Bogeng Song

Coming soon...

Previous studies investigating working memory performance in patients with mild cognitive impairment (MCI) have mainly focused on the neural mechanisms of alterations in activation. To date, very few studies have investigated background network alterations in the working memory state. Therefore, the present study investigated the static and temporal dynamic changes in the background network in MCI patients during a working memory task. A hybrid delayed-match-to-sample task was used to examine working memory performance in MCI patients. Functional magnetic resonance imaging (fMRI) data were collected and the marker of amplitude of low-frequency fluctuations (ALFF) was used to investigate alterations in the background network. The present study demonstrated static and dynamic alterations of ALFF in MCI patients during working memory tasks, relative to the resting state. Traditional static analysis revealed that ALFF decreased in the right ventrolateral prefrontal cortex (VLPFC), right dorsolateral PFC (DLPFC), and left supplementary motor area for normal controls (NCs) in the working memory state. However, the same regions showed increased ALFF in MCI patients. Furthermore, relative to NCs, MCI patients demonstrated altered performance-related functional connectivity (FC) patterns, with the right VLPFC and right DLPFC as ROIs. In terms of temporal dynamic analysis, the present study found that in the working memory state dynamic ALFF of bilateral thalamus regions was increased in NCs but decreased in MCI patients. Additionally, MCI patients demonstrated altered performance-related coefficient of variation patterns; the regions in MCI patients were larger and more widely distributed in the parietal and temporal lobes, relative to NCs. This is the first study to examine static and temporal dynamic alterations of ALFF in the background network of MCI patients in working memory states. The results extend previous studies by providing a new perspective on the neural mechanisms of working memory deficits in MCI patients.

In this project, I analyze fMRI data and write the paper results part.

This study examines how microsaccades and pupil size relate to motion perception and task difficulty.

In this project, I participated in the whole process except the data collection part.

Microsaccades, or small recurring eye movements, typically occur ~1-2 times per second. Although generally considered involuntary, the characteristics of these eye movements are task-dependent and affect performance. For example, microsaccades are flexibly allocated to precisely relocate gaze during high acuity tasks in the fovea and suppressed prior to the onset of a stimulus outside of the fovea during a motion discrimination task. Here we investigated whether and how microsaccade rates are adaptively modulated by trial difficulty when observers discriminate motion directions in the perifovea. METHODS. We used a 2AFC task to measure the discriminability of a Gabor drifting for 500ms in 1 of 8 reference directions (4 cardinal, 4 oblique) at 8 isoeccentric locations (7​​°). Observers reported a Gabor's drift direction, which was slightly clockwise or counterclockwise with respect to a reference direction. The difficulty of each trial was varied in two ways: (a) cardinal vs. oblique directions; and (b) tilt offset between reference and Gabor direction. The tilt angles were randomized using a method of constant stimuli: the Gabor's drift direction was offset from the reference direction by ± 0.5, 1, 2, 4 or 8°. RESULTS. First, we found that microsaccade rates were suppressed prior to stimulus onset. Second, microsaccade rates were modulated by trial difficulty in two ways: they decreased (1) as the angular offset between the target and standard decreased; and (2) when stimuli drifted in oblique rather than cardinal directions. CONCLUSION. Microsaccades were suppressed prior to stimulus presentation, and during the stimulus period for difficult discrimination tasks in the perifovea. This flexibility is consistent with the proposals that greater fixational stability can (1) mitigate potential blur during microsaccades, and (2) prolong the duration of evidence accumulation. As a result, microsaccades may serve as a marker of cognitive effort for visual tasks in the perifovea.

We used psychophysical and eye-tracking methods to measure behavioral differences for different motion directions (e.g., radial versus tangential). To model the behavioral data, we fit psychophysical curves, and compare performance for different motion directions.