حافظه اپیزودیک برای کلمات عاطفی و غیر عاطفی در افراد مبتلا به فقدان لذت

Anhedonia is a symptom that plays a significant role in theories of illness such as depression and schizophrenia. Some previous research suggests that participants who report high levels of social/physical anhedonia also show deficits in both self-report and physiological measures of emotional processing, particularly for measures of emotional valence as compared with emotional arousal. Little is known about memory for emotionally valenced information or how this might be related to emotional processing in anhedonia. Participants were 391 undergraduate students participating for course credit. We administered an incidental encoding task that required participants to rate emotional words on both valence and arousal dimensions. We then administered surprise recall and recognition tasks to all participants. Results indicated that higher levels of physical and social anhedonia were associated with attenuated valence ratings of emotional words but did not influence arousal ratings or the memory pattern for emotionally valenced information. These findings suggest that there is some reduction in emotional experience in individuals with anhedonia, but that this reduction does not appear to produce a deficit in memory performance, perhaps due to the intact experience of arousal.

Anhedonia, the inability to experience pleasure, is a symptom that plays a significant role in many theories of illnesses such as depression and schizophrenia. For example, in Meehl's theory of schizotaxia, primary anhedonia is thought to play a crucial role in increasing susceptibility to developing psychosis (Meehl, 1962). According to Meehl, the ability to experience and anticipate pleasure serves as a buffer of sorts to the development of a psychotic disorder, potentially by protecting against the negative influences of stress. As a result of an inability to feel pleasure, Meehl contends that anhedonia leads to an “aversive drift” or the tendency to view events as negative or threatening (Meehl, 1962) given the absence of positive hedonic cues. Despite the prominent role of anhedonia in theories such as Meehl's, relatively little empirical work has focused on understanding the specific nature of emotional processing disturbances in individuals who self-report high levels of anhedonia. The goal of the current study is to address the following three questions: (1) What are the subjective emotional responses of individuals who report anhedonia to affect-eliciting stimuli? (2) Do individuals with anhedonia have differential deficits in the valence versus the arousal dimensions of emotion? and (3) Do individuals with anhedonia experience disturbances in memory for affective stimuli? Anhedonia is typically rated based on the individual's self-report of emotional experience, usually during a clinical interview or on a questionnaire. However, relatively little is known about how individuals who report being socially or physically anhedonic actually respond to emotion eliciting stimuli. A few studies have examined the relationship between self-reports of anhedonia and other aspects of emotional processing in individuals with manifest schizophrenia. For example, a study by Berenbaum and Oltmanns (1992) found that patients with schizophrenia did not differ from controls in their self-reports of emotion in response to emotional stimuli, despite the fact that the patients reported higher levels of social and physical anhedonia in a clinical interview. Blanchard et al. (1994) found that individuals with schizophrenia who reported higher levels of physical anhedonia also reported less positive affect when watching both positive and negative film clips. However, these reduced positive affect reports among patients may have simply reflected baseline reductions in positive affect, given that patients showed a clear increase in positive affect in response to the positive as compared to negative film clips and the reduced positive effect reports were present in all valence conditions. Recent research by Mathews and Barch (2004) found that individuals with schizophrenia had intact self-reports of emotional valence and arousal in response to affectively valenced words, despite again having higher clinical ratings of anhedonia than controls. Thus overall, the existing research on schizophrenia, anhedonia, and emotional processing suggests that although patients may report high levels of anhedonia, they appear to self-report experiencing the same levels of positive emotion in response to affect eliciting stimuli. Several additional studies have examined anhedonia in individuals without a clinical diagnosis of any form of psychopathology. These studies have typically examined individuals who score highly on scales such as the Chapman social and physical anhedonia scales (Chapman et al., 1980). These individuals are of interest to psychopathology researchers, given the theorists who have argued that high levels of anhedonia constitute a vulnerability for psychosis (Meehl, 1962 and Rado, 1962). Further, studies by Chapmanet al. have shown that individuals who score more than two standard deviation above the mean are at an increased risk for the later development of psychotic disorders (Kwapil et al., 1997). A number of these studies examined the relationships between self-reports of anhedonia on questionnaires and self-reports of emotion in response to affect eliciting stimuli. Many of these studies have found that participants with high levels of anhedonia report and rate stimuli as less positive or less interesting than controls (Ferguson and Katkin, 1996, Fiorito and Simons, 1994, Fitzgibbons and Simons, 1992, Gooding et al., 2002, Putnam, 1997 and Simons et al., 1982), though one study reported no difference between high anhedonic individuals and controls (Berenbaum et al., 1987). Several studies have also examined facial expressiveness in individuals with high ratings of anhedonia, with mixed results (Berenbaum et al., 1987, Putnam, 1997, Ferguson and Katkin, 1996 and Fitzgibbons and Simons, 1992). A number of previous studies have also examined heart rate while participants viewed emotional stimuli and have consistently found that when processing emotional and neutral stimuli, individuals who report high anhedonia show reduced changes in their heart rate response when processing emotional stimuli as compared to controls (Ferguson and Katkin, 1996, Fitzgibbons and Simons, 1992, Fiorito and Simons, 1994 and Simons et al., 1982). In contrast, a number of the previous studies have also looked at skin conductance in individuals rated highly on anhedonia scales and have not found skin conductance differences between individuals who self-report high versus low anhedonia (Ferguson and Katkin, 1996, Fitzgibbons and Simons, 1992, Fiorito and Simons, 1994 and Putnam, 1997). In addition, two studies looked at emotion modulated startle responses in anhedonics and concluded that high and low anhedonic individuals demonstrated similar changes in startle as a function of exposure to emotional stimuli (Putnam, 1997 and Gooding et al., 2002). In summary, the studies examining the relationships between self-reports of anhedonia on questionnaires and various indices of emotional responding to affect-eliciting stimuli among individuals without clinically diagnosed psychopathology suggest a mixed, but potentially informative picture. Many theories of emotional processing (Russell, 1980 and Larsen and Diener, 1992) distinguish between valence (positive versus negative) and arousal (high versus low) aspects of subjective emotional responses, as research suggests that these may be partially independent aspects of emotional processing that are mediated by different neural systems (Bradley, 2000). Further, the literature on physiological indices of emotional processing in individuals reporting high levels of anhedonia suggests that there may be an important dissociation between the processing of valence versus arousal aspects of emotional responding. Previous work has suggested that heart rate tends to track the valence of emotional stimuli (e.g., positive versus negative), while skin conductance tends to track arousal irrespective of valence (e.g., high versus low arousal for both negative and positive stimuli) (Bradley et al., 1992). The literature reviewed above suggests that individuals reporting high levels of anhedonia show deficits in physiological indices linked to emotional valence (e.g., heart rate), but not emotional arousal (e.g., skin conductance). Whether this same dissociation exists in self-reports of emotional experience in anhedonia is unclear, as many of the studies reviewed above did not make this distinction. However, two studies (Fitzgibbons and Simons, 1992 and Fiorito and Simons, 1994) distinguished between arousal and valence dimensions of emotion in their self-rating tasks in anhedonia individuals. The Fitzgibbons and Simons (1992) studies found deficits only in valence reports and not arousal reports. However, Fiorito and Simons (1994) found that both the valence and arousal self-report ratings were impaired. In sum, the literature on emotional processing in high anhedonia individuals suggests consistent evidence for deficits in the processing of valence, but mixed evidence for the processing of arousal. It is also important to determine whether individual differences in anhedonia are related to the influence of emotion on other aspects of cognitive processing, as this may shed light on the ways that anhedonia could influence life function and risk for the development of psychosis. As described above, Meehl suggested that anhedonia contributes to susceptibility for developing a psychotic disorder by a reduced ability to buffer against stress and increased adverse drift. However, the mechanisms by which these effects may occur are not clear. One possibility is that anhedonia changes memory for emotional information, such that memories of positive stimuli are harder to retrieve (and thus less available to buffer against stressful or negative experiences), but memories for negative stimuli are easier to retrieve. Research in healthy individuals suggests that the emotional valence and arousal of both verbal and non-verbal stimuli can influence subsequent memory for those stimuli. It has been shown that emotional experiences, as compared with non-emotional experiences, are remembered better (Christianson, 1992) and that people show better declarative memory for emotionally salient parts of a story than for neutral parts of that story (Adolphs et al., 1997 and Cahill et al., 1995). In addition, recent research suggests that in addition to valence, arousal characteristics of emotional stimuli have a strong influence on subsequent memory for those stimuli. For example, research by Bradley et al. (1992) has found that college students who viewed emotional pictures recalled positive, highly arousing pictures better after a short delay. However, at both short and long delays, highly arousing stimuli were remembered better than low arousal stimuli. In fact, at both time periods, arousal had a bigger influence than valence on whether a picture was remembered. Research on emotional memory in schizophrenia has been limited, although one study by Koh et al. (1981) found that individuals with schizophrenia did not show the differential effect of memory for positive words that was found in controls. They suggest that this is evidence for the Pollyanna effect in controls and the effect of anhedonia in individuals with schizophrenia. Recent research by Mathews and Barch (2004) found that individuals with schizophrenia (whether or not they reported high anhedonia) demonstrated the same influence of both positive and negative emotional valence on memory as controls, with both groups demonstrating enhanced memory for high arousal over low arousal words and emotional over neutral words. Recently, Gooding and Tallent (2003) demonstrated that individuals with high social anhedonia performed more poorly than controls on a delayed match to sample task for affective stimuli. However, these same individuals also performed more poorly than controls on a spatial working memory task without affective stimuli. In addition, a study by Kerns and Berenbaum (2000) examined affective priming in social anhedonics and found that individuals with high levels of social anhedonia exhibited an effect of target valence related to priming. They suggest this is due to the tendency of social anhedonics to process affective information semantically, but refrain from processing the information affectively. In the current study, we examined the influence of emotion on memory in individuals that self-report high levels of either or both physical and social anhedonia on the Chapman Psychosis Proneness Scales. To do so, we asked participants to rate a series of words on both arousal and valence, without telling them that they would receive a subsequent memory test (we refer to this as the incidental encoding task). The participants were later given surprise recall and recognition tasks. We predicted that if individuals with high levels of anhedonia had reduced subjective responses to emotionally valenced words (at least, according to Meehl, positive words) for both valence and arousal ratings, then they should also show a reduced influence of emotion on subsequent memory. This would be especially true for positive words if Meehl's theory of hypoactive appetitive responses were related to rating and memory for positive words. However, we predicted that if high anhedonia individuals experience disturbances in the processing of valence but not arousal, they would show an intact influence of emotional valence on subsequent memory. Such a result would be predicted based on research that suggested that ratings of arousal are at least as strong a predictor as ratings of valence of subsequent memory. Further, such a result would be consistent with a study by Putnam (1997) suggesting that high anhedonic individuals self-report feeling less hedonic experience to emotional stimuli, despite demonstrating the same physiological responses (another potential indicator of “arousal”) to emotional stimuli as healthy controls.