Happy Atheist Forum

My first post in the Science section!
Anyways...

For a while, I've been fascinated with dreaming, and I used to believe that the particular events that occur in dreams had some profound meaning ( I don't anymore). Moreover, I've briefly looked up dreaming and there are different theories on the intrinsic function of it, such as: activation synthesis, or continual-activation. From what I know, I don't think that there is only one theory agreed upon.

MY question(s) is....what do you guys think about the subject? Why do we dream? Is there some type of biological benefit?  Is it the brain's way of maintaining some form of conciousness while we sleep?

I think it's the file-clean up preceding a defrag, done to maintain sufficient system memory.

Wonder what my PC dreams about when I /cleanup it...  

But I do agree in a way. I think it's a side effect of the brain doing a sort of self-analysis.

My brother is a neuroscientist that specializes in sleep research, I should get him to post here.  In my discussions with him, he stresses the enormous amount that is still unknown regarding the purpose of sleep functions, but he speculates that part of it has to do with memory consolidation - specifically the pruning of weaker associative connections that are likely to be unused.  

As I understand it, there is a great deal of research indicating that the brain, during waking hours, accumulates far more information, in the form of memories, than it can feasibly store in the long term, and it must decide what to consolidate into long-term memory, and what to dispense with.  No one is yet sure how this specifically relates to dreaming, per se, but that is one of the known functions of sleep.  This is partly why your performance on memory and concentration tasks will be impaired without regular intervals of rest.

^^^ interesting. If your brother does have the time to contribute it would be much appreciated.

Quote from: "Tank"^^^ interesting. If your brother does have the time to contribute it would be much appreciated.

I'm trying to bait him into posting....

Quote from: "The Black Jester"My brother is a neuroscientist that specializes in sleep research, I should get him to post here.  In my discussions with him, he stresses the enormous amount that is still unknown regarding the purpose of sleep functions, but he speculates that part of it has to do with memory consolidation - specifically the pruning of weaker associative connections that are likely to be unused.  

As I understand it, there is a great deal of research indicating that the brain, during waking hours, accumulates far more information, in the form of memories, than it can feasibly store in the long term, and it must decide what to consolidate into long-term memory, and what to dispense with.  No one is yet sure how this specifically relates to dreaming, per se, but that is one of the known functions of sleep.  This is partly why your performance on memory and concentration tasks will be impaired without regular intervals of rest.

Yes, most psychologists tend to believe it is a function of memory consolidation during REM Sleep.  When the brain is activating and deactivating different sections of the hippocampus to clean up our memory, we experience the activated memories as dreams.  The mind puts all the little things from our day (things you didn't know you were remembering, your mind picked up every little sight and sound from the day) into a coherent story of some sort, as a sort of test if the memory is functioning, and therefore, keepable.  That's also why we don't usually remember our dreams.  People dream 80% of all nights, but only remember about 15% of their dreams.  This lends support to the Memory Consolidation Theory.  But, when people are woken from REM sleep, they do remember what their dream was.

Fun Fact: Your dreams aren't chronological events.  Studies have shown that no matter how long a subject is in REM sleep, they always wake up remembering dreams of the same length and detail.  That's because after all the memories are 'tested,' and activated, the entire dream has been put together.  Experiencing a dream as a chronological story is an illusion, really, the whole dream is already put together from the start, and you are already experiencing the whole thing!  Have you ever been woken up from a dream before it ended, and been mad at the one who woke you up because you wanted to know how it ended?  If so, that was wrong, you HAD dreamed the dream to the end, from the very beginning.

I used to think dreams had meaning too, until I took Psych 2201.  I once had a very very long dream, that detailed me, being diagnosed with cancer, and slowly withering away (It doesn't mean anything when you die in your dreams.)  When I woke up from it I realized 2 things.  ONE: Even though I had perceived the event as taking place over a few days, it had only been 3 hours since I fell asleep.  TWO: Right before I fell asleep, there had been a commercial on for a Cancer Treatment Center.  I also realized I had an odd lump on the back of my head, maybe I should get that checked out...

Quote from: "KebertX"I also realized I had an odd lump on the back of my head, maybe I should get that checked out...

... or at least avoid dark alleys ...

Quote from: "The Black Jester"My brother is a neuroscientist that specializes in sleep research, I should get him to post here.  In my discussions with him, he stresses the enormous amount that is still unknown regarding the purpose of sleep functions, but he speculates that part of it has to do with memory consolidation - specifically the pruning of weaker associative connections that are likely to be unused.  

As I understand it, there is a great deal of research indicating that the brain, during waking hours, accumulates far more information, in the form of memories, than it can feasibly store in the long term, and it must decide what to consolidate into long-term memory, and what to dispense with.  No one is yet sure how this specifically relates to dreaming, per se, but that is one of the known functions of sleep.  This is partly why your performance on memory and concentration tasks will be impaired without regular intervals of rest.

Interesting...I hope your brother does post though! . Yea, recently, I've been remembering quite a few dreams lately, I just wanted to know the function of it. I guess the brain consolidating memory makes sense. The brain is an amazing organ!

Quote from: "The Black Jester"My brother is a neuroscientist that specializes in sleep research, I should get him to post here.  In my discussions with him, he stresses the enormous amount that is still unknown regarding the purpose of sleep functions, but he speculates that part of it has to do with memory consolidation - specifically the pruning of weaker associative connections that are likely to be unused.  

As I understand it, there is a great deal of research indicating that the brain, during waking hours, accumulates far more information, in the form of memories, than it can feasibly store in the long term, and it must decide what to consolidate into long-term memory, and what to dispense with.  No one is yet sure how this specifically relates to dreaming, per se, but that is one of the known functions of sleep.  This is partly why your performance on memory and concentration tasks will be impaired without regular intervals of rest.

So he's suggesting that dreams are the product of the brain essentially defragging?  That's awesome!

Quote from: "Cite134"MY question(s) is....what do you guys think about the subject? Why do we dream? Is there some type of biological benefit?  Is it the brain's way of maintaining some form of conciousness while we sleep?

So this is NORMAL dreaming, right..... not sleep disorder dreaming, like say night terrors or sleep paralysis?  

Cause my view on normal dreaming is pretty much what Thumpalumpacus said.  The other stuff.... well let's not go there.....

Hello, I am the aforementioned brother of The Black Jester who posted on Dreaming.  He asked me to give my thoughts on the matter, so I will do my best.  First, I'd like to give a spoiler.  I am, indeed, a neuroscientist, and I do have a background in human sleep research.  But, I am not an expert in dreaming, per se.  That is another section of the sleep field, one which has a lot of controversy with it.  There are, as some have mentioned already, a lot of theories about the "purpose" of dreams.  They range from dreams as being an epiphenomena to being relevant to memory functions to relevant to emotional regulation to relevant to consciousness.  

Before I talk about my understanding of dreams as a sleep neuroscientist, I feel there are a few things I must clarify first.  One, dreams are very heterogeneous.  There are many kinds and many forms.  This may seem pretty obvious, but it needs to be stated.  Dreams can vary from brief transient thoughts during sleep to full fledged active dreams to experiencing passive scenes.  Many have strayed away from the word dreams towards 'sleep mentation', basically thoughts you have while asleep.  These thoughts can take shape as full fledged dreams, but also as passive thoughts.  What kinds of mentation you experience really depends on what time of  night and what stage of sleep you are in.  That brings me to the second point I want to make.  Dreams is not equal to REM sleep.  Not all REM sleep is full of dreams and not all dreams come from REM sleep.  They are related, to be sure, and dreams in REM sleep are the most active most intense and most memorable.  But there is more in heaven and earth than is dreamt up in REM sleep.  he he.  Sorry, I have a bad sense of humor sometimes.  

I would not say that dreams function to prune connections or to 'defrag'.  Nor would I say that they are principally functionless,  or that they are principally associated with memory consolidation...exactly.  The role of REM sleep in memory consolidation is a bit mixed at the moment.  Evidence is emerging and some much older work from the 60s support such a role, but there is still a lot of controversy.  I will get back to that later.  

Perhaps what I should start with is what I do know about dreams.  It has been established that dreams are affected by daytime experience.  One person posted their dream was meaningless because it was about cancer and cancer was in an ad they saw before bed.  There is a study that was conducted at Harvard by Bob Stickgold back in the late 90s.  He had a bunch of people play tetris for the first time (really hard to recruit for by the way, as most people had already played tetris).  He then looked at dream reports.  This all took place in the first 3 minutes of sleep, so this was definitely not REM sleep related dreams.  What they reported was seeing blocks moving down and manipulating them.  They didn't see the computer or the room they performed the testing in.  They just saw the pieces falling down.  Some of you may have experienced this at one time or another when you play a video game for the first time.  I know I have.  So we know that at least some dreams are affected by daytime experience.  The same experiment was carried out by waking people up from REM sleep.  The dream content was a lot more associative and a lot more disconnected from the tetris, but it was related.  So REM was affected by daytime experience as well.  Some people may think this means that dreams are meaningless.  I would argue just the opposite.  The same group, just recently published a paper showing that those who learned a 3d maze, much like those seen in first person shooters, if they would dream about it at all at night, they would perform significantly better the next day.  Those that did not dream of it, did not.  I haven't looked over the paper super closely, so I don't know if this was independent of sleep stage or dependent on sleep stage.  This is important, because if it was correlated with a sleep stage, like REM, for example, one could argue dreaming didn't cause the improvement, just the physiology of REM did.  If you spend more time in REM you are also more likely to dream about it.  So it would be more association than causation.  Whereas if it was not, whatever processes going on in the brain during 'dreaming' would then be necessary to improve navigation on this task.  But how would dreaming do this?  That just leads to speculation, but sleep and REM sleep in particular has been associated with more than just memory consolidation.  In fact, the relationships between sleep and memory is very complicated.  Probably because sleep isn't just about memory, and memories themselves are very complicated.

Lets look at memory as a whole for starters.  We have many different kinds of memories.  We have episodic memories: our experiences throughout the day, memories of space and time and association.  These are particularly hippocampally dependent.  And these memories are aided by sleep.  But the story isn't one of REM.  It is actually more of a NREM story, and there is a mountain of evidence in support of this now in animals and in humans.  Specifically, oscillations in NREM sleep, slow waves and sleep spindles, are associated with facilitating consolidation and encoding of declarative, hippocampally dependent memories.  These oscillations have been associated with being linked to hippocampal-neocortical crosstalk, and this cross-talk is thought to transform memories from being hippocampally dependent to being cortically dependent.  That is one theory.  Another theory is that slow oscillations globally downscale synapses, pruning away unnecessary ones and preserving strong ones.  The relative weights of synapses are preserved and signal to noise ratio is imporved since you knocked out all the weakest ones.  This is more of a memory side-benefit of a process more designed to manage the memory demands of the brain.  These two theories are not incompatible, and there is a lot of evidence to support both.  And both implicate NREM sleep, not REM sleep in this process.  

So REM isn't really as associated with hippocampal-dependent consolidation much anymore, though it was in the 60s with all the rat experiments.  The trick is, those experiments often had an emotional component or a reward component.  This makes it more like conditioning, which relies on a different neural network and might be more REM-dependent.  There is evidence in humans now that emotional memories are tied to REM sleep and not NREM sleep.  Additionally, other more procedural forms of memory that are less dependent on the hippocampus, such as learning to ride a bike or type on a keyboard or hit a baseball, are dependent on either NREM sleep or a combination of NREM and REM sleep.  So different forms of learning, which require different neural systems, will rely on different physiological brain states in sleep.  And, more specifically, they will all rely on different oscillations occuring in each of these sleep stages.  So, in short, it's complicated.  To complicate it further, sleep isn't just about memory, but is also involved with neurometabolic, immune, and hormonal regulation.  In the memory domain, sleep isn't just about consolidation.  Sleep also facilitates next day encoding ability, integration of memories, and abstraction of general knowledge from memories which facilitates insight into problems the next day.

Much of these latter abilities (integration, abstraction, emotional processing) are tied to REM in some manner.  Which makes me think that REM isn't important for weakening associations between unnecessary items, but instead would strengthen more weakly associated items that prove helpful.

But this isn't dreams, this is sleep.  And, as I have said before, REM does not equal dreaming.  There are a lot of theories about dreaming out there.  Some more psychoanalytic, some more memory related, some more emotion regulation, and some more 'its all garbage, and epiphenomenon with no meaning'.  I really don't think it is the latter.  I just don't think the evidence out there supports it (only some of which I have talked about in this post).  Dreaming is associated with eye movements, which are associated with brain activity in areas associated with mental imagery.  Dreaming is affected by previous waking experience and predicts next day behavior.  Dreaming, or at least REM sleep dreaming, has been associated with emotion regulation, consolidating emotional memories, and facilitating problem solving the next day.  In this way, psychoanalytic, memory, and emotion regulation theories could all be correct in some fashion.  In the end, all these functions serve to enhance adaptability, which is very important from an evolutionary perspective.  

My current advisor (I am a post doc right now) has a theory about REM sleep.  He calls it the 'sleep to remember, sleep to forget' hypothesis.  He is primarily a memory researcher, and he likes to think of emotional memories as containing multiple forms of information.  You have the visceral-physical, emotional response.  But you also have the details of the experience.  In the end, what is most adaptive is to actually remember the emotional experience, even if it was traumatic.  What you want to do is instead forget the emotional, viscerl, physical response, so that every time you think on the memory you don't regurgitate the emotional intensity you did the first time.  He posits REM sleep does just this by stripping away the emotional component and strengthening the memory component.  REM is then important to deconstruct experiences and extract meaning from them to remember what is most important.  Or perhaps to learn what is most important.  There is some evidence for this in that sleep will enhance specific components of a memory and not all of them.  Emotional pieces of a scene are more remembered than their neutral counterparts.  So sleep isn't like justice, it prioritizes based on what may be most adaptive.

My boss posits that this breaks down, or fails to happen in patients with PTSD.  You can see this in that their REM dreams are less associative and weird, and more like direct replays of the trauma.  He thinks there is some process in sleep that is failing to do its job.  When done correctly, the emotional side would be separated and forgotten, whereas the knowledge one could learn is consolidated and integrated into your general knowledge base.  Take, as an example, you walk down a new path and get bitten by a snake.  You want to remember that this path is bad in the future.  You don't want to shiver and sweat and feel stressed and scarred everytime you think of that path.  That is the essence of sleep to remember, sleep to forget.  

Completely separate from memory, sleep, and particularly REM sleep, is associated with modulating your reactivity to emotional events.  As the day wears on, you find things more negative and angry, and less happy.  If you are provided a nap, this bias goes away, so sleep is important for more than just memory.  Sleep, instead, seems to be important for regulating a lot of the functions in your body from immune, to metabolic, to cognitive and emotive (not just memory in the cognitive domain either).  So I don't know if I answered any questions or created any, but I did ramble on a bit.  I think that, more than anything, proves I am an academic.

Sigh.  I love my brother....

Quote from: "LittleTheBlackJester"Hello, I am the aforementioned brother of The Black Jester who posted on Dreaming.  He asked me to give my thoughts on the matter, so I will do my best.  First, I'd like to give a spoiler.  I am, indeed, a neuroscientist, and I do have a background in human sleep research.  But, I am not an expert in dreaming, per se.  That is another section of the sleep field, one which has a lot of controversy with it.  There are, as some have mentioned already, a lot of theories about the "purpose" of dreams.  They range from dreams as being an epiphenomena to being relevant to memory functions to relevant to emotional regulation to relevant to consciousness.  

Before I talk about my understanding of dreams as a sleep neuroscientist, I feel there are a few things I must clarify first.  One, dreams are very heterogeneous.  There are many kinds and many forms.  This may seem pretty obvious, but it needs to be stated.  Dreams can vary from brief transient thoughts during sleep to full fledged active dreams to experiencing passive scenes.  Many have strayed away from the word dreams towards 'sleep mentation', basically thoughts you have while asleep.  These thoughts can take shape as full fledged dreams, but also as passive thoughts.  What kinds of mentation you experience really depends on what time of  night and what stage of sleep you are in.  That brings me to the second point I want to make.  Dreams is not equal to REM sleep.  Not all REM sleep is full of dreams and not all dreams come from REM sleep.  They are related, to be sure, and dreams in REM sleep are the most active most intense and most memorable.  But there is more in heaven and earth than is dreamt up in REM sleep.  he he.  Sorry, I have a bad sense of humor sometimes.  

I would not say that dreams function to prune connections or to 'defrag'.  Nor would I say that they are principally functionless,  or that they are principally associated with memory consolidation...exactly.  The role of REM sleep in memory consolidation is a bit mixed at the moment.  Evidence is emerging and some much older work from the 60s support such a role, but there is still a lot of controversy.  I will get back to that later.  

Perhaps what I should start with is what I do know about dreams.  It has been established that dreams are affected by daytime experience.  One person posted their dream was meaningless because it was about cancer and cancer was in an ad they saw before bed.  There is a study that was conducted at Harvard by Bob Stickgold back in the late 90s.  He had a bunch of people play tetris for the first time (really hard to recruit for by the way, as most people had already played tetris).  He then looked at dream reports.  This all took place in the first 3 minutes of sleep, so this was definitely not REM sleep related dreams.  What they reported was seeing blocks moving down and manipulating them.  They didn't see the computer or the room they performed the testing in.  They just saw the pieces falling down.  Some of you may have experienced this at one time or another when you play a video game for the first time.  I know I have.  So we know that at least some dreams are affected by daytime experience.  The same experiment was carried out by waking people up from REM sleep.  The dream content was a lot more associative and a lot more disconnected from the tetris, but it was related.  So REM was affected by daytime experience as well.  Some people may think this means that dreams are meaningless.  I would argue just the opposite.  The same group, just recently published a paper showing that those who learned a 3d maze, much like those seen in first person shooters, if they would dream about it at all at night, they would perform significantly better the next day.  Those that did not dream of it, did not.  I haven't looked over the paper super closely, so I don't know if this was independent of sleep stage or dependent on sleep stage.  This is important, because if it was correlated with a sleep stage, like REM, for example, one could argue dreaming didn't cause the improvement, just the physiology of REM did.  If you spend more time in REM you are also more likely to dream about it.  So it would be more association than causation.  Whereas if it was not, whatever processes going on in the brain during 'dreaming' would then be necessary to improve navigation on this task.  But how would dreaming do this?  That just leads to speculation, but sleep and REM sleep in particular has been associated with more than just memory consolidation.  In fact, the relationships between sleep and memory is very complicated.  Probably because sleep isn't just about memory, and memories themselves are very complicated.

Lets look at memory as a whole for starters.  We have many different kinds of memories.  We have episodic memories: our experiences throughout the day, memories of space and time and association.  These are particularly hippocampally dependent.  And these memories are aided by sleep.  But the story isn't one of REM.  It is actually more of a NREM story, and there is a mountain of evidence in support of this now in animals and in humans.  Specifically, oscillations in NREM sleep, slow waves and sleep spindles, are associated with facilitating consolidation and encoding of declarative, hippocampally dependent memories.  These oscillations have been associated with being linked to hippocampal-neocortical crosstalk, and this cross-talk is thought to transform memories from being hippocampally dependent to being cortically dependent.  That is one theory.  Another theory is that slow oscillations globally downscale synapses, pruning away unnecessary ones and preserving strong ones.  The relative weights of synapses are preserved and signal to noise ratio is imporved since you knocked out all the weakest ones.  This is more of a memory side-benefit of a process more designed to manage the memory demands of the brain.  These two theories are not incompatible, and there is a lot of evidence to support both.  And both implicate NREM sleep, not REM sleep in this process.  

So REM isn't really as associated with hippocampal-dependent consolidation much anymore, though it was in the 60s with all the rat experiments.  The trick is, those experiments often had an emotional component or a reward component.  This makes it more like conditioning, which relies on a different neural network and might be more REM-dependent.  There is evidence in humans now that emotional memories are tied to REM sleep and not NREM sleep.  Additionally, other more procedural forms of memory that are less dependent on the hippocampus, such as learning to ride a bike or type on a keyboard or hit a baseball, are dependent on either NREM sleep or a combination of NREM and REM sleep.  So different forms of learning, which require different neural systems, will rely on different physiological brain states in sleep.  And, more specifically, they will all rely on different oscillations occuring in each of these sleep stages.  So, in short, it's complicated.  To complicate it further, sleep isn't just about memory, but is also involved with neurometabolic, immune, and hormonal regulation.  In the memory domain, sleep isn't just about consolidation.  Sleep also facilitates next day encoding ability, integration of memories, and abstraction of general knowledge from memories which facilitates insight into problems the next day.

Much of these latter abilities (integration, abstraction, emotional processing) are tied to REM in some manner.  Which makes me think that REM isn't important for weakening associations between unnecessary items, but instead would strengthen more weakly associated items that prove helpful.

But this isn't dreams, this is sleep.  And, as I have said before, REM does not equal dreaming.  There are a lot of theories about dreaming out there.  Some more psychoanalytic, some more memory related, some more emotion regulation, and some more 'its all garbage, and epiphenomenon with no meaning'.  I really don't think it is the latter.  I just don't think the evidence out there supports it (only some of which I have talked about in this post).  Dreaming is associated with eye movements, which are associated with brain activity in areas associated with mental imagery.  Dreaming is affected by previous waking experience and predicts next day behavior.  Dreaming, or at least REM sleep dreaming, has been associated with emotion regulation, consolidating emotional memories, and facilitating problem solving the next day.  In this way, psychoanalytic, memory, and emotion regulation theories could all be correct in some fashion.  In the end, all these functions serve to enhance adaptability, which is very important from an evolutionary perspective.  

My current advisor (I am a post doc right now) has a theory about REM sleep.  He calls it the 'sleep to remember, sleep to forget' hypothesis.  He is primarily a memory researcher, and he likes to think of emotional memories as containing multiple forms of information.  You have the visceral-physical, emotional response.  But you also have the details of the experience.  In the end, what is most adaptive is to actually remember the emotional experience, even if it was traumatic.  What you want to do is instead forget the emotional, viscerl, physical response, so that every time you think on the memory you don't regurgitate the emotional intensity you did the first time.  He posits REM sleep does just this by stripping away the emotional component and strengthening the memory component.  REM is then important to deconstruct experiences and extract meaning from them to remember what is most important.  Or perhaps to learn what is most important.  There is some evidence for this in that sleep will enhance specific components of a memory and not all of them.  Emotional pieces of a scene are more remembered than their neutral counterparts.  So sleep isn't like justice, it prioritizes based on what may be most adaptive.

My boss posits that this breaks down, or fails to happen in patients with PTSD.  You can see this in that their REM dreams are less associative and weird, and more like direct replays of the trauma.  He thinks there is some process in sleep that is failing to do its job.  When done correctly, the emotional side would be separated and forgotten, whereas the knowledge one could learn is consolidated and integrated into your general knowledge base.  Take, as an example, you walk down a new path and get bitten by a snake.  You want to remember that this path is bad in the future.  You don't want to shiver and sweat and feel stressed and scarred everytime you think of that path.  That is the essence of sleep to remember, sleep to forget.  

Completely separate from memory, sleep, and particularly REM sleep, is associated with modulating your reactivity to emotional events.  As the day wears on, you find things more negative and angry, and less happy.  If you are provided a nap, this bias goes away, so sleep is important for more than just memory.  Sleep, instead, seems to be important for regulating a lot of the functions in your body from immune, to metabolic, to cognitive and emotive (not just memory in the cognitive domain either).  So I don't know if I answered any questions or created any, but I did ramble on a bit.  I think that, more than anything, proves I am an academic.

Wow . Insightful as well as informative. Thank you for that sir.

Quoteto transform memories from being hippocampally dependent to being cortically dependent.

I have no clue what this signifies.  Might you either explicate, or direct me to a reputable source?

Quote from: "Thumpalumpacus"

Quoteto transform memories from being hippocampally dependent to being cortically dependent.

I have no clue what this signifies. Might you either explicate, or direct me to a reputable source?

I have nudged my brother, so hopefully he will respond as well.  But my own neuroscience might be up to the task, so I will chance a preliminary answer.  I have myself taken several neuroscience courses, most of them admittedly 20 years ago, but I have taken a recent refresher course - which will be the primary source of my information, along with: Neuroscience: Exploring the Brain, by Bear, Connors, and Paradiso.

Famous cases of severe anterograde amnesia (the inability to form new memories) have fairly well established the crucial role of the Medial Temporal Lobe (MTL) in memory formation.  It should be clarified that there are several types of memory, which include declarative and procedural memory, and declarative further subdivides into episodic and semantic memory.  The type I am discussing here is declarative memory.  Procedural memory has its own pathway involving the cerebellum.  

The MTL includes the hippocampal structures, and the hippocampus specifically may be the gateway through which new declarative memories are established.  Also, the hippocampus has heavy connections with the associative areas of the neocortex.  The search for the "memory engram" lead reasearchers to discover that declarative memories appear to be stored among the same specific islands of the associative areas of the neocortex related to the higher processing of the sensory modalities involved in the orignal perception of a stimulus or experience.  

Imaging studies of subjects presented with a stimulus demonstrated that the same areas of the brain activated upon initial presentation of the stimulus as when the subjects were asked to recall that same stimulus.  So, the smell component of a memory is stored among the neocortical associative areas responsible for the higher processing of olfactory stimuli, similarly with spatio-temporal information, visual information, auditory information, etc.  And there are specialized structures - for example the Inferotemporal Cortex (or inferior temporal gyrus), which is responsible for facial recognition.  The point is the "memory engram" doesn't exist as a single region or localized neural cluster, but as a network of connections among specialized regions involved in sensory processing.

It currently appears that the hippocampus, briefly, holds in association the disparate neocortical regions involved in a specific memory, but at some point, the indirect connetions between neocortical regions via the hippocampus are replaced by direct connections between the regions themselves, without reference to the hippocampus.  This may be when a memory passes into long-term memory.  This is the process, I believe, to which my brother referred with the statement above.

How 'bout it bro'?  Did I get near the mark?

That certainly helps, thank you very much!

Dear Thumpalumpacus,

That is a good point.  Sometimes I go on without explaining things.  In the memory field at large there is a debate about how episodic memories are stored long term.  Much of this debate stems from an old observation regarding the famous patient H.M.  H.M. was an epilepsy patient in the 1950s.  The source of his epilepsy was the medial temporal lobes, which were completely removed bilaterally.  The result of this surgery was that the epilepsy was stopped.  However, the cost of this was that he could no longer form new memories.  He could remember his old remote memories just fine, but he was sort of stuck in time, unable to consciously learn new episodic experiences.  Meeting him every day was like meeting him for the first time.  However, he had no problem learning procedural thing, like the canonical mirror tracing task.  He would also learn new habits or learn to avoid painful stimuli.  But he could not remember what he did from an episodic declarative standpoint.  These set of studies in the late 50s led people to propose that memory was first stored in the short term in the medial temporal lobes somewhere, but then later on, memories are stored elsewhere.  

A mountain of studies have investigated this further and determined the following things.  One, that place in the medial temporal lobes is the hippocampus, and two, the memories are not actually stored there, per se.  Memories, it turns out, are stored all over your brain.    Take for example, my memories of my brother.  His face is stored in my 'face area' (or expertise area if you want to debate the existence of a face area), the warm brotherly love is probably stored in some emotional circuits, the sound of his voice when he read me stories in some auditory areas, and the feeling of him pummeling me when we were wrestling, probably stored in motor and pain reception areas (this one is more of a joke than real).  I won't go into what is stored in my olfactory areas.  What binds each of these disparate elements into a whole, the timing of an event, the details of that event, the feelings of that event, is the hippocampus.  It is like a directory structure.  It stores and binds all the locations of an event.  Over time, this binding in the hippocampus breaks down, and the binding in the cortex gets stronger.  In other words, the memories transform from being bound by the hippocampus to being bound cortically.  These cortical nodes become more and more bound to each other over time, freeing these memories from hippocampal dependence.  Presumably this also frees the hippocampus from having these memories, allowing the hippocampus to have more space to temporarily store newer memories.  In the sleep field, it is thought this process occurs during sleep, particularly NREM sleep.  Two sleep oscillations have been associated with this: slow waves and sleep spindles.

But why do this?  Why not keep the memories in the hippocampus forever?  This is a question that is part of the debate in the memory field, which I will get back to.  But for now, just know that there is a large faction in the memory field and a lot of evidence, that supports this theory.  One reason may be that the hippocampus is relatively small, so there is a space limit.  Another may be that in the short term, when memories form, you want your memories to be distinct with little overlapping, but in the long term you want them to be integrated into your lifetime of memories and knowledge.   Whatever the reason, this is the theory, and little is known regarding HOW these memories may transform.  Just that they seem to, relying on the hippocampus less and less with time.  So the sleep field has taken up the charge and a lot of interesting data is out there in support of sleep promoting this transformation.

For the sake of honesty, I should mention, as I did before, that there is a competing theory in the memory field.  It is called multiple trace theory (MTT).  This theory posits that the lesion literature is not fully explained by the hippocampal-neocortical model of memory consolidation (the one I outlined above).  Their point is that the more extensive the damage to the hippocampus, the more loss there is to even older memories.  Their theory is that as time passes, memories still depend on the hippocampus, but that each time a memory is recalled, it forms a new trace in the hippocampus.  Thus, older memories are more resistant to destruction due to a lesion, because there is more redundancy in these connections.  This theory, however, does not seem to jive much with the neuroimaging studies which show less activation in the hippocampus over time.  One would expect that the opposite would be true, or at least a stable level of activation would be observed, if MTT was correct.  I am not a memory expert, I am really more of a sleep guy, but I am not as much a fan of the MTT myself.  This might be my bias, because at present all sleep-memory people are couching their data and theories in the hippocampal-neocortical model.  So my position is probably not overly fair.  Also, in conclusion,  

I hope that answers your question, Thumpalumpacus.  If not, this review article would probably be more helpful to you.  I wanted to attach it, but it was too large.  I can send it to you if you want, just email me at bamander@berkeley.edu

Frankland, P. W. and B. Bontempi (2005). "The organization of recent and remote memories." Nat Rev Neurosci 6(2): 119-30.

Again, I would just like to point out, for the record, that my brother is awesome.

And also that whatever he tells you about me "pummelling" him is entirely unsupported by evidence...

Yeah seriously, LittleTheBlackJester, thanks for taking the time to help explain.  Super interesting!

Yes, this is much clearer.  Thank you both very much!

Oh, boy. O.O That is so cool to know. I've been interested in dreams for so long, and most websites about them aren't all that great.

Does anyone know the effect of sleep deprivation on dreams? : D; I read somewhere that being deprived of sleep triggers the brain to sink into REM sleep faster.  I did notice that for that period of time, I could remember many more dreams.

I'm also curious about recurring dreams. If our mind is 'defragging' and recalling memories after distortion, why do we get the same dream multiple times? Is this only for dreams that leave a huge impression on us? For example, I only get my dreams once (usually), but for a while, I'd get these horrid lucid dreams in which I'd die of asphyxiation.  They terrified me because my biggest fear is death by lack of air, and it really bothered me because I felt it. I got that same nightmare six or seven times before it went away.  Could it simply be because I was so terrified of it that it left a lasting imprint on my mind?

What a brilliant thread. Thanks for the interesting info. A lot of it is rather close to home seeing as I used to suffer terribly from night terrors. Thankfully I grew out of them (my last was when I was 12) and to this day I cannot remember any of them. My parents do, though. They would usually happen before I was about to be ill or during an illness. The worst one I had was when I had chickenpox. I was utterly inconsolable for about 2 hours, walking around the house with full-blown hallucinations and being terrified of any physical contact with my parents. I was apparently screaming about horrific things coming through the walls but if my mum tried to hug me (my dad was away on exercise for this one) I'd just freak out even more. I can't imagine how scary it must have been for her..

The doctors said it was fairly common and that I'd probably grow out of it. I'm glad he was right.

I also used to lucid dream right up until my late teens. I can remember those dreams very clearly. I've since read a few books on the subject and it turns out I was training myself to do it without realising. I had the ability to realise I was dreaming whilst in a dream state. I could come out of the dream whenever I wished and wake myself up (if it started to turn bad) or I could change the course of it at will. I used to do a lot of flying. I thought they were a normal part of sleeping but as I got older, started to realise that lucid dreaming on that kind of level is rather rare.

Apparently as you start putting toxins in your body like smoking and drinking (something I did rather a lot of in my late teens) and becoming unfit hinders your ability to lucid dream. I haven't been able to do it for years now.

I once gave my Mum a black eye when I was about 8 when she tried to wake me up from a nightmare. Little did she know I was battling an octopus so when she took hold of me to wake me up I lashed out and hit her smack in the eye. She kept having to explain what had happened in case people assumed my Dad had hit her (https://www.happyatheistforum.com/forum/proxy.php?request=http%3A%2F%2Fimg34.imageshack.us%2Fimg34%2F2438%2Fheheoc.gif&hash=50cf1131f6316b9f48965cce1bfe1877dc8f90e7)

Quote from: "karadan"I also used to lucid dream right up until my late teens. I can remember those dreams very clearly. I've since read a few books on the subject and it turns out I was training myself to do it without realising. I had the ability to realise I was dreaming whilst in a dream state. I could come out of the dream whenever I wished and wake myself up (if it started to turn bad) or I could change the course of it at will. I used to do a lot of flying. I thought they were a normal part of sleeping but as I got older, started to realise that lucid dreaming on that kind of level is rather rare.

Apparently as you start putting toxins in your body like smoking and drinking (something I did rather a lot of in my late teens) and becoming unfit hinders your ability to lucid dream. I haven't been able to do it for years now.

To combat the night terrors, sleep paralysis, and other sleep disorders that run rampant in my family I taught myself lucid dreaming by the time I was 7.  It was the ONLY way I could sleep.  Never knew what to call it until a few years ago when finally diagnosed with a sleep disorder.  Haven't read anything about the toxins/unfit causing hindering the ability though, I'm way unfit right now and in full control of 90% of my dreams.  Hmmm... off to do more research!

Something to add to the discussion Brain's Energy Restored During Sleep, Suggests Animal Study (http://www.sciencedaily.com/releases/2010/06/100629170924.htm)

QuoteScienceDaily (July 7, 2010) â€" In the initial stages of sleep, energy levels increase dramatically in brain regions found to be active during waking hours, according to new research in the June 30 issue of the Journal of Neuroscience. These results suggest that a surge of cellular energy may replenish brain processes needed to function normally while awake...

OK. I think I might need something cleared up for me. I thought, never really looked into it, hence my asking, that dreaming basically kept you from going insane while you slept.  Mind you, with my dreams it might be better if I didn't dream, but there you go.

Quote from: "GAYtheist"OK. I think I might need something cleared up for me. I thought, never really looked into it, hence my asking, that dreaming basically kept you from going insane while you slept.  Mind you, with my dreams it might be better if I didn't dream, but there you go.

I believe it's a product of the brain continuing to function. It would be awful if that vital organ completely shut down.