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。据认为，纹状体系统参与了刺激反应习惯学习和规则之间的转换。特别是，我们的团队和其他人已经证明，当需要启动新的动作时，纹状体的背侧部分被涉及，而当刺激-反应联系需要加强时，纹状体的腹侧部分被请求。海马体将有助于人类的情景记忆和联想记忆。情节记忆被定义为对可以明确陈述的自传性事件的记忆。它负责回忆过去与特定时间和地点联系在一起的个人经历。联想记忆是情景记忆的一种形式，它被定义为学习和记忆不同项目之间关系的能力。最近，有人提出纹状体和海马体实际上可能相互作用，并可能相互补充。目前的研究表明，前额叶皮质(PFC)、纹状体和海马体在依赖长期记忆的决策环境中协同工作。然而，PFC、纹状体和海马体在联想记忆过程和上下文相关决策过程中的确切作用尚未确定。在本方案中，我们将结合功能磁共振成像和两种非侵入性脑刺激方法，包括经颅磁刺激(TMS)和高清晰度经颅直接刺激(HD-TDC)，来研究这些区域的功能贡献及其在健康成年人中的相互作用。*提出的研究健康个体额叶-纹状体-海马区相互作用的方法组合是独一无二的，具有广泛的未来意义。它将提供关于前额叶、纹状体不同区域之间的因果机制以及它们与海马体相互作用的宝贵信息。我们的项目将增加关于纹状体在看似不同的认知过程中发挥类似功能的可能性的知识。这将使加拿大站在研究不同的大脑网络如何相互作用的前沿，当情节记忆和决策都需要时。最后，它还将极大地告诉我们TMS和HD-TDC的潜在调节作用，这两种药物越来越多地被使用，但对其作用机制没有广泛的了解。

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.**