Date Published: April 30, 2019
Publisher: Public Library of Science
Author(s): Jaime Vila, Cristina Morato, Ignacio Lucas, Pedro Guerra, Ana María Castro-Laguardia, María Antonieta Bobes, José A. Hinojosa.
The neuroscientific study of love has been boosted by an extended corpus of research on face-identity recognition. However, few studies have compared the emotional mechanisms activated by loved faces and names and none have simultaneously examined fMRI and autonomic measures. The present study combined fMRI with the heart rate response when 21 participants (10 males) passively viewed the face or the written name of 4 loved people and 4 unknown people. The results showed accelerative patterns in heart rate, together with brain activations, which were significantly higher for loved people than for unknown people. Significant correlations were found between heart rate and brain activation in frontal areas, for faces, and in temporal areas, for names. The results are discussed in the context of previous studies using the same passive viewing procedure, highlighting the relevance of integrating peripheral and central measures in the scientific study of positive emotion and love.
Advances in the neuroscientific study of emotions have been slower for positive than for negative emotions. Part of this imbalance has been attributed to negativity bias , , , , which states that organisms are more prepared to attend to and defend themselves from situations that signal danger/punishment, than to attend to and approach situations that signal safety/reward. Negativity bias is evident in studies on approach-avoidance conflict both in animals  and humans . The avoidance gradient -the increasing force with which organisms try to avoid a situation that is at the same time aversive and appetitive- is steeper than the approach gradient -the increasing force with which organisms try to approach that situation. The same bias is observed in the distribution of hundreds of visual and acoustic emotional stimuli from the IAPS (International Affective Picture System) and IADS (International Affective Digitized Sounds) when they are plotted in a two-dimensional space formed by the dimensions of valence and arousal , , . The distribution of the pleasant pictures and sounds is less steep and more scattered than the distribution of the unpleasant pictures and sounds. The consequence is that there are fewer pleasant pictures and sounds that are highly activating than unpleasant ones, a situation that hinders the scientific study of positive emotions from a dimensional perspective when using the methodology of viewing/hearing standardized affective pictures and sounds .
The present study showed heart rate responses that replicated, for the first time within an fMRI scanner, previous findings concerning loved familiar faces , ,  and names : larger increases in heart rate for loved faces and names than for neutral ones. Although not significant, there was also a tendency for the accelerative response to be larger for faces than names. Regarding the fMRI results, areas activated in response to loved compared to neutral stimuli were only significant for faces. However, activation for loved names seemed to be higher than activation for neutral names, but without reaching significance. This finding suggests that the activation strength of the visual perception of familiar faces surpasses the activation strength of the visual perception of their written names. In addition, the main areas activated by loved familiar faces were consistent with areas reported in the literature for personally familiar faces , , , : the medial orbito-frontal cortex, frontal inferior pars triangularis, anterior cingulate, and posterior cingulate. Although the activation was weaker, some of these areas were also activated by loved names: the frontal inferior pars triangularis and anterior cingulate.
The present study combined fMRI and heart rate measurements and showed parallel changes in the autonomic nervous system and the functional brain when participants, using the passive picture-viewing paradigm, viewed loved familiar faces and names compared to unknown neutral faces and names. The autonomic measure revealed a pattern of heart rate increases, replicating previous findings concerning loved familiar faces and names. The fMRI measures showed higher strength for faces than names, but for both types of stimuli, there are some brain regions that predicted the magnitude of cardiac response. These regions included frontal and temporal structures for faces and names respectively, and the magnitude of brain and autonomic responses to love are correlated. This set of fMRI and heart rate data highlights the relevance of integrating central and peripheral measures to advance knowledge of the complex mechanisms underlying positive emotion and love.