The olfactory system is an ideal and tractable system for exploring how the brain transforms sensory inputs into behaviour. The basic tasks of any olfactory system include odour detection, discrimination and categorization. The challenge for the olfactory system is to transform the high-dimensional space of olfactory stimuli into the much smaller space of perceived objects and valence that endows odours with meaning. Our current understanding of how neural circuits address this challenge has come primarily from observations of the mechanisms of the brain for processing other sensory modalities, such as vision and hearing, in which optimized deep hierarchical circuits are used to extract sensory features that vary along continuous physical dimensions. The olfactory system, by contrast, contends with an ill-defined, high-dimensional stimulus space and discrete stimuli using a circuit architecture that is shallow and parallelized. Here, we present recent observations in vertebrate and invertebrate systems that relate the statistical structure and state-dependent modulation of olfactory codes to mechanisms of perception and odour-guided behaviour.

嗅觉系统是一个理想且易于处理的系统，用于探索大脑如何将感官输入转化为行为。任何嗅觉系统的基本任务包括气味检测、辨别和分类。嗅觉系统面临的挑战是将嗅觉刺激的高维空间转换为感知物体和赋予气味意义的价态的小得多的空间。我们目前对神经回路如何应对这一挑战的理解主要来自对大脑处理其他感觉模式（例如视觉和听觉）的机制的观察，其中优化的深层分层电路用于提取沿着连续物理变化的感觉特征。方面。相比之下，嗅觉系统使用浅层并行电路架构来应对不明确的高维刺激空间和离散刺激。在这里，我们提出了脊椎动物和无脊椎动物系统的最新观察结果，这些观察结果将嗅觉密码的统计结构和状态依赖性调制与感知和气味引导行为的机制联系起来。