I am a postdoctoral fellow in the Physiology Department at the University of Wisconsin Madison working with Dr. Michele A. Basso. I have been a graduate student in the same lab and finished my PhD degree on Nov. 2007. My work focuses on the neuronal mechanisms of saccade target selection, spatial attention and decision-making. I am interested in these questions: how the visual system chooses a visual stimulus from the environment, how the visual information transfers into a motor command and how spatial attention is involved in this process. The saccadic eye movement system in non-human primates is my model to explore the above questions. Single neuron recording method is used in my research.
In everyday life, we face numerous visual stimuli. The eye movement system has to choose a target of interest out of multiple potential stimuli before making a rapid eye movement to it. During this process, an attention-like mechanism may be required to modulate competition between multiple stimuli. My research aims to understand how the brain performs this process of selection and makes the decision for saccadic eye movements. And the alterations in the neuronal mechanisms underlying the processes of selection and decision making likely contribute to symptoms of disease such as attention deficit disorder and also perhaps movement disorders such as Parkinson’s disease.
Recent studies
suggest that selecting a target for saccadic eye movement (or ‘saccade target
selection’) and selecting a target for perception (or ‘shifting attention’) are
not totally independent processes. These two processes may share a similar
physiological mechanism and modulate neuronal activities in a similar way. This
idea has been suggested by the premotor theory of attention and has been
supported by electrophysiological work. In my previous project, I tested this hypothesis
and studied two questions. First, does selecting a target for saccades
modulate neuronal responses in a way similar to spatial attention? In other
words, are there similarities between the neuronal effects of saccade target
selection and spatial attention? Second, how is target selection represented
within the saccadic system? To
answer the questions, I performed a series of experiments. I found that target
selection can enhance the neuronal sensitivity to contrast in the superior
colliculus like spatial attention. Two-stimulus competition in a single
response field can be altered by target selection. Moreover, target selection
modifies tuning properties of SC neurons and the noise-signal ratio included in
the tuning curves. These results suggest that we may be able to find a common
mechanism to explain both the brain processes for sensory modulation and motor
modulation.
Under
the same background, I currently focus more on how the output of the basal
ganglia changes the neuronal activity in the superior colliculus and how this
influences a monkey’s choice of a saccade target. This direction is more
related to decision making and will help us to understand the mechanisms of
basal ganglia diseases.
Publications
Li, X. and Basso, M.A. (2008). Preparing to move increases the sensitivity of superior colliculus neurons. Journal of Neuroscience 28(17):4561-4577 [PDF]
Li, X., Kim, B.,
Basso, M.A. (2006) Transient Pauses in Delay-Period Activity of
Li, X.,
Basso, M.A. (2005) Competitive Stimulus Interactions within Single Response
Fields of
Smith, J.J.,
Hadzic, V., Li, X., Liu, P., Day,
T.J., Utter, A.A., Kim, B.H., Washington, I.M. and Basso, M.A. (2006). Objective Measures of Well-Being
in Laboratory Rhesus Monkeys (Macaca mulatta). The Journal of Medical
Primatology, 36(6):388-396. [HTML]
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Last update 4/30/2008