One Biological Explanation
Monoamine Depletion Hypothesis: Receptor Sensitivity Hypothesis:
Schildkraut 1965 proposed a monoamine Antidepressant properties did not increase
depletion hypothesis of depression. availability of monoamine neurotransmitters
Argued depression is caused by abnormally which suggested there was more to
low levels of the monoamine depression than monoamine depletion.
neurotransmitters serotonin - noradrenaline Receptor Sensitivity Hypothesis argued that
and dopamine. depression is caused by changes in the
They are considered good candidates because sensitivity of postsynaptic receptors.
their known roles in regulating the functions Neurons compensate for the reduction in
of the brain’s limbic system including the neurotransmitter stimulation by increasing
amygdala, hypothalamus and hippocampus. the sensitivity of receptors and producing
Permissive hypothesis - the balance of both more of them.
serotonin and noradrenaline. In depression serotonin receptors become
Abnormally low level of serotonin ‘permits’ supersensitive.
noradrenaline to decrease as well - the Causes neurons to respond as if they are
outcome is depression. overstimulated so produce less serotonin.
BDNF Hypothesis:
Brain-derived neurotrophic factor.
Not a neurotransmitter but a chemical which
‘feeds’ neurons the nutrients they need to
survive, grow and function efficiently.
Levels of BDNF in the prefrontal cortex is
abnormally low in people with depression.
Links depression to stress because the BDNF
may be ‘switched off’ under stress - can
shrink and kill cells.
Evaluation
Strength:
Studies have found a negative correlation between blood serum levels of BDNF and the severity of
depressive symptoms.
Post-Morton studies of the brain of people with had depression have found abnormally low levels of
BDNF in the hippocampus and prefrontal cortex.
Shows a clear association between BDNF level and depression symptoms.
Monoamine Depletion Hypothesis: Receptor Sensitivity Hypothesis:
Schildkraut 1965 proposed a monoamine Antidepressant properties did not increase
depletion hypothesis of depression. availability of monoamine neurotransmitters
Argued depression is caused by abnormally which suggested there was more to
low levels of the monoamine depression than monoamine depletion.
neurotransmitters serotonin - noradrenaline Receptor Sensitivity Hypothesis argued that
and dopamine. depression is caused by changes in the
They are considered good candidates because sensitivity of postsynaptic receptors.
their known roles in regulating the functions Neurons compensate for the reduction in
of the brain’s limbic system including the neurotransmitter stimulation by increasing
amygdala, hypothalamus and hippocampus. the sensitivity of receptors and producing
Permissive hypothesis - the balance of both more of them.
serotonin and noradrenaline. In depression serotonin receptors become
Abnormally low level of serotonin ‘permits’ supersensitive.
noradrenaline to decrease as well - the Causes neurons to respond as if they are
outcome is depression. overstimulated so produce less serotonin.
BDNF Hypothesis:
Brain-derived neurotrophic factor.
Not a neurotransmitter but a chemical which
‘feeds’ neurons the nutrients they need to
survive, grow and function efficiently.
Levels of BDNF in the prefrontal cortex is
abnormally low in people with depression.
Links depression to stress because the BDNF
may be ‘switched off’ under stress - can
shrink and kill cells.
Evaluation
Strength:
Studies have found a negative correlation between blood serum levels of BDNF and the severity of
depressive symptoms.
Post-Morton studies of the brain of people with had depression have found abnormally low levels of
BDNF in the hippocampus and prefrontal cortex.
Shows a clear association between BDNF level and depression symptoms.
