In our bodies, if our knee is lightly tapped, our leg moves automatically (with no intention on our part) and independently of the experience of the tap that we sense. The information that originates in our knee, with the tap, splits up and moves through two separate pathways: one path goes to our brain through the spinal cord, where it is processed to produce the corresponding experience; the other path involves a different circuit, going through the spinal cord to the muscles that operate the leg, without ever reaching the brain. In the second path, the information takes a much shorter direct route to enable our body to react quickly to the stimulus (‘reflex arc’). There is a good reason why this dual mechanism exists. There are cases where some part of the body will be endangered by a slow reaction to an external threat. If we had to think about moving because of pain, rather than responding automatically, we might not act quickly enough to avoid harm.
What is relevant here is that the information transmitted through this ‘reflex arc’ is never experienced because it is never processed by a central nervous system. The non-centralized nervous systems of some animals operate just as reflex arcs do. Information is transmitted from the cells receiving certain stimuli to other cells which must be activated, without any involvement of subjective experience. In these cases, there is a merely mechanical transmission of information. Such reactions are not an indication of sentience.