These are strictly opinions. Notice I did not provide any sources to back up my claim.
Under what circumstances (if any) do you think psychosurgery or electrical stimulation of people’s brains might be warranted?
The only time
electroshock therapy should be used is for the worst cases of depression or mania, and that only gives temporary relief to the patient. Also, due to the large number of side-effects associated with the treatment, including long-term memory lose, it should be administered only under the consent of the individual receiving it.
Should those with a chronic history of violent criminal offenses have the option of being treated with psychosurgery or electrical brain stimulation for a reduced sentence or as an alternative to the death penalty?
Unless there is statistical evidence that suggests electroshock therapy makes a violent offender less violent, this could be a viable option. The proof, however, would have to show biological changes to the brain (or normalized hormone levels) that's associated with behavior, namely the part that handles emotions, including risk and reward. Regardless of the potential for this treatment, it shouldn't reduce the life sentence of a murdered, as there's never complete certainty that a cure has happened.
What potential ethical concerns can you think of regarding sentence reduction?
Many criminals don't feel remorse for the crimes they've committed. Possibly because they biologically lack the ability to be empathetic or have become hardened due to traumatic childhood experiences.
While there's always potential for someone to change, the extent to which that change does occur is hardly enough to allow a prisoner to roam free. In fact, I'd presume that the family member of a deceased would find it unbearable knowing that the person responsible for killing their loved one is now roaming the streets because they underwent a treatment. I'm certain they'd feel more at ease if he/she were dead or locked away for good.
It's also likely that the criminal may be faking the aftermath of the treatment, leading law enforcement to believe that an improvement has occurred (false positive). Generally it's very hard for the general public to re-accept someone or that nature back into society.
On the contrary, let's hypothetically say it does transform the criminal into a saint. That's an ethical issue of its own, because the criminal may not have wanted a complete personality change of which they cannot reverse.