Dreaming....

[The Black Jester]

to 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?

[Thumpalumpacus]

That certainly helps, thank you very much!

[LittleTheBlackJester]

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.

[The Black Jester]

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...

[pinkocommie]

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

[Thumpalumpacus]

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

[amaranthine]

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?

[karadan]

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.

[Tank]

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

[KDbeads]

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!

[Tank]

Something to add to the discussion Brain's Energy Restored During Sleep, Suggests Animal Study

ScienceDaily (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...

[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.

[Sophus]

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.