The representational geometry of emotional states in basolateral amygdala.

Sensory stimuli associated with aversive outcomes can cause multiple behavioral responses related to an animal's evolving emotional state. We employed chemogenetic inactivation and two-photon imaging to reveal how the basolateral amygdala (BLA) mediates these state changes. Mice were presented stimuli in a virtual burrow, causing two responses reflecting fear and flight to safety: tremble and ingress into the burrow. Inactivation eliminated differential tremble and ingress to aversive and neutral stimuli without eliminating responses themselves. Multiple variables, including stimulus valence and identity, and being in the tremble or ingressed state, typically modulated each neuron's activity (mixed-selectivity). BLA neural ensembles represented these variables even after neurons with apparent specialized selectivity were eliminated from analyses. Thus, implementing different readouts of BLA ensembles comprised of mixed-selectivity neurons can identify distinct emotional states defined by responses, like tremble for fear and ingress for safety. This mechanism relies on BLA's representational geometry, not its circuit specialization.

Prelimbic cortex drives discrimination of non-aversion via amygdala somatostatin interneurons.

The amygdala and prelimbic cortex (PL) communicate during fear discrimination retrieval, but how they coordinate discrimination of a non-threatening stimulus is unknown. Here, we show that somatostatin (SOM) interneurons in the basolateral amygdala (BLA) become active specifically during learned non-threatening cues and desynchronize cell firing by blocking phase reset of theta oscillations during the safe cue. Furthermore, we show that SOM activation and desynchronization of the BLA is PL-dependent and promotes discrimination of non-threat. Thus, fear discrimination engages PL-dependent coordination of BLA SOM responses to non-threatening stimuli.

Basolateral amygdala circuitry in positive and negative valence.

All organisms must solve the same fundamental problem: they must acquire rewards and avoid danger in order to survive. A key challenge for the nervous system is therefore to connect motivationally salient sensory stimuli to neural circuits that engage appropriate valence-specific behavioral responses. Anatomical, behavioral, and electrophysiological data have long suggested that the amygdala plays a central role in this process. Here we review experimental efforts leveraging recent technological advances to provide previously unattainable insights into the functional, anatomical, and genetic identity of neural populations within the amygdala that connect sensory stimuli to valence-specific behavioral responses.

Retrieval and Reconsolidation Accounts of Fear Extinction.

Extinction is the primary mode for the treatment of anxiety disorders. However, extinction memories are prone to relapse. For example, fear is likely to return when a prolonged time period intervenes between extinction and a subsequent encounter with the fear-provoking stimulus (spontaneous recovery). Therefore there is considerable interest in the development of procedures that strengthen extinction and to prevent such recovery of fear. We contrasted two procedures in rats that have been reported to cause such deepened extinction. One where extinction begins before the initial consolidation of fear memory begins (immediate extinction) and another where extinction begins after a brief exposure to the consolidated fear stimulus. The latter is thought to open a period of memory vulnerability similar to that which occurs during initial consolidation (reconsolidation update). We also included a standard extinction treatment and a control procedure that reversed the brief exposure and extinction phases. Spontaneous recovery was only found with the standard extinction treatment. In a separate experiment we tested fear shortly after extinction (i.e., within 6 h). All extinction procedures, except reconsolidation update reduced fear at this short-term test. The findings suggest that strengthened extinction can result from alteration in both retrieval and consolidation processes.

Theta oscillations in the medial prefrontal cortex are modulated by spatial working memory and synchronize with the hippocampus through its ventral subregion.

The rodent medial prefrontal cortex (mPFC) is critical for spatial working memory (SWM), but the underlying neural processes are incompletely understood. During SWM tasks, neural activity in the mPFC becomes synchronized with theta oscillations in the hippocampus, and the strength of hippocampal-prefrontal synchrony is correlated with behavioral performance. However, to what extent the mPFC generates theta oscillations and whether they are also modulated by SWM remains unclear. Furthermore, it is not known how theta oscillations in the mPFC are synchronized with theta oscillations in the hippocampus. Although the ventral hippocampus (vHPC) projects directly to the mPFC, previous studies have only examined synchrony between the mPFC and the dorsal hippocampus (dHPC), with which it is not directly connected. To address these issues, we recorded simultaneously from the dHPC, vHPC, and mPFC of mice performing a SWM task in a T-maze. The local field potential recorded in the mPFC displayed robust theta oscillations that were reflected in local measures of neuronal activity and modulated by SWM performance. mPFC theta oscillations were also synchronized with theta oscillations in both the vHPC and dHPC, and the magnitude of theta synchrony was modulated by SWM. Removing the influence of the vHPC either computationally (through partial correlations) or experimentally (through pharmacological inactivation) reduced theta synchrony between the mPFC and dHPC. These results reveal theta oscillations as a prominent feature of neural activity in the mPFC and a candidate neural mechanism underlying SWM. Furthermore, our results suggest that the vHPC plays a major role in synchronizing theta oscillations in the mPFC and the hippocampus.

Inhibition of mediodorsal thalamus disrupts thalamofrontal connectivity and cognition.

Cognitive deficits are central to schizophrenia, but the underlying mechanisms still remain unclear. Imaging studies performed in patients point to decreased activity in the mediodorsal thalamus (MD) and reduced functional connectivity between the MD and prefrontal cortex (PFC) as candidate mechanisms. However, a causal link is still missing. We used a pharmacogenetic approach in mice to diminish MD neuron activity and examined the behavioral and physiological consequences. We found that a subtle decrease in MD activity is sufficient to trigger selective impairments in prefrontal-dependent cognitive tasks. In vivo recordings in behaving animals revealed that MD-PFC beta-range synchrony is enhanced during acquisition and performance of a working memory task. Decreasing MD activity interfered with this task-dependent modulation of MD-PFC synchrony, which correlated with impaired working memory. These findings suggest that altered MD activity is sufficient to disrupt prefrontal-dependent cognitive behaviors and could contribute to the cognitive symptoms observed in schizophrenia.