Lateral Entorhinal Modulation of Piriform Cortical Activity and Fine Odor Discrimination

Abstract

The lateral entorhinal cortex (LEC) receives direct input from olfactory bulb mitral cells and piriform cortical pyramidal cells and is the gateway for olfactory input to the hippocampus. However, the LEC also projects back to the piriform cortex and olfactory bulb. Activity in the LEC is shaped by input from the perirhinal cortices, hippocampus, and amygdala, and thus could provide a rich contextual modulation of cortical odor processing. The present study further explored LEC feedback to anterior piriform cortex by examining how LEC top-down input modulates anterior piriform cortex odor evoked activity in rats. Retrograde viral tracing confirmed rich LEC projections to both the olfactory bulb and piriform cortices. In anesthetized rats, reversible lesions of the ipsilateral LEC increased anterior piriform cortical single-unit spontaneous activity. In awake animals performing an odor discrimination task, unilateral LEC reversible lesions enhanced ipsilateral piriform cortical local field potential oscillations during odor sampling, with minimal impact on contralateral activity. Bilateral LEC reversible lesions impaired discrimination performance on a well learned, difficult odor discrimination task, but had no impact on a well learned simple odor discrimination task. The simple discrimination task was impaired by bilateral reversible lesions of the anterior piriform cortex. Given the known function of LEC in working memory and multisensory integration, these results suggest it may serve as a powerful top-down modulator of olfactory cortical function and odor perception. Furthermore, the results provide potential insight into how neuropathology in the entorhinal cortex could contribute to early olfactory deficits seen in Alzheimer's disease.

Intrahippocampal Pathways Involved in Learning/Memory Mechanisms are Affected by Intracerebral Infusions of Amyloid-β25-35 Peptide and Hydrated Fullerene C60 in Rats

“…6, A). In this respect, our data are in line with evidence about high sensitivity of this bundle (a projection of the lateral EC) to AD, especially at its early stages [47], [48]. In contrast, the infrapyramidal DG (a projection of the medial EC) was practically unaffected (Fig.…”

Odor- and state-dependent olfactory tubercle local field potential dynamics in awake rats

“…While a considerable amount of information is available on odor information processing in the OB and on the transmission into and coupling of this information with downstream structures (e.g., piriform cortex, entorhinal cortex, hippocampus) (Chapuis et al 2009(Chapuis et al , 2013Staubli et al 1995), whether or not this occurs between the OB and the OT is unknown. We predicted that both the OT would share aspects of spontaneous activity with the OB (i.e., prominent theta rhythm), and spontaneous and odor-evoked LFP activity within the OT would mimic that within the OB.…”

Gamma and Beta Oscillations Define a Sequence of Neurocognitive Modes Present in Odor Processing

“…Preodor beta power and TAC beta coherence increases (Fig. 8) may be related to beta band input from the lateral entorhinal cortex associated with preafferent priming (Kay and Freeman, 1998) and odor processing (Chapuis et al, 2013). In Experiment 2, TAC preodor beta coherence is lower than in Experiment 1 and the same as GNG, indicating a system-level change in the TAC task in the context of also knowing GNG.…”

“…During this later sampling period, the OB, PC, and other olfactory and limbic areas are strongly coupled in the beta band (Figs. 1c, 8a,b) Kay and Beshel, 2010;Cohen et al, 2015a).…”