Elucidating the functional role of fronto-striatal-hippocampal networks

传统上，大脑的纹状体和海马体系统被认为是独立的。纹状体系统被认为参与刺激-反应习惯学习和规则之间的转换。特别是，我们的小组和其他人已经表明，当需要启动一个新的动作时，纹状体的背侧部分参与其中，而当需要加强刺激-反应关联时，纹状体的腹侧部分被请求。海马体可能对人类的情景记忆和联想记忆有贡献。情景记忆被定义为对可以明确陈述的自传式事件的记忆。它负责回忆与特定时间和地点有关的过去的个人经历。联想记忆是情景记忆的一种形式，它被定义为学习和记住不同事物之间关系的能力。******最近，有人提出纹状体和海马体实际上可能相互作用，并可能互补。目前的研究表明，前额叶皮层（PFC）、纹状体和海马体在依赖长期记忆的决策过程中相互合作。然而，PFC、纹状体和海马体在联想记忆过程和情境依赖决策中的确切作用尚未确定。在目前的建议中，我们将使用功能磁共振成像，以及两种非侵入性脑刺激方法，包括经颅磁刺激（TMS）和高分辨率经颅直接刺激（HD-TDCS），来研究这些区域的功能贡献以及它们在健康成人中的相互作用。******提出的研究健康人额纹状体海马体相互作用的方法组合是独特的，具有广泛的未来意义。它将提供关于PFC不同区域，纹状体及其与海马体相互作用之间发生的因果机制的宝贵信息。我们的项目将增加对纹状体在看似不同的认知过程中发挥相似功能的可能性的认识。当需要情景记忆和决策时，不同的大脑网络是如何相互作用的，这将使加拿大处于研究的前沿。最后，它还将极大地告知我们TMS和HD-TDCS的潜在调节作用，这两种药物在没有广泛了解其作用机制的情况下被越来越多地使用

Traditionally, the striatum and the hippocampus systems of the brain were conceived as independent. It was thought that the striatal system was involved in stimulus-response habit learning and shifting between rules. In particular, our group and others have shown that the dorsal part of the striatum is involved when a novel action need to be initiated, while the ventral part of the striatum is solicited when stimulus-response associations need to be reinforced. The hippocampus would contribute to episodic and associative memory in humans. Episodic memory has been defined as the memory of autobiographical events that can be explicitly stated. It is responsible for the recollection of past personal experiences that are linked with a specific time and place. Associative memory is a form of episodic memory which is defined as the ability to learn and remember the relationship between different items.******More recently, it has been proposed that the striatum and the hippocampus may actually interact and possibly complement each other. Current studies suggest that the prefrontal cortex (PFC), striatum and hippocampus co-operate in the context of decision-making dependent on long-term memory. However, the precise role of the PFC, striatum and hippocampus in associative memory processes and context-dependent decision making have yet to be determined. In the present proposal we will use a combination of functional Magnetic Resonance Imaging, together with two methods of non-invasive brain stimulation, including transcranial magnetic stimulation (TMS) and high-definition transcranial direct stimulation (HD-TDCS), to study functional contributions of these regions as well as their interactions in healthy human adults. ******The proposed combination of methods for the study of fronto-striatal-hippocampal interactions in healthy individuals is unique with broad future implications. It will provide invaluable information regarding the causal mechanisms occurring between different regions of the PFC, the striatum and their interaction with the hippocampus. Our project will increase knowledge on the possibility that the striatum serves similar functions in seemingly dissimilar cognitive processes. It will put Canada at the forefront of research regarding how different networks of the brain interact when both episodic memory and decision making are required. Finally, it will also greatly inform us on the potential modulatory effects of TMS and HD-TDCS, which are increasingly being used without extensive knowledge regarding their mechanism of action.**