It is common to hear people talk about the five senses of sight, smell, touch, hearing and taste. Of course there are plenty more senses and one of the more important is the sense of gravity and acceleration (closely related to the very literal sense of balance). This is produced by the vestibular system in the ear. The main component of this system is the otolith, a small bone which moves and brushes tiny hairs which tracks the acceleration based on the pattern of hairs triggered. The human system has advanced beyond this with more complex features integrated into the bony labyrinth but for the larval stage zebrafish used in this study the otolith is the only relevant feature.
The neural process and communication between the vestibular system and the brain which ultimately results in the sense we have is not fully understood and there is a good reason for this. If we wish to study other neurological processes in rodents or fish we can hold them still and neuroscientists can work so that their precision is perfect. Of course the problem comes from the fact the entire neurological action we wish to study is based on movement and the creature needs to be moved to trigger the vestibular system.
The method of study which has been suggested relies on optical trapping. Although using a highly focused laser to move nanoscale transparent beads is quite simple, it would be considerably harder to apply a sufficient force on a larger object within a living organism, but not impossible. As already mentioned, larval zebrafish are a good simplified neurological complex to work on and by using an infrared laser, and taking a lot of care, the fish’s otoliths were successfully forced. The larvae’s reactions of eye and tail movement to the falsified acceleration was monitored and hopefully in the future more complex neural circuitry can also be studied now it is possible to trigger the fish’s reaction without actually moving the fish.