Considering the visual brain as it pertains to forming appraisals about the aesthetics of objects we see daily, we understand that it is able to segregate properties such as colour, the intensity of light, and the motion of the object (Chatterjee & Vartanian, 2014). It is also known to be able to separate objects of higher-order, including faces, bodies, and landscapes. As humans observe other human faces, an area of the fusiform gyrus known as the ‘face area’ (FFA) becomes activated. Increased blood-oxygen levels have been noted in the FFA upon viewing a face, according to functional magnetic resonance imaging (fMRI) studies (Kawabata & Zeki, 2004). Observations of the environment around us however, engages a specific and alternate area of the visual cortex known as the parahippocampal gyrus (Yue, Vessel, & Biederman, 2007), which although nearby, rarely responds to viewing faces. As well as being involved in the classification of different objects, these sensory areas also appear to play a significant part in evaluating them. For example, faces that were rated as beautiful by a viewer, stimulate the fusiform gyrus and adjoining brain areas more than do faces deemed less beautiful (Chatterjee, Thomas, Smith & Aguirre, 2009).
Further to this, positron emission tomography (PET) research hypothesises that viewing faces is pleasurable cognitively, given the high density of cortical ?-opioid receptors in this area of the brain (Liberzon et al., 2002).The questions of what kind and how much of an assessment takes place within the sensory cortices is an area of ongoing inquiry for the neuroscience community, seeking to better understand the effects of how perception and evaluation in neural structures are integrated. Functional neuroimaging studies examining our emotional systems during visually appealing experiences are starting to reveal neural correlates (Chatterjee & Vartanian, 2014), and to extend neuroaesthetics beyond basic inclinations to stronger emotions that can result in aesthetic appeal.Studies regarding facial beauty such as those by Senior (2003), and Hahn and Perrett (2014), support that reward circuitry in the brain is activated upon the assessing of another human’s attractiveness. Researchers reported that male observers agreed with independent ratings of more beautiful faces, both for female and for male faces. Interestingly these same participants would only make intentional efforts to elongate the time they were exposed to the faces of females in the study, but not for males.
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It is suggested that these results may describe that attractive female faces were judged as both aesthetically pleasing, as well as rewarding, whereas more beautiful male faces were only pleasant to rate. In this research among heterosexual males observing opposite-sex faces that were attractive, reward circuits of the brain became activated. This included the sublenticular nucleus, ventral tegmentum, orbitofrontal cortex, and the nucleus accumbens, which are known to be involved in dopamine release regulation (Del Arco ; Mora, 2008). Conversely, when the same males viewed same-sex attractive faces that were not rewarding, a negative response was prompted in the nucleus accumbens and sublenticular nucleus. It is considered that these studies point to the engagement of some areas of the reward circuitry of the brain when rating certain faces as attractive, and that there may be a separation between attractiveness rating and processing of rewards.
When focusing on heterosexual female observers and their neural response to facial attractiveness, O’Doherty et al. (2003) observed an increased activation of areas in the medial orbitofrontal cortex upon viewing faces of the opposite sex. This brain area is involved in assigning value to a reward given, as well as the decision-making response that follows (Gourley, Zimmermann, Allen, & Taylor, 2016). Perhaps intuitively, this area’s activation was further increased when the face observed was smiling, rather than portrayed a neutral expression. This study suggests that facial stimuli activate reward centres of the brain.Adding further support to this are results detected by Cloutier, Heatherton, Whalen and Kelley (2008), whereby both males and females underwent functional neuroimaging while explicitly being asked to rate facial attractiveness by the researcher. Similar to the passive ratings above their results consistently showed an activation of reward circuit areas, with a positive linear correlation existing between increased activity, and higher attractiveness ratings.
Interestingly, there was a negative relationship noted between other specific brain area activation, and decreasing attractiveness attribution. The left medial prefrontal cortex, which is more typically understood to be involved in social information processing (Grossmann, 2013), was seen to increase in activity as faces were rated less attractive. As well as this, and reiterated by Winston, O’Doherty, Kilner, Perrett and Dolan (2007), emotional centres such as the amygdala were seen to display a larger response to both highly attractive and highly unattractive facial images, when compared to average faces. This non-linear profile of response for these limbic system neurons appears to suggest a role in assessing the social value of another human based on their face, but as Kirsch, Urgesi, and Cross point out, this emotional function involves sectors of the orbitofrontal cortex (2016) and thus reward processing. The reaction of frontal brain areas of participants completing attractiveness ratings, may not solely reveal the aesthetic value of a stimulus intrinsically to the observer, but may reflect its involvement overall in forming emotional evaluative judgements. One specific area, the dorsolateral prefrontal cortex, has displayed increased activation when participants rate facial attractiveness, compared to other assessments made based on faces.
For example, age (Winston, O’Doherty, Kilner, Perrett and Dolan, 2007) and identity judgements (Chatterjee, Thomas, Smith, ; Aguirre, 2009) appear to elicit less activity in these areas, reflecting a precise requirements of attractiveness assessments as compared to perceptual processing of facial features generally. Other studies report similar finding for the anterior component of the dorsolateral prefrontal cortex (Vartanian et al., 2013; Cloutier et al., 2008). Ferrari, Lega, Tamietto, Nadal, and Cattaneo (2015) found via the application of a mild electric current to this stimulate this area prior to viewing facial images, that increased attractiveness ratings followed.
As such, it is suggested that the prefrontal areas of the brain may indeed have a causative involvement in the attractiveness evaluation of human faces. Overall, these findings indicate that the increased activation of both prefrontal areas and the reward systems while viewing human facial images, varies based on the attractiveness (or unattractiveness) of the face, as well as the task and mindset of the observer concurrently.
