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What's a Brain Wave?

dag.stenberg at helsinki.nospam.fi dag.stenberg at helsinki.nospam.fi
Tue Apr 20 08:17:43 EST 1999


Cijadrachon <cijadra at zedat.fu-berlin.de> wrote:
> How does EEG work?
> And what was the name of stuff stuck onto the head and energies
> measured?

Metal disks are glued to or just pressed into contact with the skin of 
the scalp. Between the metal and the disk one applies electrolyte paste
to facilitate the flow of electricity from scalp to disk. 
  It has been shown that if rather large amounts of nerve cells are
excited at the same time or inhibited at the same time, their combined
electrical (or magnetic) field spreads through the extracellular fluid
of the brain through the surface of the brain through the skull bone
through the skin of the scalp and can be measured in the small metal
disk electrodes one uses for EEG.
  Comparing the electrical potential between two disk electrodes at any
one moment of time, one can decide whether nerve cells under the two
electrodes are being excited or inhibted in regard to each other.
  If disk 1 is positive compared to disk 2, then one knows from previous
studies that under disk 1, more positive ions (like sodium - Natrium) have
gone into the nerve cells from the fluid between them, and these cells
are more excited than the cells under disk 2. 
  If disk 2 is placed onto the ear lobe, it does not record any vnerve
cells. Thus, if disk 1 is positive compared to the ear lobe, nerve cells
under it are excited, and if it is negative, the nerve cells at that
place are inhibited.
  As eletrical fields weaken with distance, one can only measure fields
from cortical neurons in this way, if electrodes are not introduced deep
into the brain.
  The EEG does not measure action potentials either, because these are
so fast and never exactly at the same time in different cells, and are
thus cancelled out before they reach the scalp surface. Instead, the EEG
measures the level of excitation, which eventually is the reason for
action potentials. This level of excitation fluctuates slower, between 1
and 60 times per second.
  The "waves" occur if there is rhythmic excitation alternating with
inhibition in many cortical neurons synchronously.
  The larger amplitude the "waves" have, the larger is the number of
neurons contributing.

> >  Gamma waves have a frequency of more than 30 Hz (30 cycles/sec), have
> >small amplitude and are thus hard to record. They occur mainly during
> >focussed attention in wakefulness.
> (Maybe you more can't record them for the same reason that such is
> difficult for when trying to dock into other brains within magic?)

> >  Theta waves have a frequency in humans from 4 to 8 Hz, are not very
> >regular, and mostly occur during drowsiness and sleep.
> Which stage within sleep?

Unfortunately during all stages, but during deep sleep they are covered
by much bigger delta waves. 

> >  Delta from 0.5 to 4 Hz is irregular and occurs mainly during deep
> >sleep. 

> The deep sleep phases as such to me seemed to take turns 
> with the dream phases in one brain. 

Yes, that is correct.

> But I never watched deep sleep long, as I am bad in tuning that "low"
> and once when I tried it with a brain a few times, it seemed wrong
> (unhealthy for the other).
> So I am curious what is irregular about it?

Only the waves are irregular in shape, meaning that slightly different
neurons are activated/inhibted at each moment. Nerve cells also may
impulse in bursts and take a short break, and then fire again, unlike
wakefulness, where the activity is much more ingoing.

> >Sigma from 11 to 15 Hz occurs in 1 second bursts during sleep, 
> >and can be seen most easily during light sleep, 
> How often and what is it connected with?

These waves form the so-called "sleep spindles" (that is what we call
the bursts), and they occur from 2 to 5 times a minute. 
Sigma frequencies are seen in many mammals in the motor cortex areas
during periods of focussed attention without movement (like when a cat
watches intently before springing on its prey). But the sleep spindles
are shorter in duration.

Both sigma sleep spindles, deep sleep delta waves, and the relaxed
wakefulness alpha rhythm reflect different relationships between
cerebral cortex and two types of cell in the thalamus. The gamma
frequency of attention may also be a fourth mode of relationship between
cortex and thalamus. Once this has become known, one knows roughly what
signalling relationship exists between thalamus and cortex when the EEG
shows one of these wave patterns.

> >  Trance states
> Can you go into trance states?

I do not really think I can myself. If day-dreaming getting very real is a
trance state, then - yes. People who have had their EEG recorded during
trance states usually have more theta activity than if they were really
awake. Sometimes when I day-dream, I may drop off into sleep, and
sometimes I know I am awake, but the thoughts and images just develop as
absurdly/creatively as if I were in REM sleep. Conversely, of course,
one may be in REM sleep and wake up to the knowledge that this is a
dream, but go on creating images and thoughts as if the REM sleep
continued. I suppose this is what is called lucid dreaming. I do dream a
tremendous lot although I am 58 years old, but it varies with previous
tiredness/sleep debt, and if I have consumed wine the night before, the
dreams are different, not so rich in content.

Dag Stenberg




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