Research

We are interested in brain mechanisms involved in high-level mental functions such as executive control, decision-making, and learning and memory (see Publications for individual studies).  These mechanisms are thought to be most developed in humans through the evolutional processes.  It is important that, in most cases,
bioimaging technique must be non-invasive (i.e., surgical operation free) when examining the human brain functions.

We are mainly using functional MRI (fMRI) for a non-invasive neuroimaging technique.  fMRI provides relatively high spatial resolution (a few mm), but more importantly, it allows to measure neural-activity-related (BOLD) signals from the entire brain in a consistent manner, even from deeper and smaller brain structures.  Thus fMRI is still one of the most powerful imaging tools to examine brain-wide functional mechanisms.

However, the BOLD signal involves a greater time constant (i.e., low temporal resolution; several secs), which is much slower than the transmission speed of action potential in neurons.  This is because the BOLD signal reflects hemodynamic changes
in blood capillaries around activated neurons.  This physiological limitation sometimes becomes critical when we examine a series of mental and cognitive processes occurring in a brief period of time.  In particular, examining dynamic aspect of brain functions including inter-regional interactions and directional signaling involved in such processes is one of the important challenges in fMRI studies.

In our prior studies, we examined temporal dynamics of fMRI signal during executive control (Jimura et al. 2010; Jimura & Braver 2010) and choice behavior (Jimura et al. 2013).   These analyses were possible because the target time constants were greater than 10 secs.   We are now aiming to develop analysis framework to shorten the shortest time constant in fMRI analysis, hoping to examine causal mechanisms implemented in global brain networks involved in sophisticated mental functions.

Our current projects include:
Executive control.
Value-based choice behavior.
Interaction of executive control and decision-making.

Time domain analysis of functional MRI signal.