motivation Flashcards
Motivated behaviour
Driver/energizing of behaviour in pursuit of a goal, is a fundamental element of our interaction with the world and with each other.
Orexinogenic peptides
Endogenous occurring neuropeptide hormone such as ghrelin, orexin, Agouti related peptide, Melanin-Concentrating Hormone or neuropeptide Y which increases appetite
Anorectic peptides
Endogenous occurring neuropeptide such as aMSH or CART that suppress appetite
What is motivation?
- Driving force
- Physical need
- Wanting, liking
Hypothalamus
• Maintain homeostasis by regulating three interrelated functions
– endocrine secretion
– autonomic nervous system
– emotions and drive/behaviour
• Motivated behaviour, e.g. drinking, eating
Long term regulation of bodyweight
Bodyweight is normally stable. If an animal is force-fed, it will gain weight. the weight is lost, however as soon as the animal can regulate its own food intake. Similarly, weight lose during a period of starvation is rapidly gained when food is freely available
Feedback of leptin
fatty tissues produce leptin when satisfied
then leptin travels to the brain to tell you to stop eating
Lateral hypothalamic syndrome
diminished appetite for food; anorexia
Venteromedial hypothalamic syndrome
overeating and obesity
Response to elevated leptin levels
• Activation of arcuate neurons that release αMSH and CART peptides
– Anorectic peptides—diminish appetite
– Project to regions that orchestrate coordinated response of humoral, visceromotor, and somatic responses
Paraventricular nucleus
(humoral response)
Intermediolateral gray matter of spinal cord
(visceromotor response)
Lateral hypothalamus
(somatic response)
LH neurons stimulating feeding behaviour contain
– Melanin-concentrating hormone (MCH) • Widespread connections in the brain • Prolongs consumption – Orexin • Also with widespread cortical connections • Promotes meal initiation
Hypothalamus and the control of bodyweight and food intake
• Motivated behaviour
• Accurately regulated by leptin produced by adipose tissue and hypothalamic peptides
• Hypothalamus plays an important role in regulating feeding behaviour (long term)
• Disruption of this regulation leads to
– Hyperphagia
– Anorexia
– Bulimia nervosa
Short term regulation of feeding
• Motivation to eat also depends on:
- How long it has been since last meal
- How much one has already eaten
- What type of food has already been eaten
Satiety
- Satiety is the feeling of fullness and the suppression of hunger for a period of time after a meal
- Feelings of satiety can influence how soon and how much you next eat
- The feeling of satiety occurs due to a number of bodily signals that begin when a food or drink is consumed and continue as it enters the gut and is digested and absorbed
Short term regulation of feeding (cephalic phase)
• Cephalic: hunger
– Ghrelin released when stomach is empty
– Activates NPY/AgRP-containing neurons in arcuate nucleus
– Removal of ghrelin-secreting cells of stomach thought to cause loss of appetite
Short term regulation of feeding (satiety signals which ends meal)
– Gastric distension signals brain via vagus nerve.
– Works synergistically with CCK released in intestines in response to certain foods
– Insulin also released by β cells of the pancreas— induces satiety by acting on arcuate nucleus of the hypothalamus
Why do we eat?
• We like food
– Hedonic aspect
• We want food
– Drive reduction
– Liking and wanting mediated in part by separate brain circuits
• Dopaminergic system involved in wanting/ craving (or liking?)
Reinforcement and reward
- Positive reinforcement (anything added that follows a behavior that makes it more likely that the behavior will occur again in the future)
- Negative reinforcement (a response or behavior is strengthened by stopping, removing or avoiding a negative outcome or aversive stimulus)
Natural rewards
Food, water, sex, nurturing
Addiction
Acute reinforcement/social drug taking Escalating/compulsive use Dependence Withdrawal Protected withdrawal
potential recovery but then there could be a relapse
Dopamine and reinforcement
- Dopamine release in the nucleus accumbens is correlated with motivation but not liking (hedonic)
- Its also release in anticipation of reward
- Note that dopamine also involved in movement
Microdialysis
- Measuring neurotransmitter release in vivo
* Association with behaviour parameters
Serotonin, Food and mood
• Mood and food are connected
– 5HT in hypothalamus
• Rises in anticipation of food
• Spike during a meal (carbohydrates in particular)
• Association anorexia nervosa, bulimia with depression (low serotonin)
