ENGLISH: SUMMARY

The present thesis encloses four studies that sought to asses the neural correlates, timing and modulatory effects of a negative emotional context on the processing of task-irrelevant novel sounds within the framework of auditory-visual oddball experimentation. Study I, II and III were conducted using event-related brain potentials (ERP) and Study IV used functional magnetic resonance imaging (fMRI).

In Study I, fourteen healthy volunteers responded to a visual discrimination task, with either neutral or threatening sceneries, while a 64-channel electroencephalogram (EEG) was recorded. In Study II, fourteen healthy female volunteers responded to visual stimuli displaying either threatening or neutral sceneries, using an optimised version of the task, while a 64-channel electroencephalogram (EEG) was recorded. In Study III, fourteen female subjects and fourteen male subjects were recorded using a 64-channel electroencephalogram (EEG) while performing the same visual discrimination task as in Study II. In Study IV, seventeen healthy female volunteers responded to a visual colour discrimination task, with images of emotional facial expressions (angry, fearful or neutral), while neuroimaged in a 3Tesla scanner. In all experimental designs, single auditory stimuli, consisting of a majority of standard tones and infrequent novel environmental sounds, preceded the images and had to be ignored by the subjects.

The main results in all four studies were pointing at comparable conclusions. Novel sounds elicited a distracting effect on subjects' performance, reflected by longer response times compared to those in standard trials. This effect was consistently magnified when preceding and following images were of a negative emotional load as compared to the neutral images. In Study III, women, but not men, showed this effect.

Brain responses recorded with ERPs revealed, in Study I, an enhancement of late novelty-P3 responses to novel sounds in negative context, compared to the neutral one. Furthermore, Study II demonstrated that this modulatory effect can also occur in the early phase of this ERP component. Study III showed that the modulation of the early novelty-P3 was present only in women. Hemodynamic responses, in turn, showed that activation induced by novel sounds in superior temporal gyrus, comprising secondary cortex, planum temporale and primary auditory cortex, was enhanced when subjects responded to faces with a negative emotional expression compared to the neutral ones.

The combination of results in the four studies show that the emotional context enhances excitability of auditory novelty cerebral regions at early stages of processing, making irrelevant sounds become more available in the attentional set under threatening conditions. Still, gender differences may be present in these effects, possibly due to differences in the evaluation of the emotional stimuli.