Prior cocaine self-administration impairs attention signals in anterior cingulate cortex

Antidepressant and anxiolytic effects of activating 5HT2A receptors in the anterior cingulate cortex and the theoretical mechanisms underlying them - A scoping review of available literature

Psychedelic drugs that activate the 5HT2A receptor have long been the target of extensive clinical research, particularly in models of psychiatric illness. The aim of this literature review was to investigate the therapeutic effects of 5HT2A receptor activation in the anterior cingulate cortex (ACC) and the respective mechanisms that underlie them. Based on the available research, I suggest that 5HT2A receptors in the ACC exert profound changes in excitatory neurotransmission and brain network connectivity in a way that reduces anxious preoccupation and obsessional thoughts, as well as promoting cognitive flexibility and long-lasting mood improvements in anhedonia. This is possibly due to a complex interplay with glutamate and gamma-butyric acid neurotransmission, particularly 5HT2A activation enhances α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor signalling, thus altering the ratio of AMPA to N-methyl-D-Aspartate (NMDA) activity in the ACC, which can dismantle previously established neuronal connections and aid the formation of new ones, an effect that may be beneficial for fear extinction and reversal learning. Psychedelics potentially change intra- and internetwork connectivity, strengthening connectivity from the dorsal ACC / Salience Network to the Default Mode Network (DMN) and Central Executive Network (CEN), which correlates with improvements in attentional shifting and anti-anhedonic effects. Additionally, they may decrease inhibitory influence of the DMN over the CEN which may reduce overevaluation of internal states and ameliorate cognitive deficits. Activation of ACC 5HT2A receptors also has important downstream effects on subcortical areas, including reducing amygdala reactivity to threatening stimuli and enhancing mesolimbic dopamine, respectively improving anxiety and the experience of natural rewards.

Anterior cingulate cortex lesions impair multiple facets of task engagement not mediated by dorsomedial striatum neuron firing

The anterior cingulate cortex (ACC) has been implicated across multiple highly specialized cognitive functions-including task engagement, motivation, error detection, attention allocation, value processing, and action selection. Here, we ask if ACC lesions disrupt task performance and firing in dorsomedial striatum (DMS) during the performance of a reward-guided decision-making task that engages many of these cognitive functions. We found that ACC lesions impacted several facets of task performance-including decreasing the initiation and completion of trials, slowing reaction times, and resulting in suboptimal and inaccurate action selection. Reductions in movement times towards the end of behavioral sessions further suggested attenuations in motivation, which paralleled reductions in directional action selection signals in the DMS that were observed later in recording sessions. Surprisingly, however, beyond altered action signals late in sessions-neural correlates in the DMS were largely unaffected, even though behavior was disrupted at multiple levels. We conclude that ACC lesions result in overall deficits in task engagement that impact multiple facets of task performance during our reward-guided decision-making task, which-beyond impacting motivated action signals-arise from dysregulated attentional signals in the ACC and are mediated via downstream targets other than DMS.

Clinical efficacy of deep transcranial magnetic stimulation (dTMS) in psychiatric and cognitive disorders: A systematic review

Deep transcranial magnetic stimulation (dTMS) has gained attention as an enhanced form of traditional TMS, targeting broader and deeper regions of the brain. However, a fulsome synthesis of dTMS efficacy across psychiatric and cognitive disorders using sham-controlled trials is lacking. We systematically reviewed 28 clinical trials comparing active dTMS to a sham/controlled condition to characterize dTMS efficacy across diverse psychiatric and cognitive disorders. A comprehensive search of APA PsycINFO, Cochrane, Embase, Medline, and PubMed databases was conducted. Predominant evidence supports dTMS efficacy in patients with obsessive-compulsive disorder (OCD; n = 2), substance use disorders (SUDs; n = 8), and in those experiencing depressive episodes with major depressive disorder (MDD) or bipolar disorder (BD; n = 6). However, the clinical efficacy of dTMS in psychiatric disorders characterized by hyperactivity or hyperarousal (i.e., attention-deficit/hyperactivity disorder, posttraumatic stress disorder, and schizophrenia) was heterogeneous. Common side effects included headaches and pain/discomfort, with rare but serious adverse events such as seizures and suicidal ideation/attempts. Risk of bias ratings indicated a collectively low risk according to the Grading of Recommendations, Assessment, Development, and Evaluations checklist (Meader et al., 2014). Literature suggests promise for dTMS as a beneficial alternative or add-on treatment for patients who do not respond well to traditional treatment, particularly for depressive episodes, OCD, and SUDs. Mixed evidence and limited clinical trials for other psychiatric and cognitive disorders suggest more extensive research is warranted. Future research should examine the durability of dTMS interventions and identify moderators of clinical efficacy.

Prior cocaine self-administration does not impair the ability to delay gratification in rats during diminishing returns

Previous exposure to drugs of abuse produces impairments in studies of reversal learning, delay discounting and response inhibition tasks. While these studies contribute to the understanding of normal decision-making and how it is impaired by drugs of abuse, they do not fully capture how decision-making impacts the ability to delay gratification for greater long-term benefit. To address this issue, we used a diminishing returns task to study decision-making in rats that had previously self-administered cocaine. This task was designed to test the ability of the rat to choose to delay gratification in the short-term to obtain more reward over the course of the entire behavioral session. Rats were presented with two choices. One choice had a fixed amount of time delay needed to obtain reward [i.e. fixed delay (FD)], while the other choice had a progressive delay (PD) that started at 0 s and progressively increased by 1 s each time the PD option was selected. During the 'reset' variation of the task, rats could choose the FD option to reset the time delay associated with the PD option. Consistent with previous results, we found that prior cocaine exposure reduced rats' overall preference for the PD option in post-task reversal testing during 'no-reset' sessions, suggesting that cocaine exposure made rats more sensitive to the increasing delay of the PD option. Surprisingly, however, we found that rats that had self-administered cocaine 1-month prior, adapted behavior during 'reset' sessions by delaying gratification to obtain more reward in the long run similar to control rats.

Optogenetic Inhibition of Rat Anterior Cingulate Cortex Impairs the Ability to Initiate and Stay on Task

Our prior research has identified neural correlates of cognitive control in the anterior cingulate cortex (ACC), leading us to hypothesize that the ACC is necessary for increasing attention as rats flexibly learn new contingencies during a complex reward-guided decision-making task. Here, we tested this hypothesis by using optogenetics to transiently inhibit the ACC, while rats of either sex performed the same two-choice task. ACC inhibition had a profound impact on behavior that extended beyond deficits in attention during learning when expected outcomes were uncertain. We found that ACC inactivation slowed and reduced the number of trials rats initiated and impaired both their accuracy and their ability to complete sessions. Furthermore, drift-diffusion model analysis suggested that free-choice performance and evidence accumulation (i.e., reduced drift rates) were degraded during initial learning-leading to weaker associations that were more easily overridden in later trial blocks (i.e., stronger bias). Together, these results suggest that in addition to attention-related functions, the ACC contributes to the ability to initiate trials and generally stay on task.

Neural signals implicated in the processing of appetitive and aversive events in social and non-social contexts

In 2014, we participated in a special issue of Frontiers examining the neural processing of appetitive and aversive events. Specifically, we reviewed brain areas that contribute to the encoding of prediction errors and value versus salience, attention and motivation. Further, we described how we disambiguated these cognitive processes and their neural substrates by using paradigms that incorporate both appetitive and aversive stimuli. We described a circuit in which the orbitofrontal cortex (OFC) signals expected value and the basolateral amygdala (BLA) encodes the salience and valence of both appetitive and aversive events. This information is integrated by the nucleus accumbens (NAc) and dopaminergic (DA) signaling in order to generate prediction and prediction error signals, which guide decision-making and learning via the dorsal striatum (DS). Lastly, the anterior cingulate cortex (ACC) is monitoring actions and outcomes, and signals the need to engage attentional control in order to optimize behavioral output. Here, we expand upon this framework, and review our recent work in which within-task manipulations of both appetitive and aversive stimuli allow us to uncover the neural processes that contribute to the detection of outcomes delivered to a conspecific and behaviors in social contexts. Specifically, we discuss the involvement of single-unit firing in the ACC and DA signals in the NAc during the processing of appetitive and aversive events in both social and non-social contexts.

Percentage amplitude of fluctuation and structural covariance changes of subjective cognitive decline in patients: A multimodal imaging study

Back ground

Subjective cognitive decline (SCD) may be the first clinical sign of Alzheimer’s disease (AD). The possible neural mechanisms of SCD are not well known. This study aimed to compare percent amplitude of fluctuation (PerAF) and structural covariance patterns in patients with SCD and healthy controls (HCs).

Methods

We enrolled 53 patients with SCD and 65 HCs. Resting-state functional magnetic resonance imaging (MRI) data and T1-weighted anatomical brain 3.0-T MRI scans were collected. The PerAF approach was applied to distinguish altered brain functions between the two groups. A whole-brain voxel-based morphometry analysis was performed, and all significant regions were selected as regions of interest (ROIs) for the structural covariance analysis. Statistical analysis was performed using two-sample t-tests, and multiple regressions were applied to examine the relationships between neuroimaging findings and clinical symptoms.

Results

Functional MRI results revealed significantly increased PerAF including the right hippocampus (HIPP) and right thalamus (THA) in patients with SCD relative to HCs. Gray matter volume (GMV) results demonstrated decreased GMV in the bilateral ventrolateral prefrontal cortex (vlPFC) and right insula in patients with SCD relative to HCs. Taking these three areas including the bilateral vlPFC and right insula as ROIs, differences were observed in the structural covariance of the ROIs with several regions between the two groups. Additionally, significant correlations were observed between neuroimaging findings and clinical symptoms.

Conclusion

Our study investigated the abnormal PerAF and structural covariance patterns in patients with SCD, which might provide new insights into the pathological mechanisms of SCD.

Attentional function and inhibitory control in different substance use disorders

Attentional function in substance use disorder (SUD) is not well understood. To probe attentional function in SUD as a function of primary substance of abuse, we administered the attentional network task (ANT) to 44 individuals with Cocaine Use Disorder (CoUD), 49 individuals with Cannabis Use Disorder (CaUD), 86 individuals with Opioid Use Disorder (OUD), and 107 controls with no SUD, along with the stop-signal task (SST). The ANT quantifies the effects of (temporal) alerting cues and (spatial) orienting cues to reduce reaction time (RT) to targets, as well as probing how conflicting (target-incongruent) stimuli slow RT. The SST quantifies individuals' ability to inhibit already-initiated motor responses. After controlling for sex representation and age, OUD and CaUD participants showed blunted alerting effects compared to controls, whereas CaUD and CoUD participants showed greater stimulus conflict (flanker) effects. Finally, CoUD participants showed a trend toward increased orienting ability. In SST performance, no SUD group showed a prolonged stop-signal reaction compared to controls. However, the OUD group (and CoUD group at trend level) showed prolonged "go" RT to targets and reduced hit rates. These data indicate differences in attentional function in persons with SUD as a function of the primary substance use.

Overexpressing Histone Deacetylase 5 in Rat Dorsal Striatum Alters Reward-Guided Decision-Making and Associated Neural Encoding

Accumulating evidence in the past decade implicates histone-modifying enzymes, such as class I histone deacetylases (HDACs), in learning and memory and, recently, habit formation. However, it is unclear whether HDACs play roles in complex cognitive function. To address this issue, we examined the role of dorsal striatal HDAC5, a class II HDAC, in reward-guided decision-making and associated neural encoding in rats. We first injected adeno-associated virus to overexpress a nuclear-localized HDAC5 in dorsal striatum (DS). We then recorded neural correlates from dorsolateral striatum (DLS) as rats performed two reward-guided choice tasks, in which we manipulated either the size of or delay to reward. During these tasks, rats first learned which of two options led to the better reward and then reversed those contingencies in a second block of trials. We found that rats with HDAC5 overexpression in DS responded faster and chose higher value reward more often during the first block of trials but were less able to reverse those contingencies in the second block of trials. At the neural level, HDAC5 overexpression in DS elevated and reduced the number of cells in DLS that increased firing to stimuli and reward, respectively, and shifted encoding toward cues that predicted more immediate reward. These results suggest that the HDAC5 overexpression in DS contributes to inflexible decision-making, demonstrating a role of histone-modifying enzymes in complex cognitive function.SIGNIFICANCE STATEMENT HDACs are important for learning and habit formation. Here, we expanded on these functions and found that overexpression of HDAC5 produced faster and more automatic behavior, and related changes in dorsolateral striatal neural firing in rats performing a value-based decision-making task. These results implicate HDAC5 as a potential therapeutic target for psychiatric conditions that impair decision-making and executive function.

Prior Cocaine Exposure Increases Firing to Immediate Reward While Attenuating Cue and Context Signals Related to Reward Value in the Insula

The insula contributes to behavioral control and is disrupted by substance abuse, yet we know little about the neural signals underlying these functions or how they are disrupted after chronic drug self-administration. Here, male and female rats self-administered either cocaine (experimental group) or sucrose (control) for 12 consecutive days. After a 1 month withdrawal period, we recorded from insula while rats performed a previously learned reward-guided decision-making task. Cocaine-exposed rats were more sensitive to value manipulations and were faster to respond. These behavioral changes were accompanied by elevated counts of neurons in the insula that increased firing to reward. These neurons also fired more strongly at the start of long-delay trials, when a more immediate reward would be expected, and fired less strongly in anticipation of the actual delivery of delayed rewards. Although reward-related firing to immediate reward was enhanced after cocaine self-administration, reward-predicting cue and context signals were attenuated. In addition to revealing novel firing patterns unique to insula, our data suggest changes in such neural activity likely contribute to impaired decision making observed after drug use.SIGNIFICANCE STATEMENT The insula plays a clear role in drug addiction and drug-induced impairments of decision making, yet there is little understanding of its underlying neural signals. We found that chronic cocaine self-administration reduces cue and context encoding in insula while enhancing signals related to immediate reward. These changes in neural activity likely contribute to impaired decision making and impulsivity observed after drug use.

Anhydroecgonine methyl ester, a cocaine pyrolysis product, contributes to cocaine-induced rat primary hippocampal neuronal death in a synergistic and time-dependent manner

Crack cocaine users are simultaneously exposed to volatilized cocaine and to its main pyrolysis product, anhydroecgonine methyl ester (AEME). Although the neurotoxic effects of cocaine have been extensively studied, little is known about AEME or its combination. We investigated cell death processes using rat primary hippocampal cells exposed to cocaine (2 mM), AEME (1 mM) and their combination (C + A), after 1, 3, 6 and 12 h. Cocaine increased LC3 I after 6 h and LC3 II after 12 h, but reduced the percentage of cells with acid vesicles, suggesting failure in the autophagic flux, which activated the extrinsic apoptotic pathway after 12 h. AEME neurotoxicity did not involve the autophagic process; rather, it activated caspase-9 after 6 h and caspase-8 after 12 h leading to a high percentage of cells in early apoptosis. C + A progressively reduced the percentage of undamaged cells, starting after 3 h; it activated both apoptotic pathways after 6 h, and was more neurotoxic than cocaine and AEME alone. Also, C + A increased the phosphorylation of p62 after 12 h, but there was little difference in LC3 I or II, and a small percentage of cells with acid vesicles at all time points investigated. In summary, the present study provides new evidence for the neurotoxic mechanism and timing response of each substance alone and in combination, indicating that AEME is more than just a biological marker for crack cocaine consumption, as it may intensify and hasten cocaine neurotoxicity.

Prediction errors and valence: From single units to multidimensional encoding in the amygdala

The amygdala-one of the primary structures of the limbic system-is comprised of interconnected nuclei situated within the temporal lobe. It has a well-established role in the modulation of negative affective states, as well as in fear processing. However, its vast projections with diverse brain regions-ranging from the cortex to the brainstem-are suggestive of its more complex involvement in affective or motivational aspects of cognitive processing. The amygdala can play an invaluable role in context-dependent associative learning, unsigned prediction error learning, influencing outcome selection, and multidimensional encoding. In this review, we delve into the amygdala's role in associative learning and outcome selection, emphasizing its intrinsic involvement in the appropriate context-dependent modulation of motivated behavior.

Anterior cingulate cortex and adaptive control of brain and behavior

Research examining the functional underpinnings of anterior cingulate cortex (ACC) and its relationship to cognitive control have been described as "perennially controversial" and a "Rorschach Test" for modern neuroscience. Although there is near universal agreement that ACC is important for the adaptation of behavior, debate, despite decades of work, stems from the exact manner in which ACC goes about doing this. This chapter provides a brief overview of the various past and present theoretical arguments and research surrounding ACC function, and highlights an emerging literature of single unit ACC recordings from several species that support these theories. We will finish the chapter by focusing on our work examining the firing of single neurons in rat dorsal medial striatum (DMS) and ACC, and examining DMS's dependency on ACC to accurately signal adaptive behavioral output. Ultimately, we will conclude that ACC carries a myriad of signals (error detection, reinforcement/feedback, value, response conflict, etc.) necessary for the modulation of attention and task-relevant/irrelevant signals so that difficult decisions can be made and action plans adapted when necessary.

Anterior Cingulate Cortex Signals Attention in a Social Paradigm that Manipulates Reward and Shock

The ability to recognize emotions in others and adapt one's behavior accordingly is critical for functioning in any social context. This ability is impaired in several psychiatric disorders, such as autism and psychopathy. Recent work has identified the anterior cingulate cortex (ACC) among other brain regions involved in this process. Neural recording studies have shown that neurons in ACC are modulated by reward or shock when delivered to a conspecific and when experienced first-hand. Because previous studies do not vary reward and shock within the same experiment, it has been unclear whether the observed activity reflects how much attention is being paid to outcomes delivered to a conspecific or the valence associated with those stimuli. To address this issue, we recorded from ACC as rats performed a Pavlovian task that predicted whether reward, shock, or nothing would be delivered to the rat being recorded from or a conspecific located in the opposite chamber. Consistent with previous reports, we found that the firing of ACC neurons was modulated by aversive stimuli delivered to the recording rat and their conspecific. Activity of some of these neurons genuinely reflected outcome identity (i.e., reward or shock); however, the population of neurons as a whole responded similarly for both reward and shock, as well as for cues that predicted their occurrence (i.e., reward > neutral and shock > neutral; attention). These results suggest that ACC can process information about outcomes (i.e., identity and recipient) in the service of promoting attention in some social contexts.

In vivo reduction of striatal D1R by RNA interference alters expression of D1R signaling-related proteins and enhances methamphetamine addiction in male rats

This study sought to determine if reducing dopamine D1 receptor (D1R) expression in the dorsal striatum (DS) via RNA-interference alters methamphetamine self-administration. A lentiviral construct containing a short hairpin RNA (shRNA) was used to knock down D1R expression (D1RshRNA). D1RshRNA in male rats increased responding for methamphetamine (i.v.) under a fixed-ratio schedule in an extended access paradigm, compared to D1R-intact rats. D1RshRNA also produced a vertical shift in a dose-response paradigm and enhanced responding for methamphetamine in a progressive-ratio schedule, generating a drug-vulnerable phenotype. D1RshRNA did not alter responding for sucrose (oral) under a fixed-ratio schedule compared to D1R-intact rats. Western blotting confirmed reduced D1R expression in methamphetamine and sucrose D1RshRNA rats. D1RshRNA reduced the expression of PSD-95 and MAPK-1 and increased the expression of dopamine transporter (DAT) in the DS from methamphetamine, but not sucrose rats. Sucrose density gradient fractionation was performed in behavior-naïve controls, D1RshRNA- and D1R-intact rats to determine the subcellular localization of D1Rs, DAT and D1R signaling proteins. D1Rs, DAT, MAPK-1 and PSD-95 predominantly localized to heavy fractions, and the membrane/lipid raft protein caveolin-1 (Cav-1) and flotillin-1 were distributed equally between buoyant and heavy fractions in controls. Methamphetamine increased localization of PSD-95, Cav-1, and flotillin-1 in D1RshRNA and D1R-intact rats to buoyant fractions. Our studies indicate that reduced D1R expression in the DS increases vulnerability to methamphetamine addiction-like behavior, and this is accompanied by striatal alterations in the expression of DAT and D1R signaling proteins and is independent of the subcellular localization of these proteins.