NEURO: Motivation Flashcards
Important brain region in motivation
hypothalamus
What is motivation?
Motivation is an urge to behave or act in a way that will satisfy certain conditions, such as wishes, desires, or goals.
It is a driving force to fulfil biological needs.
What is the function of the hypothalamus?
Maintains homeostasis by regulating 3 interrelated functions:
- endocrine secretion
- autonomic nervous system
- emotions and drive/behaviour (motivated behaviour, e.g. drinking, eating)
Humoral and Visceromotor responses are regulated by
Behavioural responses are regulated by
What regulates food intake?
periventricular nucleus and medial hypothalamus
lateral hypothalamus
hypothalamus
Describe the long-term effects of feeding behaviour.
Normal energy balance leads to normal adiposity.
Prolonged positive energy balance leads to obesity.
Prolonged negative energy balance leads to starvation.
Body weight 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 lost during a period of starvation if rapidly gained when good is freely available.
How did scientists discover that there must be something regulating food intake?
Parabiosis experiment:
Parabiosis is the sharing of blood circulation between animals. This means the bloodborne signals are shared and can affect the hypothalamus.
Example 1:
A genetically obese mouse (ob/ob) means that its fat cells do not produce leptin (which inhibits food intake).
It’s connected to a normal mouse (which produces leptin), and this leads to a reduction of obesity in the ob/ob mouse.
What is Leptin?
a hormone produced by adipose (fat) cells that acts as a satiety factor in regulating appetite by signalling to the hypothalamus
When is leptin released? And what does it act on?
Leptin is released during/after feeding by adipose tissue into the blood
Travels to the brain and binds to the arcuate nucleus of the hypothalamus at the base of the third ventricle to tell you to stop eating (inhibits feeding)
Important hypothalamic regions in regulation of food intake (hence body weight) and drinking (hence blood volume/osmolarity)
ventromedial hypothalamus (VMH) the lateral hypothalamus (LH)
What was the conclusion of a VMH lesion?
It concludes that the VMH plays a role in the cessation of eating. Damage to the VMH results in prolonged and dramatic weight gain.
Lesioned VMH
Ventromedial Hypothalamic Syndrome
-over-eating and obesity
Lesioned LH
Lateral Hypothalamic Syndrome
-diminished appetite for food; anorexia
What is the response to elevated leptin after food intake?
Anorexic Response
- leptin binds receptors in the arcuate nucleus
- arcuate neurones activated
- arcuate neurones project to the lateral hypothalamus (LH) releasing anorectic peptides ⍺-MSH and CART to inhibit feeding
- arcuate neurones also project to the paraventricular nucleus (PVN) to stimulate the release of ACTH and thyrotropin from the anterior pituitary. increasing basal metabolic rate
What is the response to decreased leptin levels during starvation?
Orexigenic Response:
- Ghrelin activates NPY/AgRP arcuate neurones, which project to the lateral hypothalamus (LH), releasing orexigenic peptides NPY and AgRP to stimulate feeding
- arcuate neurone projections also to the paraventricular nucleus (PVN) to inhibit the release of ACTH and TSH from the pituitary, decreasing basal metabolic rate
Describe the competition for activation of the MC4 receptor?
One way that αMSH (an anorectic peptide) and AgRP (an prexigenic peptide) exert opposite effects on metabolism and feeding behaviour is via an interaction with the MC4 receptor on some hypothalamic neurons.
Stimulation of the MC4 receptor inhibits feeding behaviour.
a-MSH activates MC4 receptor in response to increased leptin to inhibit feeding
AgRP blocks MC4 receptor in response to low leptin to increase feeding
What do the LH neurons that stimulate feeding behaviour to contain?
Orexigenic neuropeptides
Melanin-concentrating hormone (MCH):
- has widespread connections in the brain
- prolongs consumption
Orexin
- also has widespread cortical connections
- promotes meal initiation
Feeding related disorders due to dysfunctional hypothalamus
hyperphagia
anorexia
bulimia nervosa
Describe the reward pathway.
activate mesolimbic pathway (reward system):
-dopaminergic neurones project from the ventral tegmental area (VTA) to nucleus accumbens, causing motivational drive (wanting/craving)
The ventral tegmental area (VTA) is connected to both the nucleus accumbens and the prefrontal cortex via this pathway, and it sends information to these structures via its neurones.
The neurones of the VTA contain dopamine, which is released in the nucleus accumbens and in the prefrontal cortex. This pathway is activated by a rewarding stimulus.
What is drug addiction?
Drug addiction is defined as a chronic relapsing disorder characterised by the compulsive seeking of the drug, loss of control over drug-taking and the emergence of negative emotional states (anxiety, dysphoria, irritability) and physical states when the drug is not provided (withdrawal symptoms).
activate the reward system much more than natural reward factors and are extremely rewarding
Describe the stages in the addiction cycle.
1) Positive Reinforcement: drug intake due to social pressures, inducing pleasurable effects which will trigger further drug administration
2) Escalating/Compulsive Use: pattern of escalating compulsive use due to tolerance
3) Dependance: characterised by a state of emotional and physical withdrawal symptoms (anxiety, depression etc) in short and sometimes long periods of abstinence.
4) Negative reinforcement: aversive, dysphoria experience of drug withdrawal now drives drug intake (not the positive hedonic property of drug)
