Brain -- a chemical soup

In order to create an emotional state, the activity in triggering sites must be propagaged to execution sites by means of neural connections. The emotion-execution sites identified to date include the hypothalamus, the basal forebrain, and some nuclei in the brain stem tegmentum. The hypothalamus is the master executor of many chemical responses that are part and parcel of emotions. Directly or via the pituitary gland it releases into the bloodstream chemical molecules that alter the internal milieu, the function of viscera, and the function of the central nervous system itself. Oxytocin and vasopressin, both peptides, are examples of molecules released under the control of hypothalamic nuclei with the help of the posterior pituitary gland. A host of emotional behaviors (as as attachment and nurturing) depends on the timely availability of these hormones within the brain structures that command the execution of those behaviors. Likewise, the local brain availability of molecules such as dopamine and serotonin, which modulate neural activity, causes certain behaviors to occur. For example, the sort of behaviors experienced as rewarding and pleasurable appears to depend on the release of dopamine from one particular area (the ventrotegmental area in the brain stem), and its availability in yet another area (the nucleus accumbens in the basal forebrain). In short, the basal forebrain and hypothaolamic nuclei, some nuclei in the brain stem tegmentum, and the brain stem nuclei that control the movement of the face, tongue, pharynx, and larynx are the ultimate executors of many behaviors, simple as well as complex, that define the emotions, fron courting or fleeing to laughing and crying. The complex repertoires of actions we observe are the result of the exquisite coordination of the activities of those nuclei that contribute parts of the execution in a well-concerned order and concurrence.

In all emotions, multiple volleys of neural and chemical responses change the internal milieu, the viscera, and the musculoskeletal system for a certain period and in a particular pattern. Facial expressions, vocalizations, body postures, and specific patterns of behavior (running, freezing, courting, or parenting) are thus enacted. The body chemistries as well as viscera such as the heart and lungs help along. Emotion is all about transition and commotion, sometimes real bodily upheaval. In a parallel set of commands the brain structures that support image-production and attention change as well; as a result, some areas of the cerebral cortex appear to be less active, while others become especially so.

In the simplest of diagrams, here is how a visually presented threatening stimulus triggers the emotion fear and leads to its execution.

For the purposes of providing a manageable description of the process of emotion and feeling, I have simplified them to fit into a single chain of events beginning with a single stimulus and terminating with the establishment of the substrates of the feeling related to the stimulus. In reality, as might be expected, the process spreads laterally into parallel chains of events and amplified itself. This is because the presence of the initial emotionally competent stimulus often leads to the recall of other related stimuli that are also emotionally competent. ..... Pages 63 / 64