Advantageous Object Recognition for High-Fat Food Images

Excerpt

How the human brain recognizes and differentiates objects from one another and likewise groups them into categories according to common features/actions has been a topic of neuropsychological and neuroscientific investigation for several decades. For example, ventral posterior temporal cortices have been found to play a major role not only in object processing in general (see Tanaka, 1997; Ungerleider and Haxby, 1994 for reviews), but also in category-selective processing (Moore and Price, 1999; Peissig and Tarr, 2007; Perani et al., 1995, 1999). One axis along which objects appear to be differentiated is whether their referent is something living or an artifact (i.e., manufactured). This distinction appears to hold true for visually presented stimuli (e.g., Caramazza and Shelton, 1998; Gerlach, 2007; Martin, 2007) as well as their auditory counterparts (Lewis et al., 2005; Murray et al., 2006). In addition to this categorical distinction, there is abundant evidence that the processing of faces (and places) may recruit highly specialized neural circuitry (e.g., Bentin et al., 2007; Kanwisher and Yovel, 2006). One perspective is that such specialized responsiveness follows from the social importance of faces in human interactions. More recently, investigations have revealed that objects and words can also be differentially processed according to their associated actions by regions of the ventral premotor cortex and posterior parietal areas (see Culham and Valyear, 2006; Johnson-Frey, 2004; Lewis et al., 2005; Pulvermuller, 2005 for reviews).

Applying a similar line of reasoning, other socially or biologically important object categories would also be predicted to engage specialized neural circuitry. Foods and their proper discrimination, for example, are of utmost importance for an organism’s survival. While this object category has been the subject of comparatively few functional neuroimaging studies, there is evidence to suggest that food images may activate brain regions distinct from those activated by other object categories (Killgore et al., 2003; LaBar et al., 2001; Rothemund et al., 2007; Santel et al., 2006; Simmons et al., 2005). In particular, viewing pictures of foods as opposed to nonfoods has been shown to activate frontal cortices as well as the frontal operculum and the insula (Killgore et al., 2003; LaBar et al., 2001; Simmons et al., 2005), the latter thought to be primary gustatory cortex regions (O’Doherty et al., 2001). Viewing foods can also modulate the activity in secondary gustatory regions within the orbitofrontal cortex (OFC; Beaver et al., 2006; Simmons et al., 2005). In addition to this, wider network of brain regions, striate, and extrastriate visual areas also exhibit modulated activity during the categorization of foods from tools (Killgore et al., 2003; LaBar et al., 2001; Simmons et al., 2005).

However, from this evidence alone the basis upon which foods are discriminated from other objects and categorized among each other cannot be determined. For example, it may be either the reward and/or sensory features of the stimuli that drive the observed differential responses. Also, from these data it cannot be discerned which area(s) among the network of regions exhibiting differential responses is first involved and in what sequence other regions contribute to the discrimination of foods. Rather, temporal information is essential for constructing accurate models of food discrimination and evaluation. Electrical neuroimaging based on electroencephalographic recordings has been proven to be a powerful tool to identify the spatiotemporal dynamics during the categorization of other object categories than food (e.g., tools, animals, vehicles, and faces). It has been shown that categorization and in some cases within-category discrimination occurs within the initial 100–200 ms following stimulus presentation (Bentin et al., 2007; Eger et al., 2003; Fabre-Thorpe et al., 2001; Ji et al., 1998; Johnson and Olshausen, 2003; Kanwisher and Yovel, 2006; Michel et al., 2004a; Pizzagalli et al., 1999; Proverbio et al., 2007; Thorpe et al., 1996; VanRullen and Thorpe, 2001).

Given this evidence, we hypothesized that the discrimination of food from nonfood images would occur within a similar time frame as that of other object categories. Moreover, although food is quintessential for survival, inherent differences exist with respect to nutritional and energetic value as well as hedonic attributes. As such, even though energetic value and palatability are critical factors influencing eating behavior, decisions regarding food intake are often guided by factors that can be detrimental for an individual’s health. Often, high-fat foods are consumed with more pleasure, and in larger quantities, than low-fat foods. One possibility is that the drive for hedonic experiences may lead to inappropriate food consumption behavior. In turn, overeating of detrimental foods can ultimately result in obesity, diabetes, and hypertension, which are increasingly prevalent among industrialized societies. Understanding the decision processes leading to food selection and consumption, and in particular how the brain appraises the presentation of foods before they are ingested, is likely to prove essential for learning how to control and correct inappropriate eating behavior.