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.

Hippocampal-prefrontal theta-gamma coupling during performance of a spatial working memory task

Cross-frequency coupling supports the organization of brain rhythms and is present during a range of cognitive functions. However, little is known about whether and how long-range cross-frequency coupling across distant brain regions subserves working memory. Here we report that theta–slow gamma coupling between the hippocampus and medial prefrontal cortex (mPFC) is augmented in a genetic mouse model of cognitive dysfunction. This increased cross-frequency coupling is observed specifically when the mice successfully perform a spatial working memory task. In wild-type mice, increasing task difficulty by introducing a long delay or by optogenetically interfering with encoding, also increases theta–gamma coupling during correct trials. Finally, epochs of high hippocampal theta–prefrontal slow gamma coupling are associated with increased synchronization of neurons within the mPFC. These findings suggest that enhancement of theta–slow gamma coupling reflects a compensatory mechanism to maintain spatial working memory performance in the setting of increased difficulty.

Theta- and gamma-frequency oscillatory synchrony correlates with spatial working memory performance. Here the authors report increases in theta-gamma cross-frequency coupling as a compensatory mechism associated with better working memory performance in models of cognitive dysfunction in mice.

Thalamic projections sustain prefrontal activity during working memory maintenance

The mediodorsal thalamus (MD) shares reciprocal connectivity with the prefrontal cortex (PFC), and decreased MD-PFC connectivity is observed in schizophrenia patients. Patients also display cognitive deficits including impairments in working memory, but a mechanistic link between thalamo-prefrontal circuit function and working memory is missing. Using pathway-specific inhibition, we found directional interactions between mouse MD and medial PFC (mPFC), with MD-to-mPFC supporting working memory maintenance and mPFC-to-MD supporting subsequent choice. We further identify mPFC neurons that display elevated spiking during the delay, a feature that was absent on error trials and required MD inputs for sustained maintenance. Strikingly, delay-tuned neurons had minimal overlap with spatially tuned neurons, and each mPFC population exhibited mutually exclusive dependence on MD and hippocampal inputs. These findings indicate a role for MD in sustaining prefrontal activity during working memory maintenance. Consistent with this idea, we found that enhancing MD excitability was sufficient to enhance task performance.

Direct Ventral Hippocampal-Prefrontal Input Is Required for Anxiety-Related Neural Activity and Behavior

The ventral hippocampus (vHPC), medial prefrontal cortex (mPFC), and basolateral amygdala (BLA) are each required for the expression of anxiety-like behavior. Yet the role of each individual element of the circuit is unclear. The projection from the vHPC to the mPFC has been implicated in anxiety-related neural synchrony and spatial representations of aversion. The role of this projection was examined using multi-site neural recordings combined with optogenetic terminal inhibition. Inhibition of vHPC input to the mPFC disrupted anxiety and mPFC representations of aversion, and reduced theta synchrony in a pathway-, frequency- and task-specific manner. Moreover, bilateral, but not unilateral, inhibition altered physiological correlates of anxiety in the BLA, mimicking a safety-like state. These results reveal a specific role for the vHPC-mPFC projection in anxiety-related behavior and the spatial representation of aversive information within the mPFC.

Synchrony in schizophrenia: a window into circuit-level pathophysiology

As a complex neuropsychiatric disease with both hereditary and environmental components, schizophrenia must be understood across multiple biological scales, from genes through cells and circuits to behaviors. The key to evaluating candidate explanatory models, therefore, is to establish causal links between disease-related phenomena observed across these scales. To this end, there has been a resurgence of interest in the circuit-level pathophysiology of schizophrenia, which has the potential to link molecular and cellular data from risk factor and post-mortem studies with the behavioral phenomena that plague patients. The demonstration that patients with schizophrenia frequently have deficits in neuronal synchrony, including deficits in local oscillations and long-range functional connectivity, offers a promising opportunity to forge such links across scales.