Decoding subjective decisions from orbitofrontal cortex

When making a subjective choice, the brain must compute a value for each option and compare those values to make a decision. The orbitofrontal cortex (OFC) is critically involved in this process, but the neural mechanisms remain obscure, in part due to limitations in our ability to measure and control the internal deliberations that can alter the dynamics of the decision process. Here, we tracked the dynamics by recovering temporally precise neural states from multi-dimensional data in OFC. During individual choices, OFC alternated between states associated with the value of two available options, with dynamics that predicted whether a subject would decide quickly or vacillate between the two alternatives. Ensembles of value-encoding neurons contributed to these states, with individual neurons shifting activity patterns as the network evaluated each option. Thus, the mechanism of subjective decision-making involves the dynamic activation of OFC states associated with each choice alternative.

The Role of Prefrontal Cortex in Working Memory: A Mini Review

A prominent account of prefrontal cortex (PFC) function is that single neurons within the PFC maintain representations of task-relevant stimuli in working memory. Evidence for this view comes from studies in which subjects hold a stimulus across a delay lasting up to several seconds. Persistent elevated activity in the PFC has been observed in animal models as well as in humans performing these tasks. This persistent activity has been interpreted as evidence for the encoding of the stimulus itself in working memory. However, recent findings have posed a challenge to this notion. A number of recent studies have examined neural data from the PFC and posterior sensory areas, both at the single neuron level in primates, and at a larger scale in humans, and have failed to find encoding of stimulus information in the PFC during tasks with a substantial working memory component. Strong stimulus related information, however, was seen in posterior sensory areas. These results suggest that delay period activity in the PFC might be better understood not as a signature of memory storage per se, but as a top down signal that influences posterior sensory areas where the actual working memory representations are maintained.

Capturing the temporal evolution of choice across prefrontal cortex

Activity in prefrontal cortex (PFC) has been richly described using economic models of choice. Yet such descriptions fail to capture the dynamics of decision formation. Describing dynamic neural processes has proven challenging due to the problem of indexing the internal state of PFC and its trial-by-trial variation. Using primate neurophysiology and human magnetoencephalography, we here recover a single-trial index of PFC internal states from multiple simultaneously recorded PFC subregions. This index can explain the origins of neural representations of economic variables in PFC. It describes the relationship between neural dynamics and behaviour in both human and monkey PFC, directly bridging between human neuroimaging data and underlying neuronal activity. Moreover, it reveals a functionally dissociable interaction between orbitofrontal cortex, anterior cingulate cortex and dorsolateral PFC in guiding cost-benefit decisions. We cast our observations in terms of a recurrent neural network model of choice, providing formal links to mechanistic dynamical accounts of decision-making.

DOI:http://dx.doi.org/10.7554/eLife.11945.001

In 1848, a railroad worker named Phineas Gage suffered an accident that was to secure him a place in neuroscience lore. While constructing a new railway line, a mistimed explosion propelled an iron bar into the base of his skull, where it passed behind his left eye before exiting through the top of his head. Gage survived the accident, but those who knew him reported significant changes in his personality and behaviour.

Gage’s ability to make decisions was particularly impaired by his injury. Decision-making involves weighing up the costs and benefits associated with alternative courses of action. It entails looking into the future to decide whether an anticipated reward will justify the effort or expense necessary to obtain it. This process is dependent on a region of the brain called the prefrontal cortex, the area that sustained the most damage in Phineas Gage.

While many studies have shown correlations between activity in particular parts of prefrontal cortex and the outcome of decisions, little is known about how this activity evolves over time as a decision is made. To explore this process, Hunt et al. trained macaque monkeys to choose between pairs of images that were associated with specific rewards (quantities of fruit juice) and costs (either amounts of work or fixed delays).

Electrode recordings revealed changes in prefrontal activity that varied over time as the monkeys deliberated over each pair of images, choosing for example between a large reward after a long delay versus a smaller reward immediately. This activity was consistent with a mathematical model of decision-making, which also explains data from brain imaging experiments in humans. This provides an important link between human data and electrode recordings in animals.

However, some of the patterns of activity observed in both macaques and humans appeared to reflect the speed at which decisions were made, rather than the outcome of the decisions themselves. By extracting information about decision speed on each decision from each region, it was shown that communication between regions of prefrontal cortex changes when choices are between two different amounts of work, as opposed to two different delays. Further experiments are needed to explore this phenomenon and to determine how other brain regions interact with the prefrontal cortex to support the decision-making process.

DOI:http://dx.doi.org/10.7554/eLife.11945.002

A hierarchy of intrinsic timescales across primate cortex

Specialization and hierarchy are organizing principles for primate cortex, yet there is little direct evidence for how cortical areas are specialized in the temporal domain. We measured timescales of intrinsic fluctuations in spiking activity across areas, and found a hierarchical ordering, with sensory and prefrontal areas exhibiting shorter and longer timescales, respectively. Based on our findings, we suggest that intrinsic timescales reflect areal specialization for task-relevant computations over multiple temporal ranges.

Prefrontal-amygdala interactions underlying value coding

Dissociating the source and function of value-related signals is a major challenge for understanding the role of reward in neural processing. In this issue of Neuron, Rudebeck et al. (2013) provide insight into the neuroanatomical origins of a subset of these signals.

Medial-lateral organization of the orbitofrontal cortex

Emerging evidence suggests that specific cognitive functions localize to different subregions of OFC, but the nature of these functional distinctions remains unclear. One prominent theory, derived from human neuroimaging, proposes that different stimulus valences are processed in separate orbital regions, with medial and lateral OFC processing positive and negative stimuli, respectively. Thus far, neurophysiology data have not supported this theory. We attempted to reconcile these accounts by recording neural activity from the full medial-lateral extent of the orbital surface in monkeys receiving rewards and punishments via gain or loss of secondary reinforcement. We found no convincing evidence for valence selectivity in any orbital region. Instead, we report differences between neurons in central OFC and those on the inferior-lateral orbital convexity, in that they encoded different sources of value information provided by the behavioral task. Neurons in inferior convexity encoded the value of external stimuli, whereas those in OFC encoded value information derived from the structure of the behavioral task. We interpret these results in light of recent theories of OFC function and propose that these distinctions, not valence selectivity, may shed light on a fundamental organizing principle for value processing in orbital cortex.

Inferring the value of the world

A prominent view of the function of orbitofrontal cortex (OFC) is that it is responsible for calculating the value of things in the environment. A recent study shows that this role is restricted to cases in which the value must be inferred from our knowledge of the world.

Capacity and precision in an animal model of visual short-term memory

Temporary storage of information in visual short-term memory (VSTM) is a key component of many complex cognitive abilities. However, it is highly limited in capacity. Understanding the neurophysiological nature of this capacity limit will require a valid animal model of VSTM. We used a multiple-item color change detection task to measure macaque monkeys' VSTM capacity. Subjects' performance deteriorated and reaction times increased as a function of the number of items in memory. Additionally, we measured the precision of the memory representations by varying the distance between sample and test colors. In trials with similar sample and test colors, subjects made more errors compared to trials with highly discriminable colors. We modeled the error distribution as a Gaussian function and used this to estimate the precision of VSTM representations. We found that as the number of items in memory increases the precision of the representations decreases dramatically. Additionally, we found that focusing attention on one of the objects increases the precision with which that object is stored and degrades the precision of the remaining. These results are in line with recent findings in human psychophysics and provide a solid foundation for understanding the neurophysiological nature of the capacity limit of VSTM.

Contrasting reward signals in the orbitofrontal cortex and anterior cingulate cortex

Damage to the orbitofrontal cortex (OFC) and anterior cingulate cortex (ACC) impairs decision making, but the underlying value computations that cause such impairments remain unclear. Both the OFC and ACC encode a wide variety of signals correlated with decision making. The current challenge is to determine how these two different areas support decision-making processes. Here, we review a series of experiments that have helped define these roles. A special population of neurons in the ACC, but not the OFC, multiplex value information across decision parameters using a unified encoding scheme, and encode reward prediction errors. In contrast, neurons in the OFC, but not the ACC, encode the value of a choice relative to the recent history of choice values. Together, these results suggest complementary valuation processes: OFC neurons dynamically evaluate current choices relative to the value contexts recently experienced, while ACC neurons encode choice predictions and prediction errors using a common valuation currency reflecting the integration of multiple decision parameters.

Challenges of Interpreting Frontal Neurons during Value-Based Decision-Making

The frontal cortex is crucial to sound decision-making, and the activity of frontal neurons correlates with many aspects of a choice, including the reward value of options and outcomes. However, rewards are of high motivational significance and have widespread effects on neural activity. As such, many neural signals not directly involved in the decision process can correlate with reward value. With correlative techniques such as electrophysiological recording or functional neuroimaging, it can be challenging to distinguish neural signals underlying value-based decision-making from other perceptual, cognitive, and motor processes. In the first part of the paper, we examine how different value-related computations can potentially be confused. In particular, error-related signals in the anterior cingulate cortex, generated when one discovers the consequences of an action, might actually represent violations of outcome expectation, rather than errors per se. Also, signals generated at the time of choice are typically interpreted as reflecting predictions regarding the outcomes associated with the different choice alternatives. However, these signals could instead reflect comparisons between the presented choice options and previously presented choice alternatives. In the second part of the paper, we examine how value signals have been successfully dissociated from saliency-related signals, such as attention, arousal, and motor preparation in studies employing outcomes with both positive and negative valence. We hope that highlighting these issues will prove useful for future studies aimed at disambiguating the contribution of different neuronal populations to choice behavior.

Double dissociation of value computations in orbitofrontal and anterior cingulate neurons

Damage to prefrontal cortex (PFC) impairs decision-making, but the underlying value computations that might cause such impairments remain unclear. Here we report that value computations are doubly dissociable within PFC neurons. While many PFC neurons encoded chosen value, they used opponent encoding schemes such that averaging the neuronal population eliminated value coding. However, a special population of neurons in anterior cingulate cortex (ACC) - but not orbitofrontal cortex (OFC) - multiplex chosen value across decision parameters using a unified encoding scheme, and encoded reward prediction errors. In contrast, neurons in OFC - but not ACC - encoded chosen value relative to the recent history of choice values. Together, these results suggest complementary valuation processes across PFC areas: OFC neurons dynamically evaluate current choices relative to recent choice values, while ACC neurons encode choice predictions and prediction errors using a common valuation currency reflecting the integration of multiple decision parameters.

The dynamics of learning and behavioral flexibility

Fundamental to behavior is the capacity to distinguish beneficial from detrimental environmental stimuli. In this issue of Neuron, a new study by Morrison et al. shows that underlying these processes are qualitatively different dynamical interactions between brain structures involved in processing the value of environmental stimuli.

Heterogeneous reward signals in prefrontal cortex

Neurons encode upcoming rewards throughout frontal cortex. Recent papers have helped to determine that these signals play different roles in different frontal regions. Neurons in orbitofrontal cortex (PFo) appear to be responsible for calculating the specific value of an expected reward, information that can help efficiently guide decision-making. Similar signals are also present in the cingulate sulcus (PFcs). By contrast, reward signals in lateral prefrontal cortex (PFl) are consistent with a role in using reward to guide other cognitive processes, such as the allocation of attentional resources and using value information to guide learning other relationships in the environment such as arbitrary stimulus-response mappings. A remaining issue for future work is to specify the precise roles of PFo and PFcs. These two areas show very different patterns of connectivity with other brain areas, and it is currently unclear how this effects their contribution to decision-making.

Encoding of reward and space during a working memory task in the orbitofrontal cortex and anterior cingulate sulcus

Several lines of research indicate that emotional and motivational information may be useful in guiding the allocation of attentional resources. Two areas of the frontal lobe that are particularly implicated in the encoding of motivational information are the orbital prefrontal cortex (PFo) and the dorsomedial region of prefrontal cortex, specifically the anterior cingulate sulcus (PFcs). However, it remains unclear whether these areas use this information to influence spatial attention. We used single-unit neurophysiology to examine whether, at the level of individual neurons, there was evidence for integration between reward information and spatial attention. We trained two subjects to perform a task that required them to attend to a spatial location across a delay under different expectancies of reward for correct performance. We balanced the order of presentation of spatial and reward information so we could assess the neuronal encoding of the two pieces of information independently and conjointly. We found little evidence for encoding of the spatial location in either PFo or PFcs. In contrast, both areas encoded the expected reward. Furthermore, PFo consistently encoded reward more quickly than PFcs, although reward encoding was subsequently more prevalent and stronger in PFcs. These results suggest a differential contribution of PFo and PFcs to reward encoding, with PFo potentially more important for initially determining the value of rewards predicted by sensory stimuli. They also suggest that neither PFo nor PFcs play a direct role in the control of spatial attention.

Neurons in the frontal lobe encode the value of multiple decision variables

A central question in behavioral science is how we select among choice alternatives to obtain consistently the most beneficial outcomes. Three variables are particularly important when making a decision: the potential payoff, the probability of success, and the cost in terms of time and effort. A key brain region in decision making is the frontal cortex as damage here impairs the ability to make optimal choices across a range of decision types. We simultaneously recorded the activity of multiple single neurons in the frontal cortex while subjects made choices involving the three aforementioned decision variables. This enabled us to contrast the relative contribution of the anterior cingulate cortex (ACC), the orbito-frontal cortex, and the lateral prefrontal cortex to the decision-making process. Neurons in all three areas encoded value relating to choices involving probability, payoff, or cost manipulations. However, the most significant signals were in the ACC, where neurons encoded multiplexed representations of the three different decision variables. This supports the notion that the ACC is an important component of the neural circuitry underlying optimal decision making.

Evaluating choices by single neurons in the frontal lobe: outcome value encoded across multiple decision variables

Damage to the frontal lobe can cause severe decision-making impairments. A mechanism that may underlie this is that neurons in the frontal cortex encode many variables that contribute to the valuation of a choice, such as its costs, benefits and probability of success. However, optimal decision-making requires that one considers these variables, not only when faced with the choice, but also when evaluating the outcome of the choice, in order to adapt future behaviour appropriately. To examine the role of the frontal cortex in encoding the value of different choice outcomes, we simultaneously recorded the activity of multiple single neurons in the anterior cingulate cortex (ACC), orbitofrontal cortex (OFC) and lateral prefrontal cortex (LPFC) while subjects evaluated the outcome of choices involving manipulations of probability, payoff and cost. Frontal neurons encoded many of the parameters that enabled the calculation of the value of these variables, including the onset and offset of reward and the amount of work performed, and often encoded the value of outcomes across multiple decision variables. In addition, many neurons encoded both the predicted outcome during the choice phase of the task as well as the experienced outcome in the outcome phase of the task. These patterns of selectivity were more prevalent in ACC relative to OFC and LPFC. These results support a role for the frontal cortex, principally ACC, in selecting between choice alternatives and evaluating the outcome of that selection thereby ensuring that choices are optimal and adaptive.

Orbitofrontal cortex and its contribution to decision-making

Damage to orbitofrontal cortex (OFC) produces an unusual pattern of deficits. Patients have intact cognitive abilities but are impaired in making everyday decisions. Here we review anatomical, neuropsychological, and neurophysiological evidence to determine the neuronal mechanisms that might underlie these impairments. We suggest that OFC plays a key role in processing reward: It integrates multiple sources of information regarding the reward outcome to derive a value signal. In effect, OFC calculates how rewarding a reward is. This value signal can then be held in working memory where it can be used by lateral prefrontal cortex to plan and organize behavior toward obtaining the outcome, and by medial prefrontal cortex to evaluate the overall action in terms of its success and the effort that was required. Thus, acting together, these prefrontal areas can ensure that our behavior is most efficiently directed towards satisfying our needs.

Neuronal Mechanisms in Prefrontal Cortex Underlying Adaptive Choice Behavior

This chapter aims to address two questions relating to the role of the prefrontal cortex (PFC) in reward-guided choice behavior. First, do PFC neurons encode rewards per se, or are they encoding behavioral sequelae of reward? To address this, we recorded simultaneously from multiple PFC subregions, with the rationale that neuronal selectivity that directly encoded the reward outcome should occur before selectivity that reflected reward-related sequelae. Our results indicate that neurons in the orbitofrontal cortex (OFC) encode reward information before neurons in the dorsolateral PFC (DLPFC). Furthermore, whereas DLPFC neurons encoded both the upcoming response as well as the expected reward, OFC neurons encoded the reward alone. Our interpretation of these results is that the OFC encodes the reward and passes this information to the DLPFC, which uses it to determine the behavioral response. The second question is whether the encoding is specific to the reward outcome or reflective of a more abstract value signal that could facilitate decision making. We examined this by determining whether the PFC encodes other types of information relevant to decision making, such as probability of success and effort. We found that many PFC neurons encoded at least one of these variables, but neurons in the OFC and the medial PFC (MPFC) encoded combinations of the variables indicative of encoding an abstract value signal. This signal could provide decision making with flexibility and a capacity to deal with novelty, which are two of the hallmark features of prefrontal function. Future research will focus on delineating the differential contributions of the OFC and the MPFC to decision making.

A comparison of abstract rules in the prefrontal cortex, premotor cortex, inferior temporal cortex, and striatum

The ability to use abstract rules or principles allows behavior to generalize from specific circumstances. We have previously shown that such rules are encoded in the lateral prefrontal cortex (PFC) and premotor cortex (PMC). Here, we extend these investigations to two other areas directly connected with the PFC and the PMC, the inferior temporal cortex (ITC) and the dorsal striatum (STR). Monkeys were trained to use two abstract rules: "same" or "different". They had to either hold or release a lever, depending on whether two successively presented pictures were the same or different, and depending on which rule was in effect. The rules and the behavioral responses were reflected most strongly and, on average, tended to be earlier in the PMC followed by the PFC and then the STR; few neurons in the ITC reflected the rules or the actions. By contrast, perceptual information (the identity of the pictures used as sample and test stimuli) was encoded more strongly and earlier in the ITC, followed by the PFC; they had weak, if any, effects on neural activity in the PMC and STR. These findings are discussed in the context of the anatomy and posited functions of these areas.

Hyper-Rayleigh scattering as a means of monitoring crystal nucleation in solution

Hyper-Rayleigh scattering is revealed as a very sensitive monitor of cluster formation in solution, and as a means of studying the mechanism of crystal nucleation in molecular species. Two compounds are selected with particularly high second harmonic generation (SHG) powers in the crystalline state and experimental conditions are defined allowing the measurement of the beta value for one of these as 18+/-1x10(-30) esu. It is found to agree with current theoretical prediction of 20x10(-30) esu. In the more powerful of these, two photon induced fluorescence is found to be partly responsible for the SHG. The solubilities of both compounds in methanol are measured and it is observed that these differ by a factor of ten. When the solution concentration is increased beyond 45% of the saturation value, the quadratic coefficient exhibits non-linear behaviour with respect to concentration. Additionally, the widths of the distributions of the HRS signals increase initially with concentration as expected, but, beyond 45% saturation concentrations, these narrow again. These phenomena are interpreted as indicators of cluster formation in these solutions well below saturation concentrations. A future experimental design is proposed in which the coherent component will yield information on the organisation of the molecules in such clusters.

Neuronal activity in primate dorsolateral and orbital prefrontal cortex during performance of a reward preference task

An important function of the prefrontal cortex (PFC) is the control of goal-directed behaviour. This requires information as to whether actions were successful in obtaining desired outcomes such as rewards. While lesion studies implicate a particular PFC region, the orbitofrontal cortex (OFC), in reward processing, neurons encoding reward have been reported in both the OFC and the dorsolateral prefrontal cortex (DLPFC). To compare and contrast their roles, we recorded simultaneously from both areas while two rhesus monkeys (Macaca mulatta) performed a reward preference task. The monkeys had to choose between pictures associated with different amounts of a juice reward. Neuronal activity in both areas reflected the reward amount. However, neurons in the DLPFC encoded both the reward amount and the monkeys' forthcoming response, while neurons in the OFC more often encoded the reward amount alone. Further, reward selectivity arose more rapidly in the OFC than the DLPFC. These results are consistent with reward information entering the PFC via the OFC, where it is passed to the DLPFC and used to control behaviour.

Neural circuits subserving the retrieval and maintenance of abstract rules

Behavior is often governed by abstract rules or instructions for behavior that can be abstracted from one context and applied to another. Prefrontal cortex (PFC) is thought to be important for representing rules, although the contributions of ventrolateral (VLPFC) and dorsolateral (DLPFC) regions remain under-specified. In the present study, event-related fMRI was used to examine abstract rule representation in humans. Prior to scanning, subjects learned to associate unfamiliar shapes and nonwords with particular rules. During each fMRI trial, presentation of one of these cues was followed by a delay and then by sample and probe stimuli. Match and non-match rules required subjects to indicate whether or not the sample and probe matched; go rules required subjects to make a response that was not contingent on the sample/probe relation. Left VLPFC, parietal cortex, and pre-SMA exhibited sensitivity to rule type during the cue and delay periods. Delay-period activation in these regions, but not DLPFC, was greater when subjects had to maintain response contingencies (match, non-match) relative to when the cue signaled a specific response (go). In contrast, left middle temporal cortex exhibited rule sensitivity during the cue but not delay period. These results support the hypothesis that VLPFC interacts with temporal cortex to retrieve semantic information associated with a cue and with parietal cortex to retrieve and maintain relevant response contingencies across delays. Future investigations of cross-regional interactions will enable full assessment of this account. Collectively, these results demonstrate that multiple, neurally separable processes are recruited during abstract rule representation.

From rule to response: neuronal processes in the premotor and prefrontal cortex

The ability to use abstract rules or principles allows behavior to generalize from specific circumstances (e.g., rules learned in a specific restaurant can subsequently be applied to any dining experience). Neurons in the prefrontal cortex (PFC) encode such rules. However, to guide behavior, rules must be linked to motor responses. We investigated the neuronal mechanisms underlying this process by recording from the PFC and the premotor cortex (PMC) of monkeys trained to use two abstract rules: "same" or "different." The monkeys had to either hold or release a lever, depending on whether two successively presented pictures were the same or different, and depending on which rule was in effect. The abstract rules were represented in both regions, although they were more prevalent and were encoded earlier and more strongly in the PMC. There was a perceptual bias in the PFC, relative to the PMC, with more PFC neurons encoding the presented pictures. In contrast, neurons encoding the behavioral response were more prevalent in the PMC, and the selectivity was stronger and appeared earlier in the PMC than in the PFC.

Neural correlates of categories and concepts

The ability to readily adapt to novel situations requires something beyond storing specific stimulus-response associations. Instead, many animals can detect basic characteristics of events and store them as generalized classes. Because these representations are abstracted beyond specific details of sensory inputs and motor outputs, they can be easily generalized and adapted to new circumstances. Explorations of neural mechanisms of sensory processing and motor output have progressed to the point where studies can begin to address the neural basis of abstract, categorical representations. Recent studies have revealed their neural correlates in various cortical areas of the non-human primate brain.

The prefrontal cortex: categories, concepts and cognition

The ability to generalize behaviour-guiding principles and concepts from experience is key to intelligent, goal-directed behaviour. It allows us to deal efficiently with a complex world and to adapt readily to novel situations. We review evidence that the prefrontal cortex-the cortical area that reaches its greatest elaboration in primates-plays a central part in acquiring and representing this information. The prefrontal cortex receives highly processed information from all major forebrain systems, and neurophysiological studies suggest that it synthesizes this into representations of learned task contingencies, concepts and task rules. In short, the prefrontal cortex seems to underlie our internal representations of the 'rules of the game'. This may provide the necessary foundation for the complex behaviour of primates, in whom this structure is most elaborate.

Dissociable contributions of the orbitofrontal and lateral prefrontal cortex of the marmoset to performance on a detour reaching task

To gain insight into the nature and neural specificity of the relationship between simple problem solving, inhibitory control and prefrontal cortex, comparison of the effects of excitotoxic lesions of the orbitofrontal and lateral prefrontal cortex were examined on the performance of common marmosets on a detour reaching task. Monkeys were required to inhibit reaching directly for food reward in a transparent box and instead make a detour reach around to the side of the box either having had (i) no prior experience on the task (experiment 1) or (ii) previous experience in reaching around the sides of an opaque box (experiment 2). Whilst monkeys with orbitofrontal lesions had difficulty in inhibiting direct reaches to visible food reward (experiment 1), they could resist this prepotent response tendency following extensive prior experience of detour reaching with an opaque box (experiment 2). In marked contrast, monkeys with lateral prefrontal lesions exhibited no difficulty in inhibiting reaching to visible food reward or acquiring detour reaching per se (experiment 1). However, having been given the opportunity to acquire an efficient detour reaching strategy to hidden food reward these lateral prefrontal lesioned monkeys were impaired at transferring this strategy to the new context in which the food reward was made visible (experiment 2). This double dissociation between the effects of orbitofrontal and lateral prefrontal lesions on detour reaching provides evidence for a clear distinction in the level of control over responding exerted by the orbitofrontal and lateral prefrontal cortex, consistent with hierarchical ordering of response control processes within prefrontal cortex.

1,6-interactions between dimethylamino and aldehyde groups in two biphenyl derivatives

The title compounds, 2-(dimethylamino)biphenyl-2'-carboxaldehyde, C15H15NO, and 2-(dimethylamino)biphenyl-2',6'-dicarboxaldehyde, C16H15NO2, show similar 1,6-interactions [N...C=O 2.929 (3) to 3.029 (3) A] between the dimethylamino and aldehyde groups located in the ortho positions of the two rings, which lie at 58.1 (1)-62.4 (1) degrees to each other.

Single neurons in prefrontal cortex encode abstract rules

The ability to abstract principles or rules from direct experience allows behaviour to extend beyond specific circumstances to general situations. For example, we learn the 'rules' for restaurant dining from specific experiences and can then apply them in new restaurants. The use of such rules is thought to depend on the prefrontal cortex (PFC) because its damage often results in difficulty in following rules. Here we explore its neural basis by recording from single neurons in the PFC of monkeys trained to use two abstract rules. They were required to indicate whether two successively presented pictures were the same or different depending on which rule was currently in effect. The monkeys performed this task with new pictures, thus showing that they had learned two general principles that could be applied to stimuli that they had not yet experienced. The most prevalent neuronal activity observed in the PFC reflected the coding of these abstract rules.

Inhibitory control and affective processing in the prefrontal cortex: neuropsychological studies in the common marmoset

The orbitofrontal cortex has been ascribed a role in the inhibitory control, as well as in the emotional control, of behaviour. While damage to the orbitofrontal cortex in humans and non-human primates can cause inflexibility, impulsiveness and emotional disturbance, the relationship between these effects are unclear. Excitotoxic lesion studies in marmosets comparing the effects of cell loss within specific regions of the prefrontal cortex on performance of a range of behavioural tests reveal that mechanisms of response inhibition are not unique to the orbitofrontal cortex. Instead they are present in distinct cognitive domains for lowerorder as well as higher-order processing throughout the prefrontal cortex. Thus, the lateral prefrontal cortex is involved in the selection and control of action based upon higher-order rules while the orbitofrontal and medial prefrontal cortex may be involved in different but complementary forms of lower-order rule learning, their roles dissociable, as a result of their differential contribution to different types of associative learning.