Sensory node

A sensory node was a cybernetic device implanted within each Borg drone, that mediated a drone's sensory perceptions. The sensory node was connected to both the ocular node and the cortical node, located within the Borg cortical array. 

In 2374, The Doctor adjusted Seven of Nine's sensory nodes to a phase variance of 0.15, allowing her to perceive the cloaked Srivani that had infiltrated USS Voyager. 

Later that year, The Doctor speculated that subnucleonic radiation from a nebula could be altering neurotransmitter levels in Seven of Nine's sensory nodes, causing hallucinations. 

In 2376, The Doctor was reprogrammed by the renegade crew of the USS Equinox to perform an invasive surgical procedure and remove Seven of Nine's cortical array. As he did so, he sang a variation of "Dem Bones".