HIF-1α and HIF-2α Are Upregulated in the Hippocampus but Not in the Medial Prefrontal Cortex in Experimental PTSD.

As soon as their sensory systems become functional, organisms must be able to extract meaningful information from their environment. Relevant environmental cues can be learned prenatally, stored, and subsequently used to guide appropriate behaviors postnatally. Such processing may further evolve throughout development as a result of learning, changing environmental demands, and the maturation of cognitive and perceptual systems. This is the case with olfaction, for example, as the olfactory system develops and begins functioning before birth in many species, including mammals (e.g., Gottlieb , ; Schaal ; Coureaud et al. ; Romagny et al. ). Olfaction involves organisms processing stimuli in the form of volatile molecules, which usually emanate from sources as mixtures of several odorants rather than as single‐molecule stimuli. Therefore, from early life through to adulthood, organisms primarily process odor mixtures. Understanding how such mixtures are perceptually processed is thus critical for characterizing olfactory function in ecologically valid conditions. Odor mixtures are not perceived as the simple sum of their components; they can be processed elementally, when the mixture is perceived through its individual components, or configurally, when the percept differs from the components, either due to overshadowing among odorants or the emergence of a novel odor quality (Kay et al. ; Thomas‐Danguin et al. ). In this framework, configural processing refers to the emergence of a unified percept that is not reducible to its individual components, whereas elemental processing refers to access to these components. Over the past two decades, studies of configural and elemental processing of odor mixtures have been conducted in human adults and newborn rabbits (see also Coureaud et al. [], for comparative results in rodents and bees) using two model mixtures of different complexity. In both species, these mixtures, namely a binary pineapple‐odor‐eliciting mixture (AB; Thomas‐Danguin et al. ; Le Berre, Béno, et al. ; Barkat et al. ) and a senary Red Cordial‐odor‐eliciting mixture (RC; Le Berre et al. ; Sinding et al. ), can be perceived either configurally or elementally (Coureaud et al. , ; Coureaud, Thomas‐Danguin, Datiche, et al. ; Coureaud, Thomas‐Danguin, Wilson, et al. ; Sinding et al. ; Romagny et al. ), with the mode of perception influenced by prior exposure and learning (Le Berre, Thomas‐Danguin, et al. ; Le Berre et al. ; Sinding et al. ). While human adults tend to perceive a specific configural quality (e.g., pineapple or red cordial) through robust configural processing, newborn rabbits display weak configural processing, detecting both mixture‐specific and component‐related cues. Following previous definitions (Kay et al. ; Thomas‐Danguin et al. ), robust configural processing refers to the perception of the mixture‐specific (configural) quality with limited access to the qualities of individual components, whereas weak configural processing refers to the perception of both the configural quality and the qualities of the individual components.