Emotional Processing

Summary of the organisation of some of the brain mechanisms underlying emotion, showing dual routes to the initiation of action in response to rewarding and punishing, that is emotion-producing, stimuli. The inputs from different sensory systems to brain structures such as the orbitofrontal cortex and amygdala allow these brain structures to evaluate the reward- or punishment-related value of incoming stimuli, or of remembered stimuli. The different sensory inputs allow evaluations within the orbitofrontal cortex and amygdala based mainly on the primary (unlearned) reinforcement value for taste, touch and olfactory stimuli, and on the secondary (learned) reinforcement value for visual and auditory stimuli. In the case of vision, the 'association cortex' which sends representations of objects to the amygdala and orbitofrontal cortex is the inferior temporal visual cortex. One route for the outputs from these evaluative brain structures is via projections directly to structures such as the basal ganglia (including the striatum and ventral striatum) to allow implicit, direct behavioral responses based on the reward or punishment-related evaluation of the stimuli to be made. The second route is via the language systems of the brain, which allow explicit (verbalizable) decisions involving multistep syntactic planning to be implemented. After The Brain and Emotion, Fig. 9. 4.

Some of the pathways involved in emotion described in the text are shown on this lateral view of the brain of the macaque monkey. Connections from the primary taste and olfactory cortices to the orbitofrontal cortex and amygdala are shown. Connections are also shown in the 'ventral visual system' from V1 to V2, V4, the inferior temporal visual cortex, etc., with some connections reaching the amygdala and orbitofrontal cortex. In addition, connections from the somatosensory cortical areas 1, 2 and 3 that reach the orbitofrontal cortex directly and via the insular cortex, and that reach the amygdala via the insular cortex, are shown. as, arcuate sulcus; cal, calcarine sulcus; cs, central sulcus; lf, lateral (or Sylvian) fissure; lun, lunate sulcus; ps, principal sulcus; io, inferior occipital sulcus; ip, intraparietal sulcus (which has been opened to reveal some of the areas it contains); sts, superior temporal sulcus (which has been opened to reveal some of the areas it contains). AIT, anterior inferior temporal cortex; FST, visual motion processing area; LIP, lateral intraparietal area; MST, visual motion processing area; MT, visual motion processing area (also called V5); PIT, posterior inferior temporal cortex; STP, superior temporal plane; TA, architectonic area including auditory association cortex; TE, architectonic area including high order visual association cortex, and some of its subareas TEa and TEm; TG, architectonic area in the temporal pole; V1 - V4, visual areas 1 - 4; VIP, ventral intraparietal area; TEO, architectonic area including posterior visual association cortex. The numerals refer to architectonic areas, and have the following approximate functional equivalence: 1, 2, 3, somatosensory cortex (posterior to the central sulcus); 4, motor cortex; 5, superior parietal lobule; 7a, inferior parietal lobule, visual part; 7b, inferior parietal lobule, somatosensory part; 6, lateral premotor cortex; 8, frontal eye field; 12, part of orbitofrontal cortex; 46, dorsolateral prefrontal cortex. From The Brain and Emotion, Fig. 4. 1.

The first paper in the April 2004 issue of CNS Spectrums, titled Neuroimaging of Emotions in Psychiatry, is Functional Neuroimaging Studies of Human Emotions, by K. Luan Phan, MD, Tor D. Wager, PhD, Stephan F. Taylor, MD, and Israel Liberzon, MD.  The paper is a survey of 55 PET and fMRI studies that were done to assess various aspects of brain function in response to emotional stimuli.  They set out to basically develop an atlas of corellations between different emotional responses and different parts of the brain.  This is something that is inherently difficult to do.  As you might expect, different brains can have widely different responses to the same stimuli.  In order to try to make sense of this, it is necessary to study several different people and average the results.  One of the strongest corellations they found was the relationship between fear and increased metabolic activity in the amygdala. 

Another strong correlation they found was that the medial prefrontal cortex often is activated in response to generic emotional stimuli.  By this I mean that the activation occurred without regard to the type of emotion involved.  As they put it: "The findings suggest that the MPFC may have a 'general' role in emotional processing."  Although they found that "no single brain region is commonly activated by all emotional tasks," the MPFC was the one that was turned on most often.  Its location in the prefrontal cortex suggests that it may be a linkage point between emotional processing and cognitive processing: one of the bridges between thinking and feeling.  They point out that "several studies have been recently published demonstrating that when subjects turn their attention inward toward themselves, as often required during general emotional processing, activity within the MPFC is increased.  Studies requiring subjects to determine if personality trait adjectives are descriptive of themselves (versus someone else) or to reflect on their own abilities/traits/attitudes have observed engagement of the MPFC."

Another area of interest in emotional neuroscience is the anterior cingulate cortex.  It has been know for a long time that injury to the ACC can lead to wither apathy or lability (instability).  Therefore, it is tempting to speculate that the ACC is involved in the regulation or modulation of emotional responses.  Their review of neuroimaging studies of the ACC shows that it is involved in detecting emotional cues.  For example, when watching a movie, your brain is flooded with all kinds of stimuli, but only some of them have any emotional significance.  The ACC seems to be involved in distinguishing the emotional figure  from the background noise.  The authors speculate about some possible functions: "As a detector of salient information in general, the ACC could serve to allocate brain resources, heighten sensitivity and direct attention to environmental cues produced by the evocative stimulus."  They found also that the ACC is activated when people are asked to recall events that are linked to a particular emotional state. 

Another finding with regard to the ACC is that it often is activated when people feel sad.  In fact, activity there is increased during the depressive phase of some types of major depressive disorder.  This kind of finding is interesting because it indicates that neuroimaging studies may someday be useful in the task of making diagnoses that are more specific than those made using current descriptive methods.  This, in turn, could lead to better selection of treatments. 

The third and final brain region described in the article is the insula.  The insula, like the ACC, is activated during emotional recall tasks.  Unlike the ACC, the insula is not activated by viewing external cues, such as movies, with emotional content.   This finding has been duplicated in studies of non-human primates.  It appears that the insula is activated most strongly in response to aversive or threat-related emotions.  Some, but no all, studies showed a specific activation of the insula in response to disgust.  It is activated when the brain receives visceral (primarily gastrointestinal) aversive sensations.  the authors speculate that the insula may be the center that is responsible for literal "gut feelings." 

The authors conclude that there is emerging evidence that some brain structures are involved in specific emotional states, whereas others serve a more general function of emotional processing.  They are hopeful that these and future studies will permit the understanding of the functional neuroanatomy of emotion. 

• Lateral nucleus (AL) neurons receive sensory information from the thalamus and cortex. It is a site of convergence of CS and US pathways in fear conditioning, hence a possible site of synaptic modification underlying learning (Romanski et al 1993).
• Recent studies aim at elucidating the internal connectivity of the amygdaloid complex, and understand the nature of its computation. The information pathway seems to consist in a common entry point (the lateral nucleus), several parallel streams to other nuclei (Medial, accessory basal, or basal, for example) and a common output point (the central nucleus). Each of the internal streams are modulated by other brain structures such as the hippocampus, the frontal cortex or the hypothalamus. (Pitkanen et al 1997).

Sad versus neutral. Recalling of powerful and personal autobiographical emotional episodes invoking sadness versus recalling emotionally neutral life episodes. WOEXP: 483.

Mario Pelletier; Alain Bouthillier; Johanne Levesque; Serge Carrier; Claude Breault; Vincent Paquette; Boualem Mensour; Jean-Maxime Leroux; Gilles Beaudoin; Pierre Bourgouin; Mario Beauregard. Separate neural circuits for primary emotions? Brain activity during self-induced sadness and happiness in professional actors. NeuroReport 14(8):1111-1116, 2003. PMID: 12821792. DOI: 10.1097/01.wnr.0000075421.59944.69. FMRIDCID: . WOBIB: 157.

Emotion - Sadness

Happy versus neutral. Recalling of powerful and personal autobiographical emotional episodes invoking happiness versus recalling emotionally neutral life episodes. WOEXP: 484.

Mario Pelletier; Alain Bouthillier; Johanne Levesque; Serge Carrier; Claude Breault; Vincent Paquette; Boualem Mensour; Jean-Maxime Leroux; Gilles Beaudoin; Pierre Bourgouin; Mario Beauregard. Separate neural circuits for primary emotions? Brain activity during self-induced sadness and happiness in professional actors. NeuroReport 14(8):1111-1116, 2003. PMID: 12821792. DOI: 10.1097/01.wnr.0000075421.59944.69. FMRIDCID: . WOBIB: 157.

Emotion - Happiness