STS-90 insignia
The STS-90 crew patch reflects the dedication of the mission to neuroscience in celebration of the decade of the brain. Earth is revealed through a neuron-shaped window, which symbolizes new perspectives in the understanding of nervous system development, structure and function, both here on Earth and in the microgravity environment of space.
The Space Shuttle Columbia is depicted with its open payload bay doors revealing the Spacelab within. An integral component of the mission, the laboratory/science module provided by the European Space Agency (ESA), signifies the strong international involvement in the mission. The seven crew members and two alternate payload specialists, Chiaki Naito-Mukai and Alexander W. Dunlap, are represented by the nine major stars of the constellation Cetus (the whale) in recognition of the International Year of the Ocean.
The distant stars illustrate the far reaching implications of the mission science to the many sponsoring agencies, helping prepare for long-duration space flight aboard the International Space Station (ISS).
The moon and Mars are depicted to reflect the crew's recognition that those two celestial bodies will be the next great challenges in human exploration of space and represent the key role that life science research will play in supporting such missions.
http://www.spacefacts.de/mission/english/sts-90.htm (direct link)
https://mix.msfc.nasa.gov/abstracts.php?p=3611 (direct link)
NASA Facts (Source PDF)