Research Topics

The aim of our research is to understand how our perception and behavior are regulated by signals in individual neurons, local networks, and the brain systems. To this end, we conduct single neuron recordings, local pharmacological applications, and electrical stimulation in behaving monkeys, psychophysical assessment of humans, as wells as computational analyses of models that are based on biological observations. In particular, we are interested in voluntary control of eye movements and related brain functions. Eye movements exhibit properties such as sensorimotor transformation, movement decision, learning, and memory that can be generalized to other systems. On the other hand, their reproducibility allows us to perform extensive quantitative analyses and modeling. By taking advantage of this system, we explore the functions of higher brain areas such as the cerebral cortex, basal ganglia, cerebellum and thalamus. Our ongoing projects include neural mechanisms for time perception, rule-based response selection, spatial attention and working memory.




Neuronal mechanisms for time perception

Temporal processing over a short period of time is essential for our life. Studies in these decades indicate the list of brain areas implicated in temporal processing, including the cerebellum, basal ganglia, and association areas in the frontoparietal cortices. However, how neural activity in each area represent time remains elusive. We are exploring the temporal information in individual neurons in the relevant areas as monkeys report elapsed time by making self-initiated saccades, or as they detect a single omission of regular repetitive stimuli (missing oddball paradigm). We also conduct behavioral analysis in patients with cerebellar degeneration.


Sakigake Project

Press Release

 

Intracerebral mechanisms for time perception



Rule-based response selection

It is important to select most appropriate action from many alternatives in a given situation. Observations in psychological and neurological disorders such as schizophrenia, ADHD, and Parkinson's disease suggest that information processing via the cortico-basal ganglia loop plays an essential role. To examine neuronal mechanism, we train monkeys to make eye movements either toward or away from visual stimuli depending on imposed task-rules. So far, we have found that neurons in the thalamus, the basal ganglia, and the cerebellum exhibit greater firing modulation as monkeys made saccades away from the stimulus (anti-saccades). Further pharmacological manipulation of signals in the relevant pathways will elucidate the mechanisms of how our brain selects actions.


 

Rule-based behavior selection



Top-down control of attention and working memory

All sensory inputs are not equally processed, but the brain gives a priority to particular inputs for further analysis. This is the neural mechanism of attention. The direction of one's line of sight and attention often match in daily situations, and in fact, the lateral prefrontal cortex (areas 8 and 46) participate in both the control of spatial attention and eye movements. In the previous set of experiments, we trained monkeys to attentively track moving objects without eye movements. We found that the majority of neurons in the prefrontal cortex elevated activity as attended object fell into the receptive field whereas the remaining responded to objects that needed to be ignored.


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Top-down control of spatial attention

Top-down control of spatial attention