instance, right as compared to left hemisphere stroke patients showed a higher prevalence of alexithymia [28]. In a positron- emission tomography (PET) study, Kano and colleagues [29] observed lower regional cerebral blood flow (rCBF) during the viewing of emotional faces in a distributed right-hemispheric network in high-versus low-scorers on alexithymia. Furthermore, Jessimer and Markham [30] studied the ability of high- and low- scorers on alexithymia to attribute emotional value to chimeric pictures of faces composed of conjoined emotive and nonemotive halves. Normally, right-handed individuals tend to choose the chimeric face with the emotive half on the left as being more expressive than the half on the right, indicating a leftward bias related to a predominantly right-hemispheric processing of these stimuli [31]. In contrast, high-scorers on alexithymia showed significantly less left bias on chimeric tasks than low-scorers, indirectly suggesting less right-hemispheric involvement [30]. Using a lateralized visual-matching task, Bermond and coworkers [32] demonstrated that high-scorers on alexithymia as compared to low-scorers showed a left hemisphere preference for the processing of emotional words. Finally, a dysfunction of the right hemisphere during emotional processing in alexithymia has been suggested by studies using electroencephalography (EEG) [33,34]. The electrophysiology of emotion processing in alexithymia Electrophysiology with its extremely high temporal resolution in the range of milliseconds is an excellent means to investigate how emotional processing unfolds in time and can give information about whether alexithymia primarily affects overt, appraisal- related aspects of emotional processing or whether it affects already the more automatic, early perceptual-related aspects. The findings of studies employing event-related potentials (ERPs) to address this question will be summarized below. However, it should be kept in mind that previous ERP studies mostly relied on the 20-item Toronto Alexithymia Scale (TAS-20) to assess levels of alexithymia. This scale assesses only the cognitive alexithymia dimension, i.e. difficulty identifying, analyzing, and verbalizing feelings. Therefore, previous findings of ERP studies on alexithy- mia primarily refer to cognitive deficits in emotional processing, whereas the impact of disturbances in emotional experience (affective alexithymia dimension) has remained elusive. Franz et al. [35] presented high- and low-scorers on the TAS-20 alexithymia scale with aversive versus neutral pictures and observed that high-scorers on alexithymia exhibited elevated amplitudes of the P2 component in response to aversive pictures. The authors interpreted this finding to reflect higher effort and recruitment of additional cognitive resources to process emotional stimuli in individuals with alexithymia. Bermond et al. [36] assessed alexithymia using the Bermond-Vorst Alexithymia Questionnaire (BVAQ) [8], which covers both the cognitive and the affective alexithymia dimension, and divided participants into two groups with either high or low scores on the sum score of both dimensions. The authors reported reduced P3 amplitudes during negative picture processing in female, but not male high-scorers on alexithymia, compared to low-scorers. No impact of alexithymia on latencies of the P3 was observed. Using morphed angry and disgusted facial expressions in an emotion categorization task, Vermeulen et al. [37] specifically focused on ERP latencies. Latencies of the P3 did not differ as a function of alexithymia, but the N2b/P3a complex showed delayed latencies in high-scorers on the TAS-20 scale as compared to low-scorers, indicating an overall delayed categorical perception of emotional faces in alexithymia. Pollatos and Gramann [38] investigated early electrophysiolog- ical responses to emotional pictures in order to test whether early The Sound of Feelings processing deficits contribute to deficits at later processing stages in alexithymia. The authors observed that amplitudes of the early component P1 were reduced in high-scorers on the TAS-20 scale during the processing of positive and neutral pictures, predicted by the alexithymia subscale ‘‘difficulty describing feelings’’. The same subscale predicted larger amplitudes of the N2 for negative and neutral pictures in high-scorers. In line with Bermond and colleagues [36], amplitudes of the later occurring P3 were reduced at posterior regions in response to negative pictures in high-scorers on alexithymia. Further, P1 amplitudes were found to co-vary with P3 amplitudes, indicating that early processing deficits might indeed contribute to deficits during later emotional processing in alexithymia. Confirming the observation of an impact of alexithymia on both early and late electrophysiological processing of emotions, Walker and colleagues [39] found reduced N2 and larger P2 amplitudes during the suppression of emotion elicited by negative images in low–scorers, but not high-scorers on the TAS-20 alexithymia scale. Further, they identified reduced amplitudes of the late positive potential (LPP) in a time-window of 400–600 ms post picture onset with increasing scores on alexithymia during negative emotion suppression, suggesting that alexithymia was inversely related to the magnitude of emotion-related ERP activity during emotion suppression. This alteration of late positive potentials during emotion regulation was confirmed by Pollatos and Gramann [40], who reported reductions in amplitudes of the P3 and the slow wave in the course of successful cognitive reappraisal of negative emotion only in individuals with low scores, but not in those with high scores on alexithymia. Taken together, ERP studies investigating visual emotional processing suggested that alexithymia influences both early (,300 ms) and late (.300 ms) emotional processing. At late processing stages, thought to reflect cognitive appraisal of emotion, there is converging evidence for reduced emotional processing as a function of alexithymia as reflected in diminished amplitudes of the later occurring P3 component [36,38, but see 37] and the LPP [39] as well as in a failure to down-regulate P3 and slow wave amplitudes through reappraisal of negative emotion [40]. Findings of differences in early components during emotion processing in relation to alexithymia, thought to reflect more automatic, perceptual processing, are less consistent with respect to di- rectionality as both increased [35,38] and decreased [38] amplitudes of early ERP components have been reported. Alexithymia and emotional prosody In contrast to the visual domain, auditory emotional processing has rarely been investigated in relation to alexithymia. A recent behavioral study tested the impact of emotional background music on the recognition of emotion words [41]. Exposure to angry music was found to result in decreased recognition rates of emotional words in high-scorers as compared to low-scorers on alexithymia (cognitive dimension). In an ERP study, Scha¨fer and colleagues [42] presented alexithymic versus non-alexithymic participants with aversive white noise. They identified significantly larger amplitudes of the P1-N1 complex (40–200 ms post stimulus onset) in alexithymics compared to non-alexithymics in response to aversive white noise, while intensity and pleasantness of the aversive stimuli were rated equally by the two groups. These results were interpreted as indicative of a hypersensitivity to unpleasant external stimulation and provide further evidence for a modulation of early ERP components by alexithymia. Emotional prosody, the ‘melody of speech’, is an important means to understand the emotional state and intention of others in social communication. A recent meta-analysis showed that PLoS ONE | www.plosone.org 2 May 2012 | Volume 7 | Issue 5 | e36951