<p>Short answer: Because areas of the brain needed for remembering are turned off during dreaming.</p>

<p><strong>Dream Amnesia:</strong></p>

<p>The process of converting perception into a memory construct that can be stored is called <a href="https://en.wikipedia.org/wiki/Encoding_%28memory%29">encoding</a>, and is <a href="http://www.sciencedirect.com/science/article/pii/S0166432811007492">essentially the same</a> during both wakefulness and sleep: That is, the same factors can hamper or promote successful encoding when awake or dreaming.  During sleep, the brain undergoes <a href="https://en.wikipedia.org/wiki/Sleep#Stages">cyclical changes</a> in which <a href="http://cat.inist.fr/?aModele=afficheN&amp;cpsidt=17518007">activity in some parts</a> of the brain increases (hyperactive), while other areas decrease in activity (hypoactive).  Some areas of the brain associated with memory encoding are <a href="http://www.ncbi.nlm.nih.gov/pubmed/16186026">hypoactive during dreaming</a>, resulting in most dreams being forgotten.</p>

<p><a href="https://i.sstatic.net/8fcea.jpg"><img src="https://i.sstatic.net/8fcea.jpg" alt="enter image description here"></a>
Red = hyperactive; Blue = hypoactive; F = prefrontal cortex</p>

<p>The most prominent area implicated in memory encoding of <a href="https://en.wikipedia.org/wiki/Episodic_memory#Cognitive_neuroscience">episodic memories</a> is the prefrontal cortex (PFC).  Activity in this region is correlated with memory in studies conducted in awake subjects, and is similarly correlated with dream amnesia: During dreaming, this area is typically hypoactive (turned off), and its level of activity is <a href="https://books.google.ca/books/about/The_Neuropsychology_of_Dreams.html?id=XebaAAAAMAAJ">predictive of dream recall</a>.  Activity in the PFC during sleep may be modulated by levels of <a href="http://www.sciencedirect.com/science/article/pii/S1364661302019927">acetylcholine</a>, <a href="http://www.ncbi.nlm.nih.gov/pubmed/17275369">dopamine</a>, and <a href="http://onlinelibrary.wiley.com/doi/10.1002/jnr.20602/abstract?userIsAuthenticated=false&amp;deniedAccessCustomisedMessage=">other neurotransmitters</a>.</p>

<p><strong>Vanishing Memory:</strong></p>

<p><a href="http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2814941/">Nir &amp; Tononi (2010)</a> review the issue:</p>

<blockquote>
  <p>Unless the dreamer wakes up, most dreams are forever lost. Upon
  awakening, memory for the dream often vanishes rapidly unless written
  down or recorded, even for intense emotional dreams. It is not clear
  why this is the case since from a neuroimaging perspective, limbic
  circuits in the medial temporal lobe that are implicated in memory
  processes, are highly active during REM sleep. Perhaps the
  hypoactivity of prefrontal cortex, also implicated in mnemonic
  processes, plays an important role in dream amnesia.</p>
</blockquote>

<p>Theoretically, waking up reactivates the areas of the brain that are turned off during sleep, allowing for memories to be encoded.  This process is unreliable, as memory encoding in both awake and sleeping subjects is modulated by attention - also a function of the PFC - so how much and how well dream content is remembered also depends on how much attention is given to it during waking.  Without attention, the memory trace fades quickly.  This interpretation is consistent with the <a href="http://psycnet.apa.org/psycinfo/2007-09896-004">reduced dream recall</a> in awakenings from deep (slow-wave) sleep, that are characterized by disorientation and lower PFC activity, and with <a href="http://psycnet.apa.org/journals/drm/16/1/22/">higher dream recall</a> of <a href="https://en.wikipedia.org/wiki/Lucid_dream#Awareness_and_reasoning">lucid dreaming</a>, characterized by awareness, control, and <a href="http://www.sciencedirect.com/science/article/pii/S1053810013001098">higher PFC activity</a>.</p>

<p>Note: The above is certainly an over-simplification of a complex and poorly understood system, but it does suggest that any factor affecting the processes involved in memory encoding and attention (such as certain neurotransmitters, psychoactive drugs, lesions, mood disorders, training, experience, etc) may impact dream recall.  On the other hand, NMDA, a neurotransmitter involved in long-term memory consolidation (LTP) - a different <a href="https://en.wikipedia.org/wiki/Memory_consolidation#Sleep_consolidation">activity that is increased</a> (hyperactive) during dreaming - is less likely to be implicated in dream amnesia.</p>

CC BY-SA 3.0
2015-09-26T22:19:06.603Z
2015-09-27T20:59:52.987Z
2015-09-27T20:59:52.987Z
Arnon Weinberg
<p><a href="https://en.wikipedia.org/wiki/State-dependent_memory" rel="nofollow noreferrer">State dependent memory</a> could play a role in quickly forgetting dreams after awakening.</p>

<p>See my question here: <a href="https://cogsci.stackexchange.com/questions/2034/what-is-the-scientific-term-for-unexpected-spontaneous-dream-recall">What is the scientific term for unexpected, spontaneous dream recall?</a> I ask about a phenomenon where dream recall happens much later potentially weeks or months after awakening. </p>

<p>I would venture to hypothesize that <strong><a href="https://en.wikipedia.org/wiki/Melatonin#Dreaming" rel="nofollow noreferrer">Melatonin</a></strong> might play a role as a state dependent cue that alters the state of memory for recall. Melatonin supplementation can produce extraordinarily vivid dreams that rapidly lose their grandeur upon awakening and subsequent recall. </p>

<p>Personally I take a melatonin supplement at night and can drift off to sleep while recalling dozens of dreams (seems to correlate with melatonin levels rising). My understanding is that Melatonin is suppressed by blue light, so bright lights in the morning may rapidly reduce melatonin concentration and hamper recall. </p>

CC BY-SA 3.0
2015-09-21T19:38:38.200Z
Interesting, maybe one can combine Melatonin with vitamin B6. I just posted an answer with an interesting reference [here](http://cogsci.stackexchange.com/a/12232/370)...
draks ...
CC BY-SA 3.0
2016-01-31T16:03:02.687Z
How much do you take?
draks ...
CC BY-SA 3.0
2016-02-02T14:10:46.513Z
@draks... 3mg is a standard dose sold in the US.
Alex Stone
CC BY-SA 3.0
2015-09-21T19:32:46.367Z
2015-09-21T19:32:46.367Z
2017-04-13T12:56:16.417Z
Alex Stone
<p>My suggestion would be that, as with all forms of mental imagery, short-term working memory circuits are responsible for keeping dreamt images active, i.e. in consciousness. Distraction by competing perceptual representations would cause immediate disruption of one's dreamt images; without such distraction, imagery in short-term memory typically starts to rapidly fade after about 8 seconds, unless it's highly relevant to one's immediate situation on waking, and hence promptly acted on. </p>

CC BY-SA 3.0
2014-09-08T12:24:42.663Z
Welcome to cogsci.SE!  Citations and links to back up specific claims and provide the asker with further reading will make your answer more useful.
Krysta
CC BY-SA 3.0
2014-09-08T01:03:16.673Z
2014-09-08T01:03:16.673Z
RichT
<p>Right after you wake up from a dream, you seem to be able to remember most if not all of the details.  Then, over time, these details fade and often disappear.</p>

<p>Is this a form of regression?  Why is it harder to solidify memories of dreams?</p>

CC BY-SA 3.0
2014-08-05T13:13:39.170Z
The original reference on this subject seems to be L.A. Strümpell, *Die Natur und Entstehung der Träume* (1877). You can read S. Freud comments and reference additions in *The Interpretation of Dreams* (1899), and especially the section "*Why Dreams Are Forgotten After Waking*".
Guillaume Ansanay-Alex
CC BY-SA 3.0
2014-08-05T14:29:04.683Z
In case I don't manage to find the time to dig up the reference (I have it somewhere on an external disk, no idea who the authors are): a neurotransmitter that is crucial for transforming short-term into long-term memories is inactive in the hippocampus during sleep. Interestingly, HM, a patient who couldn't achieve long-term memories due to an operation when both hippocampi were removed, described his state as constantly waking from a dream.
Ana
CC BY-SA 3.0
2015-09-14T18:53:14.070Z
@Ana which neurotransmitter is that? Serotonin?
draks ...
CC BY-SA 3.0
2015-09-14T19:47:53.710Z
@draks... - argh, I guess I never looked it up. I believe it was NMDA.
Ana
CC BY-SA 3.0
2015-09-21T18:46:48.407Z
@Ana maybe a bounty could help your weakened memory. No offense, pun intended. Cheers...
draks ...
CC BY-SA 3.0
2015-10-12T07:49:51.547Z
@Ana looks like Arnon opposes your NMDA hypothesis. What do you think?
draks ...
<memory><consciousness><dreams>
Why do dreams lose clarity quickly over time after we awaken?
CheeseConQueso
# Why do dreams lose clarity quickly over time after we awaken?

(Asked by: username_0 on 2014-08-03)

Right after you wake up from a dream, you seem to be able to remember most if not all of the details. Then, over time, these details fade and often disappear.

Is this a form of regression? Why is it harder to solidify memories of dreams?

**Tags:** memory, consciousness, dreams

> **Comments:**
> **username_1**: The original reference on this subject seems to be L.A. Strümpell, *Die Natur und Entstehung der Träume* (1877). You can read S. Freud comments and reference additions in *The Interpretation of Dreams* (1899), and especially the section "*Why Dreams Are Forgotten After Waking*".  
> **username_2**: In case I don't manage to find the time to dig up the reference (I have it somewhere on an external disk, no idea who the authors are): a neurotransmitter that is crucial for transforming short-term into long-term memories is inactive in the hippocampus during sleep. Interestingly, HM, a patient who couldn't achieve long-term memories due to an operation when both hippocampi were removed, described his state as constantly waking from a dream.  
> **username_3**: @username_2 which neurotransmitter is that? Serotonin?  
> **username_2**: @draks... - argh, I guess I never looked it up. I believe it was NMDA.  
> **username_3**: @username_2 maybe a bounty could help your weakened memory. No offense, pun intended. Cheers...  
> **username_3**: @username_2 looks like Arnon opposes your NMDA hypothesis. What do you think?  

---

## 3 answers

### Answer by username_4 on 2015-09-26. Score: 16

Short answer: Because areas of the brain needed for remembering are turned off during dreaming.

**Dream Amnesia:**

The process of converting perception into a memory construct that can be stored is called [encoding](https://en.wikipedia.org/wiki/Encoding_%28memory%29), and is [essentially the same](http://www.sciencedirect.com/science/article/pii/S0166432811007492) during both wakefulness and sleep: That is, the same factors can hamper or promote successful encoding when awake or dreaming. During sleep, the brain undergoes [cyclical changes](https://en.wikipedia.org/wiki/Sleep#Stages) in which [activity in some parts](http://cat.inist.fr/?aModele=afficheN&cpsidt=17518007) of the brain increases (hyperactive), while other areas decrease in activity (hypoactive). Some areas of the brain associated with memory encoding are [hypoactive during dreaming](http://www.ncbi.nlm.nih.gov/pubmed/16186026), resulting in most dreams being forgotten.

[![enter image description here](https://i.sstatic.net/8fcea.jpg)](https://i.sstatic.net/8fcea.jpg)
Red = hyperactive; Blue = hypoactive; F = prefrontal cortex

The most prominent area implicated in memory encoding of [episodic memories](https://en.wikipedia.org/wiki/Episodic_memory#Cognitive_neuroscience) is the prefrontal cortex (PFC). Activity in this region is correlated with memory in studies conducted in awake subjects, and is similarly correlated with dream amnesia: During dreaming, this area is typically hypoactive (turned off), and its level of activity is [predictive of dream recall](https://books.google.ca/books/about/The_Neuropsychology_of_Dreams.html?id=XebaAAAAMAAJ). Activity in the PFC during sleep may be modulated by levels of [acetylcholine](http://www.sciencedirect.com/science/article/pii/S1364661302019927), [dopamine](http://www.ncbi.nlm.nih.gov/pubmed/17275369), and [other neurotransmitters](http://onlinelibrary.wiley.com/doi/10.1002/jnr.20602/abstract?userIsAuthenticated=false&deniedAccessCustomisedMessage=).

**Vanishing Memory:**

[Nir & Tononi (2010)](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2814941/) review the issue:

> Unless the dreamer wakes up, most dreams are forever lost. Upon
> awakening, memory for the dream often vanishes rapidly unless written
> down or recorded, even for intense emotional dreams. It is not clear
> why this is the case since from a neuroimaging perspective, limbic
> circuits in the medial temporal lobe that are implicated in memory
> processes, are highly active during REM sleep. Perhaps the
> hypoactivity of prefrontal cortex, also implicated in mnemonic
> processes, plays an important role in dream amnesia.

Theoretically, waking up reactivates the areas of the brain that are turned off during sleep, allowing for memories to be encoded. This process is unreliable, as memory encoding in both awake and sleeping subjects is modulated by attention - also a function of the PFC - so how much and how well dream content is remembered also depends on how much attention is given to it during waking. Without attention, the memory trace fades quickly. This interpretation is consistent with the [reduced dream recall](http://psycnet.apa.org/psycinfo/2007-09896-004) in awakenings from deep (slow-wave) sleep, that are characterized by disorientation and lower PFC activity, and with [higher dream recall](http://psycnet.apa.org/journals/drm/16/1/22/) of [lucid dreaming](https://en.wikipedia.org/wiki/Lucid_dream#Awareness_and_reasoning), characterized by awareness, control, and [higher PFC activity](http://www.sciencedirect.com/science/article/pii/S1053810013001098).

Note: The above is certainly an over-simplification of a complex and poorly understood system, but it does suggest that any factor affecting the processes involved in memory encoding and attention (such as certain neurotransmitters, psychoactive drugs, lesions, mood disorders, training, experience, etc) may impact dream recall. On the other hand, NMDA, a neurotransmitter involved in long-term memory consolidation (LTP) - a different [activity that is increased](https://en.wikipedia.org/wiki/Memory_consolidation#Sleep_consolidation) (hyperactive) during dreaming - is less likely to be implicated in dream amnesia.


---

### Answer by username_5 on 2015-09-21. Score: 7

[State dependent memory](https://en.wikipedia.org/wiki/State-dependent_memory) could play a role in quickly forgetting dreams after awakening.

See my question here: [What is the scientific term for unexpected, spontaneous dream recall?](https://cogsci.stackexchange.com/questions/2034/what-is-the-scientific-term-for-unexpected-spontaneous-dream-recall) I ask about a phenomenon where dream recall happens much later potentially weeks or months after awakening.

I would venture to hypothesize that **[Melatonin](https://en.wikipedia.org/wiki/Melatonin#Dreaming)** might play a role as a state dependent cue that alters the state of memory for recall. Melatonin supplementation can produce extraordinarily vivid dreams that rapidly lose their grandeur upon awakening and subsequent recall.

Personally I take a melatonin supplement at night and can drift off to sleep while recalling dozens of dreams (seems to correlate with melatonin levels rising). My understanding is that Melatonin is suppressed by blue light, so bright lights in the morning may rapidly reduce melatonin concentration and hamper recall.

> **Comments:**
> **username_3**: Interesting, maybe one can combine Melatonin with vitamin B6. I just posted an answer with an interesting reference [here](http://cogsci.stackexchange.com/a/12232/370)...  
> **username_3**: How much do you take?  
> **username_5**: @draks... 3mg is a standard dose sold in the US.  

---

### Answer by username_6 on 2014-09-08. Score: 2

My suggestion would be that, as with all forms of mental imagery, short-term working memory circuits are responsible for keeping dreamt images active, i.e. in consciousness. Distraction by competing perceptual representations would cause immediate disruption of one's dreamt images; without such distraction, imagery in short-term memory typically starts to rapidly fade after about 8 seconds, unless it's highly relevant to one's immediate situation on waking, and hence promptly acted on.

> **Comments:**
> **username_7**: Welcome to cogsci.SE!  Citations and links to back up specific claims and provide the asker with further reading will make your answer more useful.  

---

