The three clap test: a window into cognitive and frontal lobe dysfunction.

The three clap test (TCT) is a simple bedside test that can elicit the so-called applause sign (AS), manifesting with more than three claps after the examiner's instruction to clap three times. Although the AS was originally described as a useful sign differentiating patients with progressive supranuclear palsy (PSP) from patients with Parkinson's disease (PD) and frontotemporal dementia (FTD), it is also known to be present in PD, Alzheimer's disease and several other diseases. It reflects the so-called stopping impulsivity and cognitive and frontal lobe dysfunction. In addition to the AS, the TCT can also elicit the non-applause sign, linked with the apathy subtype of behavioural variant of FTD and the jumping the gun sign, a sign of waiting impulsivity, also seen in PSP. This review summarizes the up-to-date clinical aspects and pathophysiology of all these signs and discuss the benefit of using the TCT in the routine clinical praxis.