This document discusses how learning occurs in the brain through changes in neurons and their connections. It explains that there are different types of learning - cognitive, psychomotor, and affective - and that learning happens through associating stimuli with new responses which strengthens synapses. Dopamine is highlighted as an important neurotransmitter involved in reward and addiction pathways in the brain. Repeated drug use can hijack these pathways and cause tolerance by changing the number of dopamine receptors, impacting the brain's ability to experience natural rewards.

1. HOW NEURONS LEARN
Neuroscience – 10/9/2013

2. What is learning?
Take a few moments and produce your own
definition of what learning is.
Consider—
What kinds of things do you learn?
How do you learn them?

3. Different Domains of Learning
COGNITIVE
 Facts and information
 Procedures (how to solve a
problem)
PSYCHOMOTOR
 Physical patterns of activity
AFFECTIVE
 Learning to “feel” something

4. Write your own example of:
 Cognitive Learning
 Psychomotor Learning
 Affective Learning
What do these types of learning have in common?

5. My brain, pre learning:
STIMULUS 1  RESPONSE 1
(Shakespearean sonnet)  (ennui)
My brain, post learning:
STIMULUS 1  RESPONSE 2!!!!!
(Shakespearean sonnet)  (happiness!)
Learning is the association of
stimuli with new responses.

6. How does learning occur?
 Our brain has about a hundred billion
neurons, but we do not grow new ones
(mostly)
 Instead , learning happens at the connection
point between different neurons—at the
synapse.

7. How can neurons
change?
 Growing longer
dendrites/axons to
make new synapses
 Releasing more vesicles
of neurotransmitter
(presynaptic cell)
 More receptors for
neurotransmitter
(postsynaptic cell)

8. In this picture, there are 3 things happening to
strengthen this synapse. Can you find them?

10. Dopamine
Dopamine is a particular neurotransmitter with
many roles in the brain, including:
- Cardiovascular and renal control
- Movement and balance
- Reward and addiction
- Pleasure, emotion
- Normal cognitive function (thinking)

12. Dopamine and disease
 Dopamine deficiency in certain parts of the
brain is related to Parkinson’s and motion
disorder.
 Excessive dopamine has been linked to
schizophrenia and delusions.

13. Mechanisms of Drug Action
 A dopamine agonist would bind to receptors instead
of dopamine and convince your neurons that
dopamine was there.
 A dopamine antagonist would bind to receptors
instead of dopamine and block normal activation.
 Other drugs inhibit reuptake, leaving more
dopamine in the synapse longer. (cocaine)
 Indirect drugs cause extra dopamine release from all
neurons (amphetamine)

14. Neurotransmitters convey “messages” across the synapse

16. Dopamine and Reward
 Dopamine is involved in a brain circuit often
called the “reward pathway”
 In studies, we observe dopamine release
when subjects are rewarded with
food/money/etc
 Generally, more dopamine is released when
the reward is unpredicted

17. Dopamine/Opioids: Brain’s incentive reward systems

18. Activation of reward center produces a “wanting” and “liking”
response

19. Natural events activate these reward systems

20. 0
50
100
150
200
0 60 120 180
Time (min)
%ofBasalDAOutput
NAc shell
Empty
Box Feeding
DiChiara et al., Neuroscience, 1999.
FOOD
Mounts
Intromissions
Ejaculations
Fiorino and Phillips,J. Neuroscience, 1997.
Natural Events Elevate Dopamine Levels
100
150
200
DAConcentration(%Baseline)
15
0
5
10
CopulationFrequency
Sample
Number
1 2 3 4 5 6 7 8
SEX
Female Present

21. Some drugs activate your reward systems since they act
on the same receptors

22. Drugs make your brain really happy…..
Normal Brain Brain on Drugs
BUT only when your brain is on drugs.

23. 0
100
200
300
400
500
600
700
800
900
1000
1100
0 1 2 3 4 5 hr
Time After Amphetamine
%ofBasalRelease
DA
DOPAC
HVA
Accumbens AMPHETAMINE
0
100
200
300
400
0 1 2 3 4 5 hr
Time After Cocaine
%ofBasalRelease
DA
DOPAC
HVA
Accumbens
COCAINE
0
100
150
200
250
0 1 2 3 4 5hr
Time After Morphine
%ofBasalRelease
Accumbens
0.5
1.0
2.5
10
Dose (mg/kg)
MORPHINE
0
100
150
200
250
0 1 2 3 hr
Time After Nicotine
%ofBasalRelease
Accumbens
Caudate
NICOTINE
DiChiara and Imperato, PNAS, 1988
Effects of Drugs on Dopamine Release

24. Repeated use of drugs trigger compensatory processes
and saturate the brain’s reward systems
 individual can become conditioned/habituated/adapted to
the intense level of drug-induced pleasure
 the normal level of natural rewards are no longer
experienced as very pleasurable
 this is caused by synaptic changes—just like learning!

25. Upregulation
Downregulation
Too much dopamine activation at the synapses leads your
neurons to decrease the number of receptors.

26. Brain on drugs after
tolerance
Brain on drugs for
an extended period
Chronic drug taking ….reorganizes the liking
and wanting systems
… drugs may no longer be pleasurable but you still want them…

27. Drugs can change your brain so that natural events are no longer
pleasurable

28. high
low
High DA
receptor
Low DA
receptor
DA Receptors and the Response to
Methylphenidate (MP)
As a group, subjects with low receptor levels found MP pleasant
while those with high levels found MP unpleasant
Adapted from Volkow et al., Am. J. Psychiatry, 1999.
Dopaminereceptorlevel