Electromyographic study of facial expressions during pathological laughing and crying

We studied facial expressions during pathological laughing and crying in 6 patients using EMG investigation. Increased EMG discharges of M. frontalis and M. corrugator supercilii are characteristic of pathological laughing and crying in addition to an increase of EMG discharges of M. orbicularis oculi, M. levator labii superiors, M. zygomaticus major, M. risorius and M. mentalis which we observed during natural laughing. Its patterns of facial expressions are similar to that of crying in normals. From the fact that normals show the same expression of laughing and crying in an extreme emotional outburst, we speculate that pathological laughing and crying is maximal manifestations of facial expressions caused by a release phenomenon of the upper center.