Slide 1What is Motivation?The hypothalamus, homeostasis, & motivated behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorLong-term regulation of feeding behaviorshort-term regulation of feeding behaviorshort-term regulation of feeding behaviorshort-term regulation of feeding behaviorshort-term regulation of feeding behaviorWhy do we eat?Reward & reinforcementReward & reinforcementReward & reinforcementReward & reinforcementSlide 26MOTIVATIONNEUR 3000Dr. Joseph J. NormandinWHAT IS MOTIVATION?•Voluntary actions are produced to satisfy a need•This need can be abstract: I need to go hiking in a Massachusetts forest•Here, the motivation is hard to describe•This need can be concrete: I need to eat•Here, the motivation is easy to describe: I feel hungry•Motivation drives behavior in a way that a particular behavior is more likely to occur•We have yet to develop a full concept of why we might want to go hiking but we do have an understanding of many of the motivations necessary for survivalTHE HYPOTHALAMUS, HOMEOSTASIS, & MOTIVATED BEHAVIOR•Recall that the hypothalamus has been described as a regulator of homeostasis•In a sense, the basic needs for survival: body temperature, fluid balance, energy balance•Hypothalamic regulation begins with sensory transduction•A regulated parameter must be measured by sensory neurons (e.g. temperature)•Periventricular hypothalamic neurons detect that this is outside the normal range•Hypothalamic neurons then orchestrate the body’s response•Humoral response: stimulating or inhibiting pituitary hormone release into the blood•Visceromotor response: adjust sympathetic/parasympathetic output•Somatic motor response: incite an appropriate somatic motor responseLONG-TERM REGULATION OF FEEDING BEHAVIOR•The brain needs energy (in the form of glucose) as much as it needs oxygen•A few minutes of glucose deprivation leads to unconsciousness•Because food availability is not assured, the body has evolved a number of mechanisms to store energy and use it when needed•We have also evolved the motivated behavior to seek out food to keep our energy stores fullLONG-TERM REGULATION OF FEEDING BEHAVIORLONG-TERM REGULATION OF FEEDING BEHAVIORLONG-TERM REGULATION OF FEEDING BEHAVIOR•The lipostatic hypothesis:•The brain monitors amounts of body fat and acts to maintain body fatLONG-TERM REGULATION OF FEEDING BEHAVIOR•The lipostatic hypothesis:•The brain monitors amounts of body fat and acts to maintain body fat•In order for this to occur, there must be some communication between body fat and the brainLONG-TERM REGULATION OF FEEDING BEHAVIOR•The lipostatic hypothesis:•The brain monitors amounts of body fat and acts to maintain body fat•In order for this to occur, there must be some communication between body fat and the brain•Leptin is secreted by adipocytes and acts on the hypothalamus to decrease appetite and increase energy expenditure•Leptin deficiency (i.e. low body fat) stimulates hunger, suppresses energy expenditure, and inhibits sexual behaviorLONG-TERM REGULATION OF FEEDING BEHAVIOR•The hypothalamus and feeding•In rats, bilateral lesions of the lateral hypothalamus produce anorexia (decreased appetite)•Bilateral lesions of the ventromedial hypothalamus produce overeating•Also occurs in humans with brain damage to these regionsLONG-TERM REGULATION OF FEEDING BEHAVIOR•Leptin and the hypothalamus•Leptin released by adipocytes binds to leptin receptors in the arcuate nucleus of the ventromedial hypothalamus•Arcuate neurons contain the neuropeptides αMSH & CART•Arcuate neurons project to different parts of the nervous system to orchestrate the body’s response to high leptin•Projections to paraventricular nucleus•Humoral response: CRH & TRH, increase metabolism•Visceromotor response: activate sympathetic ANS•Projections to spinal cord•Visceromotor response: activate sympathetic ANS•Projections to lateral hypothalamus•Somatic motor response: inhibit feeding behaviorLONG-TERM REGULATION OF FEEDING BEHAVIORLONG-TERM REGULATION OF FEEDING BEHAVIOR•Leptin and the hypothalamus•A fall in leptin levels activates other neurons in the arcuate nucleus•These arcuate neurons contain the neuropeptides NPY & AgRP•Arcuate projections from these neurons produce effects opposite those of αMSH & CART•Projections to paraventricular nucleus•Humoral response: No CRH & TRH, no increase in metabolism•Visceromotor response: activate parasympathetic nervous system•Projections to lateral hypothalamus•Somatic motor response: excite feeding behaviorLONG-TERM REGULATION OF FEEDING BEHAVIORLONG-TERM REGULATION OF FEEDING BEHAVIORLONG-TERM REGULATION OF FEEDING BEHAVIOR•The lateral hypothalamus•Leptin-sensitive arcuate neurons project to specific types of neurons in the lateral hypothalamus•Neurons containing the neuropeptide MCH•Widespread projections to cerebral cortex•In rats, injection of MCH stimulates feeding behaviors•Neurons containing the neuropeptide orexin•Widespread projections to cerebral cortex•In rats, injection of orexin stimulates feeding behaviorsSHORT-TERM REGULATION OF FEEDING BEHAVIOR•Short-term regulation of feeding is related to:•The motivation to eat since our last meal•The motivation to continue eating/stop eating once we have started•The phases of feeding•Cephalic phase•Sight and smell of food triggers a number of physiological responses•Parasympathetic and enteric ANS are activated•Saliva and gastric juices are secreted•Gastric phase•As you began eating, these responses intensify•Substrate (intestinal) phase•As stomach fills and partially digested food moves into intestines, nutrients begin to be absorbed into bloodstreamSHORT-TERM REGULATION OF FEEDING BEHAVIOR•Appetite, eating, digestion, & satiety•Feeling hungry, “appetite” signals•When the stomach is empty it produces a peptide called ghrelin which is released into the bloodstream•Ghrelin activates the NPY and AgRP-containing neurons