Our brains are the most sophisticated computing machines on the planet. They are amazingly plastic, yet macroscopically their structures are nearly identical across individuals within a species. Information, both internal and external, is processed by such stereotypical brain circuits. It flows from one sub-region in the brain to specific targets. The same way that knowing a circuit diagram for a microchip informs us about how it works, understanding the sequence of information flow in the brain is an essential step towards understanding brain function in both normal and disease conditions.
We used this rationale to try to understand the thalamus, a key structure in sensory processing, motor control, as well as nearly all other brain functions. Here we present a collection of high resolution and sensitivity images, and associated data analyses aiming to understand how the thalamus is connected to its targets in the cortex, a part of the brain necessary for integrating sensori-motor information and higher executive functions. Modern viral tracing (recombinant adeno-associated viruses, serotype 2/1) techniques and high-speed imaging (Hamamatsu, NanoZoomer Digital Pathology scope, serial # 12090) were used to label thalamic projections and image their cortical targets from 75 brains with 254 injections. A comprehensive thalamocortical projection map, with a quantitative description of the thalamic origin of 19 cortical targets is presented. The data were generated by Barbara Hunnicutt, Brian Long, Deniz Kusefoglu, Katrina Gertz, Haining Zhong, Tianyi Mao and the Mao Lab.