Emotions & Stress
Fall 2002

Emotion is difficult to define and difficult to study. The two simplest approaches are:

1) Hedonism
    Analyze approach (pleasurable)/avoidance (unpleasant) behaviors in rats.

Approach: Stimulation of the medial forebrain bundle (MFB) (called self-stimulation; Figure 16.9 & 16.10)   Avoid: Stimulation of the dorsal periaqueductal gray (PAG) 2) Physiological responses
    Measure changes in physiological responses such as heart rate, respiration rate, Galvonic Skin Response (GSR), etc. These responses are controlled by the autonomic nervous system (ANS; see page 413 and Figure 15.9). There are two parts of the ANS:
 
Autonomic N.S.
Function
Neurotransmitter
CNS exit location
1. Sympathetic N.S.
Fight or flight (short term survival)
NE
thoracic & lumbar cord
2. Parasympathetic N.S.
Energy conservation (long term)
ACh
brainstem & sacral cord

The James-Lange theory of emotion states that emotions occur in response to physiology (i.e., sympathetic nervous system activity). Although not intuitive, there is a lot of evidence to support the James-Lange theory (e.g., humans have been shown to make decisions based on phsyiological changes that are below conscious perception).
 
 

The limbic system is a collection of brain structures that contribute to emotions. These structions include the (Figure 16.4):

amygdala
hippocampus
hypothalamus
anterior nucleus of the thalamus
cingulate gyrus The amygdala appears to be important in mediating fear and aggression (Figure 16.5).
1. Amygdala lesions block fear-induced freezing in rats.
2. Activate amygdala produces fear and anxiety.


Stress

Stress is another term that is difficult to define. Scientists use definitions that allow measurement.

1. Change from homeostasis
Your body tries to maintain a set point for most functions (e.g., temperature regulation)
2. Those events that cause the release of stress hormones
Stress activates two systems:

1. The sympathetic N.S. allows an immediate short term response (e.g., fight or flight). The parasympatheticn.s. counteracts the sympathetic system by producing changes that conserve energy. (see differences in the Table above)
 

2) The HPA axis releases "stress" hormones that cause an increase in blood glucose levels for prolonged energy for fight or flight.

    HPA stands for:

a) Hypothalamus: releases corticotropin releasing hormone (CRH)
b) Anterior Pituitary: releases ACTH in response to CRH
c) Adrenal cortex (above kidney): releases cortisol in response to ACTH. Cortisol goes throughout the body to increase blood glucose levels. Fatigue typically follows stress because: 1) hormones are turned off and blood glucose levels drop.
2) sympathetic NS turns off and parasympathetic (energy conservation) turns on
  Psychosomatic diseases: physical problems caused by psychological factors (e.g. increase in blood pressure; suppression of immune system). Experiments in rats show that tumors are typically defeated by the immune system. However, chronic stress suppresses the immune system allowing tumors to grow.

This experiment is just one example of the influence of psychological factors on physiology.
 
 

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