1936, coined from lobe (in the brain sense) + medical suffix -tomy "a cutting." Figurative use is attested from 1953. Lobectomy (attested from 1911) was in use earlier in reference to lobes of other organs (lungs, liver).
Now I guess I'll have to tell 'em
That I got no cerebellum
[Ramones, "Teenage Lobotomy," 1977]