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Abstract:
Through the later half of the 20th century, neuroscience
developed at all of the molecular, cellular, system, cognitive and
computational levels and yielded many discoveries which are
landmarks in the history of modern science. One of the major
research themes covering many of these levels is the synaptic
transmission and its plasticity. Synaptic plasticity has been
conceived as the neural basis of memory and learning, and three
concrete forms have been described: sensitization, long-term
potentiation (LTP) and depression (LTD). The complex signal
transduction mechanisms underlying synaptic plasticity have been
revealed and the roles played by the synaptic plasticity in brain's
memory and learning functions have been investigated extensively.
However, some important questions remain unanswered: (a) How is
synaptic plasticity retained over the long term to account for
permanent memory? (b) How can synaptic plasticity compose memory
traces which have complex spatiotemporal patterns in our brain? (c)
How can a certain memory be read so quickly out of innumerable such
memory traces? Looking into the 21st century, neuroscience must go
further beyond synaptic plasticity, and we must investigate the
mechanisms underlying other brain functions such as emotion,
volition and consciousness. A crucial question to be addressed in
future neuroscience is what kind of elementary processes could
exist in the brain in addition to synaptic transmission and its
plasticity. In other words, it is a question of whether we can
explain our entire brain functions in terms of learning neuronal
networks and systems, or whether other basic mechanisms remain yet
to be uncovered.
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