keep the pulses centered?

[pdh0224]

Dear teacher,

The apparatus, called a BrainPort, worked beautifully. By "buzzing" her tongue once a day for 20 minutes, keeping the pulses centered, she regained normal vestibular function and was able to balance.

Q : Does "centered" in the sentence mean a place of the pulses or "sensible"?

[Alan]

Presumably 'at the centre of the scale' (on the computer readout).