2. Use of Optogenetics Techniques to Discover Pathway-specific
Feedforward Circuits Between Thalamus and Neocortex All brain
functions involve coordinated neural activities in many brain
regions. Therefore, it is important to understand how different
brain regions interact with each other. One particularly
important coupled system in the brain is the neocortex and the
thalamus. The neocortex, the thalamus, and the axonal tracts
that interconnect these structures comprise the vast majority of
the mammalian brain and are crucial for sensation, perception
and consciousness. Thalamocortical (TC) pathways provide the
major extrinsic input to neocortex, and corticothalamic (CT)
pathways are a principal source of synaptic input to thalamus.
These pathways are entwined, making their study challenging by
conventional electrical stimulation methods. We used cell-
specific expression of channelrhodopsin-2 (ChR2), a light-
sensitive cation channel, in either thalamocortical or
corticothalamic projection cells to manipulat