Neuronal activity in dorsal anterior cingulate cortex during economic choices under variable action costs

Generalized Encoding of the Relative Subjective Value of Cognitive Effort in the Dorsal ACC

Making choices about whether and when to engage cognitive effort are a common feature of everyday experience, with important consequences for academic, career, and health outcomes. Yet, despite their hypothesized importance, very little is understood about the underlying mechanisms that support this form of human cost-benefit decision-making. To investigate these mechanisms, we used the Cognitive Effort Discounting Paradigm (Cog-ED) during fMRI scanning to precisely quantify the neural encoding of varying cognitive effort demands relative to reward outcomes, within two distinct cognitive domains (working memory, speech comprehension). The findings provide strong evidence that the dorsal anterior cingulate cortex (dACC) plays a central and selective role in this decision-making process. Trial-by-trial modulations in dACC activation tracked the relative subjective value of the low-effort, low-reward option, with the strongest activity occurring when this was of greater value than the high-effort, high-reward option. In contrast, dACC activity was not modulated by decision difficulty, though such effects were found in other frontoparietal regions. Critically, dACC activity was also strongly correlated across the two decision-making task domains and further predicted subsequent choice behavior in both. Together, the results suggest that dACC activity modulation reflects a domain-general valuation comparison mechanism, which acts to bias participants away from decisions to engage in cognitive effort, when the perceived subjective costs of such engagement outweigh the reward-related benefits. These findings complement work in other cost domains and species by pointing to a clear role of the dACC in representing subjective value differences between choice options during cost-benefit decision-making.

Anterior cingulate and medial prefrontal cortex alcohol cue reactivity varies as a function of drink preference in alcohol use disorder

BACKGROUND

Functional MRI visual cue reactivity studies have not considered that brain responses to various alcohol-containing beverage types may vary as a function of an individual's drinking patterns and preferences. This study tested whether the brain's reward system responds differently to visual cues associated with an individuals' most commonly consumed ("preferred") alcohol beverage compared with less commonly consumed ("non-preferred") alcohol beverages in individuals with alcohol use disorder (AUD).

METHODS

Participants (N=70) with current AUD completed a standard visual alcohol cue reactivity procedure during fMRI and reported recent alcohol use through the Timeline Followback interview. Alcohol use patterns were used to infer drink preference. Repeated measure ANCOVAs were used to evaluate differences in subjective craving (alcohol urge) and neural reactivity to cues of individual's "preferred" versus "non-preferred" alcohol beverages.

RESULTS

Fifty-four (77%) participants were determined to have a "preferred" alcohol beverage, as defined by their pattern of alcohol use. These participants reported greater subjective alcohol urge (p=0.02) and activation in the anterior cingulate cortex (ACC) (p=0.005) and medial prefrontal cortex (mPFC) (p=0.001)) in response to visual cues associated with their "preferred" versus "non-preferred" alcohol beverage. Individuals with an alcohol preference did not differ from those with no alcohol preference on subjective or neural responses to their "preferred" and "non-preferred" alcohol cues.

DISCUSSION

Results suggest alcohol cue-elicited subjective and neural responses vary as a function of alcohol beverage preference in individuals with AUD and a behaviorally defined alcohol preference. Stronger ACC and mPFC activation may reflect greater subjective value of an individual's "preferred" alcohol beverage cue.

Value dynamics affect choice preparation during decision-making

During decision-making, neurons in the orbitofrontal cortex (OFC) sequentially represent the value of each option in turn, but it is unclear how these dynamics are translated into a choice response. One brain region that may be implicated in this process is the anterior cingulate cortex (ACC), which strongly connects with OFC and contains many neurons that encode the choice response. We investigated how OFC value signals interacted with ACC neurons encoding the choice response by performing simultaneous high-channel count recordings from the two areas in nonhuman primates. ACC neurons encoding the choice response steadily increased their firing rate throughout the decision-making process, peaking shortly before the time of the choice response. Furthermore, the value dynamics in OFC affected ACC ramping-when OFC represented the more valuable option, ACC ramping accelerated. Because OFC tended to represent the more valuable option more frequently and for a longer duration, this interaction could explain how ACC selects the more valuable response.

Abstraction of Reward Context Facilitates Relative Reward Coding in Neural Populations of the Macaque Anterior Cingulate Cortex

The anterior cingulate cortex (ACC) is believed to be involved in many cognitive processes, including linking goals to actions and tracking decision-relevant contextual information. ACC neurons robustly encode expected outcomes, but how this relates to putative functions of ACC remains unknown. Here, we approach this question from the perspective of population codes by analyzing neural spiking data in the ventral and dorsal banks of the ACC in two male monkeys trained to perform a stimulus-motor mapping task to earn rewards or avoid losses. We found that neural populations favor a low dimensional representational geometry that emphasizes the valence of potential outcomes while also facilitating the independent, abstract representation of multiple task-relevant variables. Valence encoding persisted throughout the trial, and realized outcomes were primarily encoded in a relative sense, such that cue valence acted as a context for outcome encoding. This suggests that the population coding we observe could be a mechanism that allows feedback to be interpreted in a context-dependent manner. Together, our results point to a prominent role for ACC in context setting and relative interpretation of outcomes, facilitated by abstract, or untangled, representations of task variables.SIGNIFICANCE STATEMENT The ability to interpret events in light of the current context is a critical facet of higher-order cognition. The ACC is suggested to be important for tracking contextual information, whereas alternate views hold that its function is more related to the motor system and linking goals to appropriate actions. We evaluated these possibilities by analyzing geometric properties of neural population activity in monkey ACC when contexts were determined by the valence of potential outcomes and found that this information was represented as a dominant, abstract concept. Ensuing outcomes were then coded relative to these contexts, suggesting an important role for these representations in context-dependent evaluation. Such mechanisms may be critical for the abstract reasoning and generalization characteristic of biological intelligence.

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.

Where Actions Meet Outcomes: Medial Prefrontal Cortex, Central Thalamus, and the Basal Ganglia

Medial prefrontal cortex (mPFC) interacts with distributed networks that give rise to goal-directed behavior through afferent and efferent connections with multiple thalamic nuclei and recurrent basal ganglia-thalamocortical circuits. Recent studies have revealed individual roles for different thalamic nuclei: mediodorsal (MD) regulation of signaling properties in mPFC neurons, intralaminar control of cortico-basal ganglia networks, ventral medial facilitation of integrative motor function, and hippocampal functions supported by ventral midline and anterior nuclei. Large scale mapping studies have identified functionally distinct cortico-basal ganglia-thalamocortical subnetworks that provide a structural basis for understanding information processing and functional heterogeneity within the basal ganglia. Behavioral analyses comparing functional deficits produced by lesions or inactivation of specific thalamic nuclei or subregions of mPFC or the basal ganglia have elucidated the interdependent roles of these areas in adaptive goal-directed behavior. Electrophysiological recordings of mPFC neurons in rats performing delayed non-matching-to position (DNMTP) and other complex decision making tasks have revealed populations of neurons with activity related to actions and outcomes that underlie these behaviors. These include responses related to motor preparation, instrumental actions, movement, anticipation and delivery of action outcomes, memory delay, and spatial context. Comparison of results for mPFC, MD, and ventral pallidum (VP) suggest critical roles for mPFC in prospective processes that precede actions, MD for reinforcing task-relevant responses in mPFC, and VP for providing feedback about action outcomes. Synthesis of electrophysiological and behavioral results indicates that different networks connecting mPFC with thalamus and the basal ganglia are organized to support distinct functions that allow organisms to act efficiently to obtain intended outcomes.