Intrusive thoughts in the sleep-deprived mind

Question 1

Intrusive memories

Think No-think task (TNT)

Answer 1

in everyday life we can be reminded about past experiences, which triggers memories about those experiences
HOWEVER, not all experiences we’re reminded of are pleasant
– 3 options when this happens!
STUDY - Mike Anderson (TNT task)
- first = learn association between 2 types of stimuli
eg. face and a scene
1) think condition (keep this scene in mind for as long as stimuli is presented)
2) no-think condition (eg. listen to song and actively avoid thinking about negative experience)
–> tests how good ps are at suppressing memories

• there is an ‘intrusion rating’ given
  after each trial provide a rating which relates to how often they thought about experience (eg. scene) associate with reminder (eg. face)
• score higher than 2 or 3 after a ‘no-think’ trial = shows they’re unable to keep the scene out of mind after seeing face = memory intrusion
  (typically administered in several blocks)
• we usually see participants improve in their memory suppression ability with each block
  = repeatedly inhibiting the retrieval of a memory makes it less likely to intrude during subsequent suppression attempts
  (people equally as good at avoiding negative memories as they are remembering neutral ones)

Question 2

Performance variability on TNT

Answer 2

tremendous variability in memory suppression effect

• some show memory suppression effects as large as 60%
• others very poor at suppressing thoughts
• identifying factors that contribute to this could be extremely helpful eg. PTSD, major depressive disorder

Question 3

Executive deficit hypothesis

Answer 3

individual differences in the regulation of immune memories in the aftermath of trauma may be mediated by pre-existing differences in executive control ability
- suppression ability should be diminished whenever people are in experimental conditions that tax their executive control abilities (Levy & Anderson, 2008)
- sleep plays a critical role in restoring and maintaining our cognitive and executive functions
so, it was hypothesised that: sleep deprivation might be an important factor underlying individual differences in memory suppression ability

Question 4

‘Top down’ suppression

Answer 4

retrieval suppression engages the PFC, which downregulates recollection-related activity in MTL via inhibitory top-down mechanisms (Gagnepain et al, 2017; Levi & Anderson, 2012)
PFC INHIBITS MTL
-sleep deprivation reduces functional connectivity between PFC and MTL, resulting in elevated amygdala reactivity to emotional images (Yoo et al, 2007)
Study: TNT task with functional neuroimaging methods
- during ‘THINK’ trials (p’s visualised scene associated with face) = increased activity in the hippocampus
(plays an important role in memory and is engaged during memory recollection)
- during ‘NO THINK’ trials (p’s successfully supress memories) = no increase in hippocampal activity, but, there was an increase in activity in dorsolateral PFC
(DLPFC actively inhibited activation in the hippocampus)

In think trials where faces were presented that were associated with negative images = increased activation in amygdala (region of medial temporal lobe that responds to emotional salience)

LINK to sleep deprivation:

• study found sleep deprivation REDUCES functional connectivity between the PFC and MTL
• p’s viewed emotionally negative images after a night of sleep or total sleep deprivation
• -> sleep deprived = 60% increase in amygdala (MTL) activity compared to sleep group (because they failed to engage the PFC whilst viewing negative images)

AMYGDALA = MTL = EMOTIONAL GAS PEDAL
PREFRONTAL CORTEX = BRAKES
memory control depends on same neural networks as emotion regulation (MTL/PFC), so, sleep deprivation might impair memory control by reducing top-down control of the MTL

Question 5

Motor response inhibition

go/ no-go task

Answer 5

sleep deprivation impairs the ability to inhibit motor response during go, no-go tasks
- 2 types of stimuli are presented on the screen (eg. a cross and a circle)
p’s must respond to one and ignore the other
p’s sleep deprived 5.5 hours
measured how often p’s mistakenly responded to the no-go stimulus
(more often they respond to no-go = less effective at inhibiting motor control)
FOUND:
- p’s mistakenly responded to no-go stimulus more often after 23, 31 and 55 hrs of wakefulness
- performance went back to baseline after 7 nights of recovery sleep

Neuroimaging research has consistently shown that inhibiting a motor response engages the same neutral regions as inhibiting an internal representation (eg. memory)
so, as people are unable to inhibit a motor response when they are sleep deprived, they may also be less effective at suppressing a memory representation

Question 6

Mental fatigue

Answer 6

memory suppression ability is compromised under conditions of mental fatigue (may tax exec function in the same way as sleep deprivation)
Van Schie & Anderson, 2017
- short version of task (3 sec exposure) vs long version (10 sec exposure to face) = suppress for longer = more fatiguing
- longer version = progressively better, then progressively worse = as they get fatigued they find it harder to engage the frontal network

Question 7

Psychiatry

Answer 7

• memory intrusions are common place in PTSD and MDD (Brewin et al, 2010)
• sleep disturbance is recognised as a symptom of these conditions (DSM-5) and may contribute to their onset and maintenance (Koffel et al, 2017; Rieman et al. 2001)
  (occurs in up to 90% patients)

Question 8

Memory control and emotion

Answer 8

suppressing the retrieval of emotionally negative memories in the face of reminder cues renders them less subjectively aversive

• greater success at suppressing the scene was associated with less negative subjective emotionality ratings in a subsequent rating task
• data suggests that repeatedly suppressing emotional memories alleviates them of their emotional tone (Gagnepain,, Hulbert & Anderson, 2017)
• -> more positive scores show p’s feel more positive about the scene (evaluate it more positively - positive reappraisal) after think no-think task = can reduce affective charge associated with memories

Question 9

Results and conclusions in relation to the research questions and specific hypotheses

IMPLICATIONS

Answer 9

RQ:

1) does sleep deprivation influence memory suppression ability?
2) does sleep deprivation influence the affective benefits of memory suppression>

Hypotheses:

1) sleep deprivation group will report more memory intrusions than sleep group
2) suppressing emotionally negative memories will render them less aversive
3) affect suppression for negative ‘no-think scenes’ will be greater in the sleep group relative to the sleep deprivation group

Results:
INTRUSION PROPORTION
- sleep deprivation group reported more memory intrusions than the sleep group
- intrusions became less frequent with repeated suppression
INTRUSION SLOPE
- the benefits of memory suppression for downregulating subsequent intrusions were diminished in the sleep deprivation group compared to the sleep group
(sleep dep. group were slower to downregulate each intrusion = can’t improve memory suppression ability)
RELAPSE PROPORTION
-sleep dep group reported more intrusion relapses than the sleep group
- relapses became less frequent with repeated suppression
(able to suppress memory on one trial, but not on next = relapse proportion) –> more common in sleep deprived = more susceptible to intrusions
INTRUSION CONTROL & AFFECT SUPPRESSION
-greater intrusion control predicted a shift towards moer positive affective evaluations of negative ‘no-think’ scenes
- fewer intrusions = feel more positive about negative scenes
SLEEP & AFFECT REGULATION
- sig interaction between TNT instruction (baseline, no-think) and group (sleep, sleep deprivation) on change in affect ratings towards negative images
- affect change scores for negative ‘no think’ scores was greater in sleep group than sleep deprived
sleep group = more positive overall (no real change for sleep deprived)
–> not found for baseline = specific for intrusions

CONCLUSIONS:
- sleep deprivation IMPAIRS memory suppression ability
- poor intrusion control following sleep deprivation undermines the affective benefit of suppressing negative memories
(ability to improve in suppressing memories taken away)

IMPLICATIONS:

• inhibits your ability to reduce emotional response to emotional memories = links to PTSD
• so, therapeutic strategies to improve intrusion control could prevent development of PTSD + MDD in poor sleepers
• treating underlying sleep disturbances could improve symptoms of MDD/PTSD by improving intrusion control and promoting positive reappraisal