Shigeyoshi Fujisawa, Ph.D.

Research Overview

Our main research goal is to elucidate the neuronal and network mechanisms underlying reward-related cognitive functions, particularly the contribution of the dopaminergic circuits of the basal ganglia, the prefrontal cortex and the hippocampus. Studying the physiological mechanisms of cognitive functions requires understandings not only the responses of single neurons to external stimuli but also circuit computations at the level of networks of neurons during cognitive processing. To understand the 'syntax' underlying neuronal communications, methods for monitoring and quantifying cooperative neuronal activities during cognition are required. To this end, we have been performing large-scale high-density recordings of local circuits with multi-channel silicon probes, enabling the observation of simultaneous neuronal firing activities in up to 100 neurons, as well as local field potentials in behaving animals. In addition, we are developing a new technique that combines large-scale recording and targeted simultaneous optogenetic stimulations of specific cells, such as dopaminergic neurons, to clarify the role of the different types of neurons in network processing, in freely behaving mice. Taking advantage of these methods, we try to decipher circuit computations within local and between the inter-regional networks during reward-related cognitions such as decision making and working memory.

Keywords

• Neurophysiology

Selected Publications

1. Norimoto H, Makino K, Gao M, Shikano Y, Okamoto K, Ishikawa T, Sasaki T, Hioki H, Fujisawa S, & Ikegaya Y.:
   "Hippocampal ripples down-regulate synapses."
   Science, 359:524-1527. (2018)
   10.1126/science.aao0702
2. Danjo T, Toyoizumi T, & Fujisawa S.:
   "Spatial representations of self and other in the hippocampus."
   Science, 359:213-218. (2018)
   10.1126/science.aao3898
3. Terada S, Sakurai Y, Nakahara H, & Fujisawa S..:
   "Temporal and rate coding for discrete event sequences in the hippocampus."
   Neuron, 94:1248–62 (2017)
   10.1016/j.neuron.2017.05.024
4. Stark E, Eichler R, Roux L, Fujisawa S, Rotstein HG, & Buzsáki G.:
   "Inhibition-induced theta resonance in cortical circuits."
   Neuron, 80:1263-76 (2013)
   10.1016/j.neuron.2013.09.033
5. Patel J, Schomburg EW, Berényi A, Fujisawa S, & Buzsáki G.:
   "Local generation and propagation of ripples along the septotemporal axis of the hippocampus."
   J. Neurosci. 33:17029-41 (2013).
   10.1523/JNEUROSCI.2036-13.2013
6. Patel J, Fujisawa S, Berényi A, Royer S, & Buzsáki G.:
   "Traveling Theta Waves along the Entire Septotemporal Axis of the Hippocampus."
   Neuron, 75:410-417. (2012)
   10.1016/j.neuron.2012.07.015
7. Fujisawa S & Buzsáki G.:
   "A 4-Hz oscillation adaptively synchronizes prefrontal, VTA and hippocampal activities."
   Neuron, 72:153-165. (2011)
   10.1016/j.neuron.2011.08.018
8. Sirota A, Montgomery S, Fujisawa S, Isomura Y, Zugaro M & Buzsáki G.:
   "Entrainment of neocortical neurons and gamma oscillations by hippocampal theta rhythm."
   Neuron, 60:683-697. (2008)
   10.1016/j.neuron.2008.09.014
9. Fujisawa S, Amarasingham A, Harrison MT & Buzsáki G.:
   "Behavior-dependent short-term assembly dynamics in the medial prefrontal cortex."
   Nature Neurosci., 11:823-834. (2008)
   10.1038/nn.2134
10. Fujisawa S, Matsuki N & Ikegaya Y.:
    "Single neurons can induce phase transitions of cortical recurrent networks with multiple internal states."
    Cereb Cortex, 16:639-654. (2006)
    10.1093/cercor/bhj010