Chapter 5 Flashcards
What are the three major systems of the motivation control system of the brain?
- Learning and memory system;
- Motor loop;
- Homeostatic Input.
What are the areas involved in the learning and memory system?
(Hippocampus and amygdala)
Cortex
What are the areas involved in the motor loop?
(Thalamus)
(Basal ganglia)
(Cortex)
What are the areas of the reinforcement system?
(Nucleus accumbens)
(Ventral tegmental area).
These combined are the mesolimbic dopamine system.
What area does homeostatic input influence?
The tegmental area.
What area does sensory input influence?
The Thalamus.
Where does the motor output come from?
The cortex.
What areas does the Hippocampus and Amygdala together influence?
The Cortex and Nucleus accumbens.
What does the Cortex influence?
(Hippocampus and Amgydala)
Motor output
Nucleus accumbens
Basal ganglia.
What areas does the Thalamus influence?
The cortex
What areas does the Basal ganglia influence?
Thalamus
What areas oes the Nucleus accumbens influence?
Basal ganglia
Ventral tegmental area
What areas does the ventral tegmental area influence?
Nucleus accumbens
What is addiction?
Abuse or dependence upon a drug.
DSM IV defines two stages:
Substance dependence: the need to use increased doses of the drug, withdrawal symptoms, unsuccessful attempts to cut down on dug use, and continued use in spite of the drugs harmful effects (needs three or more within 12 month period for diagnosis).
Substance abuse: more extreme, includes failure to fulfill major obligations at one’s job, at school, or family; recurrent problems with the legal issues; and persistent social or personal problems (need only one symptom for diagnosis).
What are the two necessary components of any system that controls motivation?
Must be able to energize or activate behviour
And it must be able to direct that behviour toward a particular goal and make sure the organism acts appropriately to obtain that goal.
Guided missile analogy: Needs a rocket motor to make it go, and must have guidance system that directs it to the right place.
Organism has a need: e.g., hunger - this is the rocket moor The guidance system is more complicated, but we are attracted to specific targets which have incentive (e.g., taste of sugar).
Describe activation within the motivation control system.
Activation arises when there is an imbalance or deficiency in some internal system, such as when the organism is hungry, this input stimulates the ventral tegmental area in the hindbrain. Axons from the ventral tegmental area are connected to the nucleus accumbens, and the ventral tegmental area stimulates the nucleus accumbens by releasing dopamine at its synapses. This makes up the mesolimbic dopamine system, which is the reinforcement system of the motivation control system.
Cells in the nucleus accumbens send axons back to the ventral tegmental area where they release an opioid like peptide neurotransmitter, forming a circuit.
The nucleus accumbens also sends axons to the basal ganglia, which, with parts of the cortex, belong to the motor loop.
Activation of the mesolimbic dopamine system for hunger will stimulate the motor system which causes a general increase in the activity of the organism.
How does the output of the nucleus accumbens affect the motor loop?
The output of the nuclleus accumbens normallly provides continuous inhibition of the motor system. When dopamine is released in the nucleus accumbens, it actually inhibits the inhibitory output to the motor system. This has the same effect s stimulating the motor system.
Explain how the motivation control system guides an organism.
The motivation control system receives sensory information about the environment. This information is processed by the thalamus and cortex, and then sent to the amygdala and hippocampuus which make up the learning and memory system. This system holds information about previously experienced stimuli, past actions and their outcomes.
With the aid of these memories it is determined whether these external stimuli are biologically significant (e.g., food, or a lever that ,when pressed leads to the presentation of food).
Behaviour is activated and directed so that the organism approaches objects in the environment and performs acts that have resulted in the restoration of homeostatic balance in the past. In this way, the motivation control system enhances survival.
What areas make up the learning and memory system and what does it do?
Hippocampus and amygdala - Holds information about previously experienced stimuli, past actions, and their outcomes.
Explain the reward learning hypothesis of dopamine function.
Learning and memory circuitry provides the basis for this hypothesis. Dopamine is implicated in the acquisition of operantly conditioned response-reward actions, classically conditioned stimulus-reward associations, and the coding of predictions about reward availability based on the presence of conditioned stimuli, that is, the guidance system.
How does the motivation reward system evolved?
Evolved so that an organism will be able to show maximum flexibility in a very wide variety of environmental conditions, thus ensuring its survival and increasing its chances of that it will pass its genes (including the genes that create this neural circuitry) along to another generation.
How does the motivation control system (MCS) work?
A need state occurs (e.g., hunger), it is detected by the MCS and the mesolimbic system is activated (Nucleus accumbens and ventral tegmental area = reinforcement system = mesolimbic system). This causes an increase in general activity. In the absence of any previous learning or relevant salient stimuli, this activity ensures that the animal will move around its environment and maybe find food accidentally.
Information associated with the discovery of food is stored in the cortex and hippocampus - incentive salience is given to stimuli that lead to this discovery (salience = stimuli will grab organisms attention in the future, incentive = animal will be attracted to them).
(Animal rummaging for food in the woods analogy)
In the future, when the animal gets hungry and the nucleus accumbens is stimulated by the ventral tegmental area, general activity will increase, but now the stones in the stream bed will draw the animal’s attention, it will be attracted to the and consequently find food.
The stones, the streambed, and the act of turning over the stones then acquire more incentive salience. These stimuli will then have the power to activate the nucleus accumbens, so the organism will tend to approach and spend time there, even if it is not hungry.
How do stimuli lose their incentive salience?
If there is a drought the water will dry up and no food will be under the rocks. After turning over a number of rocks and not finding any food, the behaviour will extinguish, the stream bed will lose its reinforcing and incentive value, and the activation caused by the huger would drive the animal to seek food in other places.
Explain the role of dopamine in the Motivation control system.
Surge of dopamine in the nucleus accumbens is clearly correlated with changes in the animal’s behaviour caused by reinforcement, but how does it guide behaviour?
Mice genetically manipulated to have no dopamine and mice genetically manipulated to have excess dopamine learn the same as normal mice. So dopamine surge is not responsible for acquiring the stimulus-reward association.
Dopamine may contribute to learning indirectly, through the enhancement of attention, motivation, rehearsal and memory consolidation rather than a direct “teaching” role. The dopamine surge may be a consequence, rather than a cause, of associative learning and reward prediction.
