New Kasai Paper on Synaptic Basis of Learning

Haruo Kasai is a Japanese scientist who has made important contributions to our understanding of the synaptic machinery of learning and memory.

From: http://www.bio.brandeis.edu/lismanlab/index.html

For example in an already classic paper (Matsuzaki, M., Honkura, N., Ellis-Davies, G. & Kasai, H. Structural basis of long-term potentiation in single dendritic spines. Nature 429, 761–766 (2004).,  he showed that induction of LTP at single synapses (by pairing punctate glutamate application with postsynaptic depolarization) triggers changes in strength and spine head volume, which is confined to that synapse and does not spread to neighboring synapses:

Top graph shows changes in strength and volume at a hippocampal synapse where ltp is induced, with no change at neighbors. Ignore bottom graph.

He concluded: "Our results thus indicate that spines individually follow Hebb's postulate for learning."

In the recent study (Nature Volume 525, Issue 7569, 17 September 2015, Pages 333-338), he looked at synapses in the motor neocortex during and after learning of a motor task (the ability to cling to a rotating rod). Using special molecular markers he was able to identify a set of synapses on the dendrites of a pyramidal cell that became strengthened following task learning. Then, crucially, he was able to shrink those synapses back to their original size, and show that this selectively erased learning of this task, but not others. This strongly suggests that strengthening of these synapses (presumably as a result of Hebbian ltp occurring during learning) underlies the relevant learning.

Of course we do not know which circuits these synapses belong to, or exactly what role they play in learning the task.