Contribution of local- and circuit-based mechanisms to adaptive coding in the auditory midbrain

对盛行的感觉信息进行准确编码的能力对动物的生存至关重要，大脑机制已经进化，使这些信息能够以最佳方式从环境中提取。作为这种能力的一部分，许多感觉神经元似乎能够“实时”调整自己的神经调谐，以考虑到正在展开的感觉环境。这种所谓的‘自适应编码’通常导致环境感觉环境编码的精确度提高。这在大脑中是如何实现的仍有待确定，无论是在细胞机制方面，还是在有助于在任何一个大脑中心进行适应性编码的大脑回路方面。我们的实验将研究自适应编码的三个具体方面。首先，他们将确定神经元内部的机制，这些机制有助于对声音中展开的声音强度进行自适应编码。其次，他们将评估大脑皮层反馈对低级大脑中枢自适应编码的贡献。虽然感觉信息被认为是从耳朵的外周听力传感器流向大脑高级中枢，如大脑皮层，但也有大量的大脑皮层反馈电路是已知的。这些反馈回路的功能尚不清楚，但我实验室的初步证据表明，其中一个作用是修改听觉中脑中的自适应编码，增加神经元在主流声音环境突然变化时优化其对声音强度的敏感度所需的时间。最后，实验还将检查当前正在听到的刺激特征的自适应编码的特异性，评估神经元对一个刺激参数(例如声音强度)的反应是否也意味着这些反应也适用于声源位置。

The ability to code accurately the prevailing sensory information is critical to an animal's survival, and brain mechanisms have evolved that enable this information to be extracted from the environment in an optimal manner. As part of this ability, many sensory neurons appear able to adjust their neural tuning in 'real-time' to take account of the unfolding sensory environment. This so-called 'adaptive coding' often results in improved accuracy with which the ambient sensory environment is coded. How this is achieved in the brain remains to be determined, both in terms of cellular mechanisms and in terms of brain circuits that contribute to adaptive coding in any one brain centre. Our experiments will investigate three specific aspects of adaptive coding. First, they will determine mechanisms within neurons themselves that contribute to adaptive coding for the unfolding sound intensities present in a sound. Second, they will assess the contribution of cortical feedback on adaptive coding in lower brain centres. Although sensory information is thought to 'flow' from the peripheral hearing sensors in the ears towards higher brain centres such as the cortex, a substantial number of cortical feedback circuits are also known to exist. The function of these feddback circuits remains unclear, but preliminary evidence from my laboratory suggests that one role is to modify adaptive coding in the auditory midbrain, increasing the time taken by neurons to optimise their sensitivity to sound intensity when the prevailing sound enviroment suddenly changes. Finally, experiments will also examine how specific adaptive coding is for the stimulus feature currently being heard, assessing whether or not adapting a neuron's response to one stimulus parameter (e.g. sound intensity) also means that the responses are adapted to sound-source location, for example.