"This seems to be a way of helping the brain to sort of rewire itself."
The trial has produced improvements over 12 months in long-term patients with both conditions who have already been through traditional therapies.
Parkinson's sufferers, 85 per cent of whom experience speech or language difficulties, are improving their articulation and speech intelligibility.
Stroke patients, who suffer a condition called aphasia, are finding they can recall the names of things more quickly and accurately. Aphasia is condition where sufferers can have impaired language ability including difficulty remembering words.
"The main effect's starting to show up after about a week to two months and then it's persisted up to 12 months post-stimulation," Professor Murdoch said.
"That's a bit of a breakthrough. We've never really had that sort of effect with any other treatment before."
The jury is still out on why the technique works, but studies in animals have shown it can increase the branching of some neurones in their brains.
In medical terms the equipment comes cheap at around $50,000 and it is already making a difference to the lives of patients in the trial.
"They're suddenly now seeing improvement after all these years ... it's given them a new life in a way," Professor Murdoch said.
- AAP