Neurotransmission

If you've ever seen a movie involving cocaine users, you probably know that cocaine makes people feel powerful, confident, and alert.  You probably also know that cocaine can be highly addictive, leading some people to sacrifice their families and freedom in pursuit of the high.  What you may not know is that cocaine makes you feel good because of a chemical in your brain called dopamine.  Watch the video below for more on the relationship between cocaine and dopamine.
Video Activity

Watch the video below, and try to answer the following questions about how cocaine works in the brain.

What is dopamine?  When it is normally released?

How does cocaine affect the feel-good network in the brain?


How neurotransmission works

In order to understand how emotions, cognitions and behaviors arise in the brain, it is vital to understand the process of neurotransmission.  Neurotransmitters are involved in virtually everthing that happens in the brain, from falling in love, to cocaine addiction, to mental illness.  So what are neurotransmitters?  Well, the brain is made up of billions of neurons, and these neurons require chemicals called neurotransmitters to pass on signals from one neuron to the next. To understand the basics of neurotransmission, watch the video below, and try to fill in the missing vocabulary below.


















Key words:     transporter protein          neurotransmitters          synapse          action potential          receptor sites



1.  An electrical signal that travels along a neuron is the ________________

2.  The space between two neurons is called the _________________________.  The electrical signal cannot cross space.

3.  Chemical messengers released into the synapse are ____________________

4.  Neurotransmitters attach to the ___________________ on the post-synaptic neuron, allowing the signal to carry on.

5.  Neurotransmitters release from the receptor sites, and are taken back into the pre-synaptic neuron by ________________________.


To see the process of neurotrasmission in a beautiful 3-D animation, take a look at the video below.


Key neurotransmitters: Serotonin and Dopamine

Two of the most important neurotransmitters are serotonin and dopamine.  Both of these neurotransmitters have a wide range of effects on mental processes and behavior.  Here is a quick summary of these effects.

Effects of serotonin

  • Mood. Serotonin plays a large role in regulating your mood, including your level of anxiety, happiness, and well-being.  Mood altering drugs such as Ecstasy work by causing a massive rise in serotonin levels, but can also trigger feelings of depression as the drug begins to wear off and serotonin levels in the synapse drop.

  • Sexual function. Taking medications that increase the level of serotonin (such as antidepressants) causes a decrease in libido and sexual function.  Conversely, low levels of serotonin in the intoxicated state are associated with high levels of libido and sexual aggression.

  • Depression. Some scientists believe that low levels of serotonin cause depression, although there is considerable controversy over this matter.  Most medications prescribed today to treat depression work by reducing the re-uptake of serotonin, leading to higher levels of serotonin in the synapse.  This is believed to have a positive effect on mood.

Effects of Dopamine

  • Movement and speech.  Dopamine plays an important role in facilitating movement and speech.  When dopamine-producing cells in a certain part of the brain begin to die off, people can have trouble initiating movements, leading to a condition known as Parkinson's disease.  Medication for Parkinson's disease helps the brain to produce more dopamine.

  • Pleasure, reward and learning. When people expect or receive a reward - whether it is a cheeseburger, sex, or scoring the winning touchdown in a football game - levels of dopamine increase in the brain.  This results in feelings of pleasure and reward, prompting us to alter our behavior to get more of that reward in the future.  That's how animals learn to repeatedly press a certain lever to get food, and why its so hard to eat just one chocolate.

  • Addiction.  Addictive drugs (such as cocaine, heroin, and nicotine) cause huge increases in dopamine levels, leading to the "high" that people feel.  Dopamine causes the brain to associate drug use with feelings of reward.  This motivates people to do the drug again and again - even if its harmful.  The same is true of activities that have the potential to be addictive, such as gambling and watching pornography.



Think Critically

Is love just a drug? Neurotransmitters (and other chemicals in the brain) seem to play a significant role in how we feel.  So maybe love (and every other human emotion) is nothing more than a cocktail of certain chemicals being released in the brain.  So says Larry Young, a professor of neuroscience at Emory University.  You can read more about his view on love here.

If love is indeed just a drug, the implications could be vast.  Scientists could create a "love potion" that would make you capable of falling in love with just about anyone, or a "love antidote" that would make you fall out of love with an ex-partner.  Or scientists could even design a "love test" that would measure how many of those love chemicals are really being released when you contemplate a lifetime with your partner.

On the other hand, many would argue that something as complex as love can never be explained in terms of brain chemicals alone.  Perhaps love cannot be understood without taking into account a person's culture, belief system, life experiences, and the unique relationship between two people.  Explanations that try to explain complex phenomenon in terms of simple causes are often criticised for being reductionist, because they ignore the complexity inherent in human behavior.
Research Study: Rogers

Aim: Investigate the role that serotonin plays in perceiving emotional intimacy

Procedure:  Participants were 40 healthy male adults.  Approximately half of the participants received a drink containing tryptophan, which increases levels of serotonin, while the other half received a drink not containing tryptophan.  Afterwards, participants were given photos of couples, and asked to rate how "intimate" and "romantic" the couples appeared.

Results: Participants with lower serotonin levels (those that did not receive tryptophan) rated the couples as less intimate and romantic as those that received tryptophan

Conclusion:  Serotonin appears to play a role in how we judge the emotional closeness of people's relationships.  This has implications for the study of depression.  Depressed people often report feelings of loneliness and social isolation.  It could be that low levels of serotonin are a factor in how they perceive their relationships.

Evaluation:

  • The study is based on the experimental method, demonstrating a causal relationship between levels of serotonin (the IV) and ratings of relationship intimacy (the DV)

  • Rating the emotional intimacy of couples in photographs is not something that people would ordinarily do, so the study can be said to have low ecological validity.  It would perhaps be more interesting to investigate whether serotonin levels could alter how participants feel about their own relationships

  • It is a small scale study which was conducted in one culture (the UK).  The findings should be replicated on a larger scale, with different samples
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Checklist

  • I can explain the process of neurotransmission, including the role of the synapse, receptor sites, action potential, and transporter proteins

  • I can describe effects of serotonin and dopamine on behavior

  • I can discuss why explanations of human behavior that refer only to neurochemical processes can be criticised as reductionist

  • I can describe the aim, procedure, results and conclusion of Roger's study on serotonin in perceptions of intimacy, and evaluate the study


Quiz Yourself!

1.  Which term refers to the electric signal that travels along a neuron?

(a) Neurotransmitter

(b) Synapse

(c) Receptor site

(d) Action potential


2.  What is the function of transporter proteins?

(a) Send an electrical signal across the synapse

(b) Remove neurotransmitters from the synapse

(c) Release neurotransmitters into the synapse

(d) Transport neurotransmitters from one neuron to the next


3.  Medications (SSRIs) that treat depression work by ___

(a) Blocking the reuptake of serotonin, causing more serotonin in the synapse

(b) Increasing the reuptake of serotonin, causing less serotonin in the synapse

(c) Triggering the release of serotonin, causing more serotonin in the synapse

(d) Inhibiting the release of serotonin, causing less serotinin in the synapse


4.  Which of the following is least associated with dopamine?

(a) Emotional intimacy

(b) Sex

(c) Reward

(d) Bodily movement


5.  Some scientists explain addiction to crack cocaine in terms of dopamine.  Why would this explanation be considered reductionist?

(a) Crack cocaine, unlike powder cocaine, does not trigger the release of dopamine

(b) The decision to use a drug or not is a matter of free will

(c) Not only drugs can be addictive - so can gambling, sex, and TV-watching

(d) It does not take into account sociocultural factors that influence drug use


6.  Why did Rogers give participants a drink containing tryptophan?

(a) To increase serotonin production

(b) To decrease serotonin production

(c) To increase dopamine production

(d) To decrease dopamine production
(
Answers

1 - D, 2 - B, 3 - A, 4 - A, 5 - D, 6 - A