It is not always tickling: distinct cerebral responses during perception of different laughter types.

Laughter is highly relevant for social interaction in human beings and non-human primates. In humans as well as in non-human primates laughter can be induced by tickling. Human laughter, however, has further diversified and encompasses emotional laughter types with various communicative functions, e.g. joyful and taunting laughter. Here, it was evaluated if this evolutionary diversification of ecological functions is associated with distinct cerebral responses underlying laughter perception. Functional MRI revealed a double-dissociation of cerebral responses during perception of tickling laughter and emotional laughter (joy and taunt) with higher activations in the anterior rostral medial frontal cortex (arMFC) when emotional laughter was perceived, and stronger responses in the right superior temporal gyrus (STG) during appreciation of tickling laughter. Enhanced activation of the arMFC for emotional laughter presumably reflects increasing demands on social cognition processes arising from the greater social salience of these laughter types. Activation increase in the STG for tickling laughter may be linked to the higher acoustic complexity of this laughter type. The observed dissociation of cerebral responses for emotional laughter and tickling laughter was independent of task-directed focusing of attention. These findings support the postulated diversification of human laughter in the course of evolution from an unequivocal play signal to laughter with distinct emotional contents subserving complex social functions.