Chapter 11: Physiological Signals for Emotional State Recognition

Nervous System Components
SNS and PsNS Activation
Affect and Emotion
Theories of Emotion
Circumplex Model of Affect

Nervous System Components

The central nervous system (CNS) includes the brain and spinal cord. The peripheral nervous system (PNS) connects between the CNS and the body. The PNS consists of two parts, the autonomic nervous system (ANS) and the somatic nervous system (SoNS). The ANS regulates fundamental physiological states which are typically involuntary, such as heart rate, digestion and perspiration. The SoNS mediates voluntary control of body movements via skeletal muscle.

The autonomic nervous system (ANS) is largely responsible for maintaining the equilibrium of the body’s systems. The ANS is connected to smooth muscles, cardiac muscle tissue and secretion glands of organs. The ANS is composed of three components, the sympathetic nervous system (SNS), parasympathetic nervous system (PsNS) and enteric nervous system (ENS). The SNS and PsNS work in an opposing manner to maintain the internal equilibrium of the body.

Affective stimuli can have a significant effect on the ANS and many physiological signals reflect the activity of the ANS. The SNS functions in circumstances that require quick responses. The PsNS functions in circumstances that do not orequire immediate responses. As SNS activation increases, then PsNS activation decreases and vice-versa.

SNS and PsNS Activation

SNS Activation result increases

Adrenal function (boosts cortisol, epinephrine and norepinephrine)
Blood clotting
Blood pressure
Dopamine release
Eye pupil size
Glucose utilization
Heart rate
Metabolite production (glucose, etc.)
Oxygen circulation
Vascular resistance

PsNS Activation result increases

Defecation
Digestion
Glucose storage
Salivation
Secretion of tears
Urination

SNS and PsNS effects on the body – to be tabulated

Adipose tissue:

SNS – stimulates lipolysis (fat breakdown)
PsNS – no effect

Adrenal glands:

SNS – secretion of cortisol, epinephrine and norepinephrine
PsNS – no effect

Airways:

SNS – increases diameters
PsNS – decreases diameters

Bladder:

SNS – generally relaxes bladder to inhibit urination
PsNS – constricts bladder to stimulate urination

Blood pressure:

SNS – increases blood pressure
PsNS – decreases blood pressure

Blood vessels:

SNS – effects both vasoconstriction and vasodilation
PsNS – increases vasodilation of coronary vessels, otherwise no effect

Digestive system:

SNS – inhibits peristalsis
PsNS – stimulates peristalsis

Gall bladder:

SNS – increases relaxation
PsNS – increases contraction to expel bile

Heart:

SNS – increases heart rate, contractility and stroke volume
PsNS – decreases heart rate, contractility and stroke volume

Intestines:

SNS – inhibits motility
PsNS – stimulates motility and secretions

Kidneys:

SNS – increases vasoconstriction, decreases urine production
PsNS – no effect

Liver:

SNS – increases glycogen breakdown and glucose production
PsNS – increases glycogen synthesis and stimulates bile production

Lungs:

SNS – dilates bronchioles, relaxes bronchial muscles
PsNS – constricts bronchioles, contracts bronchial muscles

Mental activity:

SNS – increases alertness
PsNS – no effect

Metabolism:

SNS – increases cellular metabolism
PsNS – no effect on cellular metabolism

Pancreas:

SNS – generally reduces secretions, effects both insulin and glucagon secretion
PsNS – increases secretions

Pilomotor muscles:

SNS – contracts muscles, causing erection of hairs and goosebumps
PsNS – no effect

Pineal gland:

SNS – melatonin synthesis and secretion
PsNS – no effect

Pupils:

SNS – dilates iris muscles
PsNS – constricts iris muscles

Reproductive system:

females:
SNS – increases glandular secretions
PsNS – increases vasodilation, erects clitoris

males:
SNS – increases glandular secretions and causes ejaculation
PsNS – increases vasodilation, erects penis

Respiration:

SNS – increases respiratory rate
PsNS – decreases respiratory rate

Salivary glands:

SNS – decreases watery salivation
PsNS – increases watery salivation

Skeletal muscles:

SNS – increases force of contraction and glycogen breakdown
PsNS – no effect

Sphincters:

SNS – increases contraction
PsNS – increases relaxation

Stomach:

SNS – generally inhibits motility
PsNS – generally stimulates motility

Sweat glands:

SNS – increases sweat secretion
PsNS – no effect

Tear glands:

SNS – no activation
PsNS – tear secretion

The ENS is the nervous system of the gastrointestinal (GI) tract. The ENS senses the physiological state of the GI tract and controls GI tract movement, blood flow and fluid exchange. The ENS is capable of autonomous (local) function. The ENS communicates with the CNS to manage the GI tract in support of the body’s changing physiological needs.

Affect and Emotion

Affect is the observable (measurable) expression of emotion.

Theories of Emotion

The James-Lange Theory of Emotion

Emotions occur as a result of physiological reactions to stimuli. The experience of the body’s physiological response generates the emotion. Emotional state depends on how the subject interprets their own reaction to any specific event. The subject’s perception of their own physiological reaction is the emotion.

The Cannon-Bard Theory of Emotion

Emotions occur when the thalamus activates the CNS in response to stimuli, which results in physiological reaction. Physiological reaction and cognitive interpretation of emotional state occur simultaneously and are largely independent. The perception of a stimulus leads to both the emotion and physiological reaction. Furthermore, different emotions can share similar physiological responses.

Schachter-Singer Theory of Emotion

In response to stimuli, a physiological reaction occurs. A cognitive label accompanies the reaction. The reaction and the label act to generate an emotion. The subject’s history provides the framework to experience their reaction and categorize it as a specific emotion. Subject’s perceive their own physiological responses and then emotionally interpret them by considering the context of their circumstances.

Circumplex Model of Affect and Motivational State

The Circumplex Model of Affect was first described in 1980 by James Russell. Affective states arise from the behavior of two independent neurophysiological systems, the arousal and valence systems. Affective states are a function of these two systems. The circumplex model is two-dimensional, with arousal and valence defined as orthogonal (perpendicular) axes. The arousal axis, plotted vertically, ranges from zero arousal to high arousal. The valence axis, plotted horizontally, ranges from negative to positive. Objective physiological indexes of affect or emotion are available. As valence examples, positive affect is indicated by increasing zygomaticus activity and negative affect is indicated by increasing corrugator activity. Physiological example indices for arousal include heart rate and electrodermal activity.

Perhaps even more fundamental to emotional state is the concept of motivational state. Motivational state is indexed by specific, bodily expressed, physiological states that can easily be measured. Motivational state is based on the concept of core relational themes, called “challenge” and “threat”. During the course of living, humans relate to difficult environmental circumstances as a combination of challenge and threat. A challenge response is similar to the aerobic physiological response and involves increased stroke volume and cardiac output, unchanged or increased heart rate, decreased vascular resistance and relatively unchanged blood pressure. This response is indicative of efficient mobilization of available energy for coping with circumstances. A threat response is characterized by increased heart rate and blood pressure, increased or little changed vascular resistance, decreased or unchanged stroke volume and relatively unchanged cardiac output. A challenge response occurs when the subject experiences sufficient resources to meet circumstantial demands in a performance situation where goals are important. A threat response occurs when the subject experiences insufficient resources to meet those same circumstantial demands. If a circumstance is determined to be challenging, then subject performance is usually adequate. If a circumstance is determined to be threatening, then subject performance tends to worsen. Motivational state information can be used to better reflect objective differences between similar circumplex model defined emotions, such as anger and fear.

Electrodermal activity (EDA) is a physiological signal that indicates increased SNS activity. EDA is representative of changes in the electrical conductance of the skin due to eccrine (sweat) gland activity. SNS activity increases sweat gland secretions. Eccrine glands only receive activation signals from the SNS, so increased EDA is an indicator of increased arousal.

Skin temperature (SKT) changes are primarily driven by variations in blood flow. These local variations are mainly caused by changes in vascular resistance or arterial blood pressure. Local vascular resistance is modulated by smooth muscle activity, which is mediated by the SNS. SKT variation reflects SNS activity, and is an indicator of emotional state.

The heart and brain are connected bidirectionally via the vagus nerve. Vagal PsNS stimulation, from the brain, influences the heart via the sino-atrial (SA) node. Baroreceptor signals, from the heart, travel back along the vagus nerve to affect the brain. The SA node is the pacemaker of the heart. The SA node receives inputs from both the SNS and PsNS. The SA node can be considered to be a spike-train generator whose inter-spike (firing) interval is modulated by both SNS and PsNS activity levels. Because both SNS and PsNS activity influence SA node spike firing, heart rate behavior can be considered to be dependent on a range of emotional states. SNS activity increases heart rate and PsNS activity decreases heart rate.

Heart rate variability (HRV) is a measure of heart rate changes over time. HRV has a frequency range of 0.003 to 0.4 Hz and is considered to have four sub-bands: HF, LF, VLF and ULF. High frequency HRV (HF-HRV) band power is in the range of 0.15 to 0.4 Hz and reflects primarily PsNS influences. HF-HRV band power reflects modulation of vagus nerve activity, as driven by respiration. This modulation is called respiratory sinus arrhythmia (RSA). Low frequency HRV (LF-HRV) band power is in the range of 0.05-0.15 Hz and reflects both SNS and PsNS influences. Very low frequency HRV (VLF-HRV) band power is in the range of 0.003-0.05 Hz and may reflect cardiovascular disease, thermo-regulatory cycles and blood plasma renin activity. Ultra low frequency HRV (ULF-HRV) band power is in the range of DC-0.003 Hz and may reflect circadian rhythm activity.

PsNS influences occur over the LF and HF frequency ranges of HRV. SNS influences drop off at about 0.15 Hz and higher. PsNS influences can affect heart rate in a fraction of a second, but SNS influences can only affect the heart rate after a few seconds. Accordingly, PsNS influences are uniquely capable of producing high speed changes in the heart rate. PsNS innervation of the heart is controlled by the right vagus nerve via the SA node. PsNS induced changes in heart rate are associated with vagal nerve activity that is modulated by respiration. Expiration causes an increase in vagal nerve activity, so heart rate decreases. Inspiration causes suppression of vagal nerve activity, so heart rate climbs back up. This combined action is known as respiratory sinus arrhythmia (RSA). RSA is considered, in part, to be a marker for vagal control of heart rate and also for emotional regulation. Total HRV appears to be positively correlated with valence.

When attention increases, there is a short term deceleration of heart rate. Arousal is also correlated to a long term acceleration in heart rate. Heart rate also provides an indication of valence. Compared to neutral stimuli, both positive and negative stimuli first exhibit a short term decrease in heart rate. Over the long term, positive stimuli are correlated with an increase in heart rate while negative stimuli usually are correlated to a decrease in heart rate (Greenwald, Cook, and Lang, 1989; Cuthbert, Bradley, and Lang, 1996).

Respiratory activity occurs via periodic contraction and relaxation of respiratory muscles, including the diaphragm, intercostal and abdominal muscles. The motor outputs for controlling respiration are generated by efferent neurons in the spinal cord. There are autonomic and voluntary breathing pathways to these respiratory-related efferent neurons. A variety of afferent (sensory) inputs influence respiratory rate and tidal volume in support of the body’s metabolic demands. SNS activity increases respiratory rate and PsNS activity reduces respiratory rate.

Several EEG studies suggest that emotional valence is linked to frontal lobe activation, typically indexed by alpha power. Positive valence is correlated to increased activation of the left frontal lobe and negative valence is correlated to increased activation of the right frontal lobe. Other studies have suggested that frontal lobe EEG activation asymmetry reflects the relative balance of motivational state, more so than emotional valence. In this work, enhanced left frontal lobe activation predicted dispositional states towards challenge and enhanced right frontal lobe activation predicted dispositional states towards threat.