Roles of the medial prefrontal cortex, mediodorsal thalamus, and their combined circuit for performance of the odor span task in rats: analysis of memory capacity and foraging behavior

Abstract

Working memory (WM), the capacity for short-term storage of small quantities of information for immediate use, is thought to depend on activity within the prefrontal cortex. Recent evidence indicates that the prefrontal neuronal activity supporting WM is driven by thalamocortical connections arising in mediodorsal thalamus (mdThal). However, the role of these connections has not been studied using olfactory stimuli leaving open the question of whether this circuit extends to all sensory modalities. Additionally, manipulations of the mdThal in olfactory memory tasks have yielded mixed results. In the present experiment, we investigated the role of connections between the rat medial prefrontal cortex (mPFC) and mdThal in the odor span task (OST) using a pharmacological contralateral disconnection technique. Inactivation of either the mPFC or mdThal alone both significantly impaired memory performance in the OST, replicating previous findings with the mPFC and confirming that the mdThal plays an essential role in intact OST performance. Contralateral disconnection of the two structures impaired OST performance in support of the idea that the OST relies on mPFC-mdThal connections, but ipsilateral control infusions also impaired performance, complicating this interpretation. We also performed a detailed analysis of rats' errors and foraging behavior and found a dissociation between mPFC and mdThal inactivation conditions. Inactivation of the mdThal and mPFC caused a significant reduction in the number of approaches rats made per odor, whereas only mdThal inactivation or mPFC-mdThal disconnection caused significant increases in choice latency. Our results confirm that the mdThal is necessary for performance of the OST and that it may critically interact with the mPFC to mediate OST performance. Additionally, we have provided evidence that the mPFC and mdThal play dissociable roles in mediating foraging behavior.

Variation of connectivity across exemplar sensory and associative thalamocortical loops in the mouse

“…Interactions between the thalamus and cortex are essential for sensory processing ( Lien and Scanziani, 2018 ; Bartlett, 2013 ), motor control ( Fresno et al, 2019 ; Guo et al, 2017 ), arousal ( Chen et al, 2015 ; Schiff, 2008 ) and multiple aspects of cognitive function ( Wimmer et al, 2015 ; Wolff and Vann, 2019 ; Jaramillo et al, 2019 ; Parnaudeau et al, 2018 ; Pergola et al, 2018 ; Rikhye et al, 2018a ; Saalmann and Kastner, 2011 ; Bolkan et al, 2017 ; Scott et al, 2020 ). How does this collection of forebrain nuclei contribute to the diversity of hypothesized functions?…”

Thalamic gray matter volume mediates the association betweenKIBRApolymorphism and olfactory function among older adults: a population-based study

“…2021 ). Accordingly, a merged functional and structural olfactory network map was defined as follows: primary olfactory cortices included piriform cortex and amygdala; and secondary olfactory cortices included orbitofrontal cortex, caudate nucleus, anterior cingulate cortex, insula, putamen, pallidum, hippocampal–parahippocampal complex, and thalamus ( Illig 2005 ; Scott et al. 2020 ).…”

High-THCCannabissmoke impairs working memory capacity in spontaneous tests of novelty preference for objects and odors in rats

“…A shortcoming in rodent literature is that traditional rodent WMC tests mimic n-back or recall WM tests used in humans that require a long training period, learned rules, and considerable experimental involvement (Barnard et al, 2022;Cowan, 2010;Daneman & Carpenter, 1980;Dudchenko, 2004;Dudchenko et al, 2013;Kirchner, 1958;Oomen et al, 2013;Scott et al, 2020;Vorhees & Williams, 2014;Wilhelm et al, 2013). Spontaneous recognition tests circumvent these weaknesses by relying on rodents' innate novelty seeking behavior as shown by preferential interaction with a novel stimulus after a delay (Broadbent et al, 2004;Ennaceur & Aggleton, 1994;Ennaceur & Delacour, 1988;Sannino et al, 2012).…”