Transcript ADDICTION - Department of Biology

ADDICTION
Derek Early
Bio 003
Feb. 5, 2002
What Is Addiction?
• An addiction is similar to
a compulsion
A compulsion is “a
repetitive, stereotyped,
and unwanted action, that
can be resisted only with
difficulty”
• Loss of voluntary control
often leading to selfdefeating behavior
Can take many forms
What Is Addiction?
• Addiction is characterized as dependence
syndrome by psychologists
• Dependence Syndrome involves “a cluster of
physiological, behavioral, and cognitive
phenomena in which the use of a substance or a
class of substances takes on a much higher priority
for a given individual than other behaviors that
once had a higher value”
What Is Addiction?
• Often there is a repeating pattern of
elements including:
High or pleasure  desensitization 
dependence and withdrawal
• High occurrence of relapse in all cases
Types of Addiction
• Substance
• Behavioral
• Is there a biological
link between these two
types of addictions???
Types of Addiction
• Substances
Depressants (Alcohol)
Stimulants (Cocaine, Caffeine, Nicotine)
Opioids (Morphine, Heroin)
Hallucinogens (LSD)
PCP (Ecstasy)
Others (Marijuana)
Types of Addiction
• Behavioral
Gambling
Food (often dopamine
deficient)
Sex (loss of control)
Shopping
Internet
What is The Basis of Addiction?
• The Brain
Addiction is connected to the brain by it’s
effects on hormones, memory, and
physically desensitization
• Psychologists have found substantial
evidence against the existence of an
“addictive personality”
What Is The Basis of Addiction?
• Short-term surges in dopamine caused by
substances or behaviors activate the brain’s
pleasure/reward system. Over time the brain
adapts to the surges and is desensitized to the
substance or behavior causing the individual to
engage in a greater amount of the activity in order
to obtain the same pleasure as before. The
desensitization can cause the brain to become
dependent, which results in withdrawal when the
compulsion is not performed.
Neurons
• 4 main parts:
– The Cell Body (houses the nucleus and organelles)
– Dendrites (usually short and numerous, receive signals)
– Axons (often only one on a neuron and can be very
long, sends signals to other neurons or effectors)
– Synapse (the junction point between two neurons or a
neuron and an effector cell, can be electrical or
chemical)
Chemical Synapses
A stimulus creates an action potential in a neuron
and sends it down the axon. Neurons store
neurotransmitters, like dopamine, in vesicles
located near the end of each axon at the synapse.
When the action potential arrives at the synapse it
causes the vesicles to fuse with the plasma
membrane of the neuron. The vesicles then
release the neurotransmitters which diffuse across
the membrane into the synaptic cleft. They cross
the synaptic cleft and bind to receptors on the next
cell’s membrane. They pass through ion channels
and create a new action potential. Enzymes break
down the left over neurotransmitter (MAO).
Changes in Neurons
• Long-Term Depression
– Decreased responsiveness to action potential by
receptor neuron
• Long-Term Potentiation
– Increased responsiveness to action potential by
receptor neuron
• LTP is essential in learning and memory
making and plays a large role in addiction
Dopamine
• Neurotransmitter located in the hippocampus, a
part of the brain involved in learning reasoning,
personality, and part of the limbic system
• Plays a role in the brain’s “reward” system (Those
who have a below normal level are prone to
engaging activities to raise the level)
• Also is involved in attention, mood, motivation,
learning, and movement
Dopamine
• Neurons can be sensitized
or desensitized to
dopamine depending on
the nature of the stimulus
• Desensitization is a
reaction on the part of the
nervous system to try and
maintain homeostasis
despite the increased
presence of dopamine
Memory
Addictive cravings may be brought on by
some of the same neurobiological processes
involved in memory and learning and
cravings are brought on by memories and
situations associated with the compulsion
This is how triggers are formed
Consequences
• Addiction causes people to compulsively
feed their cravings even if, due to
desensitization, they no longer provide
pleasure and in the face of a desire to quit
Consequences
• In the long term pathways and receptors in
the brain can wear out meaning that it is
harder for the brain’s pleasure/reward
system to function
• The brain becomes less sensitive to even
natural reinforcers  the addiction
becoming the highest priority in people’s
lives
Consequences
• Neuron’s dendrites build
more branching
projections and have more
synapses that connect to
neurons with which the
cell communicates
regularly  connections
between the cells are made
stronger
Conclusions
• It is not yet universally accepted that
substances and behaviors can produce the
same biological effects for those affected by
addiction
• Evidence supports neuroadaptation that
occurs in both cases
• Symptoms involving loss of control and
relapse are similar as well
Bibliography
“Watching Cravings in the Brain” Scientific American.
September 25, 1997
“Pathway to Addiction” Scientific American. May 13, 1998
Seligman, Martin E. Abnormal Psychology. W.W. Norton and
Co., New York, NY: 2001
Holden, Constance. “Behavioral Addictions: Do They Exist”
www.sciencemag.org
Helmuth, Laura. “Beyond the Pleasure Principle”
www.sciencemag.org