Lecture 14 Reading Flashcards
What can stress induced metabolic changes do?
Outline of the study
Results
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What regions got deactivated (4)
Stress-induced metabolic changes can have detrimental health effects
- Participants were exposed to a psychosocial stressor in PET or fMRI
- Results showed a profound deactivation of the following regions in the limbic system in subjects who reacted to the stressor with significant increases in cortisol
1-Hippocampus
2-Hypothalamus
3-Medial-orbitofrontal cortex
4-Anterior cingulate cortex
Deactivation in these structures suggests elevated activation at rest and during
non-stressful situations
What did Wang find?
And Tiford?
A study by Wang et al was able to use a mental arithmetic task in an MRI and found that activity in the ventral right PFC and left insula/putamen
-Argued that stress causes activation of pathways associated with negative
emotions, and that the right PFC plays a key role in the central stress response
-A study by Tillfors et al did a PET study and observed greater activity in the
hippocampus and amygdala during anticipated stress
What do previous animal studies on stress show?
-Animal studies have shown that the limbic system plays a role in the regulation of stress responses
-About 30-60 mins after the onset of a stressor, molecular markers (e.g. cFos) in
multiple limbic structures are increased, suggesting a stimulating effect of stress
on neural activity
-Hippocampus can have an inhibitory effect on HPA system
What was the design of this study (using the Montreal Imaging Stress Task)
Psychological stress was induced using the Montreal Imaging Stress Task in which
subjects are exposed to challenging mental math problems on the computer and have to click the right answer
Experimental condition: program adapts so the subject’s test performance is
about 45-50%, also receive negative feedback about their test performance by
examiner and computer program itself
Control condition: mental arithmetic is presented without feedback
Salivary cortisol was measured during the scanning in both the PET and fMRI studies
Cortisol stress responses and baseline measures
PET Study
- Cortisol levels increased significantly after experimental condition
- No significant cortisol increases were observed in the control or rest conditions
fMRI study
What happened to cortisol in stressor group
Were there 2 sub divisions made?
How were they different?
Cortisol levels increased significantly after stress
Split group into 2 groups
Responders: Subjects whose cortisol levels increased over the course of the experiment
Nonresponders: Subjects whose cortisol levels decreased over the
course of the experiment
-Responders had slightly lower self-esteem scores
-Right hippocampal volume was significantly lower in responders
○ Hippocampal volume was also positively related to self-esteem
Brain activation as a result of mental arithmetic
How was this calculated?
Where was activity in Control > rest?
Where was activity in experimental group > rest?
Subtracted the rest from the control and experimental conditions in both PET and fMRI study to identify the brain activations in response to stressful and non-stressful arithmetic
Control > rest: observed activity in visual association areas, angular gyrus, motor cortex, cerebellum
Experimental > rest: observed activity in the motor and premotor areas
No significant activations could be observed in these contrasts in limbic structures
Brain activation as a result of stress
What did you see activate in PET?
and in fMRI?
Subtracted control from experimental condition (looking at the difference between stressful arithmetic vs non-stressful arithmetic):
PET Study: failed to observe any significant activation in this contrast
fMRI study: activation in left premotor area, medial L PFC, bilateral area of cingulum, occipital cortex
Observed deactivations in the presence of psychosocial stress
What general area was deactivated?
In general, responding with a cortisol increase to the stressful task was associated with a decrease of activity in limbic system components
PET Study: reduced cerebral blood flow after stress in hippocampus, amygdala,
ventral striatum, PFC, anterior cingulate cortex, superior temporal gyrus, right superior insula
fMRI Study: deactivations generally replicated the ones found in the PET study
Nonresponders: deactivation in medio-orbitofrontal cortex, temporal pole, medial temporal lobe of hippocampus was mostly spared from deactivation
Responders: deactivation in medio-orbitofrontal cortex, temporal pole, left
and right hippocampus, amygdala, hypothalamus, and anterior CC
ROI analysis with hippocampus and anterior CC
Correlated the amount of deactivation with the area under the curve of the
cortisol response: significant positive correlation for hippocampus but not for
anterior CC
What were the main difference in activation changes as a result of the stressful mental
arithmetic between responders and nonresponders?
Responders showed deactivation of left anterior CC, right orbitofrontal/IFG
regions
What is stress primarily associated with?
Stress is primarily associated with a reduction of activity in the limbic system structures,
and that the amount of deactivation in the hippocampus is especially associated with the
cortisol stress response
Brain activation changes as a result of performing mental arithmetic
Visual association cortex → visual processing of mental arithmetic problems
Angular gyrus → cognitive processing associated with performing calculations
Motor cortex → operating the response box in the scanner
Deactivation of limbic system components during the presence of psychosocial stress
MRI study ROI analysis of hippocampus suggested a linear relationship between
hippocampal deactivation and HPA axis activation
Hippocampal activity and inhibition of the HPA axis: a default state of the CNS?
Deactivation in experimental condition means greater activation in control condition
Propose that processing and contextualization of sensory info taking place in the
hippocampus is a default activity
The PVN integrates signals from the hippocampus, amygdala, and PFC
-Hippocampus plays an inhibitory role
Findings suggest that a persistent activated state of the hippocampus exerts a tonic inhibition of HPA axis activity
-In response to a stressor, hippocampal activity might be curtailed to disinhibit
HPA axis and initiate stress hormone release
-Returning glucocorticoids into the CNS might then actually reactive the
hippocampus
Other fMRI studies have shown activation of limbic structures (e.g. amygdala) in the presence of novel and fearful stimuli
-Why? Distinguish between stress and fear
Fear: cognitive/emotional state that is associated with an enhanced state of vigilance
Psychosocial stress: response of the organism to a social condition that’s considered
threatening
Underlying neural mechanisms of these two responses might be distinct
- Fear increases amygdala activity
- Stress decreases hippocampal activity
Anterior CC activity did not show a correlation with cortisol release (unlike the
hippocampus)
-Appears to play a dichotomous role in the stress response
-Might be involved in the appraisal process of a stressful situation
