Introduction

Drug addiction is often characterized as a neurobiological disorder, in which individuals display compulsive drug use in spite of being aware of the associated adverse consequences [1]. However, recent perspectives challenge this traditional definition of drug addiction, calling for the acknowledgment of the multifaceted nature of drug use and the need to examine the complex interplay between psychological, socio-economic, and other relevant factors when evaluating drug choices [2]. Considering these perspectives, it is crucial to acquire a comprehensive understanding of the intricate psychological mechanisms that prompt individuals to engage in drug abuse [3, 4].

The study of the self offers a crucial perspective for elucidating the underlying psychological mechanisms of addiction. The self, referred to as “the totality of everything that an individual can call their own” [5], consists of a complex, multidimensional structure that lies at the heart of one’s inner world [6, 7]. Addiction is a complex phenomenon, and the multidimensionality and centrality of the self may prove pivotal in addressing addiction-related challenges [8, 9].

The self plays a critical role in regulating psychological processes across various domains, and our brains instinctively prioritize information relevant to ourselves. This phenomenon is commonly referred to as the self-prioritization effect [10,11,12,13]. For example, we naturally pay more attention to self-related cues, such as our own name and face [14, 15]. Additionally, research has shown that individuals are more likely to remember items that have incidentally acquired personal relevance [16]. Furthermore, the self-prioritization effect extends beyond direct personal relevance. Studies conducted by Sui et al. [12] demonstrated that even socially insignificant geometric shapes can evoke the self-prioritization effect through associative learning in a matching task [12].

Previous neurobiological research suggests that individuals struggling with drug addiction may experience deficits in the self-prioritization effect. The medial prefrontal cortex plays a crucial role in processing self-relevant information. Specifically, the rostral anterior cingulate cortex (rACC) evaluates the personal significance of stimuli [17], while the ventromedial prefrontal cortex (VMPFC) assesses the importance of self-related stimuli [18]. When processing drug-related stimuli, individuals with addiction exhibit higher activation levels in both the rACC and VMPFC compared to neutral stimuli [19,20,21]. Conversely, when processing non-drug-related stimuli, individuals with addiction show lower activation levels in both the rACC and VMPFC compared to healthy individuals [22,23,24]. These findings suggest that individuals with drug addiction may assign excessive self-relevance to drugs while assigning reduced self-relevance to other stimuli. Therefore, individuals with drug addiction may prioritize the processing of drugs, exhibiting an attentional bias towards them, while experiencing diminished processing advantages for other significant stimuli, such as not appreciating valuable job opportunities.

A recent study by Liang et al. [25] investigated whether individuals with drug addiction exhibit abnormal self-prioritization effects [25]. The study found that individuals with heroin addiction demonstrated both self-prioritization effects and drug-prioritization effects, whereas healthy individuals only showed self-prioritization effects. Additionally, there was a significant positive correlation between the intensity of self-prioritization effects and drug-prioritization effects in individuals with heroin addiction. These findings suggest that self-prioritization effects persist in individuals with drug addiction and may be amplified when self-relevance is assigned to drugs, resulting in an exaggerated response. Importantly, the study focused on self-prioritization effects at the matching level, where self-relevant stimuli are more salient and receive heightened attentional bias, leading to faster information processing. However, it remains unclear whether individuals with drug addiction also demonstrate self-prioritization effects at the memory level, where self-referenced stimuli are better remembered compared to stimuli referenced to others. Thus, the study aimed to investigate the presence of self-prioritization effects using the self-referential paradigm in drug users.

In addition to the self-prioritization effect, information pertaining to significant individuals in one’s life, such as mothers and close friends, can also elicit similar prioritization effects. As social beings, people constantly engage with others and may integrate important individuals into their self-concept. This phenomenon is particularly prominent in East Asian culture, where the interdependence between the self and others is emphasized, blurring the distinction between self and other [26]. Consequently, East Asians have been observed to exhibit cognitive advantages similar to the self-prioritization effect when processing information about their mothers [27,28,29]. For instance, encoding information related to either the mother or the self produces comparable memory enhancement effects in Chinese individuals [30, 31]. Moreover, neuroimaging evidence suggests that stimuli associated with mothers and oneself activate the same brain regions to a similar extent in Chinese individuals, but not in Westerners [32].

It remains uncertain whether such a mother-prioritization effect is impaired in individuals with addiction. One of the fundamental criteria for diagnosing drug addiction is persistent drug use despite negative consequences [33], with the prioritization of drugs taking precedence over other valued goals, such as maintaining long-term intimate relationships. Moller and Goldstein (2014) have suggested that this may be because individuals in the drug-dependent population assign excessive self-relevance to drugs while assigning insufficient self-relevance to other important aspects of life [34]. As mentioned earlier, a recent study suggests that individuals with drug addiction tend to attribute excessive self-relevance to drugs [25], resulting in a specific processing advantage for drug-related information. However, it is still unclear whether individuals with drug addiction assign insufficient self-relevance to objects that should be given high importance. For example, drug addiction is often associated with dysfunctional and impaired family relationships [35, 36]. This could be attributed to individuals with drug addiction assigning insufficient self-relevance to significant others, such as their mothers. Given these circumstances, we hypothesized that drug addiction would lead to a weaker mother-prioritization effect.

In summary, individuals with an East Asian cultural background tend to prioritize the processing of information related to themselves and their mothers in a similar manner. However, individuals with drug addiction may experience a dissociation between self-prioritization and the prioritization of their mothers. However, there is currently a lack of research specifically addressing this issue. Therefore, the aim of this study was to investigate how individuals with drug addiction process information that is relevant to themselves and information related to their mothers, both in terms of matching and memory. Heroin misusers were the focus of this study due to the high level of harm associated with the drug. All participants were recruited from a male compulsory detoxification center in Yunnan Province, China. The research consisted of three experiments. Experiment 1 utilized a matching task to examine how individuals with heroin addiction processed self-relevant and mother-related information at the matching level. Experiment 2 combined a self-referential task with a recognition task to replicate and expand the findings from Experiment 1 in the memory domain. We expected the self-prioritization effect to still be present in individuals with heroin addiction, while the mother-prioritization effect would be impaired. In Experiment 3, we further explored the clinical significance of the impaired mother-prioritization effect, predicting it to be closely associated with drug use indicators.

Study 1: Self- and mother-prioritization effects in heroin misusers at the matching level

The aim of Study 1 was twofold. Firstly, we aimed to revalidate the presence of the self-prioritization effect in heroin misusers at the matching level, as previously observed by Liang et al. [25]. Secondly, we intended to investigate whether heroin misusers exhibit the mother-prioritization effect. As mentioned earlier, our hypothesis was that self-prioritization would remain strong in heroin misusers, while the mother-prioritization effect would be attenuated compared to that of healthy controls.

Method

Participants

To ensure adequate statistical power, we utilized G*Power 3.1.9.4 software [37] to calculate the minimum sample size required for our study. Based on a moderate effect size (Cohen’s f = 0.25), we determined that a minimum of 36 participants per group would provide a power of 0.90. Therefore, we recruited a total of 49 male abstinent heroin misusers (AHM) from a drug rehab center in southern China, with ages ranging from 24 to 49 years (mean age 36.47 ± 5.96 years, mean ± SD). These participants met the following eligibility criteria: (i) a history of heroin use for more than three years, (ii) heroin as the primary substance of abuse within the past three years, and (iii) no opioid substitution treatment. We excluded participants with acute physical or psychiatric illness, those unable to follow instructions, and those experiencing withdrawal symptoms. The control group consisted of 42 healthy men (aged 24–49 years, mean age 37.29 ± 6.44 years) with no history of substance abuse, recruited from the local community. There were no significant differences in age or educational level between the two groups (ps > 0.08). This study was conducted in accordance with the latest version of the Declaration of Helsinki. The study protocol received approval from the Ethics Committee of Tsinghua University. Written informed consent was obtained from all participants prior to their involvement in the experiment.

To control for the potential impact of maternal death on mother-prioritization [30], all participants were requested to indicate whether their mother was alive. In the AHM group, forty-nine participants provided responses, with forty indicating that their mother was still alive. Similarly, in the control group, forty-two participants responded, with thirty-four indicating that their mother was alive. A chi-square test revealed no significant differences between the groups (χ2 = 0.007, p = 0.93).

Materials and procedure

Participants completed the self-mother matching task, which consisted of two phases. This task adapted the paradigm of Sui et al. [12], with two key changes: (1) comparison stimuli were altered from (self, friend, stranger) to (self, mother, stranger) to assess both self- and mother-prioritization effects; and (2) to account for potential cognitive deficits associated with repeated drug use [24], we extended the response window [13].

In the initial phase, participants were instructed to assign three geometric shapes (circle, rectangle, and triangle, each measuring 3.8° × 3.8°) to the categories of “self,” “mother,” or “stranger.” For example, they were informed that “the circle represents you, the rectangle represents your mother, and the triangle represents a stranger.” The associations between the shapes and labels (you, mother, and stranger, each measuring 2.4° × 1.6°) were counterbalanced across participants. No stimuli were presented during this phase.

In the subsequent phase, participants were required to determine whether the shape-label pairs presented simultaneously corresponded to the rule they had just learned. As illustrated in Fig. 1, each trial began with a central fixation cross (measuring 3.8° × 3.8°) displayed at the center for 500 ms. This was followed by a shape-label pair displayed for 3000 ms, during which participants were instructed to respond as quickly and accurately as possible by pressing “1” or “2” to indicate a matching or non-matching pair within the given time frame. The participants were instructed to employ both hands to independently press “1” and “2”. The shape appeared above the fixation cross, while the label appeared below it, with a distance of 3.5° between the center of the shape or label and the fixation cross. Feedback (correct, incorrect, or too slow) was provided at the end of each trial for 500 ms. Participants completed six blocks of 60 trials, with each trial type (self-matched, self-nonmatched, mother-matched, mother-nonmatched, stranger-matched, and stranger-nonmatched, based on the shape) comprising 60 trials. The trial types were randomly presented within each block. Prior to starting the first formal block, participants completed a practice block by successfully completing three consecutive trials. The experiment was conducted on a PC with a 17-inch monitor (1024 × 768 at 60 Hz) using PsychoPy3 software (v2020.1.0). A double-blind procedure was employed; neither participants nor experimenters were aware of the experimental hypothesis.

Fig. 1: Example of the arrays presented in the self-mother matching task.
Fig. 1: Example of the arrays presented in the self-mother matching task.
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Participants completed a self-mother matching task in two phases. In the first phase, they assigned three geometric shapes (circle, rectangle, and triangle) to the categories of “self,” “mother,” or “stranger.” In the second phase, they determined whether the simultaneously presented shape-label pairs followed the rules they had just learned.

Statistical analysis

As robust prioritization effects only emerged in matched trials [12, 25], we focused our analyses on matched trials. Firstly, we calculated the accuracy rate (ACC) and response time (RT) for different shape categories (self, mother, and stranger) in the matched trials for each group. Subsequently, we conducted separate analyses of ACC and RT in the matched trials using a mixed-model analysis of variance (ANOVA) with a 3 (Shape Category: Self, Mother, Stranger) x 2 (Group: AHM, Healthy Controls) design. Shape Category was treated as a within-subject variable, while Group served as a between-subject variable. Data analyses were performed using SPSS 21.0 software. Statistical analyses used a significance level of α = 0.05; where appropriate, the Bonferroni correction was applied to adjust for multiple comparisons. The results were reported in terms of ACC and RT.

Results

The ACC data (refer to Table 1) was subjected to a mixed-model ANOVA with a 3 (Shape Category: self, mother, stranger) × 2 (Group: AHM, healthy controls) design. The analysis revealed a significant main effect of Shape Category [F (2, 178) = 24.16, p < 0.001, and ηp2 = 0.21], indicating a self-association advantage over mother-associations (p = 0.04) and stranger-associations (p < 0.001), as well as a mother-association advantage over stranger-associations (p < 0.001). None of the other effects reached significance (Fs < 2.08, ps > 0.15).

Table 1 The ACC data of participants in different groups under varying matching conditions.
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The mixed-model ANOVA was conducted on the RT data (refer to Table 2) using a 3 (Shape Category: self, mother, stranger) × 2 (Group: AHM, healthy controls) design. The analysis revealed (See Fig. 2) a significant Shape Category-by-Group interaction effect [F (2, 178) = 8.24, p < 0.001, ηp2 = 0.09]. Further simple effects analyses for the healthy controls [F (2, 82) = 25.27, p < 0.001, ηp2 = 0.38] showed no significant difference between self-association and mother-association (p = 0.34), but both were significantly advantageous compared to stranger-association (ps < 0.001). For the AHM group, the simple effects analyses [F (2, 96) = 59.49, p < 0.001, ηp2 = 0.55] revealed a significant self-association advantage over both mother-association (p < 0.001) and stranger-association (p < 0.001), as well as a significant mother-association advantage over stranger-association (p < 0.001). Furthermore, a significant main effect of Shape Category was found [F (2, 178) = 79.91, p < 0.001, ηp2 = 0.47], indicating a self-association advantage over both mother-association (p < 0.001) and stranger-association (p < 0.001), as well as a mother-association advantage over stranger-association (p < 0.001). There was also a marginally significant main effect of Group [F (1, 89) = 3.79, p = 0.055, ηp2 = 0.04], suggesting a faster response in the healthy controls compared to the AHM group.

Table 2 The RT data (s) of participants in different groups under varying matching conditions.
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Fig. 2: Comparison of performance on the self-mother matching task between abstinent heroin misusers (AHM) and healthy controls (HC).
Fig. 2: Comparison of performance on the self-mother matching task between abstinent heroin misusers (AHM) and healthy controls (HC).
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Forty-nine abstinent heroin misusers and forty-two healthy controls completed the self-mother matching task. We first calculated the accuracy rate (ACC) and response time (RT) for different shape categories (self, mother, and stranger) during matched trials for each group. A mixed-model ANOVA was then performed on the RT data, utilizing a 3 (Shape Category: self, mother, stranger) × 2 (Group: AHM, healthy controls) design. Our findings indicate a reduced mother prioritization effect (MPE) in individuals with AHM compared to healthy controls, highlighted by a significant Shape Category-by-Group interaction effect. Further analysis revealed that healthy controls showed no significant difference between self-association and mother-association, but both were significantly better than stranger-association. In contrast, the AHM group exhibited a significant self-association advantage over both mother-association and stranger-association, as well as a significant mother-association advantage over stranger-association (***p < 0.001, **p < 0.01, *p < 0.05).

Our findings indicate a diminished mother prioritization effect (MPE) in individuals with AHM compared to healthy controls. To investigate this further, we analyzed the difference in response times (RTs) between self- and mother-associated stimuli. For each participant, we calculated a difference score (RTmother – RTself); higher scores indicate a smaller MPE relative to the self-prioritization effect. An independent samples t-test comparing these difference scores between the AHM and control groups revealed a significant difference, t (89) = 2.09, p = 0.04. Specifically, the AHM group exhibited a significantly larger difference between self- and mother-associated RTs (M = 0.10, SE = 0.02) than the control group (M = 0.03, SE = 0.02), consistent with a reduced MPE in AHM.

Conclusion

The present study expanded upon previous research in two aspects [25]. Firstly, it reaffirmed the long-lasting self-prioritization effect observed in individuals with substance addiction at the matching level. Secondly, it unveiled the incorporation of significant individuals, such as mothers, into the self-concept of individuals with substance addiction, resulting in a prioritization of their mothers. However, compared to the healthy controls, heroin misusers demonstrated a weakened prioritization of mothers.

Study 2: Self- and mother-prioritization effects in heroin misusers at the memory level

The aim of Study 2 was to replicate and extend the results of Study 1 at the level of memory. We employed a referential memory task [38] where participants rated whether personality trait adjectives can describe the self, the mother, or a familiar other. Following the rating task, participants underwent a recognition test. Our hypothesis was that AHM individuals would continue to demonstrate the self-prioritization effect in the recognition test, showing better memory for adjectives associated with the self compared to other targets. However, we expected the effect of prioritizing the mother to be diminished.

Method

Participants

Similar to Study 1, we utilized G*Power to determine the minimum required sample size, which indicated a need for at least 36 participants per group. To ensure robust data, we recruited 73 male AHM participants (age range: 28–47 years, mean age: 37.74 ± 4.88 years, mean ± SD) from a drug treatment center in a southern province of China. The inclusion and exclusion criteria were the same as in Study 1. As the control group, we enrolled 64 healthy men (age range: 26–49 years, mean age: 37.94 ± 5.54 years) with no history of illicit drug use from the local community. There were no significant differences in age and educational level between the two groups (ps > 0.22).

Consistent with Study 1, all participants were asked to report whether their mother was alive. Among the AHM group, 63 out of 73 participants reported that their mother was alive, while in the healthy control group, 56 out of 64 reported the same. We employed a Chi-square test to compare the data between the two groups and found no significant difference (χ2 = 0.04, p = 0.84).

Materials and procedure

All participants completed a self-mother recognition task, closely following the design of Sui et al. [39]. The primary difference was a reduction in task difficulty. Given the participants’ lower educational attainment, response time constraints during the recognition phase were removed, and only accuracy data were analyzed. The study consisted of the encoding phase and the recognition memory phase. We selected 180 personality trait words, each consisting of two Chinese characters, from established personality trait adjective pools [40], with an equal number of positive and negative words.

During the encoding phase (Fig. 3-left), participants were instructed to determine whether the presented trait-adjective described the self, mother, or a familiar other. Each trial began with a central fixation cross presented for 500 ms, followed by the target-word pair presented for 2000 ms. The target (self, mother, or familiar-other) was presented above the fixation cross, and the adjective was presented below it. The trial ended with a blank screen presented for 2000 ms, during which participants responded. Each reference condition (self, mother, or familiar-other) consisted of 30 trials, with 15 positive and 15 negative words. The word presentation order was counterbalanced across participants.

Fig. 3: Example of the arrays presented in the self-mother reference task.
Fig. 3: Example of the arrays presented in the self-mother reference task.
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All participants completed a self-mother recognition task, which included an encoding phase and a recognition memory phase. During the encoding phase (Fig. 3-left), participants determined whether each presented trait adjective described the self, mother, or a familiar other. In the recognition memory phase (Fig. 3-right), they identified whether each adjective had been previously presented (old/new judgment).

In the recognition memory phase (Fig. 3-right), 90 old words (presented during the encoding phase) and 90 new words (not presented during the self-mother reference phase) were used. Participants were required to identify whether each adjective had been previously presented (old/new judgment). Old and new words were randomly presented. Each trial began with a central fixation cross presented for 500 ms, followed by the presentation of the target stimulus (old or new adjective) on the screen. The target stimulus disappeared as soon as the participant made a response.

Statistical analysis

The objective of this research was to investigate the memory impact under self- and mother-reference conditions; therefore, we focused on the responses in the recognition memory phase. Additionally, given that participants were not required to respond as rapidly as possible in the recognition memory task, only the ACC was analyzed. Initially, the ACC was calculated under various reference conditions (self, mother, and familiar-other). Subsequently, a 3 (Reference Condition: self, mother, familiar-other) × 2 (Group: AHM, healthy controls) mixed-model analysis of variance (ANOVA) was performed, with Reference Condition as the within-subject variable and Group as the between-subject variable.

Results

The mixed-model ANOVA with a 3 (Reference Condition: self, mother, familiar-other) × 2 (Group: AHM, healthy controls) design on the ACC data (refer to Table 3) revealed (See Fig. 4) a significant interaction effect between the Reference Condition and Group [F (2, 270) = 2.43, p = 0.09, ηp2 = 0.02]. Simple effects analyses for the healthy controls [F (2, 126) = 19.72, p < 0.001, ηp2 = 0.24] showed no significant difference between self- and mother-reference effects (p > 0.99) but did find self- and mother-reference effects to be significantly stronger than familiar-other-reference effects (ps < 0.001). For the AHM group, simple effects analyses [F (2, 144) = 18.78, p < 0.001, ηp2 = 0.21] revealed a self-reference advantage over mother- (p = 0.001) and familiar-other-reference (p < 0.001), as well as a mother-reference advantage over familiar-other-reference (p < 0.001). Additionally, there was a significant main effect of the Reference Condition [F (2, 270) = 36.61, p < 0.001, ηp2 = 0.21], reflecting a self-reference advantage over mother-reference (p = 0.02) and familiar-other-reference (p < 0.001), and a mother-reference advantage over familiar-other-reference (p < 0.001). A significant main effect of Group [F (1, 89) = 3.79, p = 0.055, ηp2 = 0.04] was observed, indicating a faster response rate in the healthy controls group compared to the AHM group.

Table 3 ACC data of participants across different groups under varying reference conditions.
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Fig. 4: Comparison of the self-mother memory task performance between abstinent heroin misusers (AHM) and healthy controls (HC).
Fig. 4: Comparison of the self-mother memory task performance between abstinent heroin misusers (AHM) and healthy controls (HC).
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Seventy-three abstinent heroin misusers (AHM) and sixty-four healthy controls completed the self-mother memory task, focusing on responses from the recognition memory phase. Since participants were not required to respond as quickly as possible, only accuracy (ACC) was analyzed. Consistent with Study 1, AHM displayed a reduced mother prioritization effect (MPE) compared to healthy controls. The mixed-model ANOVA, using a 3 (Reference Condition: self, mother, familiar other) × 2 (Group: AHM, healthy controls) design, revealed a significant interaction effect between Reference Condition and Group. Simple effects analyses for healthy controls showed no significant difference between self- and mother-reference effects, but both were significantly stronger than familiar-other-reference effects. In contrast, the AHM group demonstrated a self-reference advantage over both mother- and familiar-other-references, as well as a mother-reference advantage over familiar-other-reference (***p < 0.001, **p < 0.01, *p < 0.05).

Consistent with Study 1, AHM exhibited a diminished MPE compared to healthy controls. To further examine this, we analyzed the difference in ACC between self- and mother-associated stimuli. A difference score (ACCself – ACCmother) was calculated for each participant; higher scores reflect a smaller MPE relative to self-prioritization. An independent samples t-test revealed a significant group difference in these difference scores, t (135) = 2.17, p = 0.03. AHM showed a significantly larger difference in self- versus mother-associated ACC (M = 0.04, SE = 0.01) than the healthy controls (M = 0.01, SE = 0.01), supporting the finding of a reduced MPE in AHM.

Conclusion

Study 2 extended the findings of Study 1, focusing specifically on the memory domain. The results revealed that individuals with heroin addiction exhibited a self-prioritization effect comparable to the healthy controls, whereas the mother-prioritization effect was relatively impaired.

Study 3: The mother-prioritization effect and its clinical significance in AHM

Given the potential impact of drug addiction on the mother-prioritization effect, Study 3 aimed to examine the clinical significance of this effect in individuals with drug addiction. Our hypothesis was that the magnitude of the mother-prioritization effect would be positively correlated with various addiction indicators.

Method

Participants

To maintain a similar level of statistical power as in Study 1, we determined the minimum sample size using G*Power, which suggested a minimum of 36 participants per group. In order to improve robustness of results, we recruited 47 male adults with a history of substance abuse (mean age was 34.89 ± 8.05 years, age range 21–55 years) from a drug treatment center in a southern province of China. The inclusion and exclusion criteria remained consistent with those of Study 1.

Materials and procedure

Similar to Study 1, participants underwent the self-mother matching task, followed by a questionnaire that gathered demographic data (e.g., age, education) and information related to substance abuse. As previously mentioned in Study 1, the detailed experimental procedures are delineated in Section 2.1.2. The substance abuse-related data encompassed the duration of drug use (in years), the frequency of relapses, craving (scored on a 0-100-point scale, with higher scores indicating stronger craving for drugs in the past 30 days), and confidence in abstinence (also scored on a 0-100-point scale, with higher scores indicating greater confidence in remaining abstinent) [25, 41, 42].

Statistical analysis

In a manner similar to Study 1, we computed the accuracy (ACC) and reaction times (RTs) for various shape categories (self, mother, and stranger) within matched trials. Subsequently, a one-way ANOVA was employed to examine the ACC and RTs in matched trials separately, allowing for a comparison of self-, mother-, and stranger-associations. To investigate the potential clinical implications of the mother-prioritization effect, regression analyses were conducted with the mother-prioritization effect serving as the outcome variable and substance abuse-related data acting as predictors.

Results

The one-way ANOVA analysis of the ACC data (please refer to Table 4) showed that there were significant differences in Shape Category [F (2, 92) = 6.44, p = 0.004, and ηp2 = 0.12], reflecting a self-association advantage over the stranger-association (p = 0.007). No other significant differences were found (ps > 0.12).

Table 4 The ACC and RT data of AHM in different groups under varying matching conditions.
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Similarly, the one-way ANOVA analysis of the RT data (please refer to Table 4 and Fig. 5) revealed a significant main effect of Shape Category [F (2, 92) = 28.30, p < 0.001, and ηp2 = 0.38]. This result suggests a self-association advantage over mother- (p = 0.03) and stranger-association (p < 0.001), as well as a mother-association advantage over stranger-association (p < 0.001).

Fig. 5: Performance of the abstinent heroin misusers (AHM) on the self-mother matching task in Study 3.
Fig. 5: Performance of the abstinent heroin misusers (AHM) on the self-mother matching task in Study 3.
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Only AHM completed the self-mother matching task. A one-way ANOVA of the response time (RT) data revealed a significant main effect of Shape Category, indicating a self-association advantage over both mother- and stranger-associations, as well as a mother-association advantage over stranger-association (***p < 0.001, **p < 0.01, *p < 0.05).

To assess the clinical significance of the MPE, we conducted two regression analyses using RT data. First, we examined the relationship between RTs during mother-association and several indices of drug addiction. This analysis yielded a significant change in R2 (ΔR2 = 0.28, p = 0.001). Specifically, longer RTs during mother-related trials were associated with increased relapse frequency (β = 0.30, p = 0.03) and decreased abstinence confidence (β = −0.51, p = 0.001). No significant associations were observed with duration of drug use or craving (ps > 0.11).

Second, to further clarify the clinical implications of the MPE, we performed a second regression analysis using a difference score (RTmother – RTself), with higher scores reflecting a weaker MPE. This difference score served as the dependent variable, and various drug addiction indices served as independent variables. This analysis also showed a significant change in R2 (ΔR2 = 0.14, p = 0.03), demonstrating a negative correlation between the RT difference score and abstinence confidence (β = −0.51, p = 0.003). No significant correlations were found with other drug-related indices (all p > 0.53).

Conclusion

The results of Study 3 replicated the findings of Study 1, indicating that the self-prioritization effect remained consistent among drug addicts, while the mother-prioritization effect demonstrated a relative decline. Moreover, Study 3 accentuates the clinical significance of this attenuated mother-prioritization effect, as a weaker mother-prioritization effect (indexed by longer RT) was associated with higher number of relapses and lower abstinence confidence among drug addicts.

General discussion

Although individuals across various cultures generally prioritize the processing of stimuli related to the self [12, 13, 43], research indicates that East Asians incorporate significant others, such as their mothers, into their self-concept [30,31,32, 39]. Consequently, this population exhibits a notable advantage in processing self- and mother-related information. This study aimed to investigate whether drug addiction could potentially weaken the self- and mother-prioritization effects within the Chinese cultural context. Through three studies, our research revealed a robust self-prioritization effect using the AHM. In contrast, the mother-prioritization effect was found to be attenuated in AHM as compared to healthy controls. Furthermore, the correlations between the mother-prioritization effect and indicators of drug addiction underscore the clinical significance of our findings.

The self-prioritization effect in AHM

Through three experiments, the self-prioritization effect was repeatedly demonstrated to be present in drug addicted individuals. Study 1 and 3 showed that AHM exhibited a robust self-prioritization effect in the matching task, replicating previous studies [25]. Furthermore, the results of Study 2 conceptually replicated the findings of Study 1 at the level of memory. All of these results provided solid support for the presence of the self-prioritization effect in the drug-dependent population comparable to the general population.

Although the current study indicates that drug users prioritize self-related stimuli, it remains unclear whether higher-level functions of self-awareness are impaired in this population. Self-awareness, similar to self-concept, is a complex construct consisting of multiple facets and levels [44]. In addition to basic functions, such as distinguishing oneself from others, self-awareness encompasses higher-level functions like self-monitoring of behavior and evaluation of behavioral outcomes [9]. For instance, higher-level functions of self-awareness, like recognizing the consequences of addictive behavior, significantly correlate with the desire to reduce addictive behavior and could predict subsequent treatment engagement [45,46,47]. The results of this study can only demonstrate that individuals with drug addiction can differentiate between self-related and other-related information, which is a basic function of self-awareness, and they tend to process self-related information more preferentially. However, these results do not necessarily imply that advanced functions of self-awareness are still retained.

The preservation of the self-prioritization effect among drug users holds significant clinical implications for the treatment of drug addiction. For example, this effect ensures that the goals that are most pertinent to the individual receive the utmost priority, thereby contributing to the maintenance of goal-directed behaviors [48]. Future studies could strengthen the link between self and health in the drug-dependent population, aiming to promote healthier behaviors.

The mother-prioritization effect in AHM

Previous studies have indicated that individuals within the East Asian cultural context tend to prioritize information related to the self and mother in a similar manner [31, 32]. Our findings revealed that Chinese AHM displayed an impaired mother-prioritization effect compared to the self-prioritization effect observed in Studies 1 and 3. Furthermore, this pattern was replicated at the memory level in Study 2. Significantly, Study 3 demonstrated the clinical implications of this mother-prioritization effect for drug users.

Maternal absence has been proposed as a potential cause of an impaired mother-prioritization effect, as suggested by studies demonstrating a weaker mother-prioritization effect among older adults who have lost their mothers [30]. However, the AHM group in our study did not exhibit any significant differences compared to the healthy controls in this regard, suggesting the involvement of other factors. One possibility is that drug users experience a lack of harmonious interaction with their mothers, which may contribute to the attenuated effect. This is echoed by research on schizophrenia patients, who also demonstrate impaired mother-prioritization effects and are characterized by emotional indifference and a deficiency in emotional interactions with significant individuals [49].

The weakened mother-prioritization effect observed among individuals with drug addiction suggests that this population may not attribute sufficient self-relevance to their mothers, offering a unique perspective on the clinical implications of drug addiction. This aligns with the hypothesis that addiction arises from an abnormal attribution of significance to stimuli, with drug-related stimuli receiving excessive self-relevance and other salient stimuli (e.g., social connections, health, and job opportunities) receiving inadequate self-relevance [19,20,21, 34]. For instance, previous research revealed a similar advantage in self-processing and drug-processing among individuals with drug addiction at the behavioral level, with a significant correlation between these effects [25]. However, no studies have directly examined how individuals with drug addiction process objects that inherently hold a higher degree of self-relevance. The current study is the first to demonstrate that individuals with drug addiction exhibit a reduced advantage in processing information related to their mothers, potentially due to a diminished sense of self-relevance assigned to significant others. These findings highlight the importance of considering how drug addiction affects information processing and self-relevance attribution, particularly in relation to close social relationships. In addition, these findings may have implications for developing more effective prevention and treatment strategies that focus on enhancing adaptive behavior and strengthening social connections, such as family therapy.

Limitations and future directions

It is crucial to acknowledge potential limitations of our study. First, the generalizability of these findings to female AHM and other drug user populations requires further investigation, given the exclusively male AHM sample in this study. Second, our interpretation of the mother-prioritization effect in relation to self-reported drug use characteristics should be approached with caution. As we did not track these variables over time, we cannot infer causality or rule out alternative explanations for the observed correlations. Longitudinal studies are needed to fully comprehend the underlying mechanisms. Third, our research implies that drug users may allocate less personal relevance to close social relationships. Although our study primarily focused on the mother-prioritization effect, this may be a more general pattern that can also be applied to other significant figures. Future studies should explore this phenomenon more directly, for instance, by investigating brain activity in response to images of significant others using neuroimaging techniques, such as functional magnetic resonance imaging or electroencephalography. Fourth, the cultural applicability of our findings may differ. In contrast to Westerners, individuals from East Asian cultural backgrounds are more likely to process self and mother-related information similarly [50, 51]. It is vital to note that our study focused on Chinese individuals with drug addiction. Thus, future research should explore the generalizability of these findings to individuals from other cultural backgrounds.

Conclusion

The study investigated how drug addiction shapes the processing of self- and mother-related information through a series of experiments. The results indicated that, compared to the general population, individuals struggling with drug addiction exhibited a comparable self-prioritization effect but a reduced mother-prioritization effect. This reduced mother-prioritization effect held clinical significance for addiction. These findings identify a novel target for interventions aimed at strengthening associations between the self and salient stimuli, such as increasing the concern for significant others to mitigate relapse risk. Further research is needed to explore the underlying mechanisms governing the altered processing of emotionally significant events in individuals struggling with addiction, and to examine how this information can be utilized to enhance clinical outcomes.