EmotionExpression & 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 - 1932

– stimulated different regions of the hypothalamus in anesthetized animals

– Evoked autonomic reactions including changes of heart rate, blood pressure, etc.

• Walter Hess - 1940’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 - 1884• 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 - 1927 • 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 - 1939

– 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