ERP Correlates of the spatial attention cross-modal effects in an olfactory/visual Posner task

Aim of this research was investigate how ERP components are modulated in a cross-modal Posner’s paradigm (PP) task when the cue has an olfactory valence and the target has a visual valence. Twenty subjects were recruited (10 females; mean age: 24.1 ±3.7) and submitted to an unimodal and to a cross-modal version of the PP. In the unimodal PP, spatial cues and targets (left vs right) were displayed in visual modality; in the cross-modal PP the spatial cue was an odorant administrated in the left or right nostril and a non-odorant in the other nostril through the use of an olfactometer, the target remained the same as in the unimodal task. The order of administration of the two tasks was randomized to exclude sequential effects. During the tasks, a 64-channels EEG was recorded to detect the ERP components associated with the target presentation. As pre-stimulus analysis the last 500 ms before the target onset were considered and ERP showed a slow negativity (the BP/CNV) prominent at Cz, and CPz for both tasks. For the cross-modal task, a slow prefrontal positivity (pP) peaking at AFz was additionally present. Post stimulus analysis showed significant results in most of the components taken into consideration. The prefrontal negativity (pN1) has greater amplitude in the cross-modal than in the unimodal task at Fp2 and AF7 in the expected target condition. The prefrontal (Pp1) showed greater amplitude in the cross-modal task for unexpected event and for the unimodal task for the expected event. The visual P1 showed in both tasks attention and lateralization effects on parieto-occipital areas with greater amplitude for the expected events. The prefrontal N2 (pN2) was greater in the cross-modal task and was more sensitive to attention than the unimodal pN2. Even the anterior N350 showed greater amplitudes for the cross-modal task. The P3, on the other hand, has a lower amplitude in the cross-modal task, particularly in centro-parietal areas (Cz, CPz). The results of this study showed that the olfactory cross-modal and the unimodal tasks share common attentional processing in the early post-stimulus phase, but in the pre-stimulus preparatory phase and in the late post-stimulus processing, the cross-modal task was associated with larger prefrontal and smaller posterior activities likely reflecting the anterior olfactory functions.