Lateral entorhinal cortex lesions impair odor‐context associative memory in male rats

Abstract

Lateral entorhinal cortex (LEC) has been hypothesized to process nonspatial, item information that is combined with spatial information from medial entorhinal cortex to form episodic memories within the hippocampus. Recent studies, however, have demonstrated that LEC has a role in integrating features of episodic memory prior to the hippocampus. While the precise role of LEC is still unclear, anatomical studies show that LEC is ideally placed to be a hub integrating multisensory information.The current study tests whether the role of LEC in integrating information extends to long-term multimodal item-context associations. In Experiment 1, male rats were trained on a context-dependent odor discrimination task, where two different contexts served as the cue to the correct odor. Rats were pretrained on the task and then received either bilateral excitotoxic LEC or sham lesions. Following surgery, rats were tested on the previously learned odor-context associations. Control rats showed good memory for the previously learned association but rats with LEC lesions showed significantly impaired performance relative to both their own presurgery performance and to control rats. Experiment 2 went on to test whether impairments in Experiment 1 were the result of LEC lesions impairing either odor or context memory retention alone. Male rats were trained on simple odor and context discrimination tasks that did not require integration of features to solve. Following surgery, both LEC and control rats showed good memory for previously learned odors and contexts. These data show that LEC is critical for long-term odor-context associative memory.

Distinct brain networks for remote episodic memory depending on content and emotional value

“…The brain networks recruited in Where rats, that show an incomplete memory, are more restricted and less efficient in terms of functional connectivity and specific to networks of memories with contextual and spatial information (dorsal hippocampus, retrosplenial cortex, and habenula) [46][47][48][49][50] . In contrast, WWW rats that remember all episodic information recruit larger brain networks, including the same spatial network and brain regions that are functionally connected and implicated in olfactory memory (piriform, lateral entorhinal, orbitofrontal, prelimbic and infralimbic cortices) [51][52][53][54][55][56] . A comparison of the Where and WWW profiles reveals that complete recollection of remote episodic memory recruits a core network of interconnected brain regions (medio-lateral orbitofrontal, ventral CA1 and basolateral amygdala) [57][58][59][60][61][62] that are implicated in the valence and emotional processing of information and directly correlated with memory accuracy during recall.…”

Entorhinal cortex glutamatergic and GABAergic projections bidirectionally control discrimination and generalization of hippocampal representations

“…Few studies have directly explored the role of LEC in hippocampal memory-related behavior using a loss-of-function approach. Nevertheless, those revealed important functions for LEC inputs in odor-context associative learning 72 and memory 73 in CA1 and DG 74 , as well as fear context discrimination and novel object recognition in CA1 36 . Finally, LEC lesions have been found to impair the rate remapping of CA3 place cells induced by shape or color changes of the environment 42 .…”

The Grossberg Code: Universal Neural Network Signatures of Perceptual Experience

“…These results suggest that initial odor information coded in the olfactory areas evolves towards perceptual realization through computations (long-range mechanism) in widely distributed cortical regions with different spatiotemporal dynamics [47]. Specific brain structures act appear to form hubs for integrating local multisensory cues into a spatial framework [48] enabling short-term as well as long-lasting memory traces of odors, touch sensations, sounds and visual objects in different dynamic contexts. Contextual modulation in the brain thus explains how olfactory and other sensory inputs translate into diverse and complex perceptions such as the pleasurable floral smell of flowers or the aversive smells of decaying matter.…”