Current researchPlease check out my lab website for latest research projects.
Postdoctoral ResearchI studied neural network modeling of decision making in visual discrimination experiments in Xiao-Jing Wang's lab.
Project 1:Recent electrophysiological studies of behaving monkeys using a visual discrimination reaction-time task suggest that a perceptual choice about the visual motion stimulus is made, and a saccadic eye movement is triggered, when the average firing rate of a group of neurons in the lateral intraparietal area (LIP) reaches a threshold.
These findings have raised critical questions about the decision threshold (or decision bound) that were addressed in the project. First, what is the neural substrate of the decision threshold? Second, how can the threshold be adjusted for optimal performance or reward such as in an accuracy-speed tradeoff
We propose a biophysically-based recurrent network model of noisy spiking neurons consisting of (a) a decision cortical network; (b) a superior colliculus (SC) network endowed with recurrent excitation and feedback inhibition; (c) a basal ganglia network in which the caudate nucleus (CD) receives excitation from the cortex and sends inhibition to the substantia nigra pars reticulata (SNr) which in turn inhibits the SC. Our work shows that the event of threshold crossing in LIP is detected by downstream cells in SC which initiate a saccadic response by an all-or-none burst of spikes. Furthermore, the threshold level to be detected is dynamically tuned by the LIP-CD pathway, which serves as a gating mechanism for decision making. This is interesting especially in light of the fact that the LIP-CD connection is modulated by dopamine which carries reward information. My first paper on this topic is in press now and will apear on Nature Neuroscience soon.
Please also check the News and Views article by Kiani, Hanks and Shadlen on Nature Neuroscience about our paper.
Graduate study: Sleep DynamicsMy graduate study was about sleep dynamics. That's right, a physics student studying sleep. Actually, what I was doing is studying the transitions of brain state during sleep. I joined H. E. Stanley's group in 1999. In the beginning I was learning something like heart beat statistics, multifractal, wavelet...etc, then I switched to "sleep" in the early 2000.
During the nocturnal sleep, the human brain goes through several different states. According to the EEG (brain wave) pattern, scientists categorize human sleep into 6 stages: wake, REM sleep and non-REM stage 1 to 4. The human brain transfers between these stages during the night. The transition process is very complicated, and is neither completely periodic nor completely random.
As what many physicists alway like to do, we made a simplification. We simplify this complicated six states into only two states by considering "sleep" and "wake" only. There are typically 20~50 short wake periods in a normal nocturnal sleep. We studied distributions of duration of these wake and sleep periods, and find surprisingly that, the distribution of the wake duration is completely different from that of the sleep. The wake duration follows a power-law distribution, while the sleep duration follows a exponential distribution.
My last project before graduation was to study sleep dynamics across mammalian species. We have gotten surprising results which was published in PNAS in 2004.
For more detail about my sleep research, please take a look at my publications listed below.
Presentation materials or other useful notes:
(This is just a list of media reports which I am aware of. If you find other articles about our works, please contact me at firstname.lastname@example.org. Thanks.)
Some historyI had my first paper published on Biophysical Journal in 1998. I studied time-resolved fluorescence of a specific type of protein. By calculating the anisotropic decay of its fluorescence, we were able to calculate the rotating rate of the proteins, thus the radius of gyration of the proteins. We performed experiments in different types of solvent in order to learn how this type of protein responses to the change of environment. I did this work during 1995-1996 when I was doing my master degree study in Prof. W.-S. Fann's lab at IAMS in Taiwan.