Recurrent circuitry is required to stabilize piriform cortex odor representations across brain states

Pattern completion, or the ability to retrieve stable neural activity
patterns from noisy or partial cues, is a fundamental feature of memory.
Theoretical studies indicate that recurrently connected auto-associative
or discrete attractor networks can perform this process. Although pattern
completion and attractor dynamics have been observed in various recurrent
neural circuits, the role recurrent circuitry plays in implementing these
processes remains unclear. In recordings from head-fixed mice, we found
that odor responses in olfactory bulb degrade under ketamine/ xylazine
anesthesia, while responses immediately downstream, in piriform cortex,
remain robust. Recurrent connections are required to stabilize cortical
odor representations across states. Moreover, piriform odor
representations exhibit attractor dynamics, both within and across trials,
and these are also abolished when recurrent circuitry is eliminated. Here,
we present converging evidence that recurrently-connected piriform
populations stabilize sensory representations in response to degraded
inputs, consistent with an auto-associative function for piriform cortex
supported by recurrent circuitry.

模式补全（Pattern Completion）是记忆的核心特征之一，指从带有噪声或不完整的线索中恢复稳定神经活动模式的能力。理论研究表明，具备循环连接的自联想网络（auto-associative network）或离散吸引子网络（discrete attractor network）可完成该过程。尽管已在多种循环神经环路中观测到模式补全与吸引子动力学（attractor dynamics）现象，但循环环路在实现这些过程中所扮演的具体角色仍不明确。在对头部固定小鼠（head-fixed mice）的电生理记录实验中，我们发现：氯胺酮/赛拉嗪（ketamine/xylazine）麻醉状态下，嗅球（olfactory bulb）的气味响应会出现衰减，而紧邻其下游的梨状皮层（piriform cortex）内的气味响应则保持稳定。循环连接是维持不同状态下皮层气味表征稳定性的必要条件。此外，梨状皮层的气味表征在单次试验内与跨试验间均表现出吸引子动力学特性，而当循环环路被消除后，该特性也会消失。本研究提供了汇聚性证据，表明具备循环连接的梨状皮层神经元群可在输入信号受损时稳定感官表征，这与循环环路支撑下的梨状皮层自联想功能相符。