Behaviour: Surprise in the neurons of 12-month old infants

Infant brains generate neural signals in response to violation of expectations, reports a study published online in Nature Communications. These responses develop late and only in response to unexpected events, consistent with engagement of conscious cognitive mechanisms.

Sid Kouider and colleagues investigated how infants’ brains responded to visual events that differed from their prior expectations by looking at electroencephalogram signals (EEG) taken from high-density EEG wearable nets fitted with electrodes. 12-month old infants sat in the lap of their parents and were presented with one of two sounds and a picture of either a flower or face. Infants developed an association between a category, ‘flowers’ or ‘faces’, based on the identity of the sound. During the trials, the researchers presented the sound first, and, after a 1.5 second delay, the picture. To create an expectation violation, randomly in one in four trials they presented them with a picture from the incorrect category. They analysed the EEG signals evoked by the picture and compared them.

EEG signals evoked by visual events have specific early and late signatures. They found that when the valid picture was shown, a specific early signal in the EEG was enhanced, while in response to the invalid category picture, another component of the EEG response - associated with conscious processing - was specifically amplified.

This study provides evidence that the infant brain produces signals associated with surprise or expectation violation, which is a potent indication of learning from unexpected events. This provides a neural basis for models of learning in infants. Although the slow time course of the expectation response points toward conscious processing of surprise, this needs to be confirmed by future studies.