A Theory of Sleep

yan king yin (no spam please) y.k.y at lycos.com
Sat Aug 25 23:13:18 EST 2001


"Brian" <zhil at online.no>:
> You need to go through more of the book, I spent some time digesting
> what I have read.
> They mention how the memory works more extensively.
> Not just the output.
> From "Life" they say that the Hippocampus is necessary in
> transfer of short-time memory to long-time memory (page 968, memory).
>
> "Conversations" were published in 1994, and "Life" (the edition that I have)
> was printed in 1998 (upgraded from a previous version from 1997).
> There doesn't seem to be any great changes between them on this point
> (regarding "Conversations" and "Life").

My library doesnt have "Life", but I'll read more of "Conversations with
Neils Brain". Thanks for recommanding the book =)

He doesnt really explain how is memory encoded, im not sure if he said
whether the hippocampus transfers memory or not. By the way, he has
another book called "The Cerebral Code" or something, that talks about
hexagonal columns in the cortex as units of memory that resonates with
each other. But i dont think that theory is compelling.

I am skeptical about the hippocampus transfering memory because it is
mostly based on lesion studies. Roughly speaking, since lesions of the
hippocampus cause anterograde amnesia (failure to form new
memories) but that remote memories are spared, they concluded that
hippocampus is implicated in memory formation but that memory is
stored elsewhere in the brain. But there are some problems with this
theory. Firstly, hippocampal damage also causes some retrograde
amnesia, which means some memory is stored there. So how can it
be transferring and storing memories at the same time? Secondly,
the theory does not say how is memory encoded and transferred from
place to place, and what exactly is the cellular mechanisms for that.
There must be some place where memory is stored.

> When they discuss memory, they also mention that cellular change during
> sleep as you mentioned earlier (page 966).
> Non-REM sleep were characterized by a decrease in responsiveness of
> neurons in the Thalamus-region and the cerebral cortex.
> And later: One hypothesis was that non-REM sleep restored the
> energy-reserves
> as well (no big surprise there).
> And about REM-sleep, it is familiar in all mammals, so "it is probably a
> rather basic, cellular function."
> Which reminds me a little of your first post in this thread.

Im not sure about my theory, therefore i posted it to see if someone might
support or refute it. There are a few others theories about REM sleep as
well, such as Crick's.

> I think that Hippocampus is one part of what we call consciousness
> (a 'flashlight' which lights up necessary memories).
> Of course with the Thalamus, as it relays the sensory information.
> The cortex processes these memories and give an output which
> transfers to the motor-area if we IE want to move an arm or to
> the temporal lobe if we want to form a question or answer one.

Thats a good point, that representations do not need to represent
everything, just enough to drive the appropiate responses.

> It might be that it is a one-way transfer and you ask:
> "I ask this because the main output of the hippocampus neurons is
> via the fornix, and it looks rather thin."
> It might simply be a feedback loop, to make sure the 'flashlight' doesn't
> overload.

About "Flashlight" -- its true, the mammillary bodies have efferents to
the thalamus so in a sense the thalamus also relays information comming
from hippocampus.

> _Consciousness_ as an overall, is a sum of all our parts;not just the
> 'flashlight' (short-time memory [Hippocampus] and sensory information
> [Thalamus]), but also longtime memory [Cerebral Cortex].

One question is, do long-term memories go through the hippocampus
and then stored in cortex, or are they formed in cortex at once?

y.k.y







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