features both within and across sensory modalities. While our understanding of the neural basis for visual object representation in the human and nonhuman primate brain is well advanced, a similar understanding of auditory objects is in its infancy. We used a name verification task and functional magnetic resonance imaging (fMRI) to characterize the neural circuits that are activated as human subjects match visually presented words with either simultaneously presented pictures or environmental sounds. The difficulty of the matching judgment was manipulated by varying the level of semantic detail at which the words and objects were compared. We found that blood oxygen level dependent (BOLD) signal was modulated in ventral and dorsal regions of the inferior frontal gyrus of both hemispheres during auditory and visual object categorization, potentially implicating these areas as sites for integrating polymodal object representations with concepts in semantic memory. As expected, BOLD signal increases in the fusiform gyrus varied with the semantic level of object categorization, though this effect was weak and restricted to the left hemisphere in the case of auditory objects.     

阿尔茨海默病模型大鼠感觉门控听觉诱发电位P50诱发电位的变化

背景：听觉诱发电位P50为反映大脑正常抑制功能的一种直观的脑电生理学指标。 目的：观察阿尔茨海默病模型大鼠感觉门控听觉诱发电位P50成分的变化。 设计：随机对照动物实验。 单位：昆明医学院神经科学研究所。 材料：选用雌性健康SD大鼠24只，鼠龄4～6月，体质量200～300g。按随机抽签法将大鼠分为3组：实验组、对照组、正常组，每组8只。Morris水迷宫由圆形水池和有机玻璃站台构成，水池分平台、左、右及对侧4个象限。 方法：实验于2003-09／2005-03在昆明医学院神经科学研究所完成。①实验组：切断双侧穹窿海马伞造成阿尔茨海默病模型；对照组：切断皮质、胼胝体，但不切断穹窿海马伞；正常组：未手术。②在建模后1周对所有大鼠进行包括检测定位航行能力和空间探索能力的水迷宫试验，以确定造模是否成功；每只大鼠每日训练4次，共训练5d。入池到找到站台的时间（逃避潜伏期）反映定位航行能力；大鼠1min内在池中搜索站台的游泳轨迹反映空间探索能力。③采用条件（C）-试验（T）双声刺激模式记录听觉P50诱发电位，比较各组大鼠听觉P50诱发电位的差异。计算C-P50波幅、T-P50波幅、T／C比，S2-S1波幅差的绝对值等。计量资料多组间比较用单因素方差分析，组间比较采用t检验。 主要观察指标：①各组大鼠水迷宫试验，即定位航行能力和空间探索能力检测结果比较。②各组大鼠感觉门控P50诱发电位比较。 结果：大鼠24只均进入结果分析。①水迷宫试验结果：3组大鼠随着训练天数的增加平均潜伏期缩短，前3d潜伏期均下降，之后趋平稳。实验组潜伏期明显长于正常组和对照组（P〈0．05）。正常组和对照组大鼠的游泳轨迹集中在站台象限，站台象限游泳轨迹分别占总游泳轨迹的45．23％和39．7％，与其他象限间游泳轨迹比较，差异明显（P〈0．01）。实验组大鼠在站台、右侧、对侧、左侧象限游泳轨迹占总游泳轨迹的28．31％，29．84％，20．47％和21．38％，差异不明显（P〉0．05），游泳轨迹在4个象限中基本呈随机分布。②大鼠感觉门控P50诱发电位检测结果：对照组C-P50波幅和S2-S1波幅差的绝对值分别为（21．00&;#177;2．85），（15．26&;#177;4．07）μV，正常组分别为（17．04&;#177;5．32），（10．85&;#177;4．24）μV，明显高于实验组[（9．67&;#177;3．77），（2．89&;#177;2．61）μV，P〈0．01]。对照组和正常组T-P50波幅与C-P50波幅比值分别为0．25&;#177;0．18和0．39&;#177;0．16，明显低于实验组（0．92&;#177;0．41，P〈0．01）。 结论：①用双侧海马伞切断方法可成功制备阿尔茨海默病动物模型。②双侧海马伞切断阿尔茨海默病模型大鼠存在感觉门控能力的不足。     

阿尔茨海默病模型大鼠感觉门控听觉诱发电位P50诱发电位的变化

背景听觉诱发电位P50为反映大脑正常抑制功能的一种直观的脑电生理学指标.目的观察阿尔茨海默病模型大鼠感觉门控听觉诱发电位P50成分的变化.设计随机对照动物实验.单位昆明医学院神经科学研究所.材料选用雌性健康SD大鼠24只,鼠龄4～6月,体质量200～300 g.按随机抽签法将大鼠分为3组实验组、对照组、正常组,每组8只.Morris水迷宫由圆形水池和有机玻璃站台构成,水池分平台、左、右及对侧4个象限.方法实验于2003-09/2005-03在昆明医学院神经科学研究所完成.①实验组切断双侧穹窿海马伞造成阿尔茨海默病模型;对照组切断皮质、胼胝体,但不切断穹窿海马伞;正常组未手术.②在建模后1周对所有大鼠进行包括检测定位航行能力和空间探索能力的水迷宫试验,以确定造模是否成功;每只大鼠每日训练4次,共训练5 d.入池到找到站台的时间(逃避潜伏期)反映定位航行能力;大鼠1 min内在池中搜索站台的游泳轨迹反映空间探索能力.③采用条件(C)-试验(T)双声刺激模式记录听觉P50诱发电位,比较各组大鼠听觉P50诱发电位的差异.计算C-P50波幅、T-P50波幅、T/C比、S2-S1波幅差的绝对值等.计量资料多组间比较用单因素方差分析,组间比较采用t检验.主要观察指标①各组大鼠水迷宫试验,即定位航行能力和空间探索能力检测结果比较.②各组大鼠感觉门控P50诱发电位比较.结果大鼠24只均进入结果分析.①水迷宫试验结果3组大鼠随着训练天数的增加平均潜伏期缩短,前3 d潜伏期均下降,之后趋平稳.实验组潜伏期明显长于正常组和对照组(P＜0.05).正常组和对照组大鼠的游泳轨迹集中在站台象限,站台象限游泳轨迹分别占总游泳轨迹的45.23%和39.7%,与其他象限间游泳轨迹比较,差异明显(P＜0.01).实验组大鼠在站台、右侧、对侧、左侧象限游泳轨迹占总游泳轨迹的28.31%,29.84%,20.47%和21.38%,差异不明显(P＞0.05),游泳轨迹在4个象限中基本呈随机分布.②大鼠感觉门控P50诱发电位检测结果对照组C-P50波幅和S2-S1波幅差的绝对值分别为(21.00±2.85),(15.26±4.07)μV,正常组分别为(17.04±5.32),(10.85±4.24)μV,明显高于实验组[(9.67±3.77),(2.89±2.61)μV,P＜0.01].对照组和正常组T-P50波幅与C-P50波幅比值分别为0.25±0.18和0.39±0.16,明显低于实验组(0.92±0.41,P＜0.01).结论①用双侧海马伞切断方法可成功制备阿尔茨海默病动物模型.②双侧海马伞切断阿尔茨海默病模型大鼠存在感觉门控能力的不足.     

The neural bases underlying pitch processing difficulties

Normal listeners are often surprisingly poor at processing pitch changes. The neural bases of this difficulty were explored using magnetoencephalography (MEG) by comparing participants who obtained poor thresholds on a pitch-direction task with those who obtained good thresholds. Source-space projected data revealed that during an active listening task, the poor threshold group displayed greater activity in the left auditory cortical region when determining the direction of small pitch glides, whereas there was no difference in the good threshold group. In a passive listening task, a mismatch response (MMNm) was identified for pitch-glide direction deviants, with a tendency to be smaller in the poor listeners. The results imply that the difficulties in pitch processing are already apparent during automatic sound processing, and furthermore suggest that left hemisphere auditory regions are used by these listeners to consciously determine the direction of a pitch change. This is in line with evidence that the left hemisphere has a poor frequency resolution, and implies that normal listeners may use the sub-optimal hemisphere to process pitch changes.     

The neural basis of temporal auditory discrimination

When two identical stimuli, such as a pair of clicks, are presented with a sufficiently long time-interval between them they are readily perceived as two separate events. However, as they are presented progressively closer together, there comes a point when the two separate stimuli are perceived as one. This phenomenon applies not only to hearing but also to other sensory modalities. Damage to the basal ganglia disturbs this type of temporal discrimination irrespective of sensory modality, suggesting a multimodal process is involved. Our aim was to study the neural substrate of auditory temporal discrimination in healthy subjects and to compare it with structures previously associated with analogous tactile temporal discrimination. During fMRI scanning, paired-clicks separated by variable inter-stimulus intervals (1-50 ms) were delivered binaurally, with different intensities delivered to each ear, yielding a lateralised auditory percept. Subjects were required (a) to report whether they heard one or two stimuli (TD: temporal discrimination); or (b) to report whether the stimuli were located on the right or left side of the head mid-line (SD: spatial discrimination); or (c) simply to detect the presence of an auditory stimulus (control task). Our results showed that both types of auditory discrimination (TD and SD) compared to simple detection activated a network of brain areas including regions of prefrontal cortex and basal ganglia. Critically, two clusters in pre-SMA and the anterior cingulate cortex were specifically activated by TD. Furthermore, these clusters overlap with regions activated for similar judgments in the tactile modality suggesting that they fulfill a multimodal function in the temporal processing of sensory events.     

Working memory load modulates the auditory "What" and "Where" neural networks

Working memory for sound identity (What) and sound location (Where) has been associated with increased neural activity in ventral and dorsal brain regions, respectively. To further ascertain this domain specificity, we measured fMRI signals during an n-back (n=1, 2) working memory task for sound identity or location, where stimuli selected randomly from three semantic categories (human, animal, and music) were presented at three possible virtual locations. Accuracy and reaction times were comparable in both "What" and "Where" tasks, albeit worse for the 2-back than for the 1-back condition. The analysis of fMRI data revealed greater activity in ventral and dorsal brain regions during sound identity and sound location, respectively. More importantly, there was an interaction between task and working memory load in the inferior parietal lobule (IPL). Within the right IPL, there were two sub-regions modulated differentially by working memory load: an anterior ventromedial region modulated by location load and a posterior dorsolateral region modulated by category load. These specific changes in neural activity as a function of working memory load reveal domain-specificity within the parietal cortex.     

Neural mechanisms of auditory awareness underlying verbal transformations

Prolonged listening to a repeated word without a pause produces a series of illusory transitions of the physically unchanging word, which is called verbal transformation. Verbal transformations provide a rare opportunity to examine how auditory percepts are formed in the brain. We found that verbal forms are affected by phonetic reorganization of a word, rather than by auditory adaptation and lexical distortion of it. We identified brain activity leading to individual differences between perceptual transitions and tone detection. An event-related fMRI analysis revealed that the left inferior frontal cortex (IFC), anterior cingulate cortex (ACC), and the left prefrontal cortex were activated when perceptual transitions from one verbal form to another occurred, but not when tone pips were detected. The number of perceptual transitions showed positive and negative correlations with signal intensity in the left IFC and the left ACC, respectively. The results suggest that active generation of verbal forms is linked with articulatory gestures for speech production and that the frequency of perceptual transitions is determined by a balance of the activations between the two brain regions. Structural equation modeling demonstrated that individual differences in the number of perceptual transitions rely on negative feedback from the ACC to the IFC via the posterior insula. These findings suggest that distributed frontal areas are involved in auditory awareness underlying verbal transformations.     

Neural mechanisms underlying auditory feedback control of speech

The neural substrates underlying auditory feedback control of speech were investigated using a combination of functional magnetic resonance imaging (fMRI) and computational modeling. Neural responses were measured while subjects spoke monosyllabic words under two conditions: (i) normal auditory feedback of their speech and (ii) auditory feedback in which the first formant frequency of their speech was unexpectedly shifted in real time. Acoustic measurements showed compensation to the shift within approximately 136 ms of onset. Neuroimaging revealed increased activity in bilateral superior temporal cortex during shifted feedback, indicative of neurons coding mismatches between expected and actual auditory signals, as well as right prefrontal and Rolandic cortical activity. Structural equation modeling revealed increased influence of bilateral auditory cortical areas on right frontal areas during shifted speech, indicating that projections from auditory error cells in posterior superior temporal cortex to motor correction cells in right frontal cortex mediate auditory feedback control of speech.     

Delayed auditory processing underlying stimulus detection in Down syndrome

Down syndrome (DS) is characterized by intellectual disability and development of dementia that are attributed to similar neuropathological features as observed in Alzheimer's disease (AD). The aim of this study was to investigate whether DS patients have similar impairment of preattentive auditory processing as observed in AD. Sinusoidal tones were presented to DS patients and healthy controls, and evoked auditory evoked fields (AEF) were measured with a whole-head magnetoencephalography (MEG) system. Patients with DS had significantly delayed and attenuated N100m, and delayed but not attenuated P50m responses over both hemispheres. Present results indicate that preattentive auditory processing underlying stimulus detection is impaired in DS. Given that anticholinergic drugs modulate AEFs, degeneration of cholinergic system in DS could contribute to the damaged auditory processing.     

Task-relevant modulation of primary somatosensory cortex suggests a prefrontal-cortical sensory gating system

Increasing evidence suggests that somatosensory information is modulated cortically for task-specific sensory inflow: Several studies report short-term adaptation of representational maps in primary somatosensory cortex (SI) due to attention or induced by task-related motor activity such as handwriting. Recently, it has been hypothesized that the frontal or prefrontal cortex may modulate SI. In order to test this hypothesis, we studied the functional organization of SI while subjects performed the Tower of Hanoi task. This task is known to be related to activation of frontal or prefrontal areas. The functional organization of SI while performing the Tower of Hanoi task was compared to the organization of SI during performing the same movements but without the Tower of Hanoi task and with rest. Topography of SI was assessed using neuromagnetic source imaging based on tactile stimulation of the first (D1) and fifth digits (D5). Performing the Tower of Hanoi task was accompanied by plastic changes in SI as indicated by significant shifts in the cortical representations of D1 and D5: They moved further apart during the Tower of Hanoi task compared to the control task containing the same movements but without the cognitive characteristic. Thus, we conclude that SI maps undergo dynamic modulation depending on motor tasks with different cognitive demands. The results suggest that this short-term plasticity may be regulated by a prefrontal-cortical sensory gating system.     

The removal of EMG in EEG by neural networks

In this paper, it is presented that electromyography (EMG) is a shot noise based on the generation of EMG. A novel filter is proposed by applying a neural network (NN) ensemble where the noisy input signal and the desired one are the same in a learning process. Both incremental and batch mode are applied in the learning process of NNs that is better than generalized NN filters. This NN ensemble filter not only reduces additive and multiplicative white noise inside signals, but also preserves the signals' characteristics. In clinical EEG and EMG signals processing, the filter is capable of reducing EMG in the clinical EEG, and it is proved that there is randomness in EMG.