CONSCIOUSNESS (PowerPoint)

Document Sample
CONSCIOUSNESS (PowerPoint) Powered By Docstoc
					               LECTURE 5

    DRUGS AND ALTERED
      CONSCIOUSNESS
(this material is covered in „Drugs and Behaviour‟
          section of chapter 4, Martin et al)

                     David Pearson
            Room T10, William Guild Building
             Email: d.g.pearson@abdn.ac.uk
•   The brain is protected by a tightly packed
    lining of cells called the blood-brain
    barrier.
•   However, some drugs are able to pass
    through and influence the operation of the
    brain.
•   These drugs alter consciousness by
    facilitating or inhibiting synaptic
    transmission.
       Basic Steps in Synaptic
            Transmission
1. Neurotransmitters are synthesized in the
   presynaptic (sending) neuron and stored in
   vesicles.
2. Neurotransmitters are released into the synapse,
   where they stimulate receptor sites on the
   postsynaptic (receiving) neuron.
3. Neurotransmitters are deactivated by enzymes
   or by reuptake.
Drugs that affect synaptic transmission can be
   divided into two main categories:

•   Agonist drugs
•   Antagonist drugs
               Agonist Drugs
•   Agonist drugs work by increasing the activity of
    a neurotransmitter.
This can be done by:
• Enhancing a neuron‟s ability to synthesize,
    store, or release neurotransmitters.
• Binding with and stimulating postsynaptic
    receptor sites (or increasing sensitivity of these
    sites)
• Prolonging activity of neurotransmitters (e.g., by
    inhibiting reuptake)
    Example of Agonist Action
• The brain produces natural pain-killing
  chemicals called endorphins.
• Drugs known as opiates (e.g., morphine,
  codeine) have a molecular structure similar
  to that of endorphins.
• Opiates can therefore bind to and activate
  receptor sites that normally receive
  endorphins, and duplicate their effects.
           Antagonist Drugs
• Antagonist drugs work by inhibiting or
  decreasing the action of neurotransmitters.
This can be done by:
• Reducing a neuron‟s ability to synthesize,
  store, or release neurotransmitters
• Preventing a neurotransmitter from binding
  with the postsynaptic neuron (e.g., by
  blocking the receptor sites)
  Example of Antagonist Action
• Symptoms of schizophrenia (hallucinations,
  delusions etc.) are often associated with
  abnormal overactivity of the
  neurotransmitter dopamine.
• „Antipsychotic‟ drugs have a molecular
  structure similar enough to dopamine to
  block the receptor sites, but not similar
  enough to activate them.
  Consciousness-Altering Drugs
• Depressants
• Stimulants
• Hallucinogens
              Depressants
• Depressants work by decreasing nervous
  system activity.
• In moderate doses depressants reduce
  feelings of tension and anxiety, and produce
  a state of relaxed euphoria.
• In high doses depressants can slow down
  vital life processes to the point of death.
Alcohol
•   Alcohol increases the activity of gamma-
    aminobutyric acid (GABA), a major
    inhibitory neurotransmitter.
•   Alcohol also decreases the activity of
    glutamate, which is a major excitatory
    neurotransmitter.
•   Together these effects produce a
    substantial reduction in neural firing
    within the brain.
•   Neural slowdown reduces activity in the
    inhibitory control centres in the cerebral
    cortex.
•   This leads to disinhibition and feelings of
    euphoria.
•   At higher dosage disruption of cerebral
    control centres produces disorganised
    thinking and physical coordination,
    fatigue, and psychological depression.
•   Alcohol also produces an effect known as
    alcohol myopia (Steel & Josephs, 1990).
•   Neural slowdown produces an increased
    inability to attend to and process new
    information.
•   Drinkers begin to pay attention only to those
    aspects of a situation (cues) that stand out, and
    ignore other relevant information.
•   This produces an increase in risk-taking
    behaviour and a failure to attend to long-term
    consequences of actions (MacDonald et al.,
    2000).
                 Stimulants
Amphetamines
• Amphetamines can reduce appetite and fatigue,
  decrease the need for sleep, and in some cases
  reduce feelings of depression.
• Amphetamines increase the activity of the
  neurotransmitters dopamine and norepinephrine.
• This is done by (a) causing the neuron to release
  greater amounts of these neurotransmitters, and
  (b) inhibiting reuptake.
•   Adverse effects of amphetamines include
    increased blood pressure, heart failure, cerebral
    hemorrhage.
•   Repeated high doses can result in long-term
    brain damage (Diaz, 1997).
•   Continuous heavy amphetamine use can result in
    amphetamine psychosis (Lynn, 1971).
•   Heavy amphetamine use is linked to severe
    withdrawal symptoms (“crash”) due to
    depletion of dopamine and norepinephrine
    reserves.
Cocaine
• Cocaine is a natural stimulant derived
   from the coca plant (also synthetic version
   novocain).
• It produces excitation, sense of increased
   muscular strength, and euphoria.
• Works by blocking reuptake of dopamine
   and norepinephrine.
• In large doses produces fever, vomiting,
   convulsions, hallucinations, and paranoid
   delusions.
•   Historically cocaine was hailed as a
    “wonder drug” and widely used as a local
    anaesthetic and general stimulant.
•   In 1885 John Pemberton developed a
    mixture of cocaine, syrup, and kola nut
    extract and marketed it as health tonic.
•   By 1891 there was a growing national
    debate in the USA about the negative
    aspects of cocaine.
•   By 1902 Coca-cola contained only 1/400
    of a grain of cocaine per ounce of syrup.
•   Cocaine not completely removed until
    1929.
              Hallucinogens
• In 1943 Swiss chemist Albert Hofmann
  accidentally absorbed a new chemical that he was
  synthesising:
“The dizziness…became so strong at times that
  I…had to lie down on a sofa…Everything in the
  room spun around and the familiar objects and
  pieces of furniture assumed grotesque, mostly
  threatening forms.”
• Hoffman had synthesised lysergic acid
  diethylamide (LSD).
“We were somewhere around Barstow on the edge
   of the desert when the drugs began to take hold.
   I remember saying something like “I feel a bit
   lightheaded; maybe you should drive…” And
   suddenly there was a terrible roar all around us
   and the sky was full of what looked like huge
   bats, all swooping and screeching and diving
   around the car, which was going about a
   hundred miles an hour with the top down to Las
   Vegas.”
                  Hunter S. Thompson
                  Fear and Loathing in Las Vegas
•  Hallucinogens are powerful
   consciousness-altering drugs that produce
   substantial hallucinations.
Natural Hallucinogens
• Mescaline (peyote cactus extract)
• Psilocybin (“magic” mushrooms)
Synthetic
• LSD
• Phencyclidine (“Angel Dust”)
•   Hallucinogenic effects include distorted or
    intensified sensory experience,
    synaesthesia, “mystical” experiences and
    insights, exhilaration.
•   Adverse effects can include violent
    outbursts, paranoia, panic, and
    “flashbacks” long after the drugs‟ effects
    have apparently ended.
•   Molecular structure of LSD is very similar
    to the neurotransmitter serotonin.
•   Overall LSD decreases serotonin activity.
•   During normal sleep decreased serotonin
    levels are linked to the onset of REM
    sleep.
•   Some argue that LSD‟s inhibition of
    serotonin allows dreamlike altered
    perceptions and hallucinations to emerge
    while we are still awake (Trulson &
    Jacobs, 1979).
                Summary
• Drugs can alter consciousness by
  facilitating or inhibiting synaptic
  transmission in the brain.
• Agonist drugs increase the activity of
  neurotransmitters.
• Antagonist drugs inhibit or decrease the
  activity of neurotransmitters.