VIP interneuron-mediated disinhibition underlies cortical network plasticity & perceptual learning

现代神经科学中最引人注目的问题之一是：当我们学习时，大脑是如何变化的？感官体验和知觉学习被认为与长期增强（LTP）有关，即突触连接的加强。LTP是体感觉皮层神经元可塑性的基础（S1）。我之前的研究表明，LTP依赖于亚型特异性gaba能中间神经元的协同激活。然而，这种LTP及其细胞和电路基础是否驱动了清醒小鼠的皮质网络可塑性，以及这是否构成了学习的基础，还有待观察。我假设S1中去抑制性gaba能回路的激活是皮层网络可塑性和基于触觉的感知学习的基础。小鼠将S1的很大一部分用于桶状皮质（BC），桶状皮质代表须，这是小鼠必不可少的感觉方式。短时间的节律性须刺激（RWS, 8Hz, 1min）后，可在BC的(L) 2/3层锥体神经元（PNs）中诱导LTP。先前，我发现这是由来自感觉相关和高阶丘脑输入的重复输入驱动的。这种配对增加了血管活性肠肽阳性（VIP）中间神经元的活性，这是一种抑制生长抑素阳性（SST）中间神经元活性的中间神经元亚型，而生长抑素阳性（SST）中间神经元是L2/3PN输入的守门者。我发现这种抑制性中间神经元的开启和关闭，也就是去抑制，是可塑性的驱动力。有趣的是，高阶丘脑输入被认为提供了正确的感觉处理和知觉学习所需的重要反馈信号。我提出的研究旨在了解是否去抑制电路是清醒小鼠网络可塑性和知觉学习的基础。我将使用双光子激光扫描显微镜（2PLSM）通过清醒，头部固定的小鼠颅窗，通过将cre依赖的腺相关病毒载体（AAV） GCamp6s直接注射到VIP- cre和SST- cre小鼠系的BC中，监测VIP和SST中间神经元的Ca2+反应。然后，我将监测Ca2+活性的变化，这是细胞尖峰或活动的反映，在被动节律性须刺激（RWS）期间与感知须晒任务期间。初步证据表明VIP中间神经元在RWS时迅速增加其活动，这支持了我之前的发现。我将在这两种中间神经元亚型的基础上继续研究这些发现。然后，我将使用基于须的触觉阈值检测任务结合2PLSM来研究VIP和SST中间神经元的活动，以监测Ca2+反应，以测试去抑制回路是否被激活，即VIP中间神经元活动的增加和SST中间神经元活动的减少，在实验时间轴的特定时间点。在阈下到阈下的探测范围内，向动物展示须的偏转，并训练它们通过舔舐来报告可探测到的偏转，以获得水奖励。最后，我可以在同一个2PLSM上执行两个范式，这提供了在相同的中间神经元中返回相同领域进行记录的机会。我的目标是确定在一种范式中观察到的单个中间神经元的活动是否可以预测其在另一种范式中的活动。最终，这项工作可以揭示，在学习过程中，解除抑制是调节神经元回路的一个普遍主题。这可能对人工神经网络领域很重要，并可能为利用皮层回路适应性机制提供目标，这可能对大脑健康和疾病产生广泛的影响。

One of the most compelling questions of modern neuroscience is: How does the brain change when we learn? Sensory experience and perceptual learning is thought to be associated with Long Term Potentiation (LTP), i.e. a strengthening of synaptic connections. LTP is a fundamental underpinning of neuronal plasticity in the Somatosensory Cortex (S1). My previous research has demonstrated that LTP is dependent upon concerted activation of subtype specific GABAergic interneurons. However, it remains to be seen if this LTP and its' cellular and circuit underpinnings drive cortical network plasticity in the awake mouse and if this underlies learning. I hypothesize that activation of disinhibitory GABAergic circuits in S1 underlies cortical network plasticity and tactile-based perceptual learning. The mouse dedicates a large part of S1 to the barrel cortex (BC) which cortically represents the whisker, an essential sensory modality for the mouse. LTP can be induced in Layer (L) 2/3 Pyramidal Neurons (PNs) of the BC after a brief period of rhythmic whisker stimulation (RWS, 8Hz, 1min). Previously, I found that this is driven by repetitive inputs from sensory- related and high-order thalamic inputs. This pairing increases the activity of vasoactive-intestinal-peptide-positive (VIP) interneurons, a subtype of interneurons that suppress the activity of somatostatin positive (SST) interneurons, which are the gate keepers of L2/3PN inputs. I found that this switching on and off of inhibitory interneurons, aka disinhibition, is a driving force for plasticity. Interestingly, the higher-order thalamic inputs are thought to provide important feedback signals needed for correct sensory processing and perceptual learning. My proposed research aims to understand if disinhibitory circuitry underlies plasticity and perceptual learning within the network in the awake mouse. Using 2-Photon Laser Scanning Microscopy (2PLSM) through a cranial window in awake, head-fixed, mice I will monitor Ca2+ responses in VIP & SST interneurons by injecting a Cre-dependent adeno-associated viral vector (AAV) GCamp6s, Ca2+ indicator, directly into the BC of VIP-Cre & SST-Cre mouse lines. Then I will monitor changes in Ca2+ activity, a reflection of the cell spiking or activity, during passive Rhythmic Whisker Stimulation (RWS) versus during a perceptual whisker-basked task. Preliminary evidence suggests that VIP interneurons rapidly increase their activity upon RWS which bolsters my previous findings. I will continue to build upon these findings in both interneuron subtypes. Then, I will use a whisker-based tactile threshold detection task combined with 2PLSM to investigate the activity of VIP & SST interneurons to monitor the Ca2+ responses to test if disinhibitory circuitry is activated, i.e. an increase in VIP interneuron activity and a decrease in SST interneuron activity, during specific time points along the experimental timeline. Animals are presented with whisker deflections at angles within the subliminal to liminal detection range and are trained to report detectable deflections by licking to obtain water rewards. Finally, I can perform the two paradigms on the same 2PLSM, which provides the opportunity to return to the same field to record in the same interneurons. I will aim to determine if the activity, within a single interneuron, observed in one paradigm can predict its activity during the other paradigm. Ultimately, this work could reveal that disinhibition represents a prevalent motif for tuning neuronal circuits during learning. Which may prove important for the field of artificial neuronal networks and could provide targets to harness the mechanisms underlying cortical circuit adaptability, which may have wide sweeping implications for brain health and disease.