Emotion Expression & Experience

What is emotion? No scientific definition Controlled by distinct neuronal circuits within the brain We experience emotion consciously –therefore there is a cognitive element, most likely involving the cerebral cortex Emotion can be viewed as an outcome of the interaction of peripheral & central factors

Responses to Emotion Emotion is accompanied by autonomic, endocrine & skeletomotor responses Thus it also depends on sub-cortical parts, including: –amygdala –hypothalamus –brain stem

Peripheral Responses Peripheral responses prepare the body for action Communicate emotions to other people Example – fear: –increased heart rate & respiration –dry mouth –tense muscles –sweaty palms

The Autonomic Nervous System & Emotion Most changes that accompany emotional states are mediated by autonomic nervous system The autonomic system is primarily an effector system –controls smooth muscles, heart, exocrine glands –autonomic is involuntary

Three Divisions of the ANS Sympathetic –governs fight or flight response –response to stress Parasympathetic –rest and digest –Normal conditions Enteric

Role of the Hypothalamus Contains many of the neuronal circuits that regulate functions that vary with emotion: –Temperature –heart rate –blood pressure –water and food intake also controls pituitary gland & thereby the endocrine system controls output of autonomic nervous system

Hypothalamic Control of the ANS The hypothalamus acts on ANS in 2 ways: Projects to 3 important regions in the brain stem & spinal cord: –to the nucleus of the solitary tract –receives sensory input from viscera –to the brain stem in the rostral ventral medulla –leads to general sympathetic activation –directly to the autonomic outflow of the spinal cord The hypothalamus acts on endocrine system to release hormones that influence autonomic function

Experimental Evidence Emotional states are elicited by stimulating the hypothalamus Stephen Ranson –stimulated different regions of the hypothalamus in anesthetized animals –Evoked autonomic reactions including changes of heart rate, blood pressure, etc. Walter Hess ’s –used awake animals –produced behaviors and physiologic changes characteristic of particular emotions e.g. fear

Cortical Centers of Emotion Physiological inputs to the hypothalamus act on the brain stem & autonomic nervous system. This information reaches the cerebral cortex from the peripheral organs. This gives rise to the conscious perception of emotion So where is the cortical representation of emotion?

The Limbic System Concept Is there a “system” ( a group of structures that function together) responsible for emotion? Scientists identified the limbic system as the key pathway in emotion – 1930’s –Paul Broca –James Papez

Broca’s Limbic Lobe Paul Broca – 1878 Identified a portion of cortex present in all mammals which is different from surrounding cortical tissue –These areas form a ring or border around the brainstem –Limbus = border, thus limbic lobe Includes: –cortex around the corpus callosum, especially in the cingulate gyrus –Cortex on the medial surface of the temporal lobe, including the hippocampus Broca did not relate these structures to emotion

The Papez Circuit James Papez- 1930’s Proposed that there is an emotion system that links the cortex to the hypothalamus –Emotion is determined by the activity of the cingualte cortex –Emotional expression is governed by the hypothalamus The Papez Circuit –A group of structures, each connected to the next by a major fiber tract –The cingulate cortex projects to the hippocampus, which projects to the hypothalamus through the fornix; the hypothalamus projects to the anterior nuclei of the thalamus, which reach back to the cortex

Papez Circuit

Studying Emotion Emotional expression –behavioral manifestations of internal emotion Emotional experience –subjective feelings of emotion Limitations of animal models –can study emotional expression but cannot investigate emotional experience Limitations of human experiments –very often the medical situation which provides information involves damage to or compromise of other neural structures and functions in an uncontrolled way

Theories of Emotion- James & Lange William James & Karl Lange Proposed that the experience we call emotion occurs after the cortex receives signals about physiologic changes –Emotional expression precedes emotional experience –Physiological changes occur in response to stimuli, then we feel emotions Emotion is the consequence of information from the periphery –We feel sorry because we cry The physiological changes are the emotion

Critique of James & Lange Emotions are experienced even if physiological changes aren’t sensed –Patients & animals with transected spinal cords do not have lessened emotions The same physiological changes accompany different emotions and can have other causes –e.g. fear, anger & disease can all increase heart rate & cause sweating

Theories of Emotion – Cannon & Bard Walter Cannon and Phillip Bard Stimuli cause emotional experience Emotional experience can occur independently of emotional expression The thalamus plays a pivotal role in emotional sensations Emotions are produced when signals reach the thalamus directly from sensory receptors or by descending cortical input The emotion is determined by the pattern of activation of the thalamus

The Somatic Marker Hypothesis Stanley Schacter: The cortex constructs emotion out of signals received from the periphery This is called the somatic marker hypothesis: Emotion is a story the brain concocts to explain bodily reactions –Depends expectations, experience, social context –Thus the same responses can accompany different emotions

Current Theories Antonio Damasio - Expanded somatic marker hypothesis Draws a close connection between emotion and cognition. Emotions are biologically indispensable to decisions. Studied patients with damage to the amygdala or prefrontal cortex –Research on patients with frontal lobe damage indicates that feelings normally accompany response options –Operate as a biasing device to dictate choice. “Descartes error” – separating mind & body

The Current View No single neural system produces emotions Different emotions may depend on different neural circuits, but many of these circuits converge in the same parts of the brain The limbic system may be involved in some emotional experiences, but it is not the sole neural system underlying emotion Feelings (emotion) result from the interplay between: –The amygdala, hypothalamus, brain stem & autonomic nervous system and... –between amygdala and frontal & limbic cortex

Fear & Anxiety The amygdala is the critical structure Also involves the hypothalamus & ANS Demonstrated by: Kluver-Bucy Syndrome Electrical stimulation experiments Patients with damage to the amygdala

Klüver-Bucy Syndrome Heinrich Kluver & Paul Bucy –bilateral removal of the temporal lobes in monkeys (which contains the amygdala & hippocampal formation)  Radical changes in emotional behavior –increased and bizarre sexual behavior –highly oral –failed to recognize familiar objects (psychic blindness) temporal lobe destruction of visual cortices –emotionally flat absence of fear - amygdala missing

Kluver-Bucy Syndrome

The Amygdala Structure critical to emotional part of Kluver-Bucy syndrome is the amygdala The amygdala is part of the limbic system Human patients with damaged amygdalas have reduced ability to recognize fear in others Electrical stimulation leads to fear and anxiety A learned fear response, where pain is associated with a sensory input, may involve a circuit through the basolateral nuclei & central nucleus of the amygdala These effects are mediated through the hypothalamus & autonomic nervous system.

The Amygdala

Anger and Aggression Definitions: Predatory aggression –leads to an attack for food –motive is to kill other animal Affective aggression –behavior for show to scare other animal – lots of sympathetic ANS activity Mediated by the hypothalamus, midbrain & amygdala May also involve serotonin

The Role of the Hypothalamus When the entire cerebral hemispheres are removed, sham rage results –Small stimuli provoke violent responses –Difficult to interpret because the entire neocortex is missing –Removal of anterior hypothalamus, sham rage still occurs –Removal of the posterior hypothalamus, sham rage vanishes –Conclusion: posterior hypothalamus is important for aggression and is normally inhibited by neocortex Electrical stimulation of the hypothalamus –Stimulation of medial hypothalamus leads to affective aggression - hiss and spit at mouse –Stimulation of lateral hypothalamus leads to predatory aggression

Possible Role of the Midbrain Major outputs of hypothalamus to brain stem are Medial forebrain bundle (mfb) –project to ventral tegmental area –Electrical stimulation of ventral tegmental area can cause predatory aggression –Lesions in ventral tegmental area can abolish affective aggression Dorsal longitudinal fasciculus (dlf) –project to periaqueductal gray matter –Electrical stimulation of PAG can elicit affective aggression and lesions can abolish affective aggression

Possible Role of the Amygdala Ablation experiments indicate that the amygdala is also involved in aggression –amygdalectomy reduces aggression Two pathways for aggression: Predatory aggression - cortex > amygdala > lateral hypothalamus > mfb > ventral tegmental area Affective aggression - cortex > amygdala > medial hypothalamus > dlf > periaqueductal gray matter Led to psychosurgical procedures to destroy amygdala in humans –Frontal lobotomy is another example of psychosurgery

Possible Role of Serotonin Experimental evidence suggests that blocking or reducing the synthesis or release of serotonin may increase aggressive behavior When the gene for serotonin receptors are removed in mice, they become more aggressive The type of receptor that is most effective when deleted is normally found in the amygdala, periaqueductal gray matter, and basal ganglia, as well as the raphe nuclei

Summary No single neural system produces emotions Brain structures involved in emotion are multi functional –there are interesting relationships among emotion, memory, and olfaction Emotion results from the interplay between: –The amygdala, hypothalamus, brain stem & autonomic nervous system and... –between amygdala and frontal & limbic cortex