IUBio

Signals in the brain

nospam.stenberg at cc.helsinki.fi.nospam nospam.stenberg at cc.helsinki.fi.nospam
Mon Apr 27 13:11:03 EST 1998


Dirk Wessels <d at wxs.nl> wrote:
> Can anyone help me with finding information about
> signals in the brain.
> These are:
> 1) EEG-waves.

There is a lot of information about electroencephalography (EEG), 
and I suggest you consult a textbook of physiology or neuroscience.
Briefly, EEG waves reflect fluctuations in electrical potentials near
the surface of the brain, and they derive from nerve cell function. They
are the sum of the movement of electrical charges in many nerve cells at
the same time, and the electrical charges are carried by ions like
sodium, potassium, calcium, chloride, bicarbonate, hydrogen ion and some
more.
 
> 2) Calcium waves. (are they the same).

Calcium is a cation (positively charged ion), and when it passes the
cell membrane (going in fast and being pumpedc out more slowly), there
are electrical changes which can be measured at the cellular level. What
calcium contributes to in the EEG is more unclear.

> 3) Information on SQUIDs

SQUIDs are superconducting devices, allowing electrical current flow
with very low resistance. This is usually achieved by cooling the device
to about 4 degress Kelvin. SQUIDs can be used to measure weak magnetic 
fields from the brain (magnetoencephalography, or MEG). The magnetic
field waves have some properties which make looking at them useful, and
they differ in some respects from the EEG waves.

> 4) Information on MRI

Magnetic resonance imaging (MRI) is a way to look at brain anatomy
without having to dissect the brain. Briefly, a storngish magnetic field 
is applied to the tissue to be studied, and this will perturb the
direction of atom nuclei in that tissue. As they regasin their former
position, the change in magnetic field can be recorded. By using
multiple detectors and computing an image of the tissue (like brain) can
be constructed.
  Functional MRI (fMRI) is a derivation of this technique where the
magnetic changes can be related to actual sensations, motor acts or
thought processes.

> And the relation between these waves with:
> 1) State of subject (sleeping, thinking, looking).

EEG is a traditional method for looking at wake-sleep behavior,
diagnosing epilepsy etc. It is not very accurate in localizing brain
functions, and it is not very useful to look deep into the brain.
MEG can go a bit farther into the brain, and can localize more
accurately. For looking at structure (anatomy) computed tomography (CT)
is much used, but it says nothing about function. Positron emisission
tomography (PET) and single photon emission computed tomography (SPECT)
measure the distribution of radioactive substances which can be made to
target certein brain functions (like blood flow, energy use etc.).
Calcium waves in nerve cells certainly interest basic neurophysiologists,
but as far as I know they cannot be measured in living humans. The use
of fMRI to map brain function is still quite new.

> 2) Emotions

EEG and MEG show very little related to emotions, despite a large amount
of popular literature about this. PET, SPECT and fMRI can show which 
brain areas are activated in certain emotions. For more accurate
studies, animal experiments are needed, because they allow the
scientists to make accurate measurements inside the brain. Using the
imaging techniques listed here to study emotions is a little like making
guesses as to who is travelling in an airplane by looking at its
movement from the ground.

> 3) The function of the neurons

The 10E10 neurons of the central nervous system are responsible for 
signalling. Neurons have 100 to 100,000 inputs from other neurons, 
and in turn each neuron affects tens to thousands of other 
neurons.  Signal transmission in the neuron is by movement of 
electrically charged particles. The movement is started and controlled
by the opening of channels leading through the cell wall. Signals are 
transmitted between neurons mainly by chemical agents called 
neurotransmitters, of which there are nearly a hundred different 
ones, but only 2-3 in one and the same neuron.

-- Now I have tried to be helpful.

Dag Stenberg
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Dag Stenberg     MD PhD                    stenberg at cc.helsinki.fi
Institute of Biomedicine		   tel: (int.+)358-9-1918532
Department of Physiology                   fax: (int.+)358-9-1918681
P.O.Box 9        (Siltavuorenpenger 20 J)   
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