Neuromodeling, Functional Brain Imaging and Language

这个项目的重点是了解大脑如何构建相互作用的区域网络（即，神经网络）执行认知任务，特别是与语言相关的任务，以及这些网络如何在大脑疾病中改变。这些问题是通过结合计算神经科学技术与功能性神经成像数据，使用PET或功能磁共振成像。网络分析方法使我们能够评估大脑操作在任务之间以及正常人群和患者人群之间的差异。这项研究将使我们能够确定哪些网络功能失调，以及神经可塑性在使补偿行为发生中所起的作用。在过去的一年中，评估这些网络方法的拟合优度的适当性的标准进行了检查。在过去的一年中，我们开始描绘的功能网络参与生产的自发叙事语音正常受试者使用PET测量局部脑血流量（rCBF），神经活动的指数。特别感兴趣的是后上级颞叶皮质（可能对应于Wernickes区）和额盖（可能对应于Brocas区）中的左半球（LH）外侧裂周区域。Broca区域在言语过程中与LH中的其他语言相关区域（包括后颞叶和下顶叶皮层）有很强的功能联系。韦尼克区有很强的功能联系，在讲话过程中与LH顶叶，颞顶叶和额叶perisylvian地区。大多数这些强大的功能连接在控制任务中是不存在的（这涉及产生喉和口腔发音运动和声音缺乏语言内容）。有趣的是，控制任务与右半球同源区域的相关性更大。这些结果表明，LH大脑外侧裂周围区域强烈相互作用，在语言生产过程中，但不是在一个任务，需要类似的肌肉运动和发声的讲话。在口吃的患者中，许多这些强有力的功能联系似乎是缺席的，这表明LH语言生产网络在口吃期间是异常的，为了了解在功能神经影像学研究中观察到的和潜在的神经动力学之间的关系，我们已经构建了一个大规模的神经元动力学计算机模型，执行类似于PET研究设计的视觉对象匹配任务。该模型由对应于大脑皮层中神经元组装的元素组成，并且包含不同的元素，这些元素基于猴子执行类似任务时的电生理记录所识别的类型。它包括一个涉及枕颞视觉通路和额叶回路的主动记忆网络，并且能够执行匹配样本任务，其中如果第二刺激与第一刺激匹配，则做出响应。PET研究通过向代表外侧膝状体核的模型区域呈现成对的刺激来模拟。当模型通过整合不同区域内的突触活动来执行任务时，从模型计算模拟PET数据。模拟PET数据类似于在实际PET延迟匹配样本视觉任务中发现的数据，每个脑区的正确神经元动力学也是如此。在过去的一年里，我们扩展了模型来模拟功能磁共振成像研究，特别是那些使用事件相关设计的研究。研究发现，认知活动不受实验控制，特别是在大脑前部区域（例如，额叶皮层）可以混淆功能磁共振成像活动的解释方面，其潜在的神经基板。最近，我们已经开始扩展该模型，以便它也可以模拟听觉处理。这一建模工作将与模拟研究中使用的相同类型任务的PET和fMRI实验相结合。- PET，fMRI，神经网络，语音，大脑皮层-人类受试者

This project focuses on understanding how the brain constructs networks of interacting regions (i.e., neural networks) to perform cognitive tasks, especially those associated with language, and how these networks are altered in brain disorders. These issues are addressed by combining computational neuroscience techniques with functional neuroimaging data, obtained using PET or fMRI. The network analysis methods allow us to evaluate how brain operations differ between tasks, and between normal and patient populations. This research will allow us to ascertain which networks are dysfunctional, and the role neural plasticity plays in enabling compensatory behavior to occur. During the past year, criteria for assessing the adequacy of the goodness-of-fit of some of these network methods were examined.In the last year, we began delineating the functional networks involved in the production of spontaneous narrative speech in normal subjects using PET measurements of regional cerebral blood flow (rCBF), an index of neural activity. Of special interest were left hemisphere (LH) perisylvian regions in posterior superior temporal cortex (likely corresponding to Wernickes area) and in the frontal operculum (likely corresponding to Brocas area). The Broca region had strong functional connections during speech with other language associated areas in the LH, including regions in posterior temporal and inferior parietal cortex. The Wernicke area had strong functional links during speech with LH parietal, temporoparietal and frontal perisylvian regions. Most of these strong functional connections were absent in the control task (which involved producing laryngeal and oral articulatory movements and sounds devoid of linguistic content). Interestingly, correlations with right hemisphere homologous areas were larger for the control task. These results demonstrate that LH perisylvian regions interact strongly with one another during language production, but not during a task requiring similar muscle movements and vocalizations as speech. In patients who stutter, many of these strong functional linkages seem to be absent, suggesting that LH language-production networks are abnormal during stuttering.In order to understand the relationship between what is observed in functional neuroimaging studies and the underlying neural dynamics, we had constructed a large-scale computer model of neuronal dynamics that performs a visual object-matching task similar to those designed for PET studies. The model is composed of elements that correspond to neuronal assemblies in cerebral cortex, and contain different elements that are based on types identified by electrophysiological recordings from monkeys as they perform similar tasks. It includes an active memory network involving the occipitotemporal visual pathway and a frontal circuit, and is capable of performing a match-to-sample task in which a response is made if the second stimulus matches the first. A PET study is simulated by presenting pairs of stimuli to an area of the model that represents the lateral geniculate nucleus. Simulated PET data are computed from the model as it performs the tasks by integrating synaptic activity within the different areas. Simulated PET data similar to that found in actual PET delayed match to sample visual tasks were obtained, as were the correct neuronal dynamics in each brain region. In the past year, we expanded the model to simulate fMRI studies, particularly those that use an event-related design. It was found that cognitive activity not under experimental control, especially in anterior brain regions (e.g., frontal cortex) can confound interpretation of fMRI activity in terms of its underlying neural substrate. Recently, we have begun an expansion the model so that it can also simulate auditory processing. This modeling effort will be combined with PET and fMRI experiments of the same kind of tasks used in the simulation studies. - PET, fMRI, neural networks, speech, cerebral cortex - Human Subjects