Gelastic dysarthria: Speech-triggered pathological laughter with evidence for a selective pontine gating mechanism.

We report a highly selective manifestation of pathological laughter in which speech initiation consistently triggers laughter, resulting in disrupted articulation. A 55-year-old male with bilateral pontine infarction exhibited laughter that was time-locked to speech, most prominent during speech production and absent during non-speech tasks. Functional MRI during speech demonstrated activation of language regions, medial prefrontal cortex, amygdala, and ventral pons, with concurrent subjective laughter. We propose that ventral pontine lesions disrupt inhibitory pathways, leading to disinhibition of brainstem laughter circuits. We use the descriptive term 'gelastic dysarthria' to characterize the selectively speech-triggered manifestation of pathological laughter and propose a pontine gating mechanism to account for its observed phenomenology.