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Physiological psychology is a subdivision of behavioral neuroscience (biological psychology) that studies the neural mechanisms of perception and behavior through direct manipulation of the brains of nonhuman animal subjects in controlled experiments. This field of psychology takes an empirical and practical approach when studying the brain and human behavior. Most scientists in this field believe that the mind is a phenomenon that stems from the nervous system. By studying and gaining knowledge about the mechanisms of the nervous system, physiological psychologists can uncover many truths about human behavior. Unlike other subdivisions within biological psychology, the main focus of psychological research is the development of theories that describe brain-behavior relationships.

Physiological psychology studies many topics relating to the body's response to a behavior or activity in an organism. It concerns the brain cells, structures, components, and chemical interactions that are involved in order to produce actions. Psychologists in this field usually focus their attention to topics such as sleep, emotion, ingestion, senses, reproductive behavior, learning/memory, communication, psychopharmacology, and neurological disorders. The basis for these studies all surround themselves around the notion of how the nervous system intertwines with other systems in the body to create a specific behavior.

The central nervous system is composed of the brain and spinal cord. The brain is the control center of the body and contains millions of neural connections. This organ is responsible for sending and receiving messages from the body and its environment. Each part of the brain is specialized for different aspects of the human being.

An emotional response can be divided into three major categories including behavioral, autonomic, and hormonal.

  • The behavioral component is explained by the muscular movements that accompany the emotion. For example, if a person is experiencing fear, a possible behavioral mechanism would be to run away from the fear factor.
  • The autonomic aspect of an emotion provides the ability to react to the emotion. This would be the fight-or-flight response that the body automatically receives from the brain signals.
  • Lastly, hormones released facilitate the autonomic response. For example, the autonomic response, which has sent out the fight-or-flight response, would be aided by the release of such chemicals like epinephrine and norepinephrine, both secreted by the adrenal gland, in order to further increase blood flow to aid in muscular rejuvenation of oxygen and nutrients.
  • Fear: the amygdala is the main component for acquisition, storage, and expression of fear.
  • Lesions on the central amygdaloid can lead to disruptions in the behavioral and autonomic emotional responses of fear.
  • Anger/aggression: the hypothalamus and amygdala work together to send inhibitory/excitatory impulses to the periaqueductal gray which then carries out usually defensive behaviors. Under the response to emotions, even more oxytocin is secreted therefore increasing the response further. In addition to the general effects oxytocin has on the limbic system, it provides a more specific purpose as well in the body. It acts as an anxiety suppressant mainly found in stressful and social situations. It provides a calming effect to the body during these high stress situations. Oxytocin is also seen as a strong hormone in maternal attachment and aggression found in new mothers. This hormone also plays a slight part in the female desire to pair and mate.
  • Another hormone found in the direct response from emotion is adrenocorticotropic hormone (ACTH) secreted in response to fearful stimuli. ACTH is secreted by the posterior pituitary in response to fear and plays a role in the facilitation or inhibition of behaviors and actions to follow. In most cases, a high ACTH secretion will lead to the inhibition of actions that would produce the same fearful response that just occurred.
  • Happiness is primarily controlled by the levels of dopamine and serotonin in the body. Both are monoamine neurotransmitters that act on different sites in the body. Serotonin acts on receptors in the gastrointestinal tract while dopamine acts on receptors in the brain, while both performing similar functions. Dopamine is known to be the primary hormone acting on the brain's reward system, while this has recently begun to be a point of debate in the research community. Serotonin has less known on how it carries out its function in reducing depression, but only that it works. Specific-serotonin reuptake inhibitors (SSRI) are the type of drug given to patients with depression in which the serotonin is left in the synapse to continue to be absorbed in the body.

Sleep

Sleep is a behavior that is provoked by the body initiating the feeling of sleepiness in order for people to rest for usually several hours at a time.

REM sleep is the less restful stage in which one dreams and experiences muscle movements or twitches. Also during this stage in sleep, a person's heart rate and breathing are typically irregular. The electrical activity in the brain during REM sleep causes signals the same overwhelming intensity of being awake inside. The same brain energy is used during REM sleep measured by oxygen and glucose metabolism equally to being awake. EEGs are used to observe these patterns in the brain during the different stages of REM and Non-REM sleep.

Non-REM sleep, also sometimes referred to as slow-wave sleep, is associated with deep sleep. The body's blood pressure, heart rate, and breathing are generally significantly decreased compared to an alert state. Dreaming can occur in this state; however a person is not able to remember them due to how deep in sleep they are and the inability for consolidation to occur in memory. REM cycles typically occur in 90 minute intervals and increase in length as the amount of sleep in one session progresses. In a typical night's rest, a person will have about four to six cycles of REM and Non-REM sleep. programs that are affiliated with psychology departments, or in interdisciplinary neuroscience programs. Most physiological psychologists receive PhDs in neuroscience or a related subject and either teach and carry out research at colleges or universities, are employed for research for government laboratories or other private organizations, or are hired by pharmaceutical companies to study the effects that various drugs have on an individual's behavior.