Comparative basolateral amygdala connectomics reveals dissociable single-neuron projection patterns to frontal cortex in macaques and mice.

Basolateral amygdala (BLA) is a key hub for affect in the brain,1,2,3 and dysfunction within this area contributes to a host of psychiatric disorders.4,5 BLA is extensively and reciprocally interconnected with frontal cortex,6,7,8,9 and some aspects of its function are evolutionarily conserved across rodents, anthropoid primates, and humans.10 Neuron density in BLA is substantially lower in primates compared to murine rodents,11 and frontal cortex (FC) is dramatically expanded in primates, particularly the more anterior granular and dysgranular areas.12,13,14 Yet, how these anatomical differences influence the projection patterns of single BLA neurons to frontal cortex across rodents and primates is unknown. Using a barcoded connectomic approach, we assessed the single BLA neuron connections to frontal cortex in mice and macaques. We found that BLA neurons are more likely to project to multiple distinct parts of FC in mice than in macaques. Further, while single BLA neuron projections to nucleus accumbens were similarly organized in mice and macaques, BLA-FC connections differed substantially. Notably, BLA connections to subcallosal anterior cingulate cortex (scACC) in macaques were least likely to branch to other medial frontal cortex areas compared to perigenual ACC (pgACC). This pattern of connections was reversed in the mouse homologues of these areas, infralimbic and prelimbic cortex (IL and PL), mirroring functional differences between rodents and non-human primates. Taken together, these results indicate that BLA connections to FC are not linearly scaled from mice to macaques and instead the organization of single-neuron BLA connections is distinct between these species.

Comparative basolateral amygdala connectomics reveals dissociable single-neuron projection patterns to frontal cortex in macaques and mice.

The basolateral amygdala (BLA) projects to the frontal cortex (FC) in both rodents and primates, but the comparative organization of single-neuron BLA-FC projections is unknown. Using a barcoded connectomic approach, we found that BLA neurons are more likely to project to multiple distinct parts of FC in mice than in macaques. Further, while single BLA neuron projections to nucleus accumbens are similarly organized in mice and macaques, BLA-FC connections differ.

A limited cerebellar contribution to suprasecond timing across differing task demands.

The involvement of the cerebellum in suprasecond interval timing (i.e., timing in the seconds to minutes range) is controversial. A limited amount of evidence from humans, nonhuman primates, and rodents has shown that the lateral cerebellum, including the lateral cerebellar nucleus (LCN), may be necessary for successful suprasecond timing performance. However, many existing studies have pitfalls, such as limited timing outcome measures and confounded task demands. In addition, many existing studies relied on well-trained subjects. This approach may be a drawback, as the cerebellum is hypothesized to carry out ongoing error correction to limit timing variability. By using only experienced subjects, past timing studies may have missed a critical window of cerebellar involvement. In the experiments described here, we pharmacologically inactivated the rat LCN across three different peak interval timing tasks. We structured our tasks to address past confounds, collect timing variability measures, and characterize performance during target duration acquisition. Across these various tasks, we did not find strong support for cerebellar involvement in suprasecond interval timing. Our findings support the existing distinction of the cerebellum as a subsecond interval timing brain region. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The dorsal hippocampus' role in context-based timing in rodents.

To act proactively, we must predict when future events will occur. Individuals generate temporal predictions using cues that indicate an event will happen after a certain duration elapses. Neural models of timing focus on how the brain represents these cue-duration associations. However, these models often overlook the fact that situational factors frequently modulate temporal expectations. For example, in realistic environments, the intervals associated with different cues will often covary due to a common underlying cause. According to the 'common cause hypothesis,' observers anticipate this covariance such that, when one cue's interval changes, temporal expectations for other cues shift in the same direction. Furthermore, as conditions will often differ across environments, the same cue can mean different things in different contexts. Therefore, updates to temporal expectations should be context-specific. Behavioral work supports these predictions, yet their underlying neural mechanisms are unclear. Here, we asked whether the dorsal hippocampus mediates context-based timing, given its broad role in context-conditioning. Specifically, we trained rats with either hippocampal or sham lesions that two cues predicted reward after either a short or long duration elapsed (e.g., tone-8 s/light-16 s). Then, we moved rats to a new context and extended the long cue's interval (e.g., light-32 s). This caused rats to respond later to the short cue, despite never being trained to do so. Importantly, when returned to the initial training context, sham rats shifted back toward both cues' original intervals. In contrast, lesion rats continued to respond at the long cue's newer interval. Surprisingly, they still showed contextual modulation for the short cue, responding earlier like shams. These data suggest the hippocampus only mediates context-based timing if a cue is explicitly paired and/or rewarded across distinct contexts. Furthermore, as lesions did not impact timing measures at baseline or acquisition for the long cue's new interval, our data suggests that the hippocampus only modulates timing when context is relevant.

No preference for prosocial helping behavior in rats with concurrent social interaction opportunities.

Helping behavior tasks are proposed to assess prosocial or "empathic" behavior in rodents. This paradigm characterizes the behavior of subject animals presented with the opportunity to release a conspecific from a distressing situation. Previous studies found a preference in rats for releasing restrained or distressed conspecifics over other controls (e.g., empty restrainers or inanimate objects). An empathy account was offered to explain the observed behaviors, claiming subjects were motivated to reduce the distress of others based on a rodent homologue of empathy. An opposing account attributes all previous results to subjects seeking social contact. To dissociate these two accounts for helping behavior, we presented subject rats with three simultaneous choice alternatives: releasing a restrained conspecific, engaging a nonrestrained conspecific, or not socializing. Subjects showed an initial preference for socializing with the nonrestrained conspecific, and no preference for helping. This result contradicts the empathy account, but is consistent with the social-contact account of helping behavior.

Why do learners ignore expected feedback in making metacognitive decisions about retrieval practice?

We report two experiments investigating why learners, in making metacognitive judgments, often seem to ignore or otherwise fail to appreciate that feedback following retrieval practice provides a restudy opportunity. Learners practiced word pairs for a final cued-recall test by studying each pair initially, making a judgment of learning (JOL), and then deciding whether to practice the pair again after a short or long spacing interval, or not at all. For different groups in Experiment 1, additional practice involved restudying, retrieval practice without feedback, or retrieval practice with feedback (the full pair). We used procedures (long feedback duration and covert retrieval practice) designed to rule out the possibility that feedback is ignored because it is usually brief or because participants' choices are influenced by a desire to look good by performing well on overt practice tests. In the relearning condition, learners preferred a long spacing interval for items at all JOL levels. Despite the feedback duration and the covert retrieval practice, learners in both retrieval-practice conditions preferred a short spacing interval for hard, low-JOL items and a long spacing interval for easy, high-JOL items, even though this may not be an effective strategy when feedback is provided. In Experiment 2, instructions framed feedback either as a presentation of the correct answer or as a restudy opportunity preceded by retrieval practice. Framing feedback as a restudy opportunity markedly changed the choices learners made. Apparently, the restudy function of feedback does not occur to learners unless they are specifically alerted to it.

Cerebellar D1DR-expressing neurons modulate the frontal cortex during timing tasks.

Converging lines of evidence suggest that the cerebellum plays an integral role in cognitive function through its interactions with association cortices like the medial frontal cortex (MFC). It is unknown precisely how the cerebellum influences the frontal cortex and what type of information is reciprocally relayed between these two regions. A subset of neurons in the cerebellar dentate nuclei, or the homologous lateral cerebellar nuclei (LCN) in rodents, express D1 dopamine receptors (D1DRs) and may play a role in cognitive processes. We investigated how pharmacologically blocking LCN D1DRs influences performance in an interval timing task and impacts neuronal activity in the frontal cortex. Interval timing requires executive processes such as working memory, attention, and planning and is known to rely on both the frontal cortex and cerebellum. In our interval timing task, male rats indicated their estimates of the passage of a period of several seconds by making lever presses for a water reward. We have shown that a cue-evoked burst of low-frequency activity in the MFC initiates ramping activity (i.e., monotonic increases or decreases of firing rate over time) in single MFC neurons. These patterns of activity are associated with successful interval timing performance. Here we explored how blocking right LCN D1DRs with the D1DR antagonist SCH23390 influences timing performance and neural activity in the contralateral (left) MFC. Our results indicate that blocking LCN D1DRs impaired some measures of interval timing performance. Additionally, ramping activity of MFC single units was significantly attenuated. These data provide insight into how catecholamines in the LCN may drive MFC neuronal dynamics to influence cognitive function.

Prefrontal parvalbumin cells are sensitive to stress and mediate anxiety-related behaviors in female mice.

Reduced activity of the prefrontal cortex (PFC) is seen in mood disorders including depression and anxiety. The mechanisms of this hypofrontality remain unclear. Because of their specific physiological properties, parvalbumin-expressing (PV+) inhibitory interneurons contribute to the overall activity of the PFC. Our recent work using a chronic stress mouse model showed that stress-induced increases in prefrontal PV expression correlates with increased anxiety-like behaviors in female mice. Our goal is now to provide a causal relationship between changes in prefrontal PV+ cells and changes in emotional behaviors in mice. We first show that, in addition to increasing overall level of PV expression, chronic stress increases the activity of prefrontal PV+ cells. We then used a chemogenetic approach to mimic the effects of chronic stress and specifically increase the activity of prefrontal PV+ cells. We observed that chemogenetic activation of PV+ cells caused an overall reduction in prefrontal activity, and that chronic activation of PV+ cells lead to increased anxiety-related behaviors in female mice only. These results demonstrate that activity of prefrontal PV+ cells could represent a novel sex-specific modulator of anxiety-related behaviors, potentially through changes in overall prefrontal activity. The findings also support the idea that prefrontal PV+ cells are worth further investigation to better understand mood disorders that are more prevalent in female populations.

Downregulation of Npas4 in parvalbumin interneurons and cognitive deficits after neonatal NMDA receptor blockade: relevance for schizophrenia.

Dysfunction of prefrontal parvalbumin (PV+) interneurons has been linked with severe cognitive deficits as observed in several neurodevelopmental disorders including schizophrenia. However, whether a specific aspect of PV+ neurons deregulation, or a specific molecular mechanism within PV+ neurons is responsible for cognitive deficits and other behavioral impairments remain to be determined. Here, we induced cognitive deficits and altered the prefrontal PV system in mice by exposing them neonatally to the NMDA receptor antagonist ketamine. We observed that the cognitive deficits and hyperactivity induced by neonatal ketamine were associated with a downregulation of Npas4 expression specifically in PV+ neurons. To determine whether Npas4 downregulation-induced dysfunction of PV+ neurons could be a molecular contributor to the cognitive and behavioral impairments reported after neonatal ketamine, we used a transgenic Cre-Lox approach. Reduced Npas4 expression within PV+ neurons replicates deficits in short-term memory observed after neonatal ketamine, but does not reproduce disturbances in general activity. Our data show for the first time that the brain-specific transcription factor Npas4 may be an important contributor to PV+ neurons dysfunction in neurodevelopmental disorders, and thereby could contribute to the cognitive deficits observed in diseases characterized by abnormal functioning of PV+ neurons such as schizophrenia. These findings provide a potential novel therapeutic target to rescue the cognitive impairments of schizophrenia that remain to date unresponsive to treatments.

Specificity and flexibility of social influence on spatial choice.

Rats searched for food in a situation that allowed them to determine which locations contained food after searching a small number of them, but not which of the baited locations contained more-preferred food rather than a less-preferred food. During some experimental trials, the latter information was available from the choices of model rats making choices together with the subject rats, because some of the model rats tended to choose the locations baited with more-preferred food. On the surface, the results suggest that social influence specified the locations of more-preferred food to the subject rats. However, more detailed analysis and data from a second experiment indicate that the social influence can be explained by a general tendency to approach another rat making choices, acquired if rats are exposed to a contingency between social approach and increased foraging success.

The transcription factor Npas4 contributes to adolescent development of prefrontal inhibitory circuits, and to cognitive and emotional functions: Implications for neuropsychiatric disorders.

The adolescent brain is marked by functional and structural modifications, particularly within the inhibitory system of the prefrontal cortex (PFC). These changes are necessary for the acquisition of adult cognitive functions and emotion regulation, and impairments in these processes are associated with neuropathologies such as schizophrenia and affective disorders. The molecular mechanisms regulating this adolescent refinement of prefrontal inhibitory circuits remain largely unknown. Here we demonstrate that the transcription factor Npas4 plays a major role in this process. Using a series of behavioral, molecular, pharmacological and genetic approaches in mice, we demonstrate that deficiency in Npas4 affects adolescent expression of multiple markers of GABAergic transmission in the PFC, including parvalbumin and GAD67, in a sex-specific manner. This abnormal pattern of expression of GABAergic markers is associated with sex-specific cognitive and emotional impairments that occur only when Npas4 deficiency begins at adolescence but not post-adolescence. Finally, we show that chronic treatment with the GABA enhancing drug sodium valproate during adolescence is sufficient to induce long-lasting recovery of the molecular and behavioral abnormalities observed in Npas4 deficient mice. Altogether, we provide evidence for the involvement of the transcription factor Npas4 to the structural changes that affect prefrontal inhibitory circuits during adolescence. Further investigations of Npas4 role in the adolescent brain might provide new insights on the molecular mechanisms underlying neuropsychiatric disorders that emerge during adolescence.