Dreams and their neural correlates

When do dreams happen during the night - classic view?

• REM sleep = dreaming.

• NREM 3 / slow-wave sleep (SWS) = dreamless sleep.

• Sleep onset = hallucinations

When do dreams happen during the night - process view?

• Dreaming is a process with different qualities.

• Dreaming can occur during ANY stage of sleep.

• The experience of dreaming varies depending on the sleep stage

When can dreaming really occur?

during both REM and NREM

Dream recall: REM vs NREM

Historically, researchers found higher dream recall following REM awakenings than NREM awakenings.

• REM: approximately 80%.

• NREM: approximately 43%.

Why did NREM recall increase from approximately 20% to 60% in some studies?

Instead of asking:

"Were you dreaming?"

He asked:

"What was going through your mind?"

This is important because the way researchers define dreaming influences how they measure it.

What are the different varieties of dream experiences?

Type	Definition
Hypnagogic	Experiences occurring during sleep onset
Hypnopompic	Experiences occurring upon awakening
NREM short dreams	Brief thoughts and images
REM dreams	Vivid, immersive experiences with spatial and temporal organization
Nightmares	Intensified, distressing dreams
Epic dreams	Intensified, elaborate dreams
Lucid dreams	Dreams in which the dreamer is aware they are dreaming
Sleep paralysis	Mixed sleep-wake state involving temporary inability to move
Sleepwalking	Mixed sleep-wake state involving sleep-related motor behaviour

What happens in early night N3?

sleepwalking and night terrors

What happens in NREM?

short, thought-like → recall = 43%

What happens in REM?

vivid, immersive dreams, nightmares, lucid dreams → recall = 80%

What happens in late night NREM?

more dream-like

What happens in REM to wake transition?

sleep paralysis

What happens upon awakening?

hypnopompic imagery

What is the percentage recall in each stage?

N1: 88%

N2: 56%

N3: 48%

REM: 81%

• but just because recall is experience doesn’t guarantee that content will be recalled

What are the 3 different answers a researcher can receive after waking up?

Report category	Example	What it tells us
Experience with content	"I was walking through a city."	Experience and content are accessible
Experience without content	"I was dreaming, but I lost it."	Sense of experience survives
No experience reported	"Nothing was going through my mind."	Could indicate no experience OR forgetting

What was the question behind the Hobson vs Solms debate?

Is dreaming a by-product of REM sleep, or is dreaming generated by the forebrain and REM is simply one possible trigger?

What did Hobson propose?

the activation-synthesis theory → Hobson proposed that dreaming is driven by REM sleep physiology.

What were the main ideas of Hobsons theory?

• Dreaming originates from the pontine brainstem.

• REM-on cells activate during REM sleep.

• PGO waves are involved.

• The forebrain receives internally generated signals and attempts to make sense of them.

• The cortex synthesizes these signals into a dream experience

Key idea: Dreams are the brain's attempt to make sense of internally generated neural activation

Bottom up model because activation begins in the brainstem and moves up to the cortex

What does Hobsons theory explain?

• vivid imagery

• flying, falling

• scene shifts

• bizarre, uncritical

• quickly forgotten

What is the AIM model that Hobson later developed?

Letter	Meaning	What it refers to
A	Activation	How active the brain is
I	Input source	External or internally generated information
M	Modulation	Neurochemical environment Aminergic activity: noradrenaline and serotonin Cholinergic activity: acetylcholine

• Wakefulness and REM are both highly activated.

• They differ in their input source and neurochemical environment.

• Lucid dreaming is positioned between REM and wakefulness in the model

What did Solms claim?

• The brainstem switches REM sleep on.

• However, dreaming requires the forebrain's dopaminergic "seeking" circuits.

• REM is only one possible trigger of dreaming.

This is a top-down model because the forebrain is central to generating dreams

What evidence supports Solms claims?

1. L-DOPA in Parkinson's patients: L-DOPA can intensify dreaming.

2. Frontal leucotomy: Damage or disconnection involving frontal regions can abolish dreaming.

What survives from freud?

Solms maintains that dreams are motivated by wishes and needs.

He connects dreaming to the brain's reward system and appetitive motivation

What are the weaknesses in Hobsons theory?

• Vivid dreams can occur during NREM.

• Some people lose dreaming while retaining normal REM sleep

What are the weaknesses in Solms theory?

• The theory predicts that REM could be lost while dreaming remains intact.

• This other half of the proposed double dissociation has never been directly tested

What is the covert REM theory?

• Nielsen proposed the Covert REM (C-REM) theory to reconcile the opposing ideas of Hobson and Solms

• Some dreams occurring during NREM sleep may be explained by the presence of REM-like elements within NREM

In other words:

• REM is not necessarily a completely separate, distinct state.

• REM characteristics can exist along a continuum.

• Elements of REM can appear during other sleep stages.

• These REM-like features may be associated with mental activity

What are the predictions of the Covert REM theory?

NREM sleep accompanied by dream recall should contain more REM-like features, such as:

• Muscle atonia.

• Eye movements.

• Other characteristics associated with REM sleep

What was the evidence for Nielsens theory?

• Participants underwent partial REM sleep deprivation.

• Researchers examined the quality of mental activity at sleep onset (N1).

• Following REM deprivation, mental activity in N1 became more dream-like.

• This was interpreted as REM sleep rebound occurring in N1.

What is the posterior Hot Zone?

refers to posterior cortical regions associated with conscious dream experience.

What were the findings of the posterior hot zone?

• Dream reports were associated with decreased low-frequency activity in posterior cortical areas.

• There was a corresponding increase in high-frequency activity.

• This occurred in BOTH REM and NREM sleep

What is the dream content map?

the content of the dream is related to the brain regions activated during the experience.

Where does each dream content light up what brain region?

Dream content	Associated brain region
Thought-like dreams	Frontal regions
Perceptual dreams	Posterior regions
Human faces	Fusiform area
Spatial experiences	Posterior parietal areas
Movement	Superior temporal sulcus
Language	Wernicke area

What is EEG activity like before recall?

less alpha, less delta in N2 and REM

in N2 → less delta over left frontal and temporo-parietal areas

What is the predictor for each stage?

Sleep stage	EEG finding associated with dreaming
N1	Dream imagery (compared with thinking) associated with more power below 7 Hz
N2	Dreaming associated with less power below 1 Hz and more power above 4 Hz
REM	No EEG predictor was found

Do EEG markers of dream recall replicate?

• One signal recurs: less delta activity before dream recall in NREM.

• This finding appeared in 5 out of 10 studies.

• In REM, no EEG frequency band consistently agreed across studies

What is the issue with the consistency of EEG markers?

Researchers often compare:

• People who report remembering a dream.

• People who report no dream.

However, this is NOT necessarily the same as comparing:

• People who were dreaming.

• People who were not dreaming.

Can we read dreaming from the EEG?

The EEG predicts dream reports better than chance, but accuracy is not reliable enough to determine whether an individual was dreaming at every awakening