• Research Progress
  • Critical periods begin after cortical excitatory synapses mature.

            In a research article published in Cell Reports (Online) on July 28th , entitled "Selective Maturation of Temporal Dynamics of Intracortical Excitatory Transmission at the Critical Period Onset", graduate students Qinglong Miao and Yi Yao from Dr. Xiaohui Zhang’ group in the State Key Laboratory of Cognitive Neuroscience & Learning at Beijing Normal University, revealed a novel synaptic mechanism underlying the control of onset of critical period for the experience-dependent cortical plasticity during the postnatal brain development.
            Critical periods (CP) are defined early postnatal time-windows during which the brain connectivity is highly amenable to experience. This experience-induced brain plasticity during the CP is essential for the formation of many brain cognitive functions, including sensory perception, learning and memory. Impairments of the CP plasticity often lead to lifelong irreversible negative impacts on the brain wiring and function. Although there exists a general hypothesis that the onset and duration of CP are regulated by functional maturation of synaptic circuits, in particular the inhibitory circuit, its detailed synaptic base was not well understood due to the daunting complexity of neural circuits in the brain.  Recently, Prof. Zhang’s lab has published a series of studies (J Neurosci, 2014; Nat Commun, 2014, Sci Rep, 2015) to address the circuit mechanism for regulating the CP brain plasticity, using the classical visual input-induced ocular dominance plasticity of developing mouse primary visual cortex (V1). 
            In this Cell Reports work, Miao and Yao conducted systematic electrophysiological examinations on the functional maturation of diverse synapses formed among excitatory principal neurons and different subtypes of inhibitory neurons in the layer 4 circuit of developing mouse V1 during the transition to CP.  They found that temporal dynamics of intracortical excitatory synaptic transmission are selectively matured, in a experience dependent manner, prior to the CP onset, while those of intracortical inhibitory synapses and long-range thalamocortical excitatory inputs remain unchanged. This selective maturation of synaptic dynamics results from a ubiquitous reduction of presynaptic release. Their findings provide an additional essential circuit mechanism for regulating CP onset aside from the well-known inhibitory threshold mechanism.  It also strongly suggests that critical period begins after cortical excitatory synapses mature.  
            This work was supported by a grant from the State Key Research Program of China (2011CBA00403).  Dr. Rasch L. Malte R.L, Qian Ye and Xiang Li also contributed to this study.
    Paper link:
    Miao Q.L., Yao L., Malte J.R., Ye Q., Li X. and Zhang X.H. (2016) Selective Maturation of Temporal Dynamics of Intracortical Excitatory Transmission at the Critical Period Onset. Cell Reports 16, 1–13,
    Figure: Cartoon diagram summarizing the experimental findings of selective maturation of temporal dynamics of intracortical excitatory transmission at the onset of critical period of developing mouse visual cortex. It is courteous to Ningdong Tang for drawing this graphic art.