Because behavior trees describe complex behavior, they can be used for describing a range of systems not limited to those that are computer-based.<ref name = "contracts02" /> In a biological context, BTbehavior trees can be used to piece together a procedural interpretation of biological functions described in research papers, treating the papers as the requirements documents as described above. This can help to construct a more concrete description of the process than is possible from reading only and can also be used as the basis for comparing competing theories in alternative papers. In ongoing research, the behavior tree notation is being used to develop models of the brain function in rats under [[fear conditioning]].
=== Game AI modeling ===
{{main|Behavior tree (artificial intelligence, robotics and control)}}
While BTbehavior hastrees have become popular for modeling the [[artificial intelligence]] in computer games such as [[Halo (franchise)|Halo]]<ref name = "HaloBT">Damian Isla [https://www.gamedeveloper.com/programming/gdc-2005-proceeding-handling-complexity-in-the-i-halo-2-i-ai Handling Complexity in the Halo 2 AI.]</ref> and [[Spore (2008 video game)|Spore]],<ref name = "sporeBT">Chris Hecker [http://chrishecker.com/My_Liner_Notes_for_Spore/Spore_Behavior_Tree_Docs My Liner Notes for Spore]</ref> these types of trees are very different from the ones described on this page and are closer to a combination of hierarchical [[finite-state machine]]s or [[decision trees]]. Soccer-player modeling has also been a successful application of BTbehavior trees.<ref name = "SoccerBT">Xiao-Wen Terry Liu and Jacky Baltes [http://www.cs.umanitoba.ca/~jacky/Publications/pdf/liu04:_intuit_flexib_archit_intel_mobil_robot.pdf An Intuitive and Flexible Architecture for Intelligent Mobile Robots] 2nd International Conference on Autonomous Robots and Agents, December 13–15, 2004 Palmerston North, New Zealand</ref><ref name = "HoshinoBT">Yukiko Hoshino, Tsuyoshi Takagi, Ugo Di Profio, and Masahiro Fujita [http://web.mit.edu/zoz/Public/ICRA04-Hoshino.pdf Behavior description and control using behavior module for personal robot]</ref>
