[The mu rhythm of the vertex and its reactivity: an infrequent observation (author's transl)]

The possibility arose of recording an uncommon type of E.E.G. activity: the mu rhythm of the vertex. A patient aged 76 years developed transient blindness, followed by confusion, a homonymous lateral hemianopsia, and left sensory deficiency, probably due to a cardiac embolism. An electroencephalogram one week later demonstrated localized "'arceau" rhythm around the vertex and typical centroparietal pseudo-periodic spikes (PLEDS). These activities were no longer present three days later. The vertex mu did not react to opening of the eyes or clenching the fists. It reacted to stimuli (tactile or movement) of the lower limb contralateral to the affected cerebral hemisphere. The origin of rhythmic activities corresponding to different generators is discussed, and the probable pathological significance of the mu rhythm of the vertex emphasized.