An evolutionary computational theory of prefrontal executive function in decision-making

The prefrontal cortex subserves executive control and decision-making, that is, the coordination and selection of thoughts and actions in the service of adaptive behaviour. We present here a computational theory describing the evolution of the prefrontal cortex from rodents to humans as gradually adding new inferential Bayesian capabilities for dealing with a computationally intractable decision problem: exploring and learning new behavioural strategies versus exploiting and adjusting previously learned ones through reinforcement learning (RL). We provide a principled account identifying three inferential steps optimizing this arbitration through the emergence of (i) factual reactive inferences in paralimbic prefrontal regions in rodents; (ii) factual proactive inferences in lateral prefrontal regions in primates and (iii) counterfactual reactive and proactive inferences in human frontopolar regions. The theory clarifies the integration of model-free and model-based RL through the notion of strategy creation. The theory also shows that counterfactual inferences in humans yield to the notion of hypothesis testing, a critical reasoning ability for approximating optimal adaptive processes and presumably endowing humans with a qualitative evolutionary advantage in adaptive behaviour.     

内侧前额叶与社会认知

早期的研究表明杏仁核、前额叶、颞上沟、前扣带回等与人类的社会认知活动有关;随着多种新技术的应用。越来越多的研究发现其它一些脑区结构(如岛叶、基底节、白质等)也与社会认知和行为有关。本文综述了内侧前额叶在社会认知中的作用,重点介绍了内侧前额叶在心灵理论、情绪认知、社会推理与决策、道德判断、自我认知等社会认知活动中的作用。未来研究希望能从整体和动态上认识内侧前额叶在社会认知活动中的作用。     

Role of the lateral hypothalamus and prefrontal cortex in organization of voluntary movements

Roles of the lateral hypothalamus and prefrontal cortex in organization and control of automatized food-procuring movements were studied in rats under conditions of unrestrained behavior with the use of video- and photorecording techniques, destruction of the brain structures, and recording of single neuron impulse responses. The lateral hypothalamus is considered a link in the control system for food-procuring movements, which provides formation of the motor program. The role of the prefrontal cortex is regarded as related to programing and initiation of food-procuring movements and current control of efficiency of their performance. Positions of the lateral hypothalamus and prefrontal cortex within an ensemble of the motor centers, which organizes voluntary movements, are discussed.     

Predicting functional properties of visual cortex from an evolutionary scaling law

The number of neurons in the primary visual cortex (V1) is, across primate species, related to the number of neurons in the visual thalamus (the lateral geniculate nucleus [LGN]) by a power law with an exponent of 3/2. This evolutionary scaling law is explained by a simple relation according to which the fineness of resolution in cortex is related to the number of neurons in the area of cortex used to process the information from a single point of light (the point-spread area). The same theory provides a link between two functional properties of the visual cortex, the areal cortical magnification factor (ACMF) and the receptive field (RF) area.     

Differential Contributions of Dorso-Ventral and Rostro-Caudal Prefrontal White Matter Tracts to Cognitive Control in Healthy Older Adults

Prefrontal cortex mediates cognitive control by means of circuitry organized along dorso-ventral and rostro-caudal axes. Along the dorso-ventral axis, ventrolateral PFC controls semantic information, whereas dorsolateral PFC encodes task rules. Along the rostro-caudal axis, anterior prefrontal cortex encodes complex rules and relationships between stimuli, whereas posterior prefrontal cortex encodes simple relationships between stimuli and behavior. Evidence of these gradients of prefrontal cortex organization has been well documented in fMRI studies, but their functional correlates have not been examined with regard to integrity of underlying white matter tracts. We hypothesized that (a) the integrity of specific white matter tracts is related to cognitive functioning in a manner consistent with the dorso-ventral and rostro-caudal organization of the prefrontal cortex, and (b) this would be particularly evident in healthy older adults. We assessed three cognitive processes that recruit the prefrontal cortex and can distinguish white matter tracts along the dorso-ventral and rostro-caudal dimensions –episodic memory, working memory, and reasoning. Correlations between cognition and fractional anisotropy as well as fiber tractography revealed: (a) Episodic memory was related to ventral prefrontal cortex-thalamo-hippocampal fiber integrity; (b) Working memory was related to integrity of corpus callosum body fibers subserving dorsolateral prefrontal cortex; and (c) Reasoning was related to integrity of corpus callosum body fibers subserving rostral and caudal dorsolateral prefrontal cortex. These findings confirm the ventrolateral prefrontal cortex''s role in semantic control and the dorsolateral prefrontal cortex''s role in rule-based processing, in accordance with the dorso-ventral prefrontal cortex gradient. Reasoning-related rostral and caudal superior frontal white matter may facilitate different levels of task rule complexity. This study is the first to demonstrate dorso-ventral and rostro-caudal prefrontal cortex processing gradients in white matter integrity.     

Active linking in evolutionary games

In the traditional approach to evolutionary game theory, the individuals of a population meet each other at random, and they have no control over the frequency or duration of interactions. Here we remove these simplifying assumptions. We introduce a new model, where individuals differ in the rate at which they seek new interactions. Once a link between two individuals has formed, the productivity of this link is evaluated. Links can be broken off at different rates. In a limiting case, the linking dynamics introduces a simple transformation of the payoff matrix. We outline conditions for evolutionary stability. As a specific example, we study the interaction between cooperators and defectors. We find a simple relationship that characterizes those linking dynamics which allow natural selection to favour cooperation over defection.     

The counting Stroop: a cognitive interference task

The counting Stroop is a validated Stroop task variant. Initially designed as a functional magnetic resonance imaging (fMRI) task for identifying brain regions subserving cognition and attention (dorsal anterior midcingulate cortex (daMCC) and dorsolateral prefrontal cortex (DLPFC)), it has been used to study cognition in healthy volunteers and to identify functional brain abnormalities in neuropsychiatric disorders, such as attention deficit hyperactivity disorder (ADHD). During the counting Stroop, subjects report by button-press the number of words (one to four) appearing on the screen, regardless of word meaning. Neutral-word control trials contain single semantic category common animals (e.g., 'dog' written three times), while interference trials contain number words that are incongruent with the correct response (e.g., 'two' written four times). The counting Stroop can be completed in approximately 20 min per subject and can be used offline (behavioral performance) or with fMRI, positron emission tomography, event-related potentials, magnetoencephalography or intracranial recordings.     

The neural bases of cognitive conflict and control in moral judgment

Traditional theories of moral psychology emphasize reasoning and "higher cognition," while more recent work emphasizes the role of emotion. The present fMRI data support a theory of moral judgment according to which both "cognitive" and emotional processes play crucial and sometimes mutually competitive roles. The present results indicate that brain regions associated with abstract reasoning and cognitive control (including dorsolateral prefrontal cortex and anterior cingulate cortex) are recruited to resolve difficult personal moral dilemmas in which utilitarian values require "personal" moral violations, violations that have previously been associated with increased activity in emotion-related brain regions. Several regions of frontal and parietal cortex predict intertrial differences in moral judgment behavior, exhibiting greater activity for utilitarian judgments. We speculate that the controversy surrounding utilitarian moral philosophy reflects an underlying tension between competing subsystems in the brain.     

Why there are no objective values: A critique of ethical intuitionism from an evolutionary point of view

Using concepts of evolutionary game theory, this paper presents a critique of ethical intuitionism, or non-naturalism, in its cognitivist and objectivist interpretation. While epistemological considerations suggest that human rational learning through experience provides no basis for objective moral knowledge, it is argued below that modern evolutionary theory explains why this is so, i.e., why biological organisms do not evolve so as to experience objective preferences and obligations. The difference between the modes of the cognition of objective and of valuative environmental attributes is explained with reference to different modes of natural selection acting on the cognitive apparatus of the organism. The negative implications are pointed out which the observable diversity of intraspecific behavioural adaptations and of cultural values has for the cognitivist, objectivist foundation of ethics. Eventually a non-cognitivist alternative to ethical intuitionism is outlined in terms of empirical authority relations, with the ritualisation of dominance-submission patterns as the evolutionary origin of human charismatic authority.     

Frontal lobe and cognitive development

In phylogeny as in ontogeny, the association cortex of the frontal lobe, also known as the prefrontal cortex, is a late-developing region of the neocortex. It is also one of the cortical regions to undergo the greatest expansion in the course of both evolution and individual maturation. In the human adult, the prefrontal cortex constitutes as much as nearly one-third of the totality of the neocortex. The protracted, relatively large, development of the prefrontal cortex is manifest in gross morphology as well as fine structure. In the developing individual, its late maturation is made most apparent by the late myelination of its axonal connections. This and other indices of morphological development of the prefrontal cortex correlate with the development of cognitive functions that neuropsychological studies in animals and humans have ascribed to this cortex. In broad outline, the ventromedial areas of the prefrontal cortex, which with respect to otherprefrontal areas develop relatively early, are involved in the expression and control of emotional and instinctual behaviors. On the other hand, the late maturing areas of the lateral prefrontal convexity are principally involved in higher executive functions. The most general executive function of the lateral prefrontal cortex is the temporal organization of goal-directed actions in the domains of behavior, cognition, and language. In all three domains, that global function is supported by a fundamental role of the lateral prefrontal cortex in temporal integration, that is, the integration of temporally discontinuous percepts and neural inputs into coherent structures of action. Temporal integration is in turn served by at least three cognitive functions of somewhat different prefrontal topography: working memory, preparatory set, and inhibitory control. These functions engage the prefrontal cortex in interactive cooperation with other neocortical regions. The development of language epitomizes the development of temporal integrative cognitive functions and their underlying neural substrate, notably the lateral prefrontal cortex and other late-developing cortical regions.     

Dopaminergic control of the striatum for high-level cognition

Dopamine has long been implicated in a wide variety of high-level cognitive processes, ranging from working memory to rule learning and attention switching. Notable progress has been made in the past decades, but the mechanisms underlying effects of dopamine on high-level cognition remain unclear. This article reviews evidence for an important role of the striatum and its interaction with the prefrontal cortex and suggests a variety of ways by which changes in dopamine transmission can bias high-level cognition.     

Modulating Cognition Using Transcranial Direct Current Stimulation of the Cerebellum

Numerous studies have emerged recently that demonstrate the possibility of modulating, and in some cases enhancing, cognitive processes by exciting brain regions involved in working memory and attention using transcranial electrical brain stimulation. Some researchers now believe the cerebellum supports cognition, possibly via a remote neuromodulatory effect on the prefrontal cortex. This paper describes a procedure for investigating a role for the cerebellum in cognition using transcranial direct current stimulation (tDCS), and a selection of information-processing tasks of varying task difficulty, which have previously been shown to involve working memory, attention and cerebellar functioning. One task is called the Paced Auditory Serial Addition Task (PASAT) and the other a novel variant of this task called the Paced Auditory Serial Subtraction Task (PASST). A verb generation task and its two controls (noun and verb reading) were also investigated. All five tasks were performed by three separate groups of participants, before and after the modulation of cortico-cerebellar connectivity using anodal, cathodal or sham tDCS over the right cerebellar cortex. The procedure demonstrates how performance (accuracy, verbal response latency and variability) could be selectively improved after cathodal stimulation, but only during tasks that the participants rated as difficult, and not easy. Performance was unchanged by anodal or sham stimulation. These findings demonstrate a role for the cerebellum in cognition, whereby activity in the left prefrontal cortex is likely dis-inhibited by cathodal tDCS over the right cerebellar cortex. Transcranial brain stimulation is growing in popularity in various labs and clinics. However, the after-effects of tDCS are inconsistent between individuals and not always polarity-specific, and may even be task- or load-specific, all of which requires further study. Future efforts might also be guided towards neuro-enhancement in cerebellar patients presenting with cognitive impairment once a better understanding of brain stimulation mechanisms has emerged.     

Neural representation of visual objects: encoding and top-down activation

Knowledge or experiences are voluntarily recalled from memory by reactivation of their neural representations in the association cortex. Mnemonic representations of visual objects, located in the ventral processing stream of visual perception, provide the best indication of how neuronal codes are created, organized and reactivated. Associative codes are created by neurons that have the ability to link the representations of temporally associated stimuli. Recent experiments suggest that not only bottom-up signals from the retina but also top-down signals from the prefrontal cortex can trigger the retrieval of associative codes, which may serve as a neural basis for conscious recall.     

Spatial learning and action planning in a prefrontal cortical network model

The interplay between hippocampus and prefrontal cortex (PFC) is fundamental to spatial cognition. Complementing hippocampal place coding, prefrontal representations provide more abstract and hierarchically organized memories suitable for decision making. We model a prefrontal network mediating distributed information processing for spatial learning and action planning. Specific connectivity and synaptic adaptation principles shape the recurrent dynamics of the network arranged in cortical minicolumns. We show how the PFC columnar organization is suitable for learning sparse topological-metrical representations from redundant hippocampal inputs. The recurrent nature of the network supports multilevel spatial processing, allowing structural features of the environment to be encoded. An activation diffusion mechanism spreads the neural activity through the column population leading to trajectory planning. The model provides a functional framework for interpreting the activity of PFC neurons recorded during navigation tasks. We illustrate the link from single unit activity to behavioral responses. The results suggest plausible neural mechanisms subserving the cognitive "insight" capability originally attributed to rodents by Tolman & Honzik. Our time course analysis of neural responses shows how the interaction between hippocampus and PFC can yield the encoding of manifold information pertinent to spatial planning, including prospective coding and distance-to-goal correlates.     

Hippocampal-prefrontal connectivity predicts midfrontal oscillations and long-term memory performance

The hippocampus and prefrontal cortex interact to support working memory (WM) and long-term memory [1-3]. Neurophysiologically, WM is thought to be subserved by reverberatory activity of distributed networks within the prefrontal cortex (PFC) [2, 4-8], which become synchronized with reverberatory activity in the hippocampus [1, 4]. This electrophysiological synchronization is difficult to study in humans because noninvasive electroencephalography (EEG) cannot measure hippocampus activity. Here, using a novel integration of EEG and diffusion-weighted imaging, it is shown that individuals with relatively stronger anatomical connectivity linking the hippocampus to the right ventrolateral PFC (ventral Brodmann area 46) exhibited slower frequency neuronal oscillations during a WM task. Furthermore, subjects with stronger hippocampus-PFC connectivity were better able to encode the complex pictures used in the WM task into long-term memory. These findings are consistent with models suggesting that electrophysiological oscillations provide a mechanism of long-range interactions [9] and link hippocampus-PFC structural connectivity to PFC rhythmic electrical dynamics and memory performance. More generally, these results highlight the importance of incorporating individual differences when linking structure and function to cognition.     

Testing evolutionary models of senescence: traditional approaches and future directions

From an evolutionary perspective, the existence of senescence is a paradox. Why has senescence not been more effectively selected against given its associated decreases in Darwinian fitness? Why does senescence exist and how has it evolved? Three major theories offer explanations: (1) the theory of mutation accumulation suggested by PB Medawar; (2) the theory of antagonistic pleiotropy suggested by GC Williams; and (3) the disposable soma theory suggested by TBL Kirkwood. These three theories differ in the underlying causes of aging that they propose but are not mutually exclusive. This paper compares the specific biological predictions of each theory and discusses the methods and results of previous empirical tests. Lifespan is found to be the most frequently used estimate of senescence in evolutionary investigations. This measurement acts as a proxy for an individual’s rate of senescence, but provides no information on an individual’s senescent state or “biological age” throughout life. In the future, use of alternative longitudinal measures of senescence may facilitate investigation of previously neglected aspects of evolutionary models, such as intra- and inter-individual heterogeneity in the process of aging. DNA methylation data are newly proposed to measure biological aging and are suggested to be particularly useful for such investigations.     

A right hemispheric prefrontal system for cognitive time measurement

Despite a growing body of neuroimaging data, little consensus has been reached regarding the neural correlates of temporal processing in humans. This paper presents a reanalysis of two previously published neuroimaging experiments, which used two different cognitive timing tasks and examined both sub- and supra-second intervals. By processing these data in an identical manner, this reanalysis allows valid comparison and contrasting across studies. Conjunction of these studies using inclusive masking reveals shared activity in right hemispheric dorsolateral and ventrolateral prefrontal cortex and anterior insula, supporting a general-purpose system for cognitive time measurement in the right hemispheric prefrontal cortex. Consideration of the patterns of activity in each dataset with respect to the others, and taking task characteristics into account, provides insight into the possible role of dorsolateral prefrontal cortex in working memory and of posterior parietal cortex and anterior cingulate in attentional processing during cognitive time measurement tasks.     

Introspective minds: using ALE meta-analyses to study commonalities in the neural correlates of emotional processing, social & unconstrained cognition

Previous research suggests overlap between brain regions that show task-induced deactivations and those activated during the performance of social-cognitive tasks. Here, we present results of quantitative meta-analyses of neuroimaging studies, which confirm a statistical convergence in the neural correlates of social and resting state cognition. Based on the idea that both social and unconstrained cognition might be characterized by introspective processes, which are also thought to be highly relevant for emotional experiences, a third meta-analysis was performed investigating studies on emotional processing. By using conjunction analyses across all three sets of studies, we can demonstrate significant overlap of task-related signal change in dorso-medial prefrontal and medial parietal cortex, brain regions that have, indeed, recently been linked to introspective abilities. Our findings, therefore, provide evidence for the existence of a core neural network, which shows task-related signal change during socio-emotional tasks and during resting states.     

Chronic stress alters dendritic morphology in rat medial prefrontal cortex

Chronic stress produces deficits in cognition accompanied by alterations in neural chemistry and morphology. Medial prefrontal cortex is a target for glucocorticoids involved in the stress response. We have previously demonstrated that 3 weeks of daily corticosterone injections result in dendritic reorganization in pyramidal neurons in layer II-III of medial prefrontal cortex. To determine if similar morphological changes occur in response to chronic stress, we assessed the effects of daily restraint stress on dendritic morphology in medial prefrontal cortex. Male rats were exposed to either 3 h of restraint stress daily for 3 weeks or left unhandled except for weighing during this period. On the last day of restraint, animals were overdosed and brains were stained using a Golgi-Cox procedure. Pyramidal neurons in lamina II-III of medial prefrontal cortex were drawn in three dimensions, and the morphology of apical and basilar arbors was quantified. Sholl analyses demonstrated a significant alteration of apical dendrites in stressed animals: overall, the number and length of apical dendritic branches was reduced by 18 and 32%, respectively. The reduction in apical dendritic arbor was restricted to distal and higher-order branches, and may reflect atrophy of terminal branches: terminal branch number and length were reduced by 19 and 35%. On the other hand, basilar dendrites were not affected. This pattern of dendritic reorganization is similar to that seen after daily corticosterone injections. This reorganization likely reflects functional changes in prefrontal cortex and may contribute to stress-induced changes in cognition.     

Prediction in evolutionary systems

Despite its explanatory clout, the theory of evolution has thus far compiled a modest record with respect to predictive power—that other major hallmark of scientific theories. This is considered by many to be an acceptable limitation of a theory that deals with events and processes that are intrinsically random (and historic). However, whether this is an inherent restriction or simply the sign of an incomplete theory is an open question. In an attempt to help answer that question, we propose a classification scheme for several types of prediction that might occur with regard to evolutionary systems, then explore the nature of these predictions in a system that simulates the evolution of neural architectures. This provides a platform from which to consider the relevance of such observations for real biological systems and illuminates a variety of key issues pertaining to prediction in those environments.