We visualized neuronal activity in the optic tectum of a zebrafish larva during prey perception. A moving paramecium evokes strong responses in the neurons. In contrast, motionless prey seems invisible to the predator.
In this experiments, the zebrafish larva is embedded in agarose but the eyes can move. In the beginning of this movie, before the paramecium makes its first move, the right eye of the zebrafish larva moves in the nasal (i.e., inward) direction, and a calcium signal is seen in the anterior part of the left tectum. This may be explained by a relative motion generated by the eye movement.
Muto et al., Real-Time Visualization of Neuronal Activity during Perception. Current BIology Volume 23, Issue 4, p307–311, 18 February 2013 (Open access at ScienceDirect.com)