In an extreme demonstration of this principle, flies expressing P2X2 in the TTMn-PSI-DLMns group of thoracic neurons were decapitated. The headless bodies stood characteristically motionless (Yellman et al., 1997) in the open arena until illuminated and then took flight on circuitous, collision-prone trajectories.
A caption notes:
Photostimulation experiments were performed in a cylindrical arena (diameter 8 mm, height 2 mm) that could be homogeneously illuminated with 355 nm laser light. The arena was covered by a glass ceiling in (A)-(C) but left open in (D), as decapitated flies do not spontaneously walk, jump, or fly, making their confinement unnecessary.