IUBio

EEG Vigilance/Sleep

dag.stenberg at helsinki.nospam.fi dag.stenberg at helsinki.nospam.fi
Wed May 12 09:32:17 EST 1999


Heiko Tietze <> wrote:
> Hi Dag !
> On 11 May 1999 17:35:59 GMT, dag.stenberg at helsinki.nospam.fi wrote:
> ->
> ->By vigilance one generally means the ability of anyone brain region
> ->to respond adequately to input. Increased vigilance = wakefulness.
> ->
> well, this sounds a little bit "physiological" I d like to get a
> psychological definition

That is more difficult. I was relying on Werner Koella's definition of
vigilance - he extended it to concern any part of the brain, not only
consciousness that is a function of the whole.
  Actually I think this is what makes his definition physiological - it
is separated from the mind concept, and reduced to neuronal function,
which is why I like it. Sorry.

> das reicht mir so nicht - was trennt die nichtadaequate Reaktion von
> Fehlern z.B. - die Verbindung Formatio reticularis und Thalamus
> implizieren allerdings eine Synchonisierung=alpha Anstieg, was auch
> bei verbesserter sensorischer Aufnahmebereitschaft so sein sollte.
> Vigilanz hat also auch Stadien.

Vigilance surely can vary on a scale of low vigilance... high vigilance.
But this may be a continuum. Veikko Häkkinen of the university of
Helsinki once defined seven stages of wakefulness. The
Rechtschaffen-Kales classification defines four stages of non-REM sleep.
To these four stages of the definable state non-REM sleep they added one
state of wakefulness and one state of REM sleep. A definable state of
vigilance is thus subdivisible into stages within that state. 

But you write that _increased_ sensory reactivity is correlated with
more synchronized alpha rhythm. This does not seem right to me.
If awake, increased vigilance with increased reactivity is opposite to
more alpha. During non-REM sleep, on the other hand, there is rather
little alpha activity, and sensory reactivity is inversely related
to the amount of delta waves. During REM sleep, there is also normally
not much alpha (some subjects differ), and reactivity is generally as 
during light non-REM sleep.

> ->Alpha occurs regularly in normal persons who are awake, ...
> ->...
> ->been related both to the IQ of the individual, to body temperature 
> I do not agree. IQ or personality are complex psychological
> descriptions and maybe you get relations with EEG its not determined
> by this, but other more primary circumstands.

I did not express myself clearly. Some authors have claimed that alpha
frequency is related to IQ, but that was long ago. 

> EEG ist nicht gleich Persoenlichkeit oder IQ, eher in Verbindung mit
> grundlegenderen (auch diese Merkmale bedingende bzw. beeinflussende)
> Umstaenden (z.B. Motivation als Resultat der Instruktion und der
> Versuchsdarbietung).

I suppose I can agree about that. The EEG is by necessity a very
indirect measure of brain function, and many authors have tried to give
it more meaning than it has.

> ->  As far as I understand more sleep is NOT induced as the eyes are
> -> closed more!
> Sure, but I dont mean induced sleep but alpha

> Je schlaefriger, geringer vigilant, desto oefter sind die Augen
> geschlossen. Da bei geschlossenen Augen alpha gegenueber offenen Augen
> eher Beta auftritt, sollte soch das haeufigere Schliessen der Augen
> (wenn man mal von Artefakten absieht) in einem verstaerkten Alpha
> resultieren - aber halt nur dadurch, dass die Augen zu sind (was man
> nur dann im EOG bemerkt, wenn eine Bewegung stattfindet oder man hat
> eine Videoueberwachung).

With the addition that some individuals have difficulties in producing
alpha of more than 1-2 seconds' duration at a time even when the eyes 
are closed, and many subjects can relax very well with their eyes open
(but without producing alpha).
  I have understood that the best index of sleepiness/drowsiness is the
appearance of slow eye _movements_ and one of the next best the
appearance of rhythms slower than alpha, especially theta in the EEG.

Is your interest in monitoring drowsiness during performance??

Dag Stenberg



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