在自然活动和感官刺激过程中，哺乳动物大脑皮层中的神经反应是高度可变的。用来解释这一现象的主导性假说是，警觉的动物的大脑皮层处于一种非同步的高传导状态。Nicholas Priebe及同事采用全细胞记录获得了对执行一项固定任务(fixation task)的猴子的初级视皮层中单一神经元的突触输入的直接观察结果，他们的结果支持另一个假说：在没有感官刺激的固定(fixation)过程中，神经脉冲是由非经常的关联事件驱动的。但存在视觉刺激时，该皮层就会从同步状态变成非同步状态。这一发现表明，同一皮层回路能根据感官驱动因素在同步状态和非同步状态之间变化。
In the mammalian cerebral cortex, neural responses are highly variable during spontaneous activity and sensory stimulation. To explain this variability, the cortex of alert animals has been proposed to be in an asynchronous high-conductance state in which irregular spiking arises from the convergence of large numbers of uncorrelated excitatory and inhibitory inputs onto individual neurons. Signatures of this state are that a neuron’s membrane potential (Vm) hovers just below spike threshold, and its aggregate synaptic input is nearly Gaussian, arising from many uncorrelated inputs. Alternatively, irregular spiking could arise from infrequent correlated input events that elicit large fluctuations in Vm (refs 5, 6). To distinguish between these hypotheses, we developed a technique to perform whole-cell Vm measurements from the cortex of behaving monkeys, focusing on primary visual cortex (V1) of monkeys performing a visual fixation task. Here we show that, contrary to the predictions of an asynchronous state, mean Vm during fixation was far from threshold (14 mV) and spiking was triggered by occasional large spontaneous fluctuations. Distributions of Vm values were skewed beyond that expected for a range of Gaussian input, but were consistent with synaptic input arising from infrequent correlated events. Furthermore, spontaneous fluctuations in Vm were correlated with the surrounding network activity, as reflected in simultaneously recorded nearby local field potential. Visual stimulation, however, led to responses more consistent with an asynchronous state: mean Vm approached threshold, fluctuations became more Gaussian, and correlations between single neurons and the surrounding network were disrupted. These observations show that sensory drive can shift a common cortical circuitry from a synchronous to an asynchronous state.