Biology subjects

Morici, J. F.

Publications and source records attributed to Morici, J. F..

5 recordsLinked to original sources

bioRxiv2024

Dorso-ventral hippocampal neural assemblies are preferentially reactivated during NREM sleep following an aversive experience

The integration of spatial and emotional components into episodic memory relies on coordinated interactions between hippocampal circuits and emotion-processing regions. While the dorsal hippocampus (dHPC) supports memory consolidation through sharp-wave ripple (SWR)-associated reactivation of spatial representations, it lacks direct connectivity with key emotional centers such as the amygdala. In contrast, the ventral hippocampus (vHPC) is anatomically and functionally embedded within the emotional network. How the dHPC and vHPC coordinate during sleep to support the processing of complex contextual and emotional experiences remains unclear. Here, we used simultaneous electrophysiological recordings from the dHPC and vHPC in rats performing a spatial alternation task under opposite emotional valence and during subsequent sleep. We show that dorso-ventral neuronal assemblies better disambiguate the between valence than isolated dorsal or ventral assemblies. During non-REM sleep, coordinated SWRs orchestrate assembly reactivation across the dorso-ventral hippocampal axis following both aversive and rewarding experiences; however, reactivation after aversive trials more closely mirrors the original neural patterns. This enhanced fidelity is driven by the heightened recruitment of shock-responsive neurons of the ventral hippocampus and spatial replay of the dorsal hippocampus into coordinated SWRs. Our findings identify a mechanism by which the hippocampus integrates the spatial and emotional dimensions of an experience during sleep, potentially routing information to the broader emotional memory network via synchronized SWRs.

neuroscience↗

bioRxiv2023

Behavioral, molecular and neuronal mechanisms involved in recognition memory retrieval under degraded spatial cues in the rat hippocampus

In a constantly changing environment, organisms face the challenge of adapting their behavior by retrieving previous experiences or acquiring new information. Previous research has postulated that this balance between memory generalization and differentiation manifests in a dichotomic manner. When environmental information exceeds a given threshold, activation of a stored representation could initiate retrieval, but below this threshold, a novel event could be encoded with a concomitant remapping of the internal representation in the hippocampus. Here, we examined the hippocampal molecular and neuronal mechanisms underlying retrieval in a cue-degraded environment by combining in vivo electrophysiological recordings and pharmacological manipulations. We developed a memory recognition task that allows a graded decrease in the contextual cues present during retrieval. We found that the manipulation of the number of visual cues was consistent with the activation or not of the contextual memory trace. Retrieval of a specific context memory was reflected by the level of CA3 remapping, demonstrating a clear relationship between remapping and contextual recognition. Also, manipulation of NMDAR activity in the DG-CA3 circuit bidirectionally modulated contextual memory retrieval. The blockade of NMDAR in CA3 impaired recognition in a cue-degraded, but not in a full-cue context, while their activation has the opposite effect. Conversely, blockade of NMDAR in the DG promoted retrieval under an even more cue-degraded environment, while activation had the opposite effect. Our results provide evidence for a flexible interaction between environmental cues and information stored in the hippocampus and give new insights into the biological mechanisms that balance memory encoding and retrieval.

neuroscience↗

bioRxiv2021

Hippocampal-Prefrontal cortex network dynamics predict performance during retrieval in a context-guided object memory task

Remembering life episodes is a complex process that requires the interaction between multiple brain areas. It is thought that contextual information provided by the hippocampus (HPC) can trigger the recall of a past event through the activation of medial prefrontal cortex (mPFC) neuronal ensembles, but the underlying mechanisms remain poorly understood. Indeed, little is known about how the vHPC and mPFC are coordinated during a contextual-guided recall of an object recognition memory. To address this, we performed electrophysiological recordings in behaving rats during the retrieval phase of the object-in-context memory task (OIC). Coherence, phase locking and theta amplitude correlation analysis showed an increase in vHPC-mPFC LFP synchronization in the theta range when animals explore contextually mismatched objects. Moreover, we identified ensembles of putative pyramidal cells in the mPFC that encode specific object-context associations. Interestingly, the increase of vHPC-mPFC synchronization during exploration of the contextually mismatched object and the preference of mPFC incongruent object neurons predicts the animals performance during the resolution of the OIC task. Altogether, these results identify changes in vHPC-mPFC synchronization and mPFC ensembles encoding specific object-context associations likely involved in the recall of past events.

neuroscience↗

bioRxiv2021

Dopamine modulates adaptive forgetting in medial prefrontal cortex

Active forgetting occurs in many species, but how the mechanisms that control behavior contribute to determining which memories are forgotten is still unknown. We previously found that when rats need to retrieve particular memories to guide exploration, it reduces later retention of other memories encoded in that environment. As with humans, this retrieval-induced forgetting relies on prefrontal control processes. The dopaminergic input to the prefrontal cortex is important for executive functions and cognitive flexibility. We found that, in a similar way, prefrontal dopamine signaling through D1 receptors is required for retrieval-induced forgetting in rats. Blockade of medial prefrontal cortex D1 receptors as animals encountered a familiar object impaired forgetting of the memory of a competing object in a subsequent long-term memory test. Inactivation of the ventral tegmental area produced the same pattern of behavior, a pattern that could be reversed by concomitant activation of prefrontal D1 receptors. We observed a bidirectional modulation of retrieval-induced forgetting by agonists and antagonists of D1 receptors in the medial prefrontal cortex. These findings establish the essential role of prefrontal dopamine in the active forgetting of competing memories, contributing to the shaping of retention in response to an organisms behavioral goals.

animal behavior and cognition↗

bioRxiv2019

Dentate gyrus somatostatin cells are required for contextual discrimination during episodic memory encoding

Episodic memory establishes and stores relations among the different elements of an experience, which are often similar and difficult to distinguish. Pattern separation, implemented by the dentate gyrus, is a neural mechanism that allows the discrimination of similar experiences by orthogonalizing synaptic inputs. Granule cells support such disambiguation by sparse rate coding, a process tightly controlled by highly diversified GABAergic neuronal populations, such as somatostatin-expressing cells which directly target the dendritic arbor of granule cells, massively innervated by entorhinal inputs reaching the molecular layer and conveying contextual information. Here, we tested the hypothesis that somatostatin neurons regulate the excitability of the dentate gyrus, thus controlling the efficacy of pattern separation during memory encoding in mice. Indeed, optogenetic suppression of dentate gyrus somatostatin neurons increased spiking activity in putative excitatory neurons and triggered dentate spikes. Moreover, optical inhibition of somatostatin neurons impaired both contextual and spatial discrimination of overlapping episodic-like memories during task acquisition. Importantly, effects were specific for similar environments, suggesting that pattern separation was selectively engaged when overlapping conditions ought to be distinguished. Overall, our results suggest that somatostatin cells regulate excitability in the dentate gyrus and are required for effective pattern separation during episodic memory encoding.\n\nSignificance statementMemory systems must be able to discriminate stored representations of similar experiences in order to efficiently guide future decisions. This is solved by pattern separation, implemented in the dentate gyrus by granule cells to support episodic memory formation. The tonic inhibitory bombardment produced by multiple GABAergic cell populations maintains low activity levels in granule cells, permitting the process of pattern separation. Somatostatin-expressing cells are one of those interneuron populations, selectively targeting the distal dendrites of granule cells, where cortical multimodal information reaches the dentate gyrus. Hence, somatostatin cells constitute an ideal candidate to regulate pattern separation. Here, by using optogenetic stimulation in mice, we demonstrate that somatostatin cells are required for the acquisition of both contextual and spatial overlapping memories.

neuroscience↗