Spatial and stimulus-type tuning in the LEC, MEC, POR, PrC, CA1, and CA3 during spontaneous item recognition memory

Abstract

According to the "two streams" hypothesis, the lateral entorhinal (LEC) and the perirhinal (PrC) cortices process information related to items (a "what" stream), the postrhinal (POR) and the medial entorhinal cortices (MEC) process spatial information (a "where" stream), and both types of information are integrated in the hippocampus (HIP). However, within the framework of memory function, only the HIP is reliably shown to preferentially process spatial information, and the PrC items' features. In contrast, the role of the LEC and MEC in memory is virtually unexplored, and conflicting results emerge for the POR. Moreover, the specific contribution of the hippocampal subfields CA1 and CA3 to spatial and non-spatial memory is not thoroughly understood. To investigate which of these areas is specifically tuned to spatial demands or stimulus identity (odor or object), we assessed the pattern of activation of these areas during recognition memory by detecting the immediate-early gene Arc, commonly used as a marker of neuronal activation. We report that all MTL areas were recruited during the spatial and the non-spatial tasks. However, the LEC, MEC, POR, and CA1 were activated to a comparable level in spatial and non-spatial tasks, while the PrC was tuned to stimulus-type, not spatial demands, and CA3 to spatial demands but not stimulus-type. Results are discussed within the frame of a recent model suggesting that the MTL could be segregated in terms of memory processes, such as recollection and familiarity, rather than information content.

Representation of memories in the cortical–hippocampal system: Results from the application of population similarity analyses

“…In the three areas, representations of identical events are most closely associated (correlation of odd/even trials). Thus, although PRC, LEC and MEC exhibit similarity in mixed selectivity at the single neuron level, RSA reveals that information is organized in distinct but complementary ways (see also Ahn and Lee, 2015; Beer et al, 2013; Deshmukh and Knierim, 2011; Ohyama et al, 2012). …”

Lateral Entorhinal Cortex Lesions Impair Local Spatial Frameworks

“…These include grid cells, head direction cells, border/boundary vector cells and speed cells (Hafting et al, 2005; Barry et al, 2006; Savelli et al, 2008; Solstad et al, 2008; Lever et al, 2009; Kropff et al, 2015). There is now growing support from lesion and single unit recording studies for the suggestion that LEC is involved in processing past and present locations of objects (Deshmukh and Knierim, 2011; Beer et al, 2013; Hunsaker et al, 2013; Tsao et al, 2013; Van Cauter et al, 2013; Wilson et al, 2013a,b; Chao et al, 2016; Keene et al, 2016). Our own work has shown that LEC is needed to associate together features of a local environment including spatial locations of objects (Wilson et al, 2013a,b).…”

Contrasting roles for DNA methyltransferases and histone deacetylases in single-item and associative recognition memory

“…While long-term recognition memory formation has been shown to require expression of immediate early genes and a number of transcription factors (Zhu et al, 1995, Bozon et al, 2003, Warburton et al, 2005, Soulé et al, 2008, McNulty et al, 2012, Seoane et al, 2012, Barbosa et al, 2013, Beer et al, 2013), little is known about how these genes are regulated. Epigenetic regulation processes have been shown to be important for long term memory.…”