Disinhibition account of the conditioned response (DACR).

Pavlovian conditioning is widely used to study the substrates of learning and memory in the mammalian brain. In a standard protocol, subjects are exposed to pairings of a conditioned stimulus (CS; e.g., a tone) with an unconditioned stimulus (US; e.g., an electric shock). Subsequent presentations of the CS elicit a range of behaviors that relate to the US (e.g., freezing) showing that animals learned the CS-US relation. However, it is still unclear how neuronal activity pertaining to the CS comes to excite a representation of the US, and thereby, conditioned responses. The current analysis of this problem, based on neurophysiological evidence, views Pavlovian conditioning as a process of facilitating the disinhibition, rather than the excitation, of neuronal responses representing the US. Conversely, Pavlovian extinction is viewed as a process of relearning to inhibit neuronal responses representing the US. We propose a mathematical equation that confirms the predictions made by this novel perspective on Pavlovian conditioning when applied to conditioning phenomena that fall beyond classic associative learning theories. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Circadian protein TIMELESS regulates synaptic function and memory by modulating cAMP signaling.

The regulation of neurons by circadian clock genes is thought to contribute to the maintenance of neuronal functions that ultimately underlie animal behavior. However, the impact of specific circadian genes on cellular and molecular mechanisms controlling synaptic plasticity and cognitive function remains elusive. Here, we show that the expression of the circadian protein TIMELESS displays circadian rhythmicity in the mammalian hippocampus. We identify TIMELESS as a chromatin-bound protein that targets synaptic-plasticity-related genes such as phosphodiesterase 4B (Pde4b). By promoting Pde4b transcription, TIMELESS negatively regulates cAMP signaling to modulate AMPA receptor GluA1 function and influence synaptic plasticity. Conditional deletion of Timeless in the adult forebrain impairs working and contextual fear memory in mice. These cognitive phenotypes were accompanied by attenuation of hippocampal Schaffer-collateral synapse long-term potentiation. Together, these data establish a neuron-specific function of mammalian TIMELESS by defining a mechanism that regulates synaptic plasticity and cognitive function.

A versatile and fast-sampling rate wearable analog data logger.

We propose a wearable, versatile, and open-source data logger that harvests the capacities of a low-cost microcontroller and enables fast-sampling recording of Analog signals into a microSD card. We describe here the circuit design and an exhaustive list of instructions to build a small, lightweight, and fast sampling rate data logger (up to 5 kHz for simultaneous recording of 3 channels and up to 40 kHz when using a single channel). We provide data analysis instructions, including publicly available scripts to facilitate its replication and customization. As a straightforward proof-of-concept, we tested our device embedded with a three-axial Analog accelerometer and were able to record triple axis acceleration of body movements in high resolution. A Fourier transform followed by a principal component analysis discriminated accurately between body motions of two participants and two types of movement recorded (walking VS running). Our wearable and fast-sampling rate data logger overcomes limits that we identified in previous studies, by being low-cost, capable of fast sampling rate, and easily replicated. Moreover, it can be customized to fit with a wide variety of applications in biomedical research by substituting the three-axial Analog accelerometer with virtually any type of Analog sensors or devices that output Analog signals. •We present a method to build and use a low-cost, fast-sampling rate and wearable Analog data logger, where having an engineering background is not required.•The data logger we present can collect Analog signals from 3 channels simultaneously at 5kHz and up to 40 kHz when using a single channel.•We demonstrate that our data logger can record data from a triple axis Analog accelerometer at 5 kHz, however, signals from virtually any Analog sensor or device that outputs Analog signals can be collected.

Conditioned Lick Suppression: Assessing Contextual, Cued, and Context-cue Compound Fear Responses Independently of Locomotor Activity in Mice.

Pavlovian fear conditioning is a widely used procedure to assess learning and memory processes that has also been extensively used as a model of post-traumatic stress disorder (PTSD). Freezing, the absence of movement except for respiratory-related movements, is commonly used as a measure of fear response in non-human animals. However, this measure of fear responses can be affected by a different baseline of locomotor activity between groups and/or conditions. Moreover, fear conditioning procedures are usually restricted to a single conditioned stimulus (e.g., a tone cue, the context, etc.) and thus do not depict the complexity of real-life situations where traumatic memories are composed of a complex set of stimuli associated with the same aversive event. To overcome this issue, we use a conditioned lick suppression paradigm where water-deprived mice are presented with a single conditioned stimulus (CS, a tone cue or the context) previously paired with an unconditioned stimulus (US, a foot shock) while consuming water. We use the ratio of number of licks before and during the CS presentation as a fear measure, thereby neutralizing the potential effect of locomotor activity in fear responses. We further implemented the conditioned lick suppression ratio to assess the effect of cue competition using a compound of contextual and tone cue conditioned stimuli that were extinguished separately. This paradigm should prove useful in assessing potential therapeutics and/or behavioral therapies in PTSD, while neutralizing potential confounding effects between locomotor activity and fear responses on one side, and by considering potential cue-competition effects on the other side. This protocol was validated in: Transl Psychiatry (2022), DOI: 10.1038/s41398-022-01815-2 Graphical abstract Schematic representation of the compound context-cue condition lick suppression procedure. Illustration reproduced from Bouchekioua et al. (2022).

Median raphe serotonergic neurons projecting to the interpeduncular nucleus control preference and aversion.

Appropriate processing of reward and aversive information is essential for survival. Although a critical role of serotonergic neurons in the dorsal raphe nucleus (DRN) in reward processing has been shown, the lack of rewarding effects with selective serotonin reuptake inhibitors (SSRIs) implies the presence of a discrete serotonergic system playing an opposite role to the DRN in the processing of reward and aversive stimuli. Here, we demonstrated that serotonergic neurons in the median raphe nucleus (MRN) of mice process reward and aversive information in opposite directions to DRN serotonergic neurons. We further identified MRN serotonergic neurons, including those projecting to the interpeduncular nucleus (5-HTMRN→IPN), as a key mediator of reward and aversive stimuli. Moreover, 5-HT receptors, including 5-HT2A receptors in the interpeduncular nucleus, are involved in the aversive properties of MRN serotonergic neural activity. Our findings revealed an essential function of MRN serotonergic neurons, including 5-HTMRN→IPN, in the processing of reward and aversive stimuli.

Behavioral characteristics of dopamine D5 receptor knockout mice.

Major psychiatric disorders such as attention-deficit/hyperactivity disorder and schizophrenia are often accompanied by elevated impulsivity. However, anti-impulsive drug treatments are still limited. To explore a novel molecular target, we examined the role of dopamine D5 receptors in impulse control using mice that completely lack D5 receptors (D5KO mice). We also measured spontaneous activity and learning/memory ability because these deficits could confound the assessment of impulsivity. We found small but significant effects of D5 receptor knockout on home cage activity only at specific times of the day. In addition, an analysis using the q-learning model revealed that D5KO mice displayed lower behavioral adjustment after impulsive actions. However, our results also showed that baseline impulsive actions and the effects of an anti-impulsive drug in D5KO mice were comparable to those in wild-type littermates. Moreover, unlike previous studies that used other D5 receptor-deficient mouse lines, we did not observe reductions in locomotor activity, working memory deficits, or severe learning deficits in our line of D5KO mice. These findings demonstrate that D5 receptors are dispensable for impulse control. Our results also indicate that time series analysis and detailed analysis of the learning process are necessary to clarify the behavioral functions of D5 receptors.

Serotonin 5-HT2C receptor knockout in mice attenuates fear responses in contextual or cued but not compound context-cue fear conditioning.

Previous findings have proposed that drugs targeting 5-HT2C receptors could be promising candidates in the treatment of trauma- and stress-related disorders. However, the reduction of conditioned freezing observed in 5-HT2C receptor knock-out (KO) mice in previous studies could alternatively be accounted for by increased locomotor activity. To neutralize the confound of individual differences in locomotor activity, we measured a ratio of fear responses during versus before the presentation of a conditioned stimulus previously paired with a footshock (as a fear measure) by utilizing a conditioned licking suppression paradigm. We first confirmed that 5-HT2C receptor gene KO attenuated fear responses to distinct types of single conditioned stimuli (context or tone) independently of locomotor activity. We then assessed the effects of 5-HT2C receptor gene KO on compound fear responses by examining mice that were jointly conditioned to a context and a tone and later re-exposed separately to each. We found that separate re-exposure to individual components of a complex fear memory (i.e., context and tone) failed to elicit contextual fear extinction in both 5-HT2C receptor gene KO and wild-type mice, and also abolished differences between genotypes in tone-cued fear extinction. This study delineates a previously overlooked role of 5-HT2C receptors in conditioned fear responses, and invites caution in the future assessment of molecular targets and candidate therapies for the treatment of PTSD.

Not "either-or" but "which-when": A review of the evidence for integration in sensory preconditioning.

Sensory preconditioning protocols can be used to assess how the brain integrates memories that share common features. In these protocols, animals are first exposed to pairings of two relatively innocuous stimuli, S2 and S1 (stage 1), and then to pairings of one of these stimuli, S1, with an event of motivational significance (stage 2). Following this training, test presentations of S2 elicit responses appropriate to the motivationally significant event, and these responses are taken to indicate formation of distinct S2-S1 and S1-event memories that are integrated in some way to generate that responding. This paper reviews studies of sensory preconditioning in rats, mice, rabbits and people to determine whether S2-S1 and S1-event memories are integrated through a chaining process at the time of their retrieval (i.e., test presentations of S2 trigger retrieval of S1, and thereby, responses appropriate to the event); or "online" at the time of memory formation (i.e., in stage 2, S1 activates a representation of S2 such that both stimuli associate with the motivationally significant event). It finds that the type of integration is determined by the manner in which stimuli are presented in preconditioning as well as their familiarity. When the stimuli in preconditioning are presented repeatedly and/or serially (i.e., one after the other), the S2-S1 and S1-event memories are chained at the time of retrieval/testing. In contrast, when the stimuli in preconditioning are relatively novel and/or presented simultaneously, the S2-S1 and S1-event memories are integrated online. These statements are related to prior claims regarding the circumstances that promote different types of memory integration and, more generally, mechanisms of information processing in the mammalian brain.

Higher-Order Conditioning in the Spatial Domain.

Spatial learning and memory, the processes through which a wide range of living organisms encode, compute, and retrieve information from their environment to perform goal-directed navigation, has been systematically investigated since the early twentieth century to unravel behavioral and neural mechanisms of learning and memory. Early theories about learning to navigate space considered that animals learn through trial and error and develop responses to stimuli that guide them to a goal place. According to a trial-and error learning view, organisms can learn a sequence of motor actions that lead to a goal place, a strategy referred to as response learning, which contrasts with place learning where animals learn locations with respect to an allocentric framework. Place learning has been proposed to produce a mental representation of the environment and the cartesian relations between stimuli within it-which Tolman coined the cognitive map. We propose to revisit some of the best empirical evidence of spatial inference in animals, and then discuss recent attempts to account for spatial inferences within an associative framework as opposed to the traditional cognitive map framework. We will first show how higher-order conditioning can successfully account for inferential goal-directed navigation in a variety of situations and then how vectors derived from path integration can be integrated via higher-order conditioning, resulting in the generation of higher-order vectors that explain novel route taking. Finally, implications to cognitive map theories will be discussed.

Disruption of model-based decision making by silencing of serotonin neurons in the dorsal raphe nucleus.

Adapting to changing environmental conditions requires a prospective inference of future actions and their consequences, a strategy also known as model-based decision making.1-3 In stable environments, extensive experience of actions and their consequences leads to a shift from a model-based to a model-free strategy, whereby behavioral selection is primarily governed by retrospective experiences of positive and negative outcomes. Human and animal studies, where subjects are required to speculate about implicit information and adjust behavioral responses over multiple sessions, point to a role for the central serotonergic system in model-based decision making.4-8 However, to directly test a causal relationship between serotonergic activity and model-based decision making, phase-specific manipulation of serotonergic activity is needed in a one-shot test, where learning by trial and error is neutralized. Moreover, the serotonergic origin responsible for this effect is yet to be determined. Herein, we demonstrate that optogenetic silencing of serotonin neurons in the dorsal raphe nucleus, but not in the median raphe nucleus, disrupts model-based decision making in lithium-induced outcome devaluation tasks.9-11 Our data indicate that the serotonergic behavioral effects are not due to increased locomotor activity, anxiolytic effects, or working memory deficits. Our findings provide insights into the neural mechanisms underlying neural weighting between model-free and model-based strategies.

Spatial inference without a cognitive map: the role of higher-order path integration.

The cognitive map has been taken as the standard model for how agents infer the most efficient route to a goal location. Alternatively, path integration - maintaining a homing vector during navigation - constitutes a primitive and presumably less-flexible strategy than cognitive mapping because path integration relies primarily on vestibular stimuli and pace counting. The historical debate as to whether complex spatial navigation is ruled by associative learning or cognitive map mechanisms has been challenged by experimental difficulties in successfully neutralizing path integration. To our knowledge, there are only three studies that have succeeded in resolving this issue, all showing clear evidence of novel route taking, a behaviour outside the scope of traditional associative learning accounts. Nevertheless, there is no mechanistic explanation as to how animals perform novel route taking. We propose here a new model of spatial learning that combines path integration with higher-order associative learning, and demonstrate how it can account for novel route taking without a cognitive map, thus resolving this long-standing debate. We show how our higher-order path integration (HOPI) model can explain spatial inferences, such as novel detours and shortcuts. Our analysis suggests that a phylogenetically ancient, vector-based navigational strategy utilizing associative processes is powerful enough to support complex spatial inferences.

Behavioral characteristics of 5-HT2C receptor knockout mice: Locomotor activity, anxiety-, and fear memory-related behaviors.

Pharmacological studies have suggested that the serotonin 5-HT2C receptor is involved in locomotor activity, anxiety, and fear memory. However, the results of locomotor activity and anxiety in 5-HT2C receptor knockout mice have been mixed, and the effects of 5-HT2C receptor knockout on contextual fear memory have not yet been addressed. In the present study, we reconcile these inconsistent results by analyzing behavioral data in detail and by examining the effects of 5-HT2C receptor knockout on contextual fear memory. We demonstrated that the higher locomotor activity in 5-HT2C receptor knockout mice was observed only in the late phase of the test, indicating that the analyses in the previous study using the total locomotor activity would lead to variable results. Moreover, by analyzing mouse behavior in detail, we found that 5-HT2C receptor knockout mice displayed a hesitating attitude by staying in the central area as well as risk assessment behavior in the elevated plus-maze test. However, the time spent in the open arms was longer in 5-HT2C receptor knockout mice than in wild-type littermates when a zero-maze test lacking the central area was used. In the contextual fear conditioning test, 5-HT2C receptor knockout mice showed rapid within-session extinction of fear, but not between-session extinction, compared with wild-type littermates. However, this remains inconclusive because the facilitation of extinction might be confounded with higher locomotor activity in 5-HT2C receptor knockout mice. Taken together, the present results provide reasonable explanations about previous inconsistent findings and partially filled the gaps between pharmacological and genetic findings.

Striatonigral direct pathway activation is sufficient to induce repetitive behaviors.

Pharmacological intervention in the substantia nigra is known to induce repetitive behaviors in rodents, but a direct causal relationship between a specific neural circuit and repetitive behavior has not yet been established. Here we demonstrate that optogenetic activation of dopamine D1 receptor-expressing MSNs terminals in the substantia nigra pars reticulata resulted in sustained and chronic repetitive behaviors. These data show for the first time that activation of the striatonigral direct pathway is sufficient to generate motor stereotypies.

A New Paradigm for Evaluating Avoidance/Escape Motivation.

Background: Organisms have evolved to approach pleasurable opportunities and to avoid or escape from aversive experiences. These 2 distinct motivations are referred to as approach and avoidance/escape motivations and are both considered vital for survival. Despite several recent advances in understanding the neurobiology of motivation, most studies addressed approach but not avoidance/escape motivation. Here we develop a new experimental paradigm to quantify avoidance/escape motivation and examine the pharmacological validity. Methods: We set up an avoidance variable ratio 5 task in which mice were required to press a lever for variable times to avoid an upcoming aversive stimulus (foot shock) or to escape the ongoing aversive event if they failed to avoid it. We i.p. injected ketamine (0, 1, or 5 mg/kg) or buspirone (0, 5, or 10 mg/kg) 20 or 30 minutes before the behavioral task to see if ketamine enhanced avoidance/escape behavior and buspirone diminished it as previously reported. Results: We found that the performance on the avoidance variable ratio 5 task was sensitive to the intensity of the aversive stimulus. Treatment with ketamine increased while that with buspirone decreased the probability of avoidance from an aversive stimulus in the variable ratio 5 task, being consistent with previous reports. Conclusion: Our new paradigm will prove useful for quantifying avoidance/escape motivation and will contribute to a more comprehensive understanding of motivation.

Dysfunction of ventrolateral striatal dopamine receptor type 2-expressing medium spiny neurons impairs instrumental motivation.

Impaired motivation is present in a variety of neurological disorders, suggesting that decreased motivation is caused by broad dysfunction of the nervous system across a variety of circuits. Based on evidence that impaired motivation is a major symptom in the early stages of Huntington's disease, when dopamine receptor type 2-expressing striatal medium spiny neurons (D2-MSNs) are particularly affected, we hypothesize that degeneration of these neurons would be a key node regulating motivational status. Using a progressive, time-controllable, diphtheria toxin-mediated cell ablation/dysfunction technique, we find that loss-of-function of D2-MSNs within ventrolateral striatum (VLS) is sufficient to reduce goal-directed behaviours without impairing reward preference or spontaneous behaviour. Moreover, optogenetic inhibition and ablation of VLS D2-MSNs causes, respectively, transient and chronic reductions of goal-directed behaviours. Our data demonstrate that the circuitry containing VLS D2-MSNs control motivated behaviours and that VLS D2-MSN loss-of-function is a possible cause of motivation deficits in neurodegenerative diseases.

Ventrolateral Striatal Medium Spiny Neurons Positively Regulate Food-Incentive, Goal-Directed Behavior Independently of D1 and D2 Selectivity.

The ventral striatum is involved in motivated behavior. Akin to the dorsal striatum, the ventral striatum contains two parallel pathways: the striatomesencephalic pathway consisting of dopamine receptor Type 1-expressing medium spiny neurons (D1-MSNs) and the striatopallidal pathway consisting of D2-MSNs. These two genetically identified pathways are thought to encode opposing functions in motivated behavior. It has also been reported that D1/D2 genetic selectivity is not attributed to the anatomical discrimination of two pathways. We wanted to determine whether D1- and D2-MSNs in the ventral striatum functioned in an opposing manner as previous observations claimed, and whether D1/D2 selectivity corresponded to a functional segregation in motivated behavior of mice. To address this question, we focused on the lateral portion of ventral striatum as a region implicated in food-incentive, goal-directed behavior, and recorded D1 or D2-MSN activity by using a gene-encoded ratiometric Ca2+ indicator and by constructing a fiberphotometry system, and manipulated their activities via optogenetic inhibition during ongoing behaviors. We observed concurrent event-related compound Ca2+ elevations in ventrolateral D1- and D2-MSNs, especially at trial start cue-related and first lever press-related times. D1 or D2 selective optogenetic inhibition just after the trial start cue resulted in a reduction of goal-directed behavior, indicating a shared coding of motivated behavior by both populations at this time. Only D1-selective inhibition just after the first lever press resulted in the reduction of behavior, indicating D1-MSN-specific coding at that specific time. Our data did not support opposing encoding by both populations in food-incentive, goal-directed behavior.SIGNIFICANCE STATEMENT An opposing role of dopamine receptor Type 1 or Type 2-expressing medium spiny neurons (D1-MSNs or D2-MSNs) on striatum-mediated behaviors has been widely accepted. However, this idea has been questioned by recent reports. In the present study, we measured concurrent Ca2+ activity patterns of D1- and D2-MSNs in the ventrolateral striatum during food-incentive, goal-directed behavior in mice. According to Ca2+ activity patterns, we conducted timing-specific optogenetic inhibition of each type of MSN. We demonstrated that both D1- and D2-MSNs in the ventrolateral striatum commonly and positively encoded action initiation, whereas only D1-MSNs positively encoded sustained motivated behavior. These findings led us to reconsider the prevailing notion of a functional segregation of MSN activity in the ventral striatum.

Air flow cued spatial learning in mice.

Spatial learning experiments in rodents typically employ visual cues that are associated with a goal place, even though it is now well established that they have poor visual acuity. We assessed here the possibility of spatial learning in mice based on an air flow cue in a dry version of the Morris water maze task. A miniature fan was placed at each of the four cardinal points of the circular maze, but only one blew air towards the centre of the maze. The three other fans were blowing towards their own box. The mice were able to learn the task only if the spatial relationship between the air flow cue and the position of the goal place was kept constant across trials. A change of this spatial relationship resulted in an increase in the time to find the goal place. We report here the first evidence of spatial learning relying on an air flow cue.

Spatial integration of boundaries in a 3D virtual environment.

Prior research, using two- and three-dimensional environments, has found that when both human and nonhuman animals independently acquire two associations between landmarks with a common landmark (e.g., LM1-LM2 and LM2-LM3), each with its own spatial relationship, they behave as if the two unique LMs have a known spatial relationship despite their never having been paired. Seemingly, they have integrated the two associations to create a third association with its own spatial relationship (LM1-LM3). Using sensory preconditioning (Experiment 1) and second-order conditioning (Experiment 2) procedures, we found that human participants integrated information about the boundaries of pathways to locate a goal within a three-dimensional virtual environment in the absence of any relevant landmarks. Spatial integration depended on the participant experiencing a common boundary feature with which to link the pathways. These results suggest that the principles of associative learning also apply to the boundaries of an environment.