7(2/10/09): Lecture How drugs work, brain plasticity
How drugs alter neurons Reading the brain: video Cog. Enhancing drug issues (in brief) Brain plasticity:
Across generations Developmental Experiential
Psychological context for understanding neurons
All psychological phenomena involve the operation of neurons
Change neurons then you change thought, mood, and action Stop neurons then you stop though, mood, and action Visualization techniques show neurons at work as we perceive and think
Test of these points:
Drug effects Hooking up a machine to neuronal activity
Summary: 2. Neurons can talk in a binary code: -70 mv and + 30 mv, equivalent to 0 and 1. 3. They can communicate with one another: release and binding of neurotransmitters. 4. The simplicity of the language is in sharp contrast to the incredible complexity of the neural connections. e. Perhaps 100 billion neurons f. Each neuron has many input nodes and many output nodes. g. These work in parallel and in sequence. The brain has immense coding and communication capacities. At its disposal is a simple two word vocabulary (- 70 mv and +30 mv), a finite number of neurotransmitters, and an unlimited capacity to create networks composed of neurons and neurotransmitters.
An implication of neuronal functioning relating to psychoactive drugs
Neurons provide the physical bases for psychological phenomena Neurons are biological and communicate by means of biochemicals Drugs interact with biological structures Hence, drugs can alter neurons, thereby altering psychological phenomena Each feature of neuronal functioning is an opportunity for intervention Thus, drugs alter psychological phenomena by interacting with specific features of neuronal function and communication
How drugs work (1)
Drugs that influence synthesis and storage of neurotransmitters:
L-Dopa: synthesis of dopamine to treat Parkinsons disease aspirin: blocks prostaglandin synthesis---prostaglandins induce fever and pain) reserpine: inhibits storage of dopamine, used to treat schizophrenia
Drugs that mimic endogenous neurotransmitters:
nicotine (acetylcholine) morphine (endorphin)
How drugs work (2)
Drugs that block receptors:
1st generation anti-psychotic drugs (chlorpromazine---dopamine)
Drugs that affect duration of neurotransmitter/receptor bond: Prozac, cocaine.
How does alcohol alter neuronal functioning?
Alcohol: the drug in search of a receptor Inhibits excitatory glutamate receptors and activates GABA mediated increase in chloride ions, thereby enhancing neuronal inhibition This leads to muscle relaxation, decreased cognitive function, and loss of motor coordination These effects are often accompanied by decrease in inhibitions Why should decreased cognitive function often lead to decrease in inhibitions?
Receptors are malleable (plastic) and change as a function of experience and environmental conditions
Number of receptors is changed by exercise: de Castro & Duncan (1985)
In a study with rats, simply running in a wheel for food increased concentration of dopamine in brain and decreased number of dopamine receptors by 35% (so that systems maintained an equilibrium)
Receptor binding (structure) is altered by learning. Tocco et al (1991):
Learning in rabbits changed the shape of hippocampus receptors that selectively interact with glutamate (an excitatory neurotransmitter) so that binding increased.
Behavioral adaptation can reverse environmentally induced deficits in receptor function
Background: The effects of inescapable shock on stress response and aggression The effect of aggression on effects of inescapable shock The role of GABA receptors in stress The experiment: Fighting during shock exposure attenuates the reduction of GABA receptors in the cerebral cortex...Cuadra et al. (1992)
approx 12 pulses about in 10 minutes resulted in a 33% decrease in number of GABA receptors in higher brain areas. decreases were reversed by opportunity to fight with another rat when shocked
Summary of receptor plasticity
Since neurons embody psychological phenomena. Changes in psychological functioning imply changes at the neuronal level. Recent experiments show that this logical implication is valid.
Receptors are everywhere
Receptors for a given species of neurotransmitter are typically, if not always, widely distributed in brain and periphery Some pictures: see next 3 slides..
Distribution of opiate receptors
Questions
Why does the sap from a poppy plant (opium) have the capacity to kill pain? Given broad distribution of receptors throughout brain, what do we mean when we say that a psychoactive drug has side effects.
Summary..
Given that neuronal activity is the physical basis for all thought, feeling and action, drugs should alter thought, feeling, and action. They do.
What about translating neural activity into physical action. That should be possible. Is it? http://www.youtube.com/watch?v=7-cpcoIJbOU&feat http://www.youtube.com/watch?v=L8oAz4WS4O 0
Cognitive Enhancing Drugs: Should they be made available to everyone?
Greely et al. (2008) say that we should consider the question of providing cognitive enhancing drugs for anyone who wants to use them
Empirical issues, moral issues. Empirical:
Extent and conditions that surround use Could we develop a cognitive drug that had no side effects? What do currently used (Ritalin and Adderall) drugs do?
iClicker: all answers honored
What is your guess as to the % of BC students who use prescription drugs for non-prescribed course related purposes (e.g., Ritalin or Adderall) three or more times/semester? A = 10% or less B = 11 to 25% C = 26 to 50% D = Above 50%
Based on current patterns of use, who would use the perfect cognitive enhancing drug?
Moral issues: Assume the perfect cognitive enhancing drug
Should people use it? Is it different than the perfect athletic enhancing drug? Should we distinguish between an A that did not involve drug use and one that did? Should parents be allowed to give young children the drug?
iClicker (all answers honored): Assume the perfect cognitive enhancing drug
A = It should be made available to whoever wants to use it B = Legal but with restrictions, as with alcohol and cigarettes C = It should not be used, except for individuals who suffer obvious brain damage D = It should never be used
New topic: Characteristic changes in the brain across generations, across a lifetime, and as a function of experience.. Phylogenetic changes Developmental (ontogenetic) changes Changes that are triggered by specific experiences
This graph shows the size of the brain as a function of size of the body: The higher the point on the y-axis the greater the relative brain size.
Why did brain size change so rapidly for humans?
Upright posture led to greater importance of vision and eye/hand coordination? Tendency to form social groups led to greater cognitive capacities (e.g., sharing, planning, cooperation). Tendency to communicate led to greater cognitive capacities? Something else?
There are dramatic cognitive changes within each of our lifetimes
What, speaking broadly, is the nature of these changes Are there corresponding changes in brain structure and function?
Changes in cognition that characterize infancy to early adulthood
Thought becomes more abstract, flexible, less egocentric Examples: Capacity to appreciate puns, construct hypothetical situations, see things from another point of view, manipulate ideas (as if they were objects), construct a logical plan of action, imagine ideal situations (e.g., morals, utopian thought, etc.)
to be continued