The essential role of primate orbitofrontal cortex in conflict-induced executive control adjustment

Optogenetic Inhibition of the Orbitofrontal Cortex Disrupts Inhibitory Control during Stop-Change Performance in Male Rats

Historically, the orbitofrontal cortex (OFC) has been implicated in a variety of behaviors ranging from reversal learning and inhibitory control to more complex representations of reward value and task space. While modern interpretations of the OFC's function have focused on a role in outcome evaluation, these cognitive processes often require an organism to inhibit a maladaptive response or strategy. Single-unit recordings from the OFC in rats performing a stop-change task show that the OFC responds strongly to STOP trials. To investigate the role that the OFC plays in stop-change performance, we expressed halorhodopsin (eNpHR3.0) in excitatory neurons in the OFC and tested rats on the stop-change task. Previous work suggests that the OFC differentiates between STOP trials based on trial sequence (i.e., gS trials: STOP trials preceded by a GO vs sS trials: STOP trials preceded by a STOP). We found that yellow light activation of the eNpHR3.0-expressing neurons significantly decreased accuracy only on STOP trials that followed GO trials (gS trials). Further, optogenetic inhibition of the OFC speeded reaction times on error trials. This suggests that the OFC plays a role in inhibitory control processes and that this role needs to be accounted for in modern interpretations of OFC function.

Modeling Instantaneous Firing Rate of Deep Brain Stimulation Target Neuronal Ensembles in the Basal Ganglia and Thalamus

OBJECTIVE

Deep brain stimulation (DBS) is an effective treatment for movement disorders, including Parkinson disease and essential tremor. However, the underlying mechanisms of DBS remain elusive. Despite the capability of existing models in interpreting experimental data qualitatively, there are very few unified computational models that quantitatively capture the dynamics of the neuronal activity of varying stimulated nuclei-including subthalamic nucleus (STN), substantia nigra pars reticulata (SNr), and ventral intermediate nucleus (Vim)-across different DBS frequencies.

MATERIALS AND METHODS

Both synthetic and experimental data were used in the model fitting; the synthetic data were generated by an established spiking neuron model that was reported in our previous work, and the experimental data were provided using single-unit microelectrode recordings (MERs) during DBS (microelectrode stimulation). Based on these data, we developed a novel mathematical model to represent the firing rate of neurons receiving DBS, including neurons in STN, SNr, and Vim-across different DBS frequencies. In our model, the DBS pulses were filtered through a synapse model and a nonlinear transfer function to formulate the firing rate variability. For each DBS-targeted nucleus, we fitted a single set of optimal model parameters consistent across varying DBS frequencies.

RESULTS

Our model accurately reproduced the firing rates observed and calculated from both synthetic and experimental data. The optimal model parameters were consistent across different DBS frequencies.

CONCLUSIONS

The result of our model fitting was in agreement with experimental single-unit MER data during DBS. Reproducing neuronal firing rates of different nuclei of the basal ganglia and thalamus during DBS can be helpful to further understand the mechanisms of DBS and to potentially optimize stimulation parameters based on their actual effects on neuronal activity.

Mapping causal links between prefrontal cortical regions and intra-individual behavioral variability

Intra-individual behavioral variability is significantly heightened by aging or neuropsychological disorders, however it is unknown which brain regions are causally linked to such variabilities. We examine response time (RT) variability in 21 macaque monkeys performing a rule-guided decision-making task. In monkeys with selective-bilateral lesions in the anterior cingulate cortex (ACC) or in the dorsolateral prefrontal cortex, cognitive flexibility is impaired, but the RT variability is significantly diminished. Bilateral lesions within the frontopolar cortex or within the mid-dorsolateral prefrontal cortex, has no significant effect on cognitive flexibility or RT variability. In monkeys with lesions in the posterior cingulate cortex, the RT variability significantly increases without any deficit in cognitive flexibility. The effect of lesions in the orbitofrontal cortex (OFC) is unique in that it leads to deficits in cognitive flexibility and a significant increase in RT variability. Our findings indicate remarkable dissociations in contribution of frontal cortical regions to behavioral variability. They suggest that the altered variability in OFC-lesioned monkeys is related to deficits in assessing and accumulating evidence to inform a rule-guided decision, whereas in ACC-lesioned monkeys it results from a non-adaptive decrease in decision threshold and consequently immature impulsive responses.

Cross-sectional associations between sedentary time with cognitive engagement and brain volume among community-dwelling vulnerable older adults

AIMS

Vulnerable older adults tend to decrease physical activity (PA) and increase sedentary time (ST). Previous research on the associations between ST and brain volume have yielded inconsistent findings, without considering the impact of cognitive engagement (CE) on cognitive function. We aimed to examine the association between ST with CE and brain volume.

METHODS

A structural magnetic resonance imaging survey was conducted among community-dwelling vulnerable older adults. Brain volumetric measurements were obtained using 3T magnetic resonance imaging and pre-processed using FreeSurfer. ST with low or high CE was assessed using a 12-item questionnaire. PA was assessed by the frequency of light and moderate levels of physical exercise according to the Japanese version of the Cardiovascular Health Study criteria. Participants were categorized into a low PA group and a moderate-to-high PA group.

RESULTS

Among 91 participants (83.1 ± 5.2 years old, 61.5% female), 26 were low PA. The overall sample and moderate-to-high PA group did not show significant positive associations with brain volume for ST with high CE. In the low PA group, isotemporal substitution models showed that replacing ST with low CE by ST with high CE was significantly associated with increased brain volume in some areas, including the rostral and caudal anterior cingulate (β = 0.486-0.618, all P < 0.05, adjusted R2  = 0.344-0.663).

CONCLUSIONS

Our findings suggest that replacing ST with low CE by ST with high CE is positively associated with brain volume in vulnerable older adults with low PA. Geriatr Gerontol Int 2024; 24: 82-89.

Altered White Matter Network Topology in Panic Disorder

Panic disorder (PD) is an anxiety disorder that impairs life quality and social function and is associated with distributed brain regions. However, the alteration of the structural network remains unclear in PD patients. This study explored the specific characteristics of the structural brain network in patients with PD by graph theory analysis of diffusion tensor images (DTI). A total of 81 PD patients and 48 matched healthy controls were recruited for this study. The structural networks were constructed, and the network topological properties for individuals were estimated. At the global level, the network efficiency was higher, while the shortest path length and clustering coefficient were lower in the PD group compared to the healthy control (HC) group. At the nodal level, the PD group showed a widespread higher nodal efficiency and lower average shortest path length in the prefrontal, sensorimotor, limbic, insula, and cerebellum regions. Overall, the current results showed that the alteration of information processing in the fear network might play a role in the pathophysiology of PD.

The marmoset as a model for investigating the neural basis of social cognition in health and disease

Social-cognitive processes facilitate the use of environmental cues to understand others, and to be understood by others. Animal models provide vital insights into the neural underpinning of social behaviours. To understand social cognition at even deeper behavioural, cognitive, neural, and molecular levels, we need to develop more representative study models, which allow testing of novel hypotheses using human-relevant cognitive tasks. Due to their cooperative breeding system and relatively small size, common marmosets (Callithrix jacchus) offer a promising translational model for such endeavours. In addition to having social behavioural patterns and group dynamics analogous to those of humans, marmosets have cortical brain areas relevant for the mechanistic analysis of human social cognition, albeit in simplified form. Thus, they are likely suitable animal models for deciphering the physiological processes, connectivity and molecular mechanisms supporting advanced cognitive functions. Here, we review findings emerging from marmoset social and behavioural studies, which have already provided significant insights into executive, motivational, social, and emotional dysfunction associated with neurological and psychiatric disorders.

Dynamic interaction between hippocampus, orbitofrontal cortex, and subthalamic nucleus during goal conflict in the stop signal task in rats

Action stopping depends on at least two (fast, slow) frontal circuits depending on the urgency of execution of the 'go' response. Human EEG suggests a third (even slower, limbic) circuit that activates frontal areas at frequencies typical of 'hippocampal theta'. Here we test in male rats whether stop-go conflict engages the hippocampus and so may send theta-modulated information via the frontal cortex to the subthalamic nucleus. We recorded from multi-electrode arrays in the hippocampus, orbitofrontal cortex, and subthalamus in 5 male Long Evans rats performing a stop signal task and, as in previous human experiments, assessed stop-signal specific power for effects of goal conflict. Conflict increased 11-12 Hz theta power modestly in all three structures but with the largest increase in power being at 5 Hz in the frontal cortex but not the hippocampus. There was increased conflict-related coherence in all circuits in the range 5-8 Hz and particularly at 5-6 Hz. Increased coherence coupled with an increase in conflict-induced low frequency power in the frontal cortex may reflect communication with the hippocampus. The data are consistent with a third limbic circuit that can generate stopping when go responses are particularly slow (as, e.g., in a go/no go task). [199 words; 200 max].

Dimension of visual information interacts with working memory in monkeys and humans

Humans demonstrate behavioural advantages (biases) towards particular dimensions (colour or shape of visual objects), but such biases are significantly altered in neuropsychological disorders. Recent studies have shown that lesions in the prefrontal cortex do not abolish dimensional biases, and therefore suggest that such biases might not depend on top-down prefrontal-mediated attention and instead emerge as bottom-up processing advantages. We hypothesised that if dimensional biases merely emerge from an enhancement of object features, the presence of visual objects would be necessary for the manifestation of dimensional biases. In a specifically-designed working memory task, in which macaque monkeys and humans performed matching based on the object memory rather than the actual object, we found significant dimensional biases in both species, which appeared as a shorter response time and higher accuracy in the preferred dimension (colour and shape dimension in humans and monkeys, respectively). Moreover, the mnemonic demands of the task influenced the magnitude of dimensional bias. Our findings in two primate species indicate that the dichotomy of top-down and bottom-up processing does not fully explain the emergence of dimensional biases. Instead, dimensional biases may emerge when processed information regarding visual object features interact with mnemonic and executive functions to guide goal-directed behaviour.

The neural substrate and underlying mechanisms of executive control fluctuations in primates

Trial-by-trial alterations in response time have been linked to fluctuations of executive control and transient lapses of attention. Here, we report remarkable homologies in performance-dependent fluctuations of response time between humans and monkeys. We examined the effects of selective bilateral lesions in four frontal regions on control fluctuations in the context of a rule-shifting task. Lesions within orbitofrontal cortex (OFC), but not within superior-lateral prefrontal cortex, significantly exaggerated the performance-dependent fluctuations of control and prevented its restoration following feedback. Lesions within dorsolateral prefrontal cortex (DLPFC) or within anterior-cingulate cortex (ACC) led to instability of control and disruption of its link with monkeys' upcoming decisions. Examining the activity of DLPFC and OFC cells shed more lights on the underlying neuronal mechanisms by showing that before the start of each trial, OFC cell activity conveyed detailed information regarding the current state of executive control and the likelihood of success or failure in the future decisions. This further emphasizes the crucial role of OFC in the trial-by-trial allocation (setting) of control to the ongoing task. These findings bring insights to the neural architecture of executive control in primates and suggest that DLPFC and ACC support sustained executive control, but OFC is more involved in setting and restoring the control.

Foraging with the frontal cortex: A cross-species evaluation of reward-guided behavior

Efficient foraging is essential to survival and depends on frontal cortex in mammals. Because of its role in psychiatric disorders, frontal cortex and its contributions to reward procurement have been studied extensively in both rodents and non-human primates. How frontal cortex of these animal models compares is a source of intense debate. Here we argue that translating findings from rodents to non-human primates requires an appreciation of both the niche in which each animal forages as well as the similarities in frontal cortex anatomy and function. Consequently, we highlight similarities and differences in behavior and anatomy, before focusing on points of convergence in how parts of frontal cortex contribute to distinct aspects of foraging in rats and macaques, more specifically. In doing so, our aim is to emphasize where translation of frontal cortex function between species is clearer, where there is divergence, and where future work should focus. We finish by highlighting aspects of foraging for which have received less attention but we believe are critical to uncovering how frontal cortex promotes survival in each species.

Electrolytic lesions of the bilateral ventrolateral orbital cortex not only directly reduce depression-like behavior but also decreased desperate behavior induced by chronic unpredicted mild stress in rats

BACKGROUND

Previous studies have revealed that ventrolateral orbital cortex (VLO) may play an important role in the regulation of emotional behavior. However, it is not known what effect VLO damage will have on emotion regulation.

RESULTS

Data showed that damage of VLO increased the anxiety-like behavior in open field test and elevated plus maze, and decreased the depressive behavior in forced swimming test and learned helplessness test. Besides, the impulsive aggressive behaviors were also increased while the attack latency decreased after VLO lesion. What's more, damage of VLO decreased depressive behaviors induced by chronic unpredicted mild stress in rats.

CONCLUSIONS

These results suggest that the integrity of VLO plays an important role in emotional regulation, and the damage of VLO may inhibit the development of depression-like behavior.

Processing of Task-Irrelevant Race Information is Associated with Diminished Cognitive Control in Black and White Individuals

The race of an individual is a salient physical feature that is rapidly processed by the brain and can bias our perceptions of others. How the race of others explicitly impacts our actions toward them during intergroup contexts is not well understood. In the current study, we examined how task-irrelevant race information influences cognitive control in a go/no-go task in a community sample of Black (n = 54) and White (n = 51) participants. We examined the neural correlates of behavioral effects using functional magnetic resonance imaging and explored the influence of implicit racial attitudes on brain-behavior associations. Both Black and White participants showed more cognitive control failures, as indexed by dprime, to Black versus White faces, despite the irrelevance of race to the task demands. This behavioral pattern was paralleled by greater activity to Black faces in the fusiform face area, implicated in processing face and in-group information, and lateral orbitofrontal cortex, associated with resolving stimulus-response conflict. Exploratory brain-behavior associations suggest different patterns in Black and White individuals. Black participants exhibited a negative association between fusiform activity and response time during impulsive errors to Black faces, whereas White participants showed a positive association between lateral OFC activity and cognitive control performance to Black faces when accounting for implicit racial associations. Together our findings propose that attention to race information is associated with diminished cognitive control that may be driven by different mechanisms for Black and White individuals.

Reactive and Proactive Adaptation of Cognitive and Motor Neural Signals during Performance of a Stop-Change Task

The ability to inhibit or suppress unwanted or inappropriate actions, is an essential component of executive function and cognitive health. The immense selective pressure placed on maintaining inhibitory control processes is exemplified by the relatively small number of instances in which these systems completely fail in the average person's daily life. Although mistakes and errors do inevitably occur, inhibitory control systems not only ensure that this number is low, but have also adapted behavioral strategies to minimize future failures. The ability of our brains to adapt our behavior and appropriately engage proper motor responses is traditionally depicted as the primary domain of frontal brain areas, despite evidence to the fact that numerous other brain areas contribute. Using the stop-signal task as a common ground for comparison, we review a large body of literature investigating inhibitory control processes across frontal, temporal, and midbrain structures, focusing on our recent work in rodents, in an effort to understand how the brain biases action selection and adapts to the experience of conflict.

Neural substrate and underlying mechanisms of working memory: insights from brain stimulation studies

The concept of working memory refers to a collection of cognitive abilities and processes involved in the short-term storage of task-relevant information to guide the ongoing and upcoming behavior and therefore describes an important aspect of executive control of behavior for achieving goals. Deficits in working memory and related cognitive abilities have been observed in patients with brain damage or neuropsychological disorders and therefore it is important to better understand neural substrate and underlying mechanisms of working memory. Working memory relies on neural mechanisms that enable encoding, maintenance, and manipulation of stored information as well as integrating them with ongoing and future goals. Recently, a surge in brain stimulation studies have led to development of various noninvasive techniques for localized stimulation of prefrontal and other cortical regions in humans. These brain stimulation techniques can potentially be tailored to influence neural activities in particular brain regions and modulate cognitive functions and behavior. Combined use of brain stimulation with neuroimaging and electrophysiological recording have provided a great opportunity to monitor neural activity in various brain regions and noninvasively intervene and modulate cognitive functions in cognitive tasks. These studies have shed more light on the neural substrate and underlying mechanisms of working memory in humans. Here, we review findings and insight from these brain stimulation studies about the contribution of brain regions, and particularly prefrontal cortex, to working memory.

The Role of Primate Prefrontal Cortex in Bias and Shift Between Visual Dimensions

Imaging and neural activity recording studies have shown activation in the primate prefrontal cortex when shifting attention between visual dimensions is necessary to achieve goals. A fundamental unanswered question is whether representations of these dimensions emerge from top-down attentional processes mediated by prefrontal regions or from bottom-up processes within visual cortical regions. We hypothesized a causative link between prefrontal cortical regions and dimension-based behavior. In large cohorts of humans and macaque monkeys, performing the same attention shifting task, we found that both species successfully shifted between visual dimensions, but both species also showed a significant behavioral advantage/bias to a particular dimension; however, these biases were in opposite directions in humans (bias to color) versus monkeys (bias to shape). Monkeys' bias remained after selective bilateral lesions within the anterior cingulate cortex (ACC), frontopolar cortex, dorsolateral prefrontal cortex (DLPFC), orbitofrontal cortex (OFC), or superior, lateral prefrontal cortex. However, lesions within certain regions (ACC, DLPFC, or OFC) impaired monkeys' ability to shift between these dimensions. We conclude that goal-directed processing of a particular dimension for the executive control of behavior depends on the integrity of prefrontal cortex; however, representation of competing dimensions and bias toward them does not depend on top-down prefrontal-mediated processes.

Dimensional bias and adaptive adjustments in inhibitory control of monkeys

Humans and macaque monkeys, performing a Wisconsin Card Sorting Test (WCST), show a significant behavioral bias to a particular sensory dimension (e.g. color or shape); however, lesions in prefrontal cortical regions do not abolish the dimensional biases in monkeys and, therefore, it has been proposed that these biases emerge in earlier stages of visual information processing. It remains unclear whether such dimensional biases are unique to the WCST, in which attention-shifting between dimensions are required, or affect other aspects of executive functions such as 'response inhibition' and 'error-induced behavioral adjustments'. To address this question, we trained six monkeys (Macaca mulatta) to perform a stop-signal task in which they had to inhibit their response when an instruction for inhibition was given by changing the color or shape of a visual stimulus. Stop Signal Reaction Time (SSRT) is an index of inhibitory processes. In all monkeys, SSRT was significantly shorter, and the probability of a successful inhibition was significantly higher, when a change in the shape dimension acted as the stop-cue. Humans show a response slowing following a failure in response inhibition and also adapt a proactive slowing after facing demands for response inhibition. We found such adaptive behavioral adjustments, with the same pattern, in monkeys' behavior; however, the dimensional bias did not modulate them. Our findings, showing dimensional bias in monkey, with the same pattern, in two different executive control tasks support the hypothesis that the bias to shape dimension emerges in early stages of visual information processing.

A systematic review and meta-analysis of behavioural sex differences in executive control

Literature investigating whether an individuals' sex affects their executive control abilities and performance on cognitive tasks in a normative population has been contradictory and inconclusive. Using meta-analytic procedures (abiding by PRISMA guidelines), this study attempts to identify the magnitude of behavioural sex differences in three prominent executive control domains of cognitive set-shifting, performance monitoring, and response inhibition. PubMed, Web of Science, and Scopus were systematically searched. Across 46 included studies, a total of 1988 females and 1884 males were included in the analysis. Overall, males and females did not differ on performance in any of the three domains of performance monitoring, response inhibition, or cognitive set-shifting. Task-specific sex differences were observed in the domains of performance monitoring, in the CANTAB Spatial Working Memory task-males scored statistically higher than females (Hedges' g = -0.60), and response inhibition, in the Delay Discounting task-females scored statistically higher than males (Hedges' g = 0.64). While the meta-analysis did not detect overall behavioural sex differences in executive control, significant heterogeneity and task-specific sex differences were found. To further understand sex differences within these specific tasks and domains, future research must better control for age and sex hormone levels.

The ever-changing OFC landscape: What neural signals in OFC can tell us about inhibitory control

Despite decades of research on OFC function, the exact function(s) of OFC remain elusive. In recent years, 1 of the earliest hypotheses about OFC function, namely its involvement in inhibitory control, has drifted to the periphery of the functional OFC landscape in favor of theories suggesting a role for OFC in the representation of task or state space. The reasons for this drift are valid, owing in part to the development of more sensitive behavioral approaches, a clear emphasis on cross-species and cross-method comparisons, as well as the elegant integration of reinforcement learning theories. However, recent evidence recording from OFC during the performance of traditional inhibitory control tasks has found new evidence supporting a role for OFC in inhibitory control. While the extent to which these findings can be integrated into existing frameworks is in its infancy, this review seeks to highlight these findings with the goal of providing new insights into function of OFC. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Activity in orbitofrontal neuronal ensembles reflects inhibitory control

Stopping, or inhibition, is a form of self-control that is a core element of flexible and adaptive behavior. Its neural origins remain unclear. Some views hold that inhibition decisions reflect the aggregation of widespread and diverse pieces of information, including information arising in ostensible core reward regions (i.e., outside the canonical executive system). We recorded activity of single neurons in the orbitofrontal cortex (OFC) of macaques, a region associated with economic decisions, and whose role in inhibition is debated. Subjects performed a classic inhibition task known as the stop signal task. Ensemble decoding analyses reveal a clear firing rate pattern that distinguishes successful from failed inhibition and that begins after the stop signal and before the stop signal reaction time (SSRT). We also found a different and orthogonal ensemble pattern that distinguishes successful from failed stopping before the beginning of the trial. These signals were distinct from, and orthogonal to, value encoding, which was also observed in these neurons. The timing of the early and late signals was, respectively, consistent with the idea that neuronal activity in OFC encodes inhibition both proactively and reactively.

Withdrawal from escalated cocaine self-administration impairs reversal learning by disrupting the effects of negative feedback on reward exploitation: a behavioral and computational analysis

Addiction is regarded as a disorder of inflexible choice with behavior dominated by immediate positive rewards over longer-term negative outcomes. However, the psychological mechanisms underlying the effects of self-administered drugs on behavioral flexibility are not well understood. To investigate whether drug exposure causes asymmetric effects on positive and negative outcomes we used a reversal learning procedure to assess how reward contingencies are utilized to guide behavior in rats previously exposed to intravenous cocaine self-administration (SA). Twenty-four rats were screened for anxiety in an open field prior to acquisition of cocaine SA over six daily sessions with subsequent long-access cocaine SA for 7 days. Control rats (n = 24) were trained to lever-press for food under a yoked schedule of reinforcement. Higher rates of cocaine SA were predicted by increased anxiety and preceded impaired reversal learning, expressed by a decrease in lose-shift as opposed to win-stay probability. A model-free reinforcement learning algorithm revealed that rats with high, but not low cocaine escalation failed to exploit previous reward learning and were more likely to repeat the same response as the previous trial. Eight-day withdrawal from high cocaine escalation was associated, respectively, with increased and decreased dopamine receptor D2 (DRD2) and serotonin receptor 2C (HTR2C) expression in the ventral striatum compared with controls. Dopamine receptor D1 (DRD1) expression was also significantly reduced in the orbitofrontal cortex of high cocaine-escalating rats. These findings indicate that withdrawal from escalated cocaine SA disrupts how negative feedback is used to guide goal-directed behavior for natural reinforcers and that trait anxiety may be a latent variable underlying this interaction.

Negative Emotional Stimuli Enhance Conflict Resolution Without Altering Arousal

In our daily life, we frequently need to make decisions between competing behavioral options while we are exposed to various contextual factors containing emotional/social information. We examined how changes in emotional/arousal state influence resolving conflict between behavioral rules. Visual stimuli with emotional content (positive, negative and neutral) and music (High/Low tempo), which could potentially alter emotional/arousal states, were included in the task context while participants performed the Wisconsin Card Sorting Test (WCST). The WCST requires the application of abstract matching rules, to resolve conflict between competing behavioral options. We found that conflict influenced both accuracy and response time (RT) in implementing rules. Measuring event-related autonomic responses indicated that these behavioral effects were accompanied by concomitant alterations in arousal levels. Performance in the WCST was modulated by the emotional content of visual stimuli and appeared as a faster response and higher accuracy when trials commenced with negative emotional stimuli. These effects were dependent on the level of conflict but were not accompanied by changes in arousal levels. Here, we report that visual stimuli with emotional content influence conflict processing without trial-by-trial changes in arousal level. Our findings indicate intricate interactions between emotional context and various aspects of executive control such as conflict resolution and suggest that these interactions are not necessarily mediated through alterations in arousal level.

Context-Dependent Adjustments in Executive Control of Goal-Directed Behaviour: Contribution of Frontal Brain Areas to Conflict-Induced Behavioural Adjustments in Primates

Psychophysical studies in humans indicate that the performance in various tasks is affected by contextual factors such as conflict level and error commission. It is generally believed that contextual factors influence the executive control processes and consequently modulate ongoing behaviour. Imaging studies suggest that dorsolateral prefrontal cortex and anterior cingulate cortex play crucial roles in mediating these context-dependent adjustments in executive control of behaviour. However, the underlying neuronal processes are to a great extent unknown. Recent studies in non-human primates indicate great similarities in conflict-induced behavioural adjustments between humans and macaque monkeys. Animal models have provided the opportunity to conduct various detailed neurobiological techniques to reveal the neural underpinning of conflict-induced behavioural modulations. In this chapter, we review the latest findings in humans and non-human primate models regarding the neural substrate and underlying mechanisms of conflict-dependent executive control adjustments.

The impact of drugs of abuse on executive function: characterizing long-term changes in neural correlates following chronic drug exposure and withdrawal in rats

Addiction has long been characterized by diminished executive function, control, and impulsivity management. In particular, these deficits often manifest themselves as impairments in reversal learning, delay discounting, and response inhibition. Understanding the neurobiological substrates of these behavioral deficits is of paramount importance to our understanding of addiction. Within the cycle of addiction, periods during and after withdrawal represent a particularly difficult point of intervention in that the negative physical symptoms associated with drug removal and drug craving increase the likelihood that the patient will relapse and return to drug use in order to abate these symptoms. Moreover, it is often during this time that drug induced deficits in executive function hinder the ability of the patient to refrain from drug use. Thus, it is necessary to understand the physiological and behavioral changes associated with withdrawal and drug craving-largely manifesting as deficits in executive control-to develop more effective treatment strategies. In this review, we address the long-term impact that drugs of abuse have on the behavioral and neural correlates that give rise to executive control as measured by reversal learning, delay discounting, and stop-signal tasks, focusing particularly on our work using rats as a model system.

Distinct Roles for the Anterior Cingulate and Dorsolateral Prefrontal Cortices During Conflict Between Abstract Rules

Distinct patterns of activity within the anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (dlPFC) reported in neuroimaging studies during tasks involving conflict between competing responses have often been cited as evidence for their key contributions to conflict-monitoring and behavioral adaptation, respectively. However, supporting evidence from neuropsychological patients has been scarce and contradictory. We administered a well-studied analog of the Wisconsin Card Sorting Test, designed to elicit conflict between 2 abstract rules, to a cohort of 6 patients with damage to ACC or dlPFC. Patients who had sustained more significant damage to the ACC were not impaired either on a measure of "conflict cost" nor on measures of "conflict-induced behavioral adaptation." In contrast, damage to dlPFC did not affect the conflict cost measure but abolished the patients' ability to adapt their behavior following exposure to conflict, compared with controls. This pattern of results complements the findings from nonhuman primates with more circumscribed lesions to ACC or dlPFC on the same task and provides converging evidence that ACC is not necessary for performance when conflict is elicited between 2 abstract rules, whereas dlPFC plays a fundamental role in behavioral adaptation.

Interactive effects of music and prefrontal cortex stimulation in modulating response inhibition

Influential hypotheses propose that alterations in emotional state influence decision processes and executive control of behavior. Both music and transcranial direct current stimulation (tDCS) of prefrontal cortex affect emotional state, however interactive effects of music and tDCS on executive functions remain unknown. Learning to inhibit inappropriate responses is an important aspect of executive control which is guided by assessing the decision outcomes such as errors. We found that high-tempo music, but not low-tempo music or low-level noise, significantly influenced learning and implementation of inhibitory control. In addition, a brief period of tDCS over prefrontal cortex specifically interacted with high-tempo music and altered its effects on executive functions. Measuring event-related autonomic and arousal response of participants indicated that exposure to task demands and practice led to a decline in arousal response to the decision outcome and high-tempo music enhanced such practice-related processes. However, tDCS specifically moderated the high-tempo music effect on the arousal response to errors and concomitantly restored learning and improvement in executive functions. Here, we show that tDCS and music interactively influence the learning and implementation of inhibitory control. Our findings indicate that alterations in the arousal-emotional response to the decision outcome might underlie these interactive effects.

Functional Heterogeneity within Rat Orbitofrontal Cortex in Reward Learning and Decision Making

Rat orbitofrontal cortex (OFC) is located in the dorsal bank of the rhinal sulcus, and is divided into the medial orbital area, ventral orbital area, ventrolateral orbital area, lateral orbital area, dorsolateral orbital area, and agranular insular areas. Over the past 20 years, there has been a marked increase in the number of publications focused on the functions of rat OFC. While collectively this extensive body of work has provided great insight into the functions of OFC, leading to theoretical and computational models of its functions, one issue that has emerged relates to what is defined as OFC because targeting of this region can be quite variable between studies of appetitive behavior, even within the same species. Also apparent is that there is an oversampling and undersampling of certain subregions of rat OFC for study, and this will be demonstrated here. The intent of the Viewpoint is to summarize studies in rat OFC, given the diversity of what groups refer to as "OFC," and to integrate these with the findings of recent anatomical studies. The primary aim is to help discern functions in reward learning and decision-making, clearing the course for future empirical work.

Control without Controllers: Toward a Distributed Neuroscience of Executive Control

Executive control refers to the regulation of cognition and behavior by mental processes and is a hallmark of higher cognition. Most approaches to understanding its mechanisms begin with the assumption that our brains have anatomically segregated and functionally specialized control modules. The modular approach is intuitive: Control is conceptually distinct from basic mental processing, so an organization that reifies that distinction makes sense. An alternative approach sees executive control as self-organizing principles of a distributed organization. In distributed systems, control and controlled processes are colocalized within large numbers of dispersed computational agents. Control then is often an emergent consequence of simple rules governing the interaction between agents. Because these systems are unfamiliar and unintuitive, here we review several well-understood examples of distributed control systems, group living insects and social animals, and emphasize their parallels with neural systems. We then reexamine the cognitive neuroscience literature on executive control for evidence that its neural control systems may be distributed.

Neuronal responses support a role for orbitofrontal cortex in cognitive set reconfiguration

We are often faced with the need to abandon no-longer beneficial rules and adopt new ones. This process, known as cognitive set reconfiguration, is a hallmark of executive control. Although cognitive functions like reconfiguration are most often associated with dorsal prefrontal structures, recent evidence suggests that the orbitofrontal cortex (OFC) may play an important role as well. We recorded the activity of OFC neurons while rhesus macaques performed an analogue of the Wisconsin Card Sorting Task that involved a trial and error stage. The OFC neurons demonstrated two types of switch-related activity, an early (switch-away) signal and a late (switch-to) signal, when the new task set was established. We also found a pattern of match modulation: a significant change in activity for the stimulus that matched the current perceptual rule (and would therefore be selected). These results extend our understanding of the executive functions of the OFC. They also allow us to directly compare the OFC with the complementary datasets we previously collected in the ventral (VS) and dorsal (DS) striatum. Although both effects are observed in all three areas, the timing of responses aligns the OFC more closely with DS than with VS.

A distributed, hierarchical and recurrent framework for reward-based choice

Many accounts of reward-based choice argue for distinct component processes that are serial and functionally localized. In this Opinion article, we argue for an alternative viewpoint, in which choices emerge from repeated computations that are distributed across many brain regions. We emphasize how several features of neuroanatomy may support the implementation of choice, including mutual inhibition in recurrent neural networks and the hierarchical organization of timescales for information processing across the cortex. This account also suggests that certain correlates of value are emergent rather than represented explicitly in the brain.

Transcranial magnetic stimulation to dorsolateral prefrontal cortex affects conflict-induced behavioural adaptation in a Wisconsin Card Sorting Test analogue

A substantial body of literature has proposed a role for dorsolateral prefrontal cortex (dlPFC) in supporting behavioural adaptation during conflict tasks. The vast majority of the evidence in support of this interpretation comes from neuroimaging studies. However, in order to unequivocally ascribe such a role to dlPFC, it is important to determine whether or not it is essential for this mechanism, and this can only be achieved by lesioning the area or interfering with its activity. In this study, we investigated the effects of repeated Transcranial Magnetic Stimulation (rTMS) to dlPFC on performance on a conflict version of a Wisconsin Card Sorting Test analogue (used previously in circumscribed lesion studies in monkeys) in neurologically healthy human participants. Our results supported the view of dlPFC as a fundamental structure for optimal conflict-induced behavioural adaptation, as stimulation cancelled out the adaptation effect normally observed on control trials. We show that there is some indication of differential modulation of trial types by stimulation and we hypothesize that this might suggest a role for dlPFC in conflict-induced adaptation that is more specifically concerned with the maintenance of conflict-history information online across trials.

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Dorsolateral prefrontal cortex stimulation abolishes conflict-induced adaptation.

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Adaptation is abolished via differential modulation of trial types.

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Dorsolateral prefrontal areas may aid adaptation via conflict history maintenance.

Imbalanced Activity in the Orbitofrontal Cortex and Nucleus Accumbens Impairs Behavioral Inhibition

Contemporary models of behavioral regulation maintain that balanced activity between cognitive control areas (prefrontal cortex, PFC) and subcortical reward-related regions (nucleus accumbens, NAC) mediates the selection of appropriate behavioral responses, whereas imbalanced activity (PFC < NAC) results in maladaptive behavior [1-6]. Imbalance can arise from reduced engagement of PFC (via fatigue or stress [7]) or from excessive activity in NAC [8]. Additionally, a concept far less researched is that an imbalance can result from simultaneously low PFC activity and high NAC activity. This occurs during adolescence, when the maturation of PFC lags behind that of NAC and NAC is more functionally active compared to adulthood or pre-adolescence [2, 5, 9, 10]. Accordingly, activity is disproportionately higher in NAC than in PFC, which may contribute to impulsivity and risk-taking exhibited by adolescents [5, 6, 10-12]. Despite having explanatory value, support for this notion has been solely correlational. Here, we causally tested this using chemogenetics to simultaneously decrease neural activity in the orbitofrontal cortex (OFC) and increase activity in NAC in adult rats, mimicking the imbalance during adolescence. We tested the effects on negative occasion setting, an important yet understudied form of inhibitory learning that may be particularly relevant during adolescence. Rats with combined manipulation of OFC and NAC were impaired in learning to use environmental cues to withhold a response, an effect that was greater than that of either manipulation alone. These findings provide direct evidence that simultaneous underactivity in OFC and overactivity in NAC can negatively impact behavioral control and provide insight into the neural systems that underlie inhibitory learning.

Neural activity of orbitofrontal cortex contributes to control of waiting

The willingness to wait for delayed reward and information is of fundamental importance for deliberative behaviors. The orbitofrontal cortex (OFC) is thought to be a core component of the neural circuitry underlying the capacity to control waiting. However, the neural correlates of active waiting and the causal role of the OFC in the control of waiting still remain largely unknown. Here, we trained rats to perform a waiting task (waiting for a pseudorandom time to obtain the water reward), and recorded neuronal ensembles in the OFC throughout the task. We observed that subset OFC neurons exhibited ramping activities throughout the waiting process. Receiver operating characteristic analysis showed that neural activities during the waiting period even predicted the trial outcomes (patient vs. impatient) on a trial-by-trial basis. Furthermore, optogenetic activation of the OFC during the waiting period improved the waiting performance, but did not influence rats' movement to obtain the reward. Taken together, these findings reveal that the neural activity in the OFC contributes to the control of waiting.

Working Memory in the Service of Executive Control Functions

Working memory is a type of short-term memory which has a crucial cognitive function that supports ongoing and upcoming behaviors, allowing storage of information across delay periods. The content of this memory may typically include tangible information about features such as the shape, color or texture of an object, and its location and motion relative to the body, as well as phonological information. The neural correlate of working memory has been found in different brain areas that are involved in organizing perceptual or motor functions. In particular, neuronal activity in prefrontal areas encodes task-related information corresponding to working memory across delay periods, and lesions in the prefrontal cortex severely affect the ability to retain this type of memory. Recent studies have further expanded the scope and possible role of working memory by showing that information of a more abstract nature (including a behavior-guiding rule, or the occurrence of a conflict in information processing) can also be maintained in short-term memory, and used for adjusting the allocation of executive control in dynamic environments. It has also been shown that neuronal activity in the prefrontal cortex encodes and maintains information about such abstract entities. These findings suggest that the prefrontal cortex plays crucial roles in the organization of goal-directed behavior by supporting many different mnemonic processes, which maintain a wide range of information required for the executive control of ongoing and upcoming behaviors.

Behavioral consequences of selective damage to frontal pole and posterior cingulate cortices

Frontal pole cortex (FPC) and posterior cingulate cortex (PCC) have close neuroanatomical connections, and imaging studies have shown coactivation or codeactivation of these brain regions during performance of certain tasks. However, they are among the least well-understood regions of the primate brain. One reason for this is that the consequences of selective bilateral lesions to either structure have not previously been studied in any primate species. We studied the effects of circumscribed bilateral lesions to FPC or PCC on monkeys' ability to perform an analog of Wisconsin Card Sorting Test (WCST) and related tasks. In contrast to lesions in other prefrontal regions, neither posttraining FPC nor PCC lesions impaired animals' abilities to follow the rule switches that frequently occurred within the WCST task. However, FPC lesions were not without effect, because they augmented the ability of animals to adjust cognitive control after experiencing high levels of conflict (whereas PCC lesions did not have any effect). In addition, FPC-lesioned monkeys were more successful than controls or PCC-lesioned animals at remembering the relevant rule across experimentally imposed distractions involving either an intervening secondary task or a surprising delivery of free reward. Although prefrontal cortex posterior to FPC is specialized for mediating efficient goal-directed behavior to maximally exploit reward opportunities from ongoing tasks, our data led us to suggest that FPC is, instead, specialized for disengaging executive control from the current task and redistributing it to novel sources of reward to explore new opportunities/goals.

Executive control signals in orbitofrontal cortex during response inhibition

Orbitofrontal cortex (OFC) lesions produce deficits in response inhibition and imaging studies suggest that activity in OFC is stronger on trials that require suppression of behavior, yet few studies have examined neural correlates at the single-unit level in a behavioral task that probes response inhibition without varying other factors, such as anticipated outcomes. Here we recorded from single neurons in lateral OFC in a task that required animals in the minority of trials to STOP or inhibit an ongoing movement and respond in the opposite direction. We found that population and single-unit firing was modulated primarily by response direction and movement speed, and that very few OFC neurons exhibited a response independent inhibition signal. Remarkably, the strength of the directional signal was not diminished on STOP trials and was actually stronger on STOP trials during conflict adaptation. Finally, directional signals were stronger during sessions in which rats had the most difficulty inhibiting behavior. These results suggest that "inhibition" deficits observed with OFC interference studies reflect deficits unrelated to signaling the need to inhibit behavior, but instead support a role for OFC in executive functions related to dissociating between two perceptually similar actions during response conflict.