Taro Toyoizumi

Thursday 6th June 2019

Time:4.00pm

Ground Floor Seminar Room

25 Howland Street, London, W1T 4JG

Exploring the learning principle in the brain

Animals adapt to the environment for survival. Synaptic plasticity is considered a major mechanism underlying this process. However, the best-known form of synaptic plasticity, i.e., Hebbian plasticity that depends on pre- and post-synaptic activity, can surge coincident activity in model neurons beyond a physiological range. Our lab has explored how neural circuits learn about the environment by synaptic plasticity. The instability of Hebbian plasticity could be mitigated by a global factor that modulates its outcome. For example, TNF-alpha that mediates homeostatic synaptic scaling is released by glia, reflecting the activity level of surrounding neurons. I show that a specific interaction of Hebbian plasticity with this global factor accounts for the time course of adaptation to the altered environment (Toyoizumi et al. 2015). At a more theoretical level, I ask what is the optimal synaptic plasticity rule for achieving an efficient representation of the environment. A solution is the error-gated Hebbian rule, whose update is proportional to the product of Hebbian change and a specific global factor. I show that this rule, suitable also in neuromorphic devices, robustly extracts hidden independent sources in the environment (Isomura and Toyoizumi 2016, 2018, 2019). Finally, I introduce that synapses change by intrinsic spine dynamics, even in the absence of synaptic plasticity. I show that physiological spine-volume distribution and stable cell assemblies are both achieved when intrinsic spine dynamics are augmented in a model (Humble et al. 2019). 

Bio:
Taro Toyoizumi is a Team Leader at RIKEN Center for Brain Science. He received his B.S. in physics from Tokyo Institute of Technology in 2001, and his M.S. and Ph.D. in computational neuroscience from the University of Tokyo in 2003 and 2006, respectively. He studied at the Center for Theoretical Neuroscience at Columbia University as a JSPS and Patterson Trust Postdoctoral Fellow. He then came to RIKEN Brain Science Institute as a Special Postdoctoral Researcher in 2010, was promoted to a Lab Head in 2011, and holds the current position since 2018. He has been studying the theory of neural plasticity by asking how neural circuits self-organize in the environment. Toyoizumi has received the International Neural Network Society, Young Investigator Award in 2008 and the Commendation for Science and Technology by the MEXT Japan, Young Scientists’ Prize in 2016.