A Prefrontal-Hippocampal Comparator for Goal-Directed Behavior: The Intentional Self and Episodic Memory

Hippocampal neuronal activity is aligned with action plans

Neurons in the hippocampus are correlated with different variables, including space, time, sensory cues, rewards and actions, in which the extent of tuning depends on ongoing task demands1-8. However, it remains uncertain whether such diverse tuning corresponds to distinct functions within the hippocampal network or whether a more generic computation can account for these observations9. Here, to disentangle the contribution of externally driven cues versus internal computation, we developed a task in mice in which space, auditory tones, rewards and context were juxtaposed with changing relevance. High-density electrophysiological recordings revealed that neurons were tuned to each of these modalities. By comparing movement paths and action sequences, we observed that external variables had limited direct influence on hippocampal firing. Instead, spiking was influenced by online action plans and modulated by goal uncertainty. Our results suggest that internally generated cell assembly sequences are selected and updated by action plans towards deliberate goals. The apparent tuning of hippocampal neuronal spiking to different sensory modalities might emerge due to alignment to the afforded action progression within a task rather than representation of external cues.

Hippocampal neuronal activity is aligned with action plans

Neurons in the hippocampus are correlated with different variables, including space, time, sensory cues, rewards, and actions, where the extent of tuning depends on ongoing task demands. However, it remains uncertain whether such diverse tuning corresponds to distinct functions within the hippocampal network or if a more generic computation can account for these observations. To disentangle the contribution of externally driven cues versus internal computation, we developed a task in mice where space, auditory tones, rewards, and context were juxtaposed with changing relevance. High-density electrophysiological recordings revealed that neurons were tuned to each of these modalities. By comparing movement paths and action sequences, we observed that external variables had limited direct influence on hippocampal firing. Instead, spiking was influenced by online action plans modulated by goal uncertainty. Our results suggest that internally generated cell assembly sequences are selected and updated by action plans toward deliberate goals. The apparent tuning of hippocampal neuronal spiking to different sensory modalities might emerge due to alignment to the afforded action progression within a task rather than representation of external cues.

A hippocampo-cortical pathway detects changes in the validity of an action as a predictor of reward

Much research has been dedicated to understanding the psychological and neural bases of goal-directed action, yet the relationship between context and goal-directed action is not well understood. Here, we used excitotoxic lesions, chemogenetics, and circuit-specific manipulations to demonstrate the role of the ventral hippocampus (vHPC) in contextual learning that supports sensitivity to action-outcome contingencies, a hallmark of goal-directed action. We found that chemogenetic inhibition of the ventral, but not dorsal, hippocampus attenuated sensitivity to instrumental contingency degradation. We then tested the hypothesis that this deficit was due to an inability to discern the relative validity of the action compared with the context as a predictor of reward. Using latent inhibition and Pavlovian context conditioning, we confirm that degradation of action-outcome contingencies relies on intact context-outcome learning and show that this learning is dependent on vHPC. Finally, we show that chemogenetic inhibition of vHPC terminals in the medial prefrontal cortex also impairs both instrumental contingency degradation and context-outcome learning. These results implicate a hippocampo-cortical pathway in adapting to changes in instrumental contingencies and indicate that the psychological basis of this deficit is an inability to learn the predictive value of the context. Our findings contribute to a broader understanding of the neural bases of goal-directed action and its contextual regulation.

Hippocampal non-theta state: The "Janus face" of information processing

The vast majority of studies on hippocampal rhythms have been conducted on animals or humans in situations where their attention was focused on external stimuli or solving cognitive tasks. These studies formed the basis for the idea that rhythmical activity coordinates the work of neurons during information processing. However, at rest, when attention is not directed to external stimuli, brain rhythms do not disappear, although the parameters of oscillatory activity change. What is the functional load of rhythmical activity at rest? Hippocampal oscillatory activity during rest is called the non-theta state, as opposed to the theta state, a characteristic activity during active behavior. We dedicate our review to discussing the present state of the art in the research of the non-theta state. The key provisions of the review are as follows: (1) the non-theta state has its own characteristics of oscillatory and neuronal activity; (2) hippocampal non-theta state is possibly caused and maintained by change of rhythmicity of medial septal input under the influence of raphe nuclei; (3) there is no consensus in the literature about cognitive functions of the non-theta-non-ripple state; and (4) the antagonistic relationship between theta and delta rhythms observed in rodents is not always observed in humans. Most attention is paid to the non-theta-non-ripple state, since this aspect of hippocampal activity has not been investigated properly and discussed in reviews.

The inter-relationships of the neural basis of rumination and inhibitory control: neuroimaging-based meta-analyses

Rumination, as a clinical manifestation and pathogenic factor of depression, has long been the focus of psychological research regarding its causes and ameliorating approaches. Behavioral studies have shown that rumination is related to inhibitory control deficits, which provides ideas for reducing it. However, the neural relationship between them has not been clearly discussed. In this study, we first used multi-level kernel density analysis to conduct two meta-analyses of published functional magnetic resonance imaging studies: one was rumination comprising 17 studies with 180 foci, and the other was inhibitory control comprising 205 studies with 3791 foci. Conjunction analysis was then performed to explore the common brain regions and further decode them through Neurosynth to confirm the cognitive specificity. Results showed that rumination was mainly related to the default mode network (DMN), while inhibitory control was associated with the frontoparietal network (FPN). In addition, the common activation areas were mainly concentrated in the bilateral precuneus, right superior frontal gyrus, bilateral median cingulate, paracingulate gyri, and the left triangular part of inferior frontal gyrus (IFG). Decoding results also revealed they were involved in inhibition, memory retrieval, and self-related processes. Our findings support that rumination is associated with inhibitory control and can be explained neurologically by an antagonistic relationship between the DMN and FPN. In sum, inhibitory control may be related to rumination via inhibiting task-unrelated attention and controlling self-related processing. This research will help us understand and predict rumination from the perspective of inhibitory control and reduce rumination through behavioral training of inhibitory control or the application of neuromodulation techniques to common activation regions.

From mechanisms to functions: The role of theta and gamma coherence in the intrahippocampal circuits

Brain rhythms are essential for information processing in neuronal networks. Oscillations recorded in different brain regions can be synchronized and have a constant phase difference, that is, they can be coherent. Coherence between local field potential (LFP) signals from different brain regions may be correlated with the performance of cognitive tasks, indicating that these regions of the brain are jointly involved in the information processing. Why does coherence occur and how is it related to the information transfer between different regions of the hippocampal formation? In this article, we discuss possible mechanisms of theta and gamma coherence and its role in the hippocampus-dependent attention and memory processes, since theta and gamma rhythms are most pronounced in these processes. We review in vivo studies of interactions between different regions of the hippocampal formation in theta and gamma frequency bands. The key propositions of the review are as follows: (1) coherence emerges from synchronous postsynaptic currents in principal neurons as a result of synchronization of neuronal spike activity; (2) the synchronization of neuronal spike patterns in two regions of the hippocampal formation can be realized through induction or resonance; (3) coherence at a specific time point reflects the transfer of information between the regions of the hippocampal formation; (4) the physiological roles of theta and gamma coherence are different due to their different functions and mechanisms of generation. All hippocampal neurons are involved in theta activity, and theta coherence arranges the firing order of principal neurons throughout the hippocampal formation. In contrast, gamma coherence reflects the coupling of active neuronal ensembles. Overall, the coherence of LFPs between different areas of the brain is an important physiological process based on the synchronized neuronal firing, and it is essential for cooperative information processing.

The Prefrontal-Hippocampal Comparator: Volition and Episodic Memory

This review describes recent research that is relevant to the prefrontal-hippocampal comparator model with the following conclusions: 1. Hippocampal area CA1 serves, at least in part, as an associative match-mismatch comparator. 2. Voluntary movement strengthens episodic memories for goal-directed behavior. 3. Hippocampal theta power serves as a prediction error signal during hippocampal dependent tasks. 4. The self-referential component of episodic memory in humans is mediated by the corollary discharge (the efference copy of the action plan developed by prefrontal cortex and transmitted to hippocampus where it is stored as a working memory; CA1 uses this efference copy to compare the expected consequences of action to the actual consequences of action). 5. Impairments in the production or transmission of this corollary discharge may contribute to some of the symptoms of schizophrenia. Unresolved issues and suggestions for future research are discussed.

The Differential Impact of a Response's Effectiveness and its Monetary Value on Response-Selection

While known reinforcers of behavior are outcomes that are valuable to the organism, recent research has demonstrated that the mere occurrence of an own-response effect can also reinforce responding. In this paper we begin investigating whether these two types of reinforcement occur via the same mechanism. To this end, we modified two different tasks, previously established to capture the influence of a response's effectiveness on the speed of motor-responses (indexed here by participants' reaction times). Specifically, in six experiments we manipulated both a response's 'pure' effectiveness and its outcome value (e.g., substantial versus negligible monetary reward) and measured the influence of both on the speed of responding. The findings strongly suggest that post action selection, responding is influenced only by pure effectiveness, as assessed by the motor system; thus, at these stages responding is not sensitive to abstract representations of the value of a response (e.g., monetary value). We discuss the benefit of distinguishing between these two necessary aspects of adaptive behavior namely, fine-tuning of motor-control and striving for desired outcomes. Finally, we embed the findings in the recently proposed Control-based response selection (CBRS) framework and elaborate on its potential for understanding motor-learning processes in developing infants.

Glucocorticoid-sensitive ventral hippocampal-orbitofrontal cortical connections support goal-directed action - Curt Richter Award Paper 2019

In an ever-changing and often ambiguous environment, organisms must use previously learned associations between antecedents and outcomes to predict future associations and make optimal choices. Chronic stress can impair one's ability to flexibly adjust behaviors when environmental contingencies change, particularly in cases of early-life stress. In mice, exposure to elevated levels of the primary stress hormone, corticosterone (CORT), during early adolescence is sufficient to impair response-outcome decision making later in life, biasing response strategies towards inflexible habits. Nevertheless, neurobiological mechanisms are still being defined. Here, we report that exposure to excess CORT in adolescence causes a loss of dendritic spines on excitatory pyramidal neurons in the lateral, but not medial, orbital prefrontal cortex (loPFC) of mice, and spine loss correlates with the severity of habit biases in adulthood. Excess CORT also reduces the presence of ventral hippocampal (vHC) axon terminals in the loPFC. To identify functional consequences, we inactivated vHC→loPFC projections in typical healthy mice during a period when mice must update response-outcome expectations to optimally acquire food reinforcers. Inactivation impaired the animals' subsequent ability to sustainably choose actions based on likely outcomes, causing them to defer to habit-based response strategies. Thus, vHC→loPFC projections are necessary for response-outcome expectancy updating and a target of excess glucocorticoids during early-life development. Their degradation is likely involved in long-term biases towards habit-based behaviors following glucocorticoid excess in adolescence.

Environmental enrichment and physical exercise revert behavioral and electrophysiological impairments caused by reduced adult neurogenesis

It is well known that adult neurogenesis occurs in two distinct regions, the subgranular zone of the dentate gyrus and the subventricular zone along the walls of the lateral ventricles. Until now, the contribution of these newly born neurons to behavior and cognition is still uncertain. The current study tested the functional impacts of diminished hippocampal neurogenesis on emotional and cognitive functions in transgenic Gfap-tk mice. Our results showed that anxiety-related behavior evaluated both in the elevated plus maze as well as in the open field, social interaction in the sociability test, and spatial working memory in the spontaneous alternation test were not affected. On the other hand, recognition and emotional memory in the object recognition test and contextual fear conditioning, and hippocampal long-term potentiation were impaired in transgenic mice. Furthermore, we evaluated whether environmental enrichment together with physical exercise could improve or even restore the level of adult neurogenesis, as well as the behavioral functions. Our results clearly demonstrated that environmental enrichment together with physical exercise successfully elevated the overall number of progenitor cells and young neurons in the dentate gyrus of transgenic mice. Furthermore, it led to a significant improvement in object recognition memory and contextual fear conditioning, and reverted impairments in hippocampal long-term potentiation. Thus, our results confirm the importance of adult neurogenesis for learning and memory processes and for hippocampal circuitry in general. Environmental enrichment and physical exercise beneficially influenced adult neurogenesis after it had been disrupted and most importantly recovered cognitive functions and long-term potentiation. © 2016 Wiley Periodicals, Inc.

Cognitive control of meal onset and meal size: Role of dorsal hippocampal-dependent episodic memory

There is a large gap in our understanding of how top-down cognitive processes, such as memory, influence energy intake. Similarly, there is limited knowledge regarding how the brain controls the timing of meals and meal frequency. Understanding how cognition influences ingestive behavior and how the brain controls meal frequency will provide a more complete explanation of the neural mechanisms that regulate energy intake and may also increase our knowledge of the factors that contribute to diet-induced obesity. We hypothesize that dorsal hippocampal neurons, which are critical for memory of personal experiences (i.e., episodic memory), form a memory of a meal, inhibit meal onset during the period following a meal, and limit the amount ingested at the next meal. In support, we describe evidence from human research suggesting that episodic memory of a meal inhibits intake and review data from human and non-human animals showing that impaired hippocampal function is associated with increased intake. We then describe evidence from our laboratory showing that inactivation of dorsal hippocampal neurons decreases the interval between sucrose meals and increases intake at the next meal. We also describe our evidence suggesting that sweet orosensation is sufficient to induce synaptic plasticity in dorsal hippocampal neurons and raise the possibility that impaired dorsal hippocampal function and episodic memory deficits contribute to the development and/or maintenance of diet-induced obesity. Finally, we raise some critical questions that need to be addressed in future research.

Being Present in Action: A Theoretical Model About the "Interlocking" Between Intentions and Environmental Affordances

Recent neuropsychological evidence suggest that a key role in linking perceptions and intentions is played by sense of presence. Despite this phenomenon having been studied primarily in the field of virtual reality (conceived as the illusion of being in the virtual space), recent research highlighted that it is a fundamental feature of everyday experience. Specifically, the function of presence as a cognitive process is to locate the Self in a physical space or situation, based on the perceived possibility to act in it; so, the variations in sense of presence allow one to continuously adapt his own action to the external environment. Indeed intentions, as the cognitive antecedents of action, are not static representations of the desired outcomes, but dynamic processes able to adjust their own representational content according to the opportunities/restrictions emerging in the environment. Focusing on the peculiar context of action mediated by interactive technologies, we here propose a theoretical model showing how each level of an intentional hierarchy (future-directed; present directed; and motor intentions) can “interlock” with environmental affordances in order to promote a continuous stream of action and activity.