Prefrontal cell activities related to monkeys' success and failure in adapting to rule changes in a Wisconsin Card Sorting Test analog

Flexible gating between subspaces in a neural network model of internally guided task switching

Behavioral flexibility relies on the brain's ability to switch rapidly between multiple tasks, even when the task rule is not explicitly cued but must be inferred through trial and error. The underlying neural circuit mechanism remains poorly understood. We investigated recurrent neural networks (RNNs) trained to perform an analog of the classic Wisconsin Card Sorting Test. The networks consist of two modules responsible for rule representation and sensorimotor mapping, respectively, where each module is comprised of a circuit with excitatory neurons and three major types of inhibitory neurons. We found that rule representation by self-sustained persistent activity across trials, error monitoring and gated sensorimotor mapping emerged from training. Systematic dissection of trained RNNs revealed a detailed circuit mechanism that is consistent across networks trained with different hyperparameters. The networks' dynamical trajectories for different rules resided in separate subspaces of population activity; the subspaces collapsed and performance was reduced to chance level when dendrite-targeting somatostatin-expressing interneurons were silenced, illustrating how a phenomenological description of representational subspaces is explained by a specific circuit mechanism.

Learning to learn: Single session acquisition of new rules by freely moving mice

Learning from examples and adapting to new circumstances are fundamental attributes of human cognition. However, it is unclear what conditions allow for fast and successful learning, especially in nonhuman subjects. To determine how rapidly freely moving mice can learn a new discrimination criterion (DC), we design a two-alternative forced-choice visual discrimination paradigm in which the DCs governing the task can change between sessions. We find that experienced animals can learn a new DC after being exposed to only five training and three testing trials. The propensity for single session learning improves over time and is accurately predicted based on animal experience and criterion difficulty. After establishing the procedural learning of a paradigm, mice continuously improve their performance in new circumstances. Thus, mice learn to learn.

The prefrontal cortex: from monkey to man

The prefrontal cortex is so important to human beings that, if deprived of it, our behaviour is reduced to action-reactions and automatisms, with no ability to make deliberate decisions. Why does the prefrontal cortex hold such importance in humans? In answer, this review draws on the proximity between humans and other primates, which enables us, through comparative anatomical-functional analysis, to understand the cognitive functions we have in common and specify those that distinguish humans from their closest cousins. First, a focus on the lateral region of the prefrontal cortex illustrates the existence of a continuum between rhesus monkeys (the most studied primates in neuroscience) and humans for most of the major cognitive functions in which this region of the brain plays a central role. This continuum involves the presence of elementary mental operations in the rhesus monkey (e.g. working memory or response inhibition) that are constitutive of 'macro-functions' such as planning, problem-solving and even language production. Second, the human prefrontal cortex has developed dramatically compared to that of other primates. This increase seems to concern the most anterior part (the frontopolar cortex). In humans, the development of the most anterior prefrontal cortex is associated with three major and interrelated cognitive changes: (i) a greater working memory capacity, allowing for greater integration of past experiences and prospective futures; (ii) a greater capacity to link discontinuous or distant data, whether temporal or semantic; and (iii) a greater capacity for abstraction, allowing humans to classify knowledge in different ways, to engage in analogical reasoning or to acquire abstract values that give rise to our beliefs and morals. Together, these new skills enable us, among other things, to develop highly sophisticated social interactions based on language, enabling us to conceive beliefs and moral judgements and to conceptualize, create and extend our vision of our environment beyond what we can physically grasp. Finally, a model of the transition of prefrontal functions between humans and non-human primates concludes this review.

Fast adaptation to rule switching using neuronal surprise

In humans and animals, surprise is a physiological reaction to an unexpected event, but how surprise can be linked to plausible models of neuronal activity is an open problem. We propose a self-supervised spiking neural network model where a surprise signal is extracted from an increase in neural activity after an imbalance of excitation and inhibition. The surprise signal modulates synaptic plasticity via a three-factor learning rule which increases plasticity at moments of surprise. The surprise signal remains small when transitions between sensory events follow a previously learned rule but increases immediately after rule switching. In a spiking network with several modules, previously learned rules are protected against overwriting, as long as the number of modules is larger than the total number of rules-making a step towards solving the stability-plasticity dilemma in neuroscience. Our model relates the subjective notion of surprise to specific predictions on the circuit level.

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.

Prefrontal dynamics and encoding of flexible rule switching

Behavioral flexibility, the ability to adjust behavioral strategies in response to changing environmental contingencies and internal demands, is fundamental to cognitive functions. Despite a large body of pharmacology and lesion studies, the underlying neurophysiological correlates and mechanisms that support flexible rule switching remain elusive. To address this question, we trained mice to distinguish complex sensory cues comprising different perceptual dimensions (set shifting). Endoscopic calcium imaging revealed that medial prefrontal cortex (mPFC) neurons represented multiple task-related events and exhibited pronounced dynamic changes during rule switching. Notably, prominent encoding capacity in the mPFC was associated with switching across, but not within perceptual dimensions. We then showed the involvement of the ascending modulatory input from the locus coeruleus (LC), as inhibiting the LC impaired rule switching behavior and impeded mPFC dynamic processes and encoding. Our results highlight the pivotal role of the mPFC in set shifting processes and demonstrate the profound impact of ascending neuromodulation on shaping prefrontal neural dynamics and behavioral flexibility.

Continuous multiplexed population representations of task context in the mouse primary visual cortex

Effective task execution requires the representation of multiple task-related variables that determine how stimuli lead to correct responses. Even the primary visual cortex (V1) represents other task-related variables such as expectations, choice, and context. However, it is unclear how V1 can flexibly accommodate these variables without interfering with visual representations. We trained mice on a context-switching cross-modal decision task, where performance depends on inferring task context. We found that the context signal that emerged in V1 was behaviorally relevant as it strongly covaried with performance, independent from movement. Importantly, this signal was integrated into V1 representation by multiplexing visual and context signals into orthogonal subspaces. In addition, auditory and choice signals were also multiplexed as these signals were orthogonal to the context representation. Thus, multiplexing allows V1 to integrate visual inputs with other sensory modalities and cognitive variables to avoid interference with the visual representation while ensuring the maintenance of task-relevant variables.

Beta traveling waves in monkey frontal and parietal areas encode recent reward history

Brain function depends on neural communication, but the mechanisms of this communication are not well understood. Recent studies suggest that one form of neural communication is through traveling waves (TWs)-patterns of neural oscillations that propagate within and between brain areas. We show that TWs are robust in microarray recordings in frontal and parietal cortex and encode recent reward history. Two adult male monkeys made saccades to obtain probabilistic rewards and were sensitive to the (statistically irrelevant) reward on the previous trial. TWs in frontal and parietal areas were stronger in trials that followed a prior reward versus a lack of reward and, in the frontal lobe, correlated with the monkeys' behavioral sensitivity to the prior reward. The findings suggest that neural communication mediated by TWs within the frontal and parietal lobes contribute to maintaining information about recent reward history and mediating the impact of this history on the monkeys' expectations.

Non-overlapping sets of neurons encode behavioral response determinants across different tasks in the posterior medial prefrontal cortex

Higher mammals are able to simultaneously learn and perform a wide array of complex behaviors, which raises questions about how the neural representations of multiple tasks coexist within the same neural network. Do neurons play invariant roles across different tasks? Alternatively, do the same neurons play different roles in different tasks? To address these questions, we examined neuronal activity in the posterior medial prefrontal cortex of primates while they were performing two versions of arm-reaching tasks that required the selection of multiple behavioral tactics (i.e., the internal protocol of action selection), a critical requirement for the activation of this area. During the performance of these tasks, neurons in the pmPFC exhibited selective activity for the tactics, visuospatial information, action, or their combination. Surprisingly, in 82% of the tactics-selective neurons, the selective activity appeared in a particular task but not in both. Such task-specific neuronal representation appeared in 72% of the action-selective neurons. In addition, 95% of the neurons representing visuospatial information showed such activity exclusively in one task but not in both. Our findings indicate that the same neurons can play different roles across different tasks even though the tasks require common information, supporting the latter hypothesis.

Modelling continual learning in humans with Hebbian context gating and exponentially decaying task signals

Humans can learn several tasks in succession with minimal mutual interference but perform more poorly when trained on multiple tasks at once. The opposite is true for standard deep neural networks. Here, we propose novel computational constraints for artificial neural networks, inspired by earlier work on gating in the primate prefrontal cortex, that capture the cost of interleaved training and allow the network to learn two tasks in sequence without forgetting. We augment standard stochastic gradient descent with two algorithmic motifs, so-called "sluggish" task units and a Hebbian training step that strengthens connections between task units and hidden units that encode task-relevant information. We found that the "sluggish" units introduce a switch-cost during training, which biases representations under interleaved training towards a joint representation that ignores the contextual cue, while the Hebbian step promotes the formation of a gating scheme from task units to the hidden layer that produces orthogonal representations which are perfectly guarded against interference. Validating the model on previously published human behavioural data revealed that it matches performance of participants who had been trained on blocked or interleaved curricula, and that these performance differences were driven by misestimation of the true category boundary.

Long-term memory, synaptic plasticity and dopamine in rodent medial prefrontal cortex: Role in executive functions

Mnemonic functions, supporting rodent behavior in complex tasks, include both long-term and (short-term) working memory components. While working memory is thought to rely on persistent activity states in an active neural network, long-term memory and synaptic plasticity contribute to the formation of the underlying synaptic structure, determining the range of possible states. Whereas, the implication of working memory in executive functions, mediated by the prefrontal cortex (PFC) in primates and rodents, has been extensively studied, the contribution of long-term memory component to these tasks received little attention. This review summarizes available experimental data and theoretical work concerning cellular mechanisms of synaptic plasticity in the medial region of rodent PFC and the link between plasticity, memory and behavior in PFC-dependent tasks. A special attention is devoted to unique properties of dopaminergic modulation of prefrontal synaptic plasticity and its contribution to executive functions.

Comparing rapid rule-learning strategies in humans and monkeys

Inter-species comparisons are key to deriving an understanding of the behavioral and neural correlates of human cognition from animal models. We perform a detailed comparison of macaque monkey and human strategies on an analogue of the Wisconsin Card Sort Test, a widely studied and applied multi-attribute measure of cognitive function, wherein performance requires the inference of a changing rule given ambiguous feedback. We found that well-trained monkeys rapidly infer rules but are three times slower than humans. Model fits to their choices revealed hidden states akin to feature-based attention in both species, and decision processes that resembled a Win-stay lose-shift strategy with key differences. Monkeys and humans test multiple rule hypotheses over a series of rule-search trials and perform inference-like computations to exclude candidates. An attention-set based learning stage categorization revealed that perseveration, random exploration and poor sensitivity to negative feedback explain the under-performance in monkeys.

The implications of categorical and category-free mixed selectivity on representational geometries

The firing rates of individual neurons displaying mixed selectivity are modulated by multiple task variables. When mixed selectivity is nonlinear, it confers an advantage by generating a high-dimensional neural representation that can be flexibly decoded by linear classifiers. Although the advantages of this coding scheme are well accepted, the means of designing an experiment and analyzing the data to test for and characterize mixed selectivity remain unclear. With the growing number of large datasets collected during complex tasks, the mixed selectivity is increasingly observed and is challenging to interpret correctly. We review recent approaches for analyzing and interpreting neural datasets and clarify the theoretical implications of mixed selectivity in the variety of forms that have been reported in the literature. We also aim to provide a practical guide for determining whether a neural population has linear or nonlinear mixed selectivity and whether this mixing leads to a categorical or category-free representation.

Age effect in expert cognitive flexibility in Guinea baboons (Papio papio)

Cognitive flexibility in non-human primates is traditionally measured with the conceptual set shifting task (CSST). In our laboratory, Guinea baboons (N = 24) were continuously tested with a CSST task during approximately 10 years. Our task involved the presentation of three stimuli on a touch screen all made from 3 possible colours and 3 shapes. The subjects had to touch the stimulus containing the stimulus dimension (e.g., green) that was constantly rewarded until the stimulus dimension changed. Analysis of perseveration responses, scores and response times collected during the last two years of testing (approximately 1.6 million trials) indicate (1) that the baboons have developed an "expert" form of cognitive flexibility and (2) that their performance was age-dependent, it was at a developing stage in juveniles, optimal in adults, declining in middle-aged, and strongly impaired in the oldest age group. A direct comparison with the data collected by Bonté , Flemming & Fagot (2011) on some of the same baboons and same task as in the current study indicates that (3) the performance of all age groups has improved after 10 years of training, even for the now old individuals. All these data validate the use of non-human primates as models of human cognitive flexibility and suggest that cognitive flexibility in humans has a long evolutionary history.

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.

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.

More Prominent Nonlinear Mixed Selectivity in the Dorsolateral Prefrontal than Posterior Parietal Cortex

Neurons in the dorsolateral prefrontal cortex (dlPFC) and posterior parietal cortex (PPC) are activated by different cognitive tasks and respond differently to the same stimuli depending on task. The conjunctive representations of multiple tasks in nonlinear fashion in single neuron activity, is known as nonlinear mixed selectivity (NMS). Here, we compared NMS in a working memory task in areas 8a and 46 of the dlPFC and 7a and lateral intraparietal cortex (LIP) of the PPC in macaque monkeys. NMS neurons were more frequent in dlPFC than in PPC and this was attributed to more cells gaining selectivity in the course of a trial. Additionally, in our task, the subjects' behavioral performance improved within a behavioral session as they learned the session-specific statistics of the task. The magnitude of NMS in the dlPFC also increased as a function of time within a single session. On the other hand, we observed minimal rotation of population responses and no appreciable differences in NMS between correct and error trials in either area. Our results provide direct evidence demonstrating a specialization in NMS between dlPFC and PPC and reveal mechanisms of neural selectivity in areas recruited in working memory tasks.

A One-Shot Shift from Explore to Exploit in Monkey Prefrontal Cortex

Much animal learning is slow, with cumulative changes in behavior driven by reward prediction errors. When the abstract structure of a problem is known, however, both animals and formal learning models can rapidly attach new items to their roles within this structure, sometimes in a single trial. Frontal cortex is likely to play a key role in this process. To examine information seeking and use in a known problem structure, we trained monkeys in an explore/exploit task, requiring the animal first to test objects for their association with reward, then, once rewarded objects were found, to reselect them on further trials for further rewards. Many cells in the frontal cortex showed an explore/exploit preference aligned with one-shot learning in the monkeys' behavior: the population switched from an explore state to an exploit state after a single trial of learning but partially maintained the explore state if an error indicated that learning had failed. Binary switch from explore to exploit was not explained by continuous changes linked to expectancy or prediction error. Explore/exploit preferences were independent for two stages of the trial: object selection and receipt of feedback. Within an established task structure, frontal activity may control the separate processes of explore and exploit, switching in one trial between the two.SIGNIFICANCE STATEMENT Much animal learning is slow, with cumulative changes in behavior driven by reward prediction errors. When the abstract structure a problem is known, however, both animals and formal learning models can rapidly attach new items to their roles within this structure. To address transitions in neural activity during one-shot learning, we trained monkeys in an explore/exploit task using familiar objects and a highly familiar task structure. When learning was rapid, many frontal neurons showed a binary, one-shot switch between explore and exploit. Within an established task structure, frontal activity may control the separate operations of exploring alternative objects to establish their current role, then exploiting this knowledge for further reward.

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.

Emergence of Nonlinear Mixed Selectivity in Prefrontal Cortex after Training

Neurons in the PFC are typically activated by different cognitive tasks, and also by different stimuli and abstract variables within these tasks. A single neuron's selectivity for a given stimulus dimension often changes depending on its context, a phenomenon known as nonlinear mixed selectivity (NMS). It has previously been hypothesized that NMS emerges as a result of training to perform tasks in different contexts. We tested this hypothesis directly by examining the neuronal responses of different PFC areas before and after male monkeys were trained to perform different working memory tasks involving visual stimulus locations and/or shapes. We found that training induces a modest increase in the proportion of PFC neurons with NMS exclusively for spatial working memory, but not for shape working memory tasks, with area 9/46 undergoing the most significant increase in NMS cell proportion. We also found that increased working memory task complexity, in the form of simultaneously storing location and shape combinations, does not increase the degree of NMS for stimulus shape with other task variables. Lastly, in contrast to the previous studies, we did not find evidence that NMS is predictive of task performance. Our results thus provide critical insights on the representation of stimuli and task information in neuronal populations, in working memory.SIGNIFICANCE STATEMENT How multiple types of information are represented in working memory remains a complex computational problem. It has been hypothesized that nonlinear mixed selectivity allows neurons to efficiently encode multiple stimuli in different contexts, after subjects have been trained in complex tasks. Our analysis of prefrontal recordings obtained before and after training monkeys to perform working memory tasks only partially agreed with this prediction, in that nonlinear mixed selectivity emerged for spatial but not shape information, and mostly in mid-dorsal PFC. Nonlinear mixed selectivity also displayed little modulation across either task complexity or correct performance. These results point to other mechanisms, in addition to nonlinear mixed selectivity, representing complex information about stimulus and task context in neuronal activity.

Internal manipulation of perceptual representations in human flexible cognition: A computational model

Executive functions represent a set of processes in goal-directed cognition that depend on integrated cortical-basal ganglia brain systems and form the basis of flexible human behaviour. Several computational models have been proposed for studying cognitive flexibility as a key executive function and the Wisconsin card sorting test (WCST) that represents an important neuropsychological tool to investigate it. These models clarify important aspects that underlie cognitive flexibility, particularly decision-making, motor response, and feedback-dependent learning processes. However, several studies suggest that the categorisation processes involved in the solution of the WCST include an additional computational stage of category representation that supports the other processes. Surprisingly, all models of the WCST ignore this fundamental stage and they assume that decision making directly triggers actions. Thus, we propose a novel hypothesis where the key mechanisms of cognitive flexibility and goal-directed behaviour rely on the acquisition of suitable representations of percepts and their top-down internal manipulation. Moreover, we propose a neuro-inspired computational model to operationalise this hypothesis. The capacity of the model to support cognitive flexibility was validated by systematically reproducing and interpreting the behaviour exhibited in the WCST by young and old healthy adults, and by frontal and Parkinson patients. The results corroborate and further articulate the hypothesis that the internal manipulation of representations is a core process in goal-directed flexible cognition.

Short-term research projects in cognitive neuroscience for undergraduate students: a contingency plan to maintain quality teaching during COVID-19 pandemic

The Corona Virus Disease 19 (COVID-19) pandemic has imposed serious restrictions for academic institutions to maintain their research and teaching practical subjects. Universities have implemented adaptive measures to maintain educational activities and achieve the learning objectives for undergraduate and postgraduate students by shifting to online teaching and learning. Although such approaches have enabled delivering the theoretical content of courses during the pandemic, universities have faced serious difficulties in running practicals with actual research experiments and teaching hand-on skills because such activities potentially override the required safety guidelines. Here, we report an adaptive measure, implemented at Monash University, to run home-based studies in cognitive neuroscience and achieve learning objectives, which are normally delivered in face-to-face practicals. We introduce two specifically designed short-term research projects and describe how different aspects of these projects, such as tutorials, experiments, and assessments, were modified to meet the required social distancing. The results of cognitive tests were closely comparable between the laboratory-based and home-based experiments indicating that students followed the guidelines and the required procedures for a reliable data collection. Our assessments of students' performance and feedback indicate that the majority of our educational goals were achieved, while all safety guidelines and distancing requirements were also met.

Effects of therapeutic instrumental music performance and motor imagery on chronic post-stroke cognition and affect: A randomized controlled trial

BACKGROUND

The burden of post-stroke cognitive impairment, as well as affective disorders, remains persistently high. With improved stroke survival rates and increasing life expectancy, there is a need for effective interventions to facilitate remediation of neurocognitive impairments and post-stroke mood disorders.

OBJECTIVE

To investigate the effects of Therapeutic Instrumental Music Performance (TIMP) training with and without Motor Imagery on cognitive functioning and affective responding in chronic post-stroke individuals.

METHODS

Thirty chronic post-stroke, community-dwelling participants were randomized to one of three experimental arms: (1) 45 minutes of active TIMP, (2) 30 minutes of active TIMP followed by 15 minutes of metronome-cued motor imagery (TIMP+cMI), (3) 30 minutes of active TIMP followed by 15 minutes of motor imagery without cues (TIMP+MI). Training took place three times a week for three weeks, using a selection of acoustic and electronic instruments. Assessments, administered at two baselines and post-training, included the Trail Making Test (TMT) - Part B to assess mental flexibility, the Digit Span Test (DST) to determine short-term memory capacity, the Multiple Affect Adjective Checklist - Revised (MAACL-R) to ascertain current affective state, and the General Self-Efficacy Scale (GSE) to assess perceived self-efficacy. The Self-Assessment Maniqin (SAM) was also administered prior to and following each training session.

RESULTS

Thirty participants completed the protocol, ten per arm [14 women; mean age = 55.9; mean time post-stroke = 66.9 months]. There were no statistically significant differences between pooled group baseline measures. The TIMP+MI group showed a statistically significant decrease in time from pre-test 2 to post-test on the TMT. The TIMP group showed a significant increase on MAACL sensation seeking scores, as well as on the Valence and Dominance portions of the SAM; TIMP+cMI showed respective increases and decreases in positive and negative affect on the MAACL, and increases on the Valence, Dominance, and Arousal portions of the SAM. No statistically significant association between cognitive and affective measures was obtained.

CONCLUSIONS

The mental flexibility aspect of executive functioning appears to be enhanced by therapeutic instrumental music training in conjunction with motor imagery, possibly due to multisensory integration and consolidation of representations through motor imagery rehearsal following active practice. Active training using musical instruments appears to have a positive impact on affective responding; however, these changes occurred independently of improvements to cognition.

The Dorsal Lateral Habenula-Interpeduncular Nucleus Pathway Is Essential for Left-Right-Dependent Decision Making in Zebrafish

How animals behave using suitable information to adapt to the environment is not well known. We address this issue by devising an automated system to let zebrafish exploit either internal (choice of left or right turn) or external (choice of cue color) navigation information to achieve operant behavior by reward reinforcement learning. The results of behavioral task with repeated rule shift indicate that zebrafish can learn operant behavior using both internal-directional and external-cued information. The learning time is reduced as rule shifts are repeated, revealing the capacity of zebrafish to adaptively retrieve the suitable rule memory after training. Zebrafish with an impairment in the neural pathway from the lateral subregion of the dorsal habenula to the interpeduncular nucleus, known to be potentiated in the winners of social conflicts, show specific defects in the application of the internal-directional rule, suggesting the dual roles of this pathway.

Mouse prefrontal cortex represents learned rules for categorization

The ability to categorize sensory stimuli is crucial for an animal’s survival in a complex environment. Memorizing categories instead of individual exemplars enables greater behavioural flexibility and is computationally advantageous. Neurons that show category selectivity have been found in several areas of the mammalian neocortex^1–4, but the prefrontal cortex seems to have a prominent role^4,5 in this context. Specifically, in primates that are extensively trained on a categorization task, neurons in the prefrontal cortex rapidly and flexibly represent learned categories^6,7. However, how these representations first emerge in naive animals remains unexplored, leaving it unclear whether flexible representations are gradually built up as part of semantic memory or assigned more or less instantly during task execution^8,9. Here we investigate the formation of a neuronal category representation throughout the entire learning process by repeatedly imaging individual cells in the mouse medial prefrontal cortex. We show that mice readily learn rule-based categorization and generalize to novel stimuli. Over the course of learning, neurons in the prefrontal cortex display distinct dynamics in acquiring category selectivity and are differentially engaged during a later switch in rules. A subset of neurons selectively and uniquely respond to categories and reflect generalization behaviour. Thus, a category representation in the mouse prefrontal cortex is gradually acquired during learning rather than recruited ad hoc. This gradual process suggests that neurons in the medial prefrontal cortex are part of a specific semantic memory for visual categories.

Neurons in the mouse medial prefrontal cortex acquire category-selective responses with learning.

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.

Choice-dependent cross-modal interaction in the medial prefrontal cortex of rats

Cross-modal interaction (CMI) could significantly influence the perceptional or decision-making process in many circumstances. However, it remains poorly understood what integrative strategies are employed by the brain to deal with different task contexts. To explore it, we examined neural activities of the medial prefrontal cortex (mPFC) of rats performing cue-guided two-alternative forced-choice tasks. In a task requiring rats to discriminate stimuli based on auditory cue, the simultaneous presentation of an uninformative visual cue substantially strengthened mPFC neurons' capability of auditory discrimination mainly through enhancing the response to the preferred cue. Doing this also increased the number of neurons revealing a cue preference. If the task was changed slightly and a visual cue, like the auditory, denoted a specific behavioral direction, mPFC neurons frequently showed a different CMI pattern with an effect of cross-modal enhancement best evoked in information-congruent multisensory trials. In a choice free task, however, the majority of neurons failed to show a cross-modal enhancement effect and cue preference. These results indicate that CMI at the neuronal level is context-dependent in a way that differs from what has been shown in previous studies.

A modeling framework for adaptive lifelong learning with transfer and savings through gating in the prefrontal cortex

The prefrontal cortex encodes and stores numerous, often disparate, schemas and flexibly switches between them. Recent research on artificial neural networks trained by reinforcement learning has made it possible to model fundamental processes underlying schema encoding and storage. Yet how the brain is able to create new schemas while preserving and utilizing old schemas remains unclear. Here we propose a simple neural network framework that incorporates hierarchical gating to model the prefrontal cortex's ability to flexibly encode and use multiple disparate schemas. We show how gating naturally leads to transfer learning and robust memory savings. We then show how neuropsychological impairments observed in patients with prefrontal damage are mimicked by lesions of our network. Our architecture, which we call DynaMoE, provides a fundamental framework for how the prefrontal cortex may handle the abundance of schemas necessary to navigate the real world.

Spatial encoding in dorsomedial prefrontal cortex and hippocampus is related during deliberation

Deliberation is thought to involve the internal simulation of the outcomes of candidate actions, the valuation of those outcomes, and the selection of the actions with the highest expected value. While it is known that deliberation involves prefrontal cortical areas, specifically the dorsomedial prefrontal cortex (dmPFC), as well as the hippocampus (HPC) and other brain regions, how these areas process prospective information and select actions is not well understood. We recorded simultaneously from ensembles in dmPFC and CA1 of dorsal HPC in rats during performance of a spatial contingency switching task, and examined the relationships between spatial and reward encoding in these two areas during deliberation at the choice point. We found that CA1 and dmPFC represented either goal locations or the current position simultaneously, but that when goal locations were encoded, HPC and dmPFC did not always represent the same goal location. Ensemble activity in dmPFC predicted when HPC would represent goal locations, but on a broad timescale on the order of seconds. Also, reward encoding in dmPFC increased during hippocampal theta cycles where CA1 ensembles represented the goal location. These results suggest that dmPFC and HPC share prospective information during deliberation, that dmPFC may influence whether HPC represents prospective information, and that information recalled about goal locations by HPC may be integrated into dmPFC reward representations on fast timescales.

Methylphenidate affects task-switching and neural signaling in non-human primates

RATIONALE

Low doses of psychostimulants such as methylphenidate (MPH), which increase extracellular dopamine and norepinephrine by inhibiting their reuptake, are the most commonly used treatment for attention deficit hyperactivity disorder (ADHD). Therapeutic doses of these drugs may improve focused attention at the expense of hindering other cognitive functions, including the ability to adapt behavior in response to changing circumstances-cognitive flexibility. Cognitive flexibility is thought to depend on proper operation of the prefrontal cortex (PFC) and is also linked to reward processing, which is dopamine-dependent. Additionally, reward outcome signals have been recorded from the PFC.

OBJECTIVES

This study tested the hypothesis that therapeutic doses of MPH impair cognitive flexibility and that this impairment in performance resulted from interference in reward signals within the PFC.

METHODS

Four rhesus monkeys were given therapeutically relevant doses of oral MPH (0, 3, and 6 mg/kg) while performing an oculomotor switching task to evaluate its effect on task performance. Single-unit recordings in the PFC of two monkeys were taken before and after MPH administration during task performance.

RESULTS

The results show that MPH does hinder switching task performance, an effect that was correlated with a reduction in the amplitude of outcome signals found in the discharges of some neurons in the PFC.

CONCLUSIONS

Methylphenidate impaired task-switching performance, which can be used as a measure of cognitive flexibility. This detriment may result from degraded outcome signaling within the PFC. This study has implications for the use of MPH in the treatment of ADHD.

Neural Correlates of Strategy Switching in the Macaque Orbital Prefrontal Cortex

We can adapt flexibly to environment changes and search for the most appropriate rule to a context. The orbital prefrontal cortex (PFo) has been associated with decision making, rule generation and maintenance, and more generally has been considered important for behavioral flexibility. To better understand the neural mechanisms underlying the flexible behavior, we studied the ability to generate a switching signal in monkey PFo when a strategy is changed. In the strategy task, we used a visual cue to instruct two male rhesus monkeys either to repeat their most recent choice (i.e., stay strategy) or to change it (i.e., shift strategy). To identify the strategy switching-related signal, we compared nonswitch and switch trials, which cued the same or a different strategy from the previous trial, respectively. We found that the switching-related signal emerged during the cue presentation and it was combined with the strategy signal in a subpopulation of cells. Moreover, the error analysis showed that the activity of the switch-related cells reflected whether the monkeys erroneously switched or not the strategy, rather than what was required for that trial. The function of the switching signal could be to prompt the use of different strategies when older strategies are no longer appropriate, conferring the ability to adapt flexibly to environmental changes. In our task, the switching signal might contribute to the implementation of the strategy cued, overcoming potential interference effects from the strategy previously cued. Our results support the idea that ascribes to PFo an important role for behavioral flexibility.SIGNIFICANCE STATEMENT We can flexibly adapt our behavior to a changing environment. One of the prefrontal areas traditionally associated with the ability to adapt to new contingencies is the orbital prefrontal cortex (PFo). We analyzed the switching related activity using a strategy task in which two rhesus monkeys were instructed by a visual cue either to repeat or change their most recent choice, respectively using a stay or a shift strategy. We found that PFo neurons were modulated by the strategy switching signal, pointing to the importance of PFo in behavioral flexibility by generating control over the switching of strategies.

A Visual Two-Choice Rule-Switch Task for Head-Fixed Mice

Cognitive flexibility is the innate ability of the brain to change mental processes and to modify behavioral responses according to an ever-changing environment. As our brain has a limited capacity to process the information of our surroundings in any given moment, it uses sets as a strategy to aid neural processing systems. With assessing the capability of shifting between task sets, it is possible to test cognitive flexibility and executive functions. The most widely used neuropsychological task for the evaluation of these functions in humans is the Wisconsin Card Sorting Test (WCST), which requires the subject to alter response strategies and use previously irrelevant information to solve a problem. The test has proven clinical relevance, as poor performance has been reported in multiple neuropsychiatric conditions. Although, similar tasks have been used in pre-clinical rodent research, many are limited because of their manual-based testing procedures and their hardware attenuates neuronal recordings. We developed a two-choice rule-switch task whereby head-fixed C57BL/6 mice had to choose correctly one of the two virtual objects presented to retrieve a small water reward. The animals learnt to discriminate the visual cues and they successfully switched their strategies according to the related rules. We show that reaching successful performance after the rule changes required more trials in this task and that animals took more time to execute decisions when the two rules were in conflict. We used optogenetics to inhibit temporarily the medial prefrontal cortex (mPFC) during reward delivery and consumption, which significantly increased the number of trials needed to perform the second rule successfully (i.e., succeed in switching between rules), compared to control experiments. Furthermore, by assessing two types of error animals made after the rule switch, we show that interfering with the positive feedback integration, but leaving the negative feedback processing intact, does not influence the initial disengagement from the first rule, but impedes the maintenance of the newly acquired response set. These findings support the role of prefrontal networks in mice for cognitive flexibility, which is impaired during numerous neuropsychiatric diseases, such as schizophrenia and depression.

Striatal action-value neurons reconsidered

It is generally believed that during economic decisions, striatal neurons represent the values associated with different actions. This hypothesis is based on studies, in which the activity of striatal neurons was measured while the subject was learning to prefer the more rewarding action. Here we show that these publications are subject to at least one of two critical confounds. First, we show that even weak temporal correlations in the neuronal data may result in an erroneous identification of action-value representations. Second, we show that experiments and analyses designed to dissociate action-value representation from the representation of other decision variables cannot do so. We suggest solutions to identifying action-value representation that are not subject to these confounds. Applying one solution to previously identified action-value neurons in the basal ganglia we fail to detect action-value representations. We conclude that the claim that striatal neurons encode action-values must await new experiments and analyses.

The Correlation Between Cognitive and Movement Shifting and Brain Activity in Children With ADHD

OBJECTIVE

We assessed the correlation between the deficits of cognition, movement, and brain activity in children with Attention Deficit Hyperactvity Disorder (ADHD).

METHOD

We recruited 15 children with ADHD and 15 age- and sex-matched healthy control participants. Clinical symptoms, cognitive shifting, movement shifting, and brain activity were assessed using the Korean ADHD Rating Scale, the Wisconsin Card Sorting Test (WCST), the 7- and 14-ring drill test with hop jumps (7 HJ and 14 HJ), and 3.0 Tesla functional magnetic resonance imaging scanner, respectively.

RESULTS

ADHD children showed an increased distance traveled and decreased speed on the 14 HJ task. In response to the WCST task, ADHD children showed decreased activation within right gyrus. Total distance on the 14 HJ task was negatively correlated with the mean β value of Cluster 2 in ADHD children.

CONCLUSION

These results suggested that children with ADHD showed difficulty with attention shifting as well as with movement shifting.

Solving the Credit Assignment Problem With the Prefrontal Cortex

In naturalistic multi-cue and multi-step learning tasks, where outcomes of behavior are delayed in time, discovering which choices are responsible for rewards can present a challenge, known as the credit assignment problem. In this review, I summarize recent work that highlighted a critical role for the prefrontal cortex (PFC) in assigning credit where it is due in tasks where only a few of the multitude of cues or choices are relevant to the final outcome of behavior. Collectively, these investigations have provided compelling support for specialized roles of the orbitofrontal (OFC), anterior cingulate (ACC), and dorsolateral prefrontal (dlPFC) cortices in contingent learning. However, recent work has similarly revealed shared contributions and emphasized rich and heterogeneous response properties of neurons in these brain regions. Such functional overlap is not surprising given the complexity of reciprocal projections spanning the PFC. In the concluding section, I overview the evidence suggesting that the OFC, ACC and dlPFC communicate extensively, sharing the information about presented options, executed decisions and received rewards, which enables them to assign credit for outcomes to choices on which they are contingent. This account suggests that lesion or inactivation/inhibition experiments targeting a localized PFC subregion will be insufficient to gain a fine-grained understanding of credit assignment during learning and instead poses refined questions for future research, shifting the focus from focal manipulations to experimental techniques targeting cortico-cortical projections.

Contributions of Lateral and Orbital Frontal Regions to Abstract Rule Acquisition and Reversal in Monkeys

The ability to learn and follow abstract rules relies on intact prefrontal regions including the lateral prefrontal cortex (LPFC) and the orbitofrontal cortex (OFC). Here, we investigate the specific roles of these brain regions in learning rules that depend critically on the formation of abstract concepts as opposed to simpler input-output associations. To this aim, we tested monkeys with bilateral removals of either LPFC or OFC on a rapidly learned task requiring the formation of the abstract concept of same vs. different. While monkeys with OFC removals were significantly slower than controls at both acquiring and reversing the concept-based rule, monkeys with LPFC removals were not impaired in acquiring the task, but were significantly slower at rule reversal. Neither group was impaired in the acquisition or reversal of a delayed visual cue-outcome association task without a concept-based rule. These results suggest that OFC is essential for the implementation of a concept-based rule, whereas LPFC seems essential for its modification once established.

Outcome Modulation Across Tasks in the Primate Dorsolateral Prefrontal Cortex

Animals need to learn and to adapt to new and changing environments so that appropriate actions that lead to desirable outcomes are acquired within each context. The prefrontal cortex (PF) is known to underlie such function that directly implies that the outcome of each response must be represented in the brain for behavioral policies update. However, whether such PF signal is context dependent or it is a general representation beyond the specificity of a context is still unclear. Here, we analyzed the activity of neurons in the dorsolateral PF (PFdl) recorded while two monkeys performed two perceptual magnitude discrimination tasks. Both tasks were well known by the monkeys and unexpected changes did not occur but the difficulty of the task varied from trial to trial and thus the monkeys made mistakes in a proportion of trials. We show a context-independent coding of the response outcome with neurons maintaining similar selectivity in both task contexts. Using a classification method of the neural activity, we also show that the trial outcome could be well predicted from the activity of the same neurons in the two contexts. Altogether, our results provide evidence of high degree of outcome generality in PFdl.

Simians in the Shape School: A comparative study of executive attention

Executive functions (EF) have been studied extensively in children and adults. However, EF tasks for young children can be difficult to administer and interpret. Espy (1997, Developmental Neuropsychology, 13, 495-499) designed the Shape School task to measure inhibition and switching in preschool-aged children. Shape School presents cartoon-like characters that children must flexibly name by their color, their shape, or both, depending on cues that indicate the appropriate rule. Shape School has been found to be age sensitive as well as predictive of performance on other EF tasks. We presented a computerized analogue of Shape School to seven rhesus macaques. Monkeys were trained to categorize characters by color or shape, or to inhibit this response, depending on whether the characters had eyes open, eyes closed, or wore hats. Monkeys performed above chance on the inhibition and switching components of the task. Long runs of a single classification rule and long runs of noninhibition trials had no significant impact on performance when the rule changed or inhibition was required. This nonverbal adaptation of Shape School can measure EF in nonhuman animals and could be used in conjunction with other EF tasks to provide a clearer picture of both human and nonhuman executive functions.

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.

Mixed selectivity morphs population codes in prefrontal cortex

The prefrontal cortex maintains working memory information in the presence of distracting stimuli. It has long been thought that sustained activity in individual neurons or groups of neurons was responsible for maintaining information in the form of a persistent, stable code. Here we show that, upon the presentation of a distractor, information in the lateral prefrontal cortex was reorganized into a different pattern of activity to create a morphed stable code without losing information. In contrast, the code in the frontal eye fields persisted across different delay periods but exhibited substantial instability and information loss after the presentation of a distractor. We found that neurons with mixed-selective responses were necessary and sufficient for the morphing of code and that these neurons were more abundant in the lateral prefrontal cortex than the frontal eye fields. This suggests that mixed selectivity provides populations with code-morphing capability, a property that may underlie cognitive flexibility.

Neural correlates for task switching in the macaque superior colliculus

Successful task switching requires a network of brain areas to select, maintain, implement, and execute the appropriate task. Although frontoparietal brain areas are thought to play a critical role in task switching by selecting and encoding task rules and exerting top-down control, how brain areas closer to the execution of tasks participate in task switching is unclear. The superior colliculus (SC) integrates information from various brain areas to generate saccades and is likely influenced by task switching. Here, we investigated switch costs in nonhuman primates and their neural correlates in the activity of SC saccade-related neurons in monkeys performing cued, randomly interleaved pro- and anti-saccade trials. We predicted that behavioral switch costs would be associated with differential modulations of SC activity in trials on which the task was switched vs. repeated, with activity on the current trial resembling that associated with the task set of the previous trial when a switch occurred. We observed both error rate and reaction time switch costs and changes in the discharge rate and timing of activity in SC neurons between switch and repeat trials. These changes were present later in the task only after fixation on the cue stimuli but before saccade onset. These results further establish switch costs in macaque monkeys and suggest that SC activity is modulated by task-switching processes in a manner inconsistent with the concept of task set inertia.NEW & NOTEWORTHY Task-switching behavior and superior colliculus (SC) activity were investigated in nonhuman primates performing randomly interleaved pro- and anti-saccade tasks. Here, we report error rate and reaction time switch costs in macaque monkeys and associated differences in stimulus-related activity of saccade-related neurons in the SC. These results provide a neural correlate for task switching and suggest that the SC is modulated by task-switching processes and may reflect the completion of task set reconfiguration.

Context-Dependent Accumulation of Sensory Evidence in the Parietal Cortex Underlies Flexible Task Switching

Switching behavior based on multiple rules is a fundamental ability of flexible behavior. Although interactions among the frontal, parietal, and sensory cortices are necessary for such flexibility, little is known about the neural computations concerning context-dependent information readouts. Here, we provide evidence that neurons in the lateral intraparietal area (LIP) accumulate relevant information preferentially depending on context. We trained monkeys to switch between direction and depth discrimination tasks and analyzed the buildup activity in the LIP depending on task context. In accordance with behavior, the rate of buildup to identical visual stimuli differed between tasks and buildup was prominent only for the stimulus dimension relevant to the task. These results indicate that LIP neurons accumulate relevant information depending on context to decide flexibly where to move the eye, suggesting that flexibility is, at least partly, implemented in the form of temporal integration gain control.

SIGNIFICANCE STATEMENT

Flexible behavior depending on context is a hallmark of human cognition. During flexible behavior, the frontal and parietal cortices have complex representations that hinder efforts to conceptualize their underlying computations. We now provide evidence that neurons in the lateral intraparietal area accumulate relevant information preferentially depending on context. We suggest that behavioral flexibility is implemented in the form of temporal integration gain control in the parietal cortex.

Plasticity of prefrontal cortex connectivity in schizophrenia in response to antisaccade practice

People with schizophrenia exhibit difficulties in cognitive control that are often attributed to deficits in prefrontal cortex (PFC) circuitry. Practice paradigms have been used to improve these PFC-mediated deficits. The neural consequences of practice on task-based PFC activation have been addressed. Effects on task-based PFC connectivity, however, are largely unknown. We recruited people with schizophrenia and controls to practice antisaccades, a measure of PFC-mediated cognitive control that is disrupted in people with schizophrenia. Subjects performed antisaccades during functional magnetic resonance imaging (fMRI) before and after eight days of antisaccade practice. A group (schizophrenia, controls) × time (pre-, post-test) repeated measures ANOVA on the results of a psychophysiological interaction (PPI) analysis was used to evaluate changes in PFC connectivity; a similar model was used to evaluate changes in antisaccade behavior. After practice, antisaccade behavior improved and PFC connectivity with insular/temporal regions (involved in bottom-up orienting processes) increased in the schizophrenia group. The level of connectivity at post-test in the schizophrenia group was similar to that seen at pre-test in controls and positively correlated with antisaccade performance. Increases in connectivity between bottom-up and top-down regions may underlie behavioral improvements in people with schizophrenia after cognitive control practice.

Adaptive Encoding of Outcome Prediction by Prefrontal Cortex Ensembles Supports Behavioral Flexibility

The prefrontal cortex (PFC) is thought to play a critical role in behavioral flexibility by monitoring action-outcome contingencies. How PFC ensembles represent shifts in behavior in response to changes in these contingencies remains unclear. We recorded single-unit activity and local field potentials in the dorsomedial PFC (dmPFC) of male rats during a set-shifting task that required them to update their behavior, among competing options, in response to changes in action-outcome contingencies. As behavior was updated, a subset of PFC ensembles encoded the current trial outcome before the outcome was presented. This novel outcome-prediction encoding was absent in a control task, in which actions were rewarded pseudorandomly, indicating that PFC neurons are not merely providing an expectancy signal. In both control and set-shifting tasks, dmPFC neurons displayed postoutcome discrimination activity, indicating that these neurons also monitor whether a behavior is successful in generating rewards. Gamma-power oscillatory activity increased before the outcome in both tasks but did not differentiate between expected outcomes, suggesting that this measure is not related to set-shifting behavior but reflects expectation of an outcome after action execution. These results demonstrate that PFC neurons support flexible rule-based action selection by predicting outcomes that follow a particular action.SIGNIFICANCE STATEMENT Tracking action-outcome contingencies and modifying behavior when those contingencies change is critical to behavioral flexibility. We find that ensembles of dorsomedial prefrontal cortex neurons differentiate between expected outcomes when action-outcome contingencies change. This predictive mode of signaling may be used to promote a new response strategy at the service of behavioral flexibility.