The process of detecting environmental novelty and the process of recognition memory are very similar behavioral events; however, they do require a distinction (Medina & Lisberger, 2008; Eichenbaum, Yonelinas & Ranganath, 2007; Eichenbaum & Lipton, 2008). To recognize something as familiar is equivalent to identifying it as being previously experienced; however, to detect novelty requires the identification of a conceptual mismatch between a current environmental stimulus and an existing memory representation of that stimulus (i.e., what we currently see is different than what we remember; Cormier, 1986; Eichenbaum et al., 2007; Wiebe, Cheatham, Lukowski, Haight, Muehleck & Bauer, 2006). This conceptual stimulus mismatch process of match-mismatch novelty recognition is simply a yes-no judgment of identity between a stimulus and an internal representation. The aforementioned simplicity is derived from the fact that a difference between stimuli can be detected without the necessity of defining the difference (Cormier, 1986). Often referred to as ‘orienting responses’, these processes of novelty recognition are critical across species as biological and evolutionary imperatives require organisms to constantly attenuate to familiar stimuli as well as identify novel stimuli and formulate appropriate reactions (Honey, Watt & Good, 1998; Knight, 1996). For example, once an internal memory representation has been formed (e.g., the nesting location of a particular organism), the importance of that representation will be judged based on the extent to which it is useful; namely, the extent to which it promotes species survival (e.g., the identification of any alterations to that organism’s nesting location potentially caused by predators; see Cormier, 1986). Additionally, the ability to detect novelty in familiar environments is of significant importance in the day-to-day living of older adults (Maylor, Smith, Della Salla & Logie, 2002; McDaniel & Einstein, 2007a, 2007b). For example, this is process may be critical when considering the ability of an older adult to correctly identify when the label of a commonly used medication, or that medication’s position in the pharmacy, has changed.
As elaborated by Cormier (1986) and Eichenbaum et al. (2007), match-mismatch recognition (MMR) is not a neurologically localized process. Rather, this process is potentially a compilation of integrated neural processes, all of which are loosely associated around the general act of stimulus recognition (see Eichenbaum et al., 2007). Research suggesting that the process of MMR is composed of a number of distinct neuronal processes is relatively recent. Historically, the component processes of MMR were very challenging to elucidate. This opacity was caused by the seemingly intuitive nature of some type of ‘comparison process’ being present for the recognition and retrieval of memory representations, leading to a generalization of the component construction of MMR. For example, Tolman (1932) suggested that the identification of environmental novelty in humans and rodents could be generally defined as ‘purposive behavior’ (see Hull, 1943; Tolman, 1932; Wearden, 1989). The general theory of ‘purposive behavior’ states that behaviors are always going to be directed toward some larger goal (e.g., a rat running a maze to receive a reward). Tolman (1948) built on this idea and came to suggest that there may be more components involved in learning than a simple stimulus-response association. It was hypothesized that during the process of learning an animal would establish a field map of the environment within the brain, where a mismatch between the field map representation and the actual environment would imply novelty (Tolman, 1948). This hypothesis was the first step in identifying a potential neural mechanism behind match-mismatch recognition. A number of recent studies have utilized rodent models to shown that tasks measuring natural exploratory behavior may be ideal paradigms for studying these types of match-mismatch processes (Hauser, Totentino, Pirogovsky, Weston & Gilbert, 2009; Lee, Hunsaker & Kesner, 2005; Save, Poucet, Foreman & Buhot, 1992).
There is a growing body of literature from a number of mammalian species demonstrating that the hippocampus plays a critical role in spatial memory (Gilbert & Kesner, 2002, 2003; Kesner, 2007; Kesner, Gilbert & Wallenstein, 2000; Moser, Kropff & Moser, 2008; Rolls, 1996). Additionally, there are a large number of studies that implicate the hippocampus as being a critical substrate in performing exploratory-based novelty detection paradigms involving object-place associations (Best, White & Minai, 2001; Bunsey & Eichenbaum, 1996; Gilbert, Kesner & DeCoteau, 1998; Gothard, Skaggs & McNaughton, 1996; Hampson, Jarrard & Deadwyler, 1999; Honey et al., 1998; Lee, Buckley, Pegman, Spiers, Scahill, Gaffan, Bussey, Davies, Kapur, Hodges & Graham, 2005; Lee, Jerman & Kesner, 2005; Lee, Hunsaker & Kesner, 2005; Save et al., 1992; Squire, 1992; Vann, Brown, Erichsen & Aggleton, 2000; Wan, Aggleton & Brown, 1999). The hippocampus receives inputs from almost all cortical association areas, including those in the parietal, temporal, and frontal lobes. These inputs arrive by way of structures adjacent to the hippocampus, such as the parahippocampal gyrus and entorhinal cortex (see Rolls, 1996; Squire, Shimamura & Amaral, 1989). These cortical afferents ultimately find convergence within the hippocampus. Thus, the hippocampus is likely responsible for the integration of highly processed, multimodal sensory information (Rolls, 1996; Rolls & Kesner, 2006). Although there may be topographical organization maintained in the cortical afferents to the hippocampus, the literature is unclear as to whether or not the hippocampus represents/maintains this information in any obvious topographic format (see Hampson, Simeral & Deadwyler, 1999; Moser & Moser, 1998). Yet, despite the current lack of any obvious organizational topography, it is the structural anatomy of the medial temporal lobe, the hippocampal formation, and the hippocampus proper (see below) that allow the functional integration of such highly processed sensory information from the different cortical regions (see Van Strien, Cappaert & Witter, 2009).