[Long-latency evoked potentials and mnemonic processing of faces and words]

Evoked potentials are real-time electrophysiological markers of cognitive operations and especially mnemonic processes. The N400 wave has traditionally been studied to characterise the processes involved in memorising verbal material. To investigate the existence of specific memory processes for each information domain, functional analogues of this wave were examined during the processing of non-verbal stimuli, such as faces.

Using an inter-subject design, the classic verbal N400 wave was compared with its functional analogue during the processing of faces in a contextual preactivation task adapted to the visual domain of faces.

After several sessions dedicated to learning a set of faces, another evoked potential recording session was held in order to analyse the effects of the existence of structural inconsistencies in these stimuli and to compare them, with regard to their topographic distribution and neural generators, with those observed in the classic verbal N400 task.

A verbal N400 wave was observed with a (slightly right) centro-parietal distribution, and this response was distinguished from another negative wave obtained during the processing of facial inconsistencies in the same group of participants, with a predominantly occipital localisation and differentiated neural generators.

These findings support the hypothesis of the specificity of the neural mechanisms involved in the mnemonic processing of faces and words, which is in line with the neurocognitive models that suggest the independence or modularity of memory processes in different domains of information.