李朝义院士简介

生物谷

Chao-Yi Li, Professor

Rm 309, ION Building
Institute of Neuroscience
Chinese Academy of Sciences
Shanghai 200031
China
Email: cyli@ ion.ac.cn
Phone: 86-21-5492 1777

Prof. Chao-Yi Li was born in Chungqing, China. He graduated from the Chinese Medical University in 1956. He is involved in a series of nationally funded research projects and is in charge of some of them. He became an academician of the Chinese Academy of Sciences in 1999. Throughout his research career, extending over twenty years, Prof. Li has concentrated on central neural mechanisms underlying visual processing. This work has focused on the contributions of the classical and non-classical receptive fields (RF) to response selectivity and underlying mechanisms. A major contribution to research in this field has been the demonstration of an extensive, disinhibitory region (DIR) outside the inhibitory surround of RFs of retinal ganglion cells and lateral geniculate neurons, whose size is tens of times as large as the RF. He demonstrated that DIR plays important roles in the transmission of area contrast and luminance gradients of visual images, and proposed a "triple concentric model" to describe the functions of the RFs of retinal ganglion and the lateral geniculate neurons. Furthermore, he has demonstrated and investigated an extensive integration field (IF) beyond the classical RF of cortical neurons, and has shown that different structures of the IF are adapted to the analysis of diverse visual texture patterns. In recognition of his work, Prof Li was awarded the Natural Science Prize (second class) from the CAS in 1991, the Chinese National Natural Science Prize (second class) in 1997, and the HLHL Prize for Medical Science and Materia Medica in 2000. Additional information is available in website for Laboratory of Vision and Cognition.

Research Interests
	Recent neurophysiological studies have indicated that visual stimuli presented in regions outside the classical receptive field (CRF) of visual cortical cells, although ineffective alone, can modulate cells' responses to stimuli within the CRF. These effects can be either facilitatory or inhibitory and are differentially selective to various attributes of the visual stimuli (Li and Li, Vision Research, 1994). We refer to this broad field outside the CRF as the "integration field" (IF). End- and side-regions of the IF may be identical or different with reference to facilitation and inhibition; the differences in the structure of IFs might be adapted to the analysis of different visual texture patterns (Li, News in Physiological Sciences, 1996). A recent study (Yao and Li, Neuron, 2002) has shown that, in the striate cortex of the cat, neurons with facilitatory or inhibitory IF are organised in clusters, with facilitatory and inhibitory clusters being randomly distributed in all cortical layers, independent of orientation and ocular dominance columns. In addition, the velocity and direction of a moving stimuli presented within the IF of cortical neurons has been demonstrated to modify the velocity preferences of cells to stimuli restricted to the CRF. Such "centre-surround" interactions may be the neural substrate of perceptual enhancement of speed contrast between adjacent fields (Li, Lei and Yao, PNAS, 1999). Moreover, this also suggests that the structure and tuning properties of the CRF and the IF of cortical neurons may not be static; i.e. they adapt to the contextual spatial (shape) and temporal (speed) characteristics of visual stimuli. In the course of our investigations, we developed a new method that allows stable, in vivo whole-cell recording in the visual cortex by treating the dura with the enzyme collagenase, so that it can be penetrated by an electrode without damage to the electrode tip (Zhu, Wang and Li, Cerebral Cortex, 2002). Using intracellular recordings, it was shown that, for cells with a facilitatory IF, surround stimuli produce depolarization of the membrane potential, whereas for cells with inhibitory IF, surround stimuli cause hyperpolarization. Morphological studies based on intracellular staining have revealed that cells showing facilitatory and inhibitory integration, respectively, differ substantially in terms of the shape and density of their dendrite spines and the extent of axon collaterals. Our multidisciplinary approach to the understanding of the functional roles of IFs in visual information processing and the cellular and synaptic mechanisms underlying facilitatory and inhibitory integration makes use of single- and multi-unit recordings, optical imaging, and the newly developed technique of in vivo intracellular recording and intracellular staining. These investigations are carried out using either anaesthetised animals or awake animals trained in various behavioural tasks.

	Ongoing Projects
	By performing reverse correlation analysis, we are studying transfer characteristics of cortical neurons in V1 and V2 of the awake monkey, and comparing the transfer function between neurons showing facilitatory integration and neurons showing inhibitory integration. Using optical imaging combined with single-unit recording, we are studying the roles of inhibitory integration neurons in figure-ground segregation and in the generation of subjective contours. Using in vivo intracellular recording, intracellular staining, and immunohistological techniques, we are exploring the cellular and synaptic mechanisms underlying the facilitatory and inhibitory integration effects, with a focus on the distribution of the excitatory and inhibitory transmitter receptors on the dendrites of the labeled cells (Fig.1) . By training the cells with specific patterns of visual stimuli that induce long-term plasticity in the CRF and IF organization, we are interesting in understanding the plasticity of horizontal connections underlying these receptive field properties. We are devising new analysis methods to map the micro-structure of the excitatory and inhibitory IFs of the striate cortical neurons. Based on the excitatory and inhibitory maps, we are characterizing the spatiotemporal organization of CRFs and IFs of the facilitatory and inhibitory integration neurons. We are devising new protocols to manipulate the spatiotemporal structures of CRF and IF by varying apparent motion, temporal frequency, or figure/ground coherence between the two fields. The spatiotemporal dynamics are investigated in conjunction with self-adapting capacities of the visual neurons. Using single and multi-electrode recordings and natural scene stimulation, we are simultaneously monitoring the responses of neuronal assemblies in the same or different cortical areas of the awake monkey (Fig.2). Combined with various linear and nonlinear analysis methods, these experiments will help us understand what visual features are encoded in the neuronal spiking activity at each stage of cortical processing, and how the neural code is transformed between cortical areas.

	Publications
	Liu, G., Zhang, Y., Pettigrew, J., Xu, W., and Li, C. (2003) Spreading and synchronization of intrinsic signals in visual cortex of macaque monkey evoked by a localized visual stimulus. Brain Res., 985: 13-20 Yao, H., and Li, C. (2002) Clustered organization of neurons with similar extra-receptive field property in the primary visual cortex. Neuron, 35: 547-553 Zhu, Z., Wang, Y., Xu, Z., and Li, C. (2002) A simple and effective method for obtaining stable in vivo whole-cell recordings from visual cortical neurons. Cerebral Cortex, 12: 585-589 Li, C., Lei, J., and Yao, H. (1999) Shift in speed selectivity of visual cortex neurons: A neural basis of perceived motion contrast. Proc. Natl. Acad. Sci. USA, 96: 4052-4056 Guo, K., and Li, C. (1997) Eye-position dependent activation of VI neurons of Macaque monkey. NeuroReport, 8: 1405-1409 Li, C. (1996) Unresponsive field beyond the classical receptive field: Organization and functional properties. News In Physiological Sciences, 11: 181-186 Li. C., and Guo, K. (1995) Measurements of geometric illusion, illusory contours and stereo-depth at luminance contrast and at colour contrast. Vision Res., 35: 1713-1720 Li, C., and Li, W. (1994) Extensive integration field beyond the classical receptive field of cat's striate cortical neurons-classification and tuning properties. Vision Res., 34: 2337-2355 Yin, Z., Li, C., Pei, X., Vaegan., and Fung, X. (1994) Development of pattern ERG and pattern VEP spatial resolusion in kittens with unilateral esotropia. Invest. Ophthal. and Visual Science, 35: 626-634 Li, C., Zhou, Y., Pei, X., Qiu, F., Tang, C., and Xu, X. (1992) Extensive disinhibitory region beyond the classical receptive field of cat retinal ganglion cells. Vision Res., 32: 219-228 Li, C., Pei, X., Zhow, Y., and Mitzlaff, H. (1991) Role of the extensive area outside the X-cell receptive field in brightness information transmission. Vision Res., 31: 1529-1540