[Show abstract][Hide abstract]ABSTRACT: Converging evidence suggests that addiction can be considered a disease of aberrant learning and memory with impulsive decision-making. In the past decades, numerous studies have demonstrated that drug addiction is involved in multiple memory systems such as classical conditioned drug memory, instrumental learning memory and the habitual learning memory. However, most of these studies have focused on the contributions of non-declarative memory, and declarative memory has largely been neglected in the research of addiction. Based on a recent finding that hippocampus, as a core functioning region of declarative memory, was proved biased the decision-making process based on past experiences by spreading associated reward values throughout memory. Our present study focused on the hippocampus. By utilizing seed-based network analysis on the resting-state functional MRI datasets with the seed hippocampus we tested how the intrinsic hippocampal memory network altered towards drug addiction, and examined how the functional connectivity strength within the altered hippocampal network correlated with behavioral index 'impulsivity'. Our results demonstrated that HD group showed enhanced coherence between hippocampus which represents declarative memory system and non-declarative reward-guided learning memory system, and also showed attenuated intrinsic functional link between hippocampus and top-down control system, compared to the CN group. This alteration was furthered found to have behavioral significance over the behavioral index 'impulsivity' measured with Barratt Impulsiveness Scale (BIS). These results provide insights into the mechanism of declarative memory underlying the impulsive behavior in drug addiction.
[Show abstract][Hide abstract]ABSTRACT: Neuroimaging methods have been employed to study cue-reactivity-induced neural correlates in the human brain. However, very few studies have focused on characterizing the dynamic neural responses to the factorial interactions between the cues and the subjects. Fifteen right-handed heroin-dependent subjects and 12 age-matched nondrug using subjects participated in this study. Cue-reactivity paradigms were employed, while changes in blood oxygenation level-dependent (BOLD) signals were acquired by functional MRI (fMRI). The fMRI datasets were analyzed with AFNI software and repeated two-way ANOVA was employed for factorial analyses. Neural correlates of factorial interactions between cue-factor and subject-factor were identified in the regions of the ventral tegmental area (VTA), the left and right amygdala, the left and right fusiform cortex, and the precuneus in the mesocorticolimbic system, and in the superior frontal, dorsal lateral prefrontal, and orbitofrontal cortices in the prefrontal cortex system. The neural response patterns in the prefrontal systems are dynamic: decreased response to neutral-cues and increased response to heroin-cues. Further, heroin-cue-induced neural responses within the subregions in the PFC system are significantly intercorrelated. In conclusion, the cue-reactivity paradigms significantly activated the dynamic neural activations in the prefrontal system. It is suggested that the dynamic response patterns in the PFC system characterize the impaired brain control functions in heroin-dependent subjects.
[Show abstract][Hide abstract]ABSTRACT: Heroin, like various illicit substances, has a negative impact on the frontal cognitive function after repeated abuse. We used functional magnetic resonance imaging (fMRI) to examine the neural substrates of response inhibition and competition in 18 healthy controls and assess the frontal neurocognition in 30 abstinent heroin dependents (AHD) as they performed a Go/NoGo Association task with reaction times recorded spontaneously. The neural response which was induced by response inhibition was prominent in the midline structure, specifically the bilateral medial prefrontal gyrus and anterior cingulated cortex, as well as the left middle frontal gyrus, insula, bilateral inferior frontal gyrus and limbic system. Unlike drug-naïve controls, only the bilateral superior frontal gyrus and left middle frontal gyrus were activated in AHD. Furthermore, the RT of AHD was significantly longer than that of controls. The results suggest that: (1) the ACC, mPFC and inferior frontal lobe play an important role in response inhibition and competition; (2) heroin dependents had an impaired response inhibition function that lasted even months into abstinence, which indicates that the negative effect of heroin on the inhibitory function still continues in early protracted withdrawal state.