Intermittent Theta-Burst Stimulation of the Right Dorsolateral Prefrontal Cortex to Promote Metaphor Comprehension in Parkinson Disease: A Case Study

• Metaphor comprehension was impaired at baseline in our Parkinson disease case.
• Time for interhemispheric inhibition was abnormally long at baseline.
• Intermittent theta-burst stimulation of the right dorsolateral prefrontal cortex significantly improved metaphor comprehension.
• This was correlated with functional plasticity in the right (stimulated) hemisphere.

This single-case research-designed study explored whether intermittent theta-burst stimulation (iTBS) of the right dorsolateral prefrontal cortex (DLPFC) could improve metaphor comprehension in people with Parkinson disease (PD) and language impairments. A right-handed participant with PD diagnosed 9 years ago, receiving long-term treatment with levodopa, and with metaphor comprehension impairment was recruited to undergo 10 sessions of sham stimulation (in 2wk), a washout period (6wk), and then 10 sessions of iTBS (in 2wk). Clinical scores of metaphor comprehension and motor evaluation (Unified Parkinson Disease Rating Scale part III) and transcranial magnetic stimulation to test the excitability of the primary motor cortex (M1) were used at baseline, postsham, post-iTBS, and at 3 follow-ups (8, 14, and 20wk post-iTBS). Metaphor comprehension was improved after iTBS, and the highest scores were obtained 8 weeks later (P=.01). This improvement was correlated with the increase of the right M1 excitability (r=−.86, P=.03) and with the decrease of transcallosal inhibition latency from the left to the right hemisphere (r=−.88, P=.02). Sham yielded no effect (P>.05). Administration of iTBS over the right DLPFC improved metaphor comprehension likely by a long-term influence on brain synaptic plasticity, including improvement of interhemispheric dialogue. More studies are warranted to confirm these findings in larger samples of participants with PD.