Research Topics

I. Memory function in aging, neurological, and psychiatric disorders

Mismatch negativity (MMN), or its magnetic equivalent (MMNm), has been a useful electrophysiological signal to determine the integrity of sensory memory, mainly mediated by the superior temporal generators, and involuntary attention switching, subserved by the inferior frontal cortex. From the biological perspective, MMN plays an important role since it allows brains to detect novel events within a series of background stimuli. In addition to superior temporal and inferior frontal regions, we also discover other neural correlates related to MMN responses, such as inferior parital lobule (IPL), orbitofrontal cortex (OFC) and inferior frontal gyrus (IFG). The integrity of MMN/MMNm has been related to the performance of higher order of cognitive function, such as working memory, attention, and language. In addition to the account of sensory memory, the predictive coding hypothesis has also been proposed to elucidate the production of MMN/MMNm. Over the past years, we have examined the MMN/MMNm function in many sub-clinical and clinical populations, such as healthy older adults, individuals with subjective memory decline, mild cognitive impairment, and panic disorders.

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II. Sensory gating in aging, neurological, and psychiatric disorders

Aging not only affects physical conditions, but also has a great impact on brain function, such as attention, episodic memory, language and executive function. Most importantly, cortical inhibition or sensory gating to repetitive background stimulation also plays an essential role in the higher-order operations. Biologically, brains were born to detect significant/novel signals and to ignore repetitive/redundant stimulation. Excessive responses to repetitive stimuli indicate a failure in cortical inhibition. It has been evident that the disrupted inhibition has a detrimental effect on executive function in patients with AD. The paired-pulse protocol is a useful technique to examine the integrity of cortical inhibition. By applying electrophysiological recordings, auditory P50 (P50m in MEG recordings) or/and N100 (N100m in MEG recordings) have been extensively used to determine this neural function. We also found a functional correlation between P50m and MMNm, suggesting those with poor inhibition function exhibit deteriorated deviance detection. This phenomenon implies that early-stage cortical inhibition function might have influence on the later-stage novelty discrimination. In addition to the auditory cortex, somatosensory cortex (SI and SII) and visual cortex might also demonstrate aging-related changes in terms of repetition inhibition. it has been shown that SI cortical inhibition deficits correlate with the clinical degradation of tactile perception. Most importantly, we found that SII areas are more sensitive to aging than SI in terms of repetition suppression.

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III. Inhibitory function in aging and sub-clinical populations

Inhibiting responses to irrelevant stimuli or inappropriate behaviors is an essential cognitive ability for humans in everyday life. For example, to precisely execute certain tasks in a distractible environment, task-relevant information is not only enhanced but task-irrelevant information is selectively inhibited at the same time. Inhibition function can be categorized as automatic (bottom-up) and attentive (top-down) aspects. The automatic inhibition function in the sensory cortex could be evaluated with paired-stimulation paradigms, and the attentive inhibition function could be studied with Go-Nogo or stop-signal paradigms. We are currently applying MEG to investigate the neural representations of cognitive control in the healthy adults and also to study how aging process influences this cognitive component. In addition, we are also interested in the factors that modulate inter-individual variabilities. Thus, we try to ask questions such that "if brain oscillations mediating the behavioral performance of inhibition control", "if the neurotransmitters within a certain brain region modulate the inhibition function" or "if the neural representation of inhibition control is modality-dependent or independent", etc. We have found several interesting findings in the cortical somatosensory and auditory systems, and these data provided the empirical evidence for the modulation of inhibition control through multiple levels, i.e., through a neurotransmitter-neurophysiological-behavioral axis.

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IV. Cognitive neuroscience and rehabilitation sciences: Neuroimaging approach

I welcome talented students to propose novel issues in terms of brain sciences, neuro-cognitive and behavioral sciences. Although my lab is currently targeting on the population of the elderly and aging-related diseases, any topic related to cognitive neuroscience in healthy adults or patients is also welcome. In addition, I am also interested in the training effects on the brain function, either in the healthy participants and those with diseases. Through the empirical evidence provided by neuroimaging studies, we hope to help bridge the gap between basic research and clinical application.

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