شواهد الکتروفیزیولوژیک اختلالات پردازش اولیه در آلکسیتیمیا

Alexithymia describes difficulties to identify and describe one's emotions. Previous research focused on difficulties associated with the later processing stages of appraisal in alexithymia. We tested whether early processing deficits are apparent in alexithymic persons and whether these abnormalities contribute to later processing difficulties. 20 participants were selected and identified as either having high (HDA) or low (LDA) degrees of alexithymia. IAPS pictures were presented while EEG was recorded. For HDA subjects processing of emotional pictures was accompanied by reduced P1 amplitudes most pronounced for pleasant and neutral pictures. In response to unpleasant pictures the P3 amplitudes were reduced. These amplitude modulations were predicted only by one alexithymia facet. P1 amplitudes systematically covaried with P3 amplitudes supporting the assumption that deficits in early emotional processing contribute to later processing deficits.

Alexithymia, a syndrome that involves a marked inability to identify, describe, regulate, and express one's emotions (Sifneos, 1976 and Taylor and Doody, 1985), was originally described by Sifneos in patients with psychosomatic disorders and has been related to a broad range of physical and psychiatric disorders (e.g., alcoholism, drug addiction, and post traumatic stress disorders; see Taylor et al., 1999). At the present time, both within clinical and nonclinical populations, alexithymia is considered a continuous personality trait, with people differing in their ability to identify and describe their feelings (Jessimer and Markham, 1997). The construct of alexithymia is most widely assessed by the Toronto Alexithymia Scale (Bagby et al., 1994), a well-validated self-report questionnaire (Bagby et al., 1994, Mattila et al., 2007 and Parker et al., 2003), whereby three main facets, namely Difficulties in Identifying Feelings (DIF), Difficulties in Describing Feelings (DDF) and Externally Oriented Thinking or a preoccupation with the details of external events (EOT), can be differentiated. There is growing empirical evidence that these facets probably refer to different aspects of emotional processing ( Coffey et al., 2003, Luminet et al., 2006, de Timary et al., 2008 and Gohm and Clore, 2000) with high intercorrelations between the DIF and DDF subscales and low intercorrelations of the DIF and DDF subscales with the EOT subscale ( Gohm and Clore, 2000, de Timary et al., 2008 and Parker et al., 2003). In addition, these facets might be differentially linked to observed abnormalities in the processing of stress and negative emotions ( de Timary et al., 2008). Several authors hypothesized that hampered regulation of emotion in alexithymia might be based on deficits in the perception and further processing of emotional stimuli (Aleman, 2005 and Lane et al., 2000) which was empirically supported by imaging data (Berthoz et al., 2002, Kano et al., 2003, Lane et al., 1997, Mantani et al., 2005, Moriguchi et al., 2006a and Moriguchi et al., 2006b). Berthoz et al. (2002) emphasized that deficits in emotion processing in alexithymia are characterized by abnormalities during the appraisal of emotional stimulus content whereas perceptual aspects of stimulus processing remain unaffected. While imaging approaches (e.g., fMRI, PET) allow for identifying brain areas involved in emotional processing with high spatial accuracy, they lack the fine temporal resolution to investigate the time course of emotional stimulus processing. Some studies provide evidence that alexithymia is associated with impaired processing of emotional stimuli, supporting the view that mainly aspects of stimulus appraisal are affected in alexithymia. Franz et al. (2004) provided evidence that alexithymia might be characterized by a processing deficit to emotional aversive stimuli. Using a modified odd-ball paradigm with three different stimulus categories (aversive probes and affective neutral pictures serving as nontargets and instructed targets) they demonstrated that subjects with alexithymia displayed increased positive deflections (especially of the P2 component) of the visual event-related potential after probe presentation as compared to subjects without alexithymia. The authors concluded that subjects with alexithymia do not express difficulties in perceptual aspects of emotional stimuli but may need more effort and cognitive resources to process emotional information. Results from Aftanas and co-workers (Aftanas et al., 2003, Aftanas and Varlamov, 2004 and Aftanas and Varlamov, 2007) confirm the importance of appraisal processes for emotional processing in alexithymia. The authors showed that alexithymics revealed enhanced event-related theta synchronization over right anterior cortical regions in response to negative stimuli or to negative and positive film clips. Furthermore, very few studies indicate that also early perceptual-related processes are altered in alexithymia. Schaefer et al. (2007) demonstrated that high alexithymic participants exhibited higher P1–N1 amplitudes when confronted with acoustic stimuli of increasing intensity. The authors argued that alexithymia may be associated with a general stimulus augmentation to prevent individuals from ignoring stimuli that might be dangerous. Further evidence for perceptual differences in alexithymia stems from research on anhedonia, a personality trait associated with a decrease in the ability to feel pleasure. Anhedonia is conceptualized as linked to alexithymia, an assumption which was partly supported empirically (e.g., Deborde et al., 2006, Loas et al., 1997 and Loas et al., 1998). Franken et al. (2006) used a visual oddball paradigm and found that both early, middle and late ERP components of subjects with low levels of hedonic tone were attenuated compared with ERPs of subjects with high levels of hedonic tone. The authors suggested that decreased hedonic tone is associated with reductions in both automatic and effortful cognitive processing of relevant stimuli. In accordance to this finding Rey et al. (2010) reported that anhedonics experience less positive feelings when confronted with positive pictures differing in luminance which might be associated with the perceptual encoding and emotional processing in anhedonia. In summary, previous research suggests emotion processing abnormalities in alexithymia that might be investigated by means of event-related potentials (ERP). There is converging empirical evidence that late potentials such as the P3 associated with higher order aspects of cognitive information processing are reduced in alexithymia (Hajcak and Olvet, 2008). As the P3 is positively related to experienced intensity of feelings (Hamm et al., 2003, Polich and Kok, 1995 and Pollatos et al., 2007) this hypothesis is in accordance to numerous empirical studies showing reduced self-reported arousal in alexithymia, e.g. demonstrating reduced arousal in participants with high degrees of alexithymia (Pollatos et al., 2008b and Roedema and Simons, 1999), less pronounced arousal increases after exposure to negative film clips (Stone and Nielson, 2001) or a trend towards lower self-rated intensity during emotional imagery (Mantani et al., 2005). Importantly, there is also some evidence that early components of the ERP like the P1 and N2 could be affected in alexithymia (Franken et al., 2006 and Schaefer et al., 2007). This is relevant because early deficits in perceptual encoding could account for later processing abnormalities. In the present study we focused on participants within a non-clinical range of alexithymia to obtain a sample contrasting high vs. low scores in alexithymia in order to have a representative selection of individuals without psychiatric or neurological problems and without reported drug intake or currently received medication. The present study aimed to investigate the time course of brain dynamics accompanying emotion inducing stimulation in response to affective pictures (Cuthbert et al., 2000, Keil et al., 2002, Pollatos et al., 2005, Schupp et al., 2000 and Waldstein et al., 2000) in alexithymia by the use of event-related potentials technique. We hypothesized that a reduced P3 in alexithymia is accompanied by a modulation of the P1 component reflecting perceptual difficulties in processing of emotional information. With respect to the N2 it is known that N2 amplitudes are more pronounced when stimuli are difficult to encode (Nittono et al., 2007). This could be a consequence of processing abnormalities on a prior perceptual level as assumed in alexithymia. We therefore hypothesized this component to be increased in alexithymia reflecting a consecutive higher cognitive demand to encode emotional information. Taking previous work on the different facets of alexithymia into account (e.g. de Timary et al., 2008, Luminet et al., 2006, Pollatos et al., 2008a, Pollatos et al., 2008b and Vermeulen et al., 2006), we hypothesized that the emotional aspects of alexithymia as reflected in the DDF and DIF subscales would interact with the processing of emotional stimuli while the cognitive aspects as reflected in the EOT scale would not interfere with emotion processing.