Impaired proactive control in individuals with methamphetamine use disorder: Evidence from ERPs.

BACKGROUND: Research suggests that methamphetamine use is associated with impaired cognitive control, which may contribute to impulsive drug use. Cognitive control is dynamically mediated by proactive and reactive control (reflecting various processing stages of cognitive control with different properties), and it is crucial to determine whether methamphetamine use impairs proactive and/or reactive control. To address this issue, we conducted an event-related potential (ERP) study to examine proactive and reactive control in individuals with methamphetamine use disorder (MUD). METHODS: Abstinent individuals with MUD (n = 25) and healthy controls (HC, n = 27) completed a cued task-switching task while brain electrical activity was recorded. Cue- and target-locked ERP components modulated by task switching were linked to proactive and reactive control, respectively. RESULTS: No behavioral differences between the groups were found. However, the HC group showed cue-locked switch-positivity (i.e., more positive amplitudes for switch than repeat trials) in both the early and late time windows, although the MUD group only showed late switch-positivity, which was smaller than the HC group. Independent of switch or congruent condition, the MUD group had smaller target-locked positivity than the HC group. CONCLUSIONS: These findings suggest that individuals with MUD exhibit reduced proactive control and mobilize extra reactive control efforts to compensate. Our study contributes to a better understanding of cognitive control impairment in individuals with MUD and has implications for potential interventions.

Reduced response inhibition after exposure to drug-related cues in male heroin abstainers.

RATIONALE: Deficits in response inhibition associated with heroin use could last several months after abstinence in heroin users, and their response inhibition can also be interfered with task-irrelevant drug-related cues. However, it is unclear whether exposure to drug-related cues affects subsequent response inhibition in heroin users following abstinence. OBJECTIVES: The present study aimed to investigate how drug-related cues with different durations between stimulus presentations, referred to as stimulus onset asynchronies (SOAs), affect subsequent response inhibition in heroin abstainers (HAs) with different length of abstinence. METHODS: Sixty-seven male HAs performed a modified Go/NoGo task in which a motor response to frequent Go targets and no response to rare NoGo targets were required and a Go or NoGo target was displayed after either a heroin-related or a neutral picture presented for the 200 ms and 600 ms SOAs. RESULTS: The HAs responded significantly faster to Go targets following the neutral pictures for the 600 ms SOA compared to other conditions. They also made more commission errors following heroin-related pictures compared to neutral pictures regardless of the SOAs. The shorter-term HAs made more commission errors compared to the longer-term HAs following the 200 ms SOA, and it was only a trend when the SOA was 600 ms. Additionally, negative correlations between the duration of current abstinence and commission errors were observed following cues with the 200 ms SOA. CONCLUSIONS: Impaired response inhibition in HAs can be improved through protracted drug abstinence. However, that effect can be reduced by exposure to drug-related cues, which may increase the risk of relapse.

Preferential accumulation of small (<300 µm) microplastics in the sediments of a coastal plain river network in eastern China.

Microplastics are a global concern for their threat to marine ecosystems. Recent studies report a lack of smaller microplastics (<300 µm) in oceans attributed to a "loss in ocean". Several hypotheses have been proposed to explain the absence of smaller microplastics, but their fate and transport remain an enigma. Our study recovered high concentrations of microplastics (32947 ±â€¯15342 items kg-1 dry sediment) from sediments of a coastal plain river network in eastern China, with the <300 µm fraction accounting for ∼85% of total microplastic particles. Microplastic concentrations were generally higher in sediments from tributary streams and streams surrounded by industrial land use. The high variability of microplastics within the watershed indicates that the distribution of microplastics is regulated by several factors, such as distance to source(s), river flow characteristics, buoyancy behavior, degradation, etc. Fragment and foam forms dominated the small microplastics, while fibers were less prevalent in the <300 µm fraction and more abundant in downstream sites. The dominance of small microplastics in riverine sediments in this study provides a possible mechanism to explain the relative absence of small microplastics in the ocean, and advocates for quantification of the whole size spectrum of microplastics in future studies of riverine microplastic fluxes.

Reduction in N2 amplitude in response to deviant drug-related stimuli during a two-choice oddball task in long-term heroin abstainers.

RATIONALE: Chronic heroin use can cause deficits in response inhibition, leading to a loss of control over drug use, particularly in the context of drug-related cues. Unfortunately, heightened incentive salience and motivational bias in response to drug-related cues may exist following abstinence from heroin use. OBJECTIVES: The present study aimed to examine the effect of drug-related cues on response inhibition in long-term heroin abstainers. METHODS: Sixteen long-term (8-24 months) male heroin abstainers and 16 male healthy controls completed a modified two-choice oddball paradigm, in which a neutral "chair" picture served as frequent standard stimuli; the neutral and drug-related pictures served as infrequent deviant stimuli of different conditions respectively. Event-related potentials were compared across groups and conditions. RESULTS: Our results showed that heroin abstainers exhibited smaller N2d amplitude (deviant minus standard) in the drug cue condition compared to the neutral condition, due to smaller drug-cue deviant-N2 amplitude compared to neutral deviant-N2. Moreover, heroin abstainers had smaller N2d amplitude compared with the healthy controls in the drug cue condition, due to the heroin abstainers having reduced deviant-N2 amplitude compared to standard-N2 in the drug cue condition, which reversed in the healthy controls. CONCLUSIONS: Our findings suggested that heroin addicts still show response inhibition deficits specifically for drug-related cues after longer-term abstinence. The inhibition-related N2 modulation for drug-related could be used as a novel electrophysiological index with clinical implications for assessing the risk of relapse and treatment outcome for heroin users.

Effect of drug-related cues on response inhibition through abstinence: A pilot study in male heroin abstainers.

BACKGROUND: Chronic heroin use can cause a deficit of inhibitory function, leading to a loss of control over drug use. Exposure to drug-related cues is considered as one of the contributing factors. However, it is unclear whether there are dynamic changes on the effect of drug-related cues on response inhibition following prolonged abstinence. OBJECTIVE: The present study investigated the effect of drug-related cues on response inhibition in heroin abstainers at different abstinent phases. METHODS: 26 shorter-term (2-6 months) and 26 longer-term (19-24 months) male heroin abstainers performed on a modified two-choice Oddball task, which included two conditions: in the cued condition, neutral pictures served as the background of standard stimuli (yellow frame) and heroin-related pictures served as the background of deviant stimuli (blue frame), reversed in the controlled conditions. RESULTS: Compared to longer-term abstainers, mean reaction time (RT) for drug deviants in shorter-term abstainers was significantly longer. Shorter-term abstainers also showed markedly slower response to neutral deviants relative to drug deviants, but this tendency was not observed in longer-term abstainers. Nevertheless, both groups had similar RT for standard stimuli regardless of their paired background pictures. CONCLUSION: Effect of drug-related cues on response inhibition remains at the early stage of abstinence; however, this effect may be reduced following a longer period of drug abstinence. Our findings highlight the importance of assessing and improving the ability of inhibiting drug-related cue reactivity during treatment.