|The cerebellum is coloured green in this model|
Bakheit's patient, a 54-year-old bilingual man, suffered a stroke that caused damage to the left side of his brain stem and both hemispheres of his cerebellum - that's the cauliflower-shaped structure, associated with motor control and other functions, which hangs off the back of the brain. The man's brain damage left him unsteady on his feet, gave him difficulty with swallowing and his speech was slightly slurred. But remarkably, his life-long stammer, characterised by repetitions of sounds, and which caused him social anxiety and avoidance, was entirely gone - an account corroborated by his wife. By the time of his discharge from hospital, the slowing of his speech was much improved and yet thankfully his stammer remained absent.
The researchers can't be sure, but they think the remission of the man's stammer is likely related to his cerebellum damage, which may have had the effect of inhibiting excessive neural activation in that structure. This would be consistent with previous research showing that people who stammer have exaggerated activation in the cerebellum compared with controls, and with the finding that successful speech therapy is associated with reductions to cerebellum activation compared with pre-treatment. A second, related possibility is that, pre-stroke, the man's cerebellum was somehow having a detrimental effect on his basal ganglia (a group of sub-cortical structures involved in motor control and other functions) and that this adverse effect was ameliorated by the stroke-induced damage. This would be consistent with reports of stammers developing in patients with diseases, such as Parkinson's, that affect the basal ganglia.
A third and final possibility, the researchers said, is simply that the slowing of the man's speech somehow aided his stammer. Indeed, reducing the rate of speech is a therapeutic approach. However, this certainly wasn't a conscious strategy employed by the patient, and as we've seen, his stammer remained in remission even as his speech rate improved.
'The complete remission of stammering following a posterior circulation stroke in our patient suggests that the cerebellum and/or its connections with brain structures has an important role in maintaining developmental stammering,' the researchers concluded.
Bakheit AM, Frost J, and Ackroyd E (2011). Remission of life-long stammering after posterior circulation stroke. Neurocase : case studies in neuropsychology, neuropsychiatry, and behavioural neurology, 17 (1), 41-5 PMID: 20799135
Post written by Christian Jarrett (@psych_writer) for the BPS Research Digest.