Emotions: From neuropsychology to functional imaging

Recent developments in functional imaging techniques, such as Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging (fMRI), allow us to characterize more precisely the functional neuroanatomy mediating emotional responding. This corpus of studies has led to the development of affective neuroscience. First, we present a summary of the studies aimed at understanding the underlying mechanisms of the emotional response, which were conducted prior to the use of the brain imaging techniques. Then, this paper reviews the studies investigating the neural substrates implicated in the processing of facial expressions and those implicated in the production of experimentally induced emotional responses. This review of the literature includes a meta-analysis of eight studies using PET and one fMRI study reporting the neural correlates of experimentally induced emotions in healthy individuals. The methods and results of these studies are described through figures drawn from the reported Talairach's coordinates depicting the cerebral regions activated in relation to different experimental conditions. The implications of the results and the role of the cerebral structures that have been identified are discussed. As regards the studies on the neural bases of the processing of facial expressions of emotion, there are separable neural circuits that are involved in mediating responding to differing categories of facial expressions of emotion. Fearful expressions have relatively consistently been found to activate the amygdala, as, occasionally, have sad and happy expressions. The anterior insula and the putamen seem to be particularly involved in disgust expression recognition, whereas the facial expression of anger seems to be predominantly associated with anterior cingular and orbitofrontal cortex activity. Among the cerebral structures that have appeared to be activated by experimentally induced emotions, the anterior cingulate cortex seems to play a specific role in representing subjective emotional responses.