Our goal is to understand the neural mechanisms that support decision making, interval timing and event memory. We investigate how neural processes underlying these functions are implemented in the rodent brain by examining discharge characteristics of neuronal ensembles in behaving animals, by examining effects of manipulating specific neural systems on animal's behavior and neural activity, and by computational modeling. We take these approaches under the premise that understanding neural circuit dynamics is a key to understanding the neural basis of brain functions as well as malfunctions.

Decision making 

    Decision making in a dynamic environment consists of multiple underlying processes such as representing values of potential choices, making choices based on these values, and updating the values based on the outcome of a choice. We investigate how these processes are implemented in the fronto-basal ganglia loop. We also investigate how multiple decision making systems (trial-and-error-based vs. deliberate control system) interact to yield a final action selection. To this end, we examine neuronal ensemble activity and manipulate neural activity in rodents, because they allow large-size neuronal ensemble recordings, use of genetically-modified animals, and relatively easy application of optogenetic techniques on top of that the nervous system is much simpler than that of the primate. We also conduct theoretical studies of reinforcement learning and neural network modeling.

Event memory

    One of the central issues in cognitive neuroscience is to understand the neural basis of event memory. Although it is well known that the hippocampus plays a crucial role in encoding event memory, its underlying neural mechanisms remain unclear despite a long history of intensive investigations. We investigate how different types of information are integrated in the hippocampus during the formation of event memory (‘what happened’ ‘where’ and ‘when’) by conducting behavioral and neurophysiological experiments in rats. We also use genetically-engineered mice with specific disruptions in distinct sub-regions of the hippocampus (dentate gyrus, CA3 and CA1) to investigate functional roles played by each hippocampal sub-region in encoding event memory.

Interval timing

    Time and space are fundamental dimensions for all living organisms. The ability to anticipate the timing of predictable events is critical for survival in many animal species including humans. In particular, time interval estimation in the range of a few seconds (interval timing) is involved in numerous behavioral processes. However, it is unknown how interval timing-related functions are implemented in the brain in large part because of the paucity of physiological studies. In order to investigate how the brain keeps track of the elapse of time, we record and analyze neuronal activity in different brain structures as rodents perform various time interval discrimination tasks.