Visual Cognition Laboratory, Department of Medicine, University of Fribourg, Chemin du Musée 5, CH-1700 Fribourg, Switzerland.
Eur J Neurosci. 2012 Apr;35(8):1270-80. doi: 10.1111/j.1460-9568.2012.08052.x. Epub 2012 Apr 4.
Acetylcholine is an important neuromodulator involved in cognitive function. The impact of cholinergic neuromodulation on computations within the cortical microcircuit is not well understood. Here we investigate the effects of layer-specific cholinergic drug application in the tree shrew primary visual cortex during visual stimulation with drifting grating stimuli of varying contrast and orientation. We describe differences between muscarinic and nicotinic cholinergic effects in terms of both the layer of cortex and the attribute of visual representation. Nicotinic receptor activation enhanced the contrast response in the granular input layer of the cortex, while tending to reduce neural selectivity for orientation across all cortical layers. Muscarinic activation modestly enhanced the contrast response across cortical layers, and tended to improve orientation tuning. This resulted in highest orientation selectivity in the supra- and infragranular layers, where orientation selectivity was already greatest in the absence of pharmacological stimulation. Our results indicate that laminar position plays a crucial part in functional consequences of cholinergic stimulation, consistent with the differential distribution of cholinergic receptors. Nicotinic receptors function to enhance sensory representations arriving in the cortex, whereas muscarinic receptors act to boost the cortical computation of orientation tuning. Our findings suggest close homology between cholinergic mechanisms in tree shrew and primate visual cortices.
乙酰胆碱是一种参与认知功能的重要神经调质。胆碱能神经调制对皮质微电路内计算的影响还不太清楚。在这里，我们研究了在视觉刺激期间，用不同对比度和方向的漂移光栅刺激，在树鼩初级视觉皮层中进行层特异性胆碱能药物应用的效果。我们根据皮层的层和视觉表现的属性，描述了毒蕈碱和烟碱型胆碱能作用之间的差异。烟碱型受体的激活增强了皮层颗粒输入层的对比度反应，而倾向于降低所有皮层层的神经选择性。毒蕈碱型激活适度增强了整个皮层的对比度反应，并倾向于改善方向调谐。这导致在超颗粒和次颗粒层中具有最高的方向选择性，而在没有药物刺激的情况下，这些层的方向选择性已经最大。我们的结果表明，层位置在胆碱能刺激的功能后果中起着至关重要的作用，这与胆碱能受体的差异分布一致。烟碱型受体的功能是增强到达皮层的感觉表示，而毒蕈碱型受体则作用于增强皮层的方向调谐计算。我们的发现表明，树鼩和灵长类动物视觉皮层中的胆碱能机制具有密切的同源性。
