Abnormal laughter-like vocalisations replacing speech in primary progressive aphasia

Abstract

We describe ten patients with a clinical diagnosis of primary progressive aphasia (PPA) (pathologically confirmed in three cases) who developed abnormal laughter-like vocalisations in the context of progressive speech output impairment leading to mutism. Failure of speech output was accompanied by increasing frequency of the abnormal vocalisations until ultimately they constituted the patient's only extended utterance. The laughter-like vocalisations did not show contextual sensitivity but occurred as an automatic vocal output that replaced speech. Acoustic analysis of the vocalisations in two patients revealed abnormal motor features including variable note duration and inter-note interval, loss of temporal symmetry of laugh notes and loss of the normal decrescendo. Abnormal laughter-like vocalisations may be a hallmark of a subgroup in the PPA spectrum with impaired control and production of nonverbal vocal behaviour due to disruption of fronto-temporal networks mediating vocalisation.

Fig. 1

A) Mean laugh note duration (s) for the first four notes of pooled laughter samples from Case 2 (diamonds), Case 5 (squares), disease control cases without abnormal laughter-like vocalisations (patient with familial Alzheimer's disease, open circles; patient with behavioural variant FTLD, open squares), and a healthy control sample (triangles and dotted line, with error bars representing mean standard deviation) of 28 healthy female subjects (data from Provine and Yong [10]). B) Trends in mean laugh note amplitude for pooled laughter-like vocalisation samples from Case 2, Case 5, disease control cases without the syndrome and a control sample of 51 healthy subjects (data from Provine and Yong [10]). Symbols as in (A). Amplitude units are arbitrary; samples have been normalised to a mean amplitude of 1.