12-1Identifying the Causes of Behavior

Our inner subjective feelings (emotions) and goal-directed thoughts (motivations) influence how we behave and adapt as individuals and as a species. Emotion and motivation are inferred states that can escape conscious awareness or intent and make the case for free will difficult to argue.

Biologically, reward motivates animals to engage in behavior. Aversive circumstances prompt brain circuits to produce behaviors that will reduce them. Such are the effects of sensory deprivation. The brain inherently needs stimulation. In its absence, the brain will seek it out.

Sensory stimulation leads to hormone activity and to dopamine activity in the brainstem. Neural circuits organized in the brainstem control species-typical behaviors, such as mouse killing by cats and singing by birds. These brainstem circuits manifest their evolutionary advantage: they are rewarding. Rewarding behavior motivates living beings. When animals disengage from behaviors that motivate their species, they go extinct.

12-2The Chemical Senses

In the olfactory and gustatory senses, chemical neuroreceptors in the nose and tongue interact with chemosignals, leading to neural activity in cranial nerve 1 for olfaction and cranial nerves 7, 9, and 10 for taste. The cranial nerves enter the brainstem, and through a series of synapses, pass into the forebrain. Smell and taste inputs merge in the orbitofrontal cortex to produce our perception of flavor.

12-3Evolution, Environment, and Behavior

Behavior is controlled by its consequences as well as by its biology. Consequences may affect a species’ evolution or an individual’s behavior. Behaviors selected by evolution are often triggered by innate releasing mechanisms. Behaviors selected only in an individual animal are shaped by that animal’s environment and are learned.

12-4Neuroanatomy of Motivated and Emotional Behavior

The neural structures that initiate emotional and motivated behaviors are the hypothalamus, pituitary gland, amygdala, the dopaminergic and noradrenergic activating pathways from nuclei in the lower brainstem, and the frontal lobes.

The experience of both emotion and motivation is controlled by activity in the ANS, hypothalamus, and forebrain, especially the amygdala and frontal cortex. Emotional and motivated behavior may be unconscious responses to internal or external stimuli controlled either by the activity of innate releasing mechanisms or by cognitive responses to events or thoughts.

12-4Control of Regulatory and NonregulatoryBehavior

The two distinctly different types of motivated behaviors are (1) regulatory (homeostatic) behaviors that maintain vital body system balance and (2) nonregulatory behaviors, basically all nonreflexive behaviors and behaviors not controlled by a homeostatic mechanism. Feeding is a regulatory behavior controlled by the interaction of the digestive and hormonal systems, the enteric nervous system, and the hypothalamic and cortical circuits. Sexual activity is a nonregulatory behavior motivated by the amygdala. Copulatory behavior is controlled by the hypothalamus (ventromedial hypothalamus in females and the preoptic area in males). Sexual orientation (a person’s attraction to the opposite or same sex) and gender identity (a person’s feeling of being male or female) are related to the organization of the hypothalamus. Differences in hypothalamic organization are likely related to epigenetic effects in early development.

12-4Reward

Survival depends on maximizing contact with some environmental stimuli and minimizing contact with others. The reward mechanism controls this differential. Two independent features of reward are wanting and liking. The wanting component is thought to be controlled by dopaminergic activating systems, whereas the liking component is thought to be controlled by opioid and GABA–benzodiazepine systems.