Abstract
BackgroundEmotional stimuli are preferentially processed compared to neutral ones. Measuring the magnetic resonance blood-oxygen level dependent (BOLD) response or EEG event-related potentials, this has also been demonstrated for emotional versus neutral words. However, it is currently unclear whether emotion effects in word processing can also be detected with other measures such as EEG steady-state visual evoked potentials (SSVEPs) or optical brain imaging techniques. In the present study, we simultaneously performed SSVEP measurements and near-infrared diffusing-wave spectroscopy (DWS), a new optical technique for the non-invasive measurement of brain function, to measure brain responses to neutral, pleasant, and unpleasant nouns flickering at a frequency of 7.5 Hz.ResultsThe power of the SSVEP signal was significantly modulated by the words' emotional content at occipital electrodes, showing reduced SSVEP power during stimulation with pleasant compared to neutral nouns. By contrast, the DWS signal measured over the visual cortex showed significant differences between stimulation with flickering words and baseline periods, but no modulation in response to the words' emotional significance.ConclusionsThis study is the first investigation of brain responses to emotional words using simultaneous measurements of SSVEPs and DWS. Emotional modulation of word processing was detected with EEG SSVEPs, but not by DWS. SSVEP power for emotional, specifically pleasant, compared to neutral words was reduced, which contrasts with previous results obtained when presenting emotional pictures. This appears to reflect processing differences between symbolic and pictorial emotional stimuli. While pictures prompt sustained perceptual processing, decoding the significance of emotional words requires more internal associative processing. Reasons for an absence of emotion effects in the DWS signal are discussed.
Highlights
Emotional stimuli are preferentially processed compared to neutral ones
There was a trend for electrode position (F(2, 22) = 2.75, p = 0.086), and for the interaction between emotional category and electrode position (F(4, 44) = 2.34, p = 0.070), reflecting a stronger emotion effect at positions Oz and O1 compared to O2
Since the present diffusing-wave spectroscopy (DWS) instrumentation allowed recording only from a part of the visual cortex, existing activation differences suggested by some previous fMRI studies [28,29,30] may show a regional distribution different from the one captured by the present design
Summary
Measuring the magnetic resonance blood-oxygen level dependent (BOLD) response or EEG event-related potentials, this has been demonstrated for emotional versus neutral words. It is currently unclear whether emotion effects in word processing can be detected with other measures such as EEG steady-state visual evoked potentials (SSVEPs) or optical brain imaging techniques. The amygdala is an almond-shaped structure in the anterior medial temporal lobe strongly involved in emotion processing [16]. Through this so-called “reentrant processing” the amygdala may enhance neural responses to emotionally relevant stimuli [15]
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