I read this story sometime between 1989 and 1991 in a SF&F magazine (Asimov's Science Fiction? The Magazine of Fantasy and Science Fiction? Amazing Stories?) and I've looked for it for years, in archives, online, etc. with no success. Can anyone help, please?
It takes place in the future. A neurosurgeon uses MRI scans to map out a person's neural map. Upon finding cancer or clots, he programs nanobots to enter the body and clean up the disease.
His ex-wife, whom he still loves, comes for treatment. When she leaves, he experiments with showing his photograph to the simulated retina and finds where it lights up in the simulation. Seeing a blocked neuron, he programs the nanobots to destroy her cancer and to re-establish contact to this cluster by reconnecting the block.
After her surgery, she falls back in love with him, but after a while, discovers the manipulation and leaves him. To forget about her, he scans his own neurons, finds her cluster, and programs nanobots to clip the connections, with the unfortunate consequence of also cutting off the neural pathways to breathing, heart regulation, etc.