As I understand it, the brain emits tiny rhythmic electromagnetic
waves, brainwaves, that are detectable via EEG. The waves are
categorized into different frequency ranges called alpha, beta, delta,
theta. My guess is that enough neurons in the brain must be firing in
synchronous rhythm to produce those detectable waves. But I'd think
that given all the sensory input, thinking, and movement our brains
handle, the various neurons in different parts of the brain would all
be firing at different and rapidly changing rates.

What causes the rhythmic detectable brainwaves? What drives the
process by which a sufficient number of neurons would fire in
synchronous rhythm, given all the various activities of the brain that
must be occurring even if the person is in a relatively calm state? 
(While my Google searches have located numerous webpages describing
the brainwave states, I haven't yet found a website that explains what
causes them.) Thanks.

Hi,  

The cause of rhythmic detectable brainwaves lies in the "action
potentials" signals produced by the brain's nerve cells. These Action
Potentials move from one cell to another across the synapse.
Neurotransmitters, which are chemicals in the brain help to move the
signals across the gap. There are two types of neurotransmitters; one
to help the Action Potential to move to the next cell, and one to stop
it from moving to another cell. The normal functionality of the brain
shows that it tries to keep an equal amount of these neurotransmitters
working.

Source: SCIENCE, VOL. 249 (1989)
"The Mind Revealed"
by Marcia Barinaga

"...  It was in his recording that Singer noticed that, for short
periods of less than half a second, the field potential was
oscillating--alternately rising and dipping--with a frequency of 40
hertz. Those oscillations reflected a synchronous, repeating pattern
of current flow into the neurons in the vicinity of the electrode. And
since such an ion flow often triggers an action potential, that meant
that many of those neurons must be firing action potentials together,
in brief phase-locked synchrony."
...
"... The neurons typically stay phase-locked for several hundred
milliseconds, which would allow them to make and break their liaisons
in roughly the same period that a person's attention moves from one
subject to the next."

http://groups.msn.com/Tyrannicidae/brainandsoundfrequencies3.msnw

So yes, your thought that a great many of these Action Potentials must
be firing at the same time to create detectable waves is agreed with.

It is documented that several internal and external stimulations drive
the changes of these Action Potential signals in the brain to fluxuate
their different types of waves. Sound, radar dishes, light, darkness,
emotional state and stress are all recorded as having impact on the
state of the Action Potential signals. We do know that the brain seeks
balance and equilibrium, and changes from wave states reluctantly in a
normal healthy specimen.

" ?Actional potential? is the technical term used to describe a nerve
impulse. It consists of a brief, reversible polarization that
propagates along an axon. It differs from a receptor potential
(synaptic potential) in several respects.

First of all, an action potential does not propagate passively, but
actively, by means of special voltage-senstive ion channels in the
axon. In addition, mammals have a particular mechanism that
accelerates the propagation of the action potential. ..."
http://www.thebrain.mcgill.ca/flash/a/a_01/a_01_cl/a_01_cl_fon/a_01_cl_fon.html


" "A framework for consciousness", Francis Crick and Christof Koch, 2003 (Ref 1).
"The cortex is a very highly and specifically interconnected neural
network. It has many types of excitatory and inhibitory interneurons
and acts by forming transient coalitions of neurons, the members of
which support one another. 'Coalitions' implies 'assemblies' [...]
plus competition among them. [...]. In general, at any moment the
winning coalition is somewhat sustained, and embodies what we are
conscious of."
http://www.syberg.be/zMentalSpace/sSys/dreamsJ/06seriesJ/J66e.htm




Source links

NEURAL COMMUNICATION
http://www.thebrain.mcgill.ca/flash/i/i_01/i_01_cl/i_01_cl_fon/i_01_cl_fon.html

The Action Potential
http://www.ualberta.ca/~neuro/OnlineIntro/NeuronAP.htm

Introduction to EEG
http://www.ebme.co.uk/arts/eegintro/

Discovery Magazine January 2000 
http://www.terra.es/personal/kirke1/gerwu.htm



Links of Interest

The Senses As Wavelike Systems
http://www.johnkharms.com/senses.htm

Missing Links: The Role of Phase synchronous gamma oscillations in
Normal Cognition and their Dysfunction in Schizoprenia [ PDF file ]
http://www.brain-dynamics.net/publications/pub_files/haig_2002_thesis.pdf

Brain Imaging
http://en.wikipedia.org/wiki/Brain_imaging

Magnetoencephalography
http://en.wikipedia.org/wiki/Magnetoencephalography

Electroencephalography
http://en.wikipedia.org/wiki/Electroencephalography

Google Searches

+"action potentials" +"brain wave"
+"phase-locked synchrony"
+"action potentials" +"brain"



thanks, 

webadept-ga

---

Request for Answer Clarification by philroy-ga on 29 Jan 2005 07:40 PST

I'm a little familiar with neurotransmitter action potentials from
seeing those ubiquitous illustrations showing how SSRI antidepressants
affect the gap between synapses. But I'm having trouble following the
rest of your explanation.

A couple of your references focus specifically on the frequency of 40
Hz, for neurons in a given area of the brain and lasting less than
half a second. According to the Wikipedia article on
Electroencephalography, 40 Hz is up high in the beta range. Do these
brief and independent localized bursts account for the beta waves
measured by EEG? What about the other EEG frequency ranges?

I'm reading between the lines that getting a sufficient number of
neurons to fire synchronously (or nearly so, in order to be detectable
on EEG) must be due to a "cascade" firing effect, where a few neurons
trigger several others, which then trigger others, etc. Is that
correct?

Are there one or more "clock" portions in the brain (as guzzi-ga
suggests in the comments) which are the initiators of these
synchronous cascade effects, for the different brain wave frequency
ranges? What parts(s) of the brain are responsible for these clocks?

Thank you.

---

Clarification of Answer by webadept-ga on 01 Feb 2005 14:19 PST

Hi again, 

I really like your analogy of the car and four gears, below with
guzzi-ga (who by the way my thanks go out to for helping out with this
question).

We know a great deal now about how brain waves effect us, what could
possibility change the brain waves on a macro level, and what the
brain waves might be telling us about the condition of the brain we
are monitoring. But our knowledge at this point is "Driver only"
knowledge. In other words, using your analogy, we can switch gears and
really take the brain around the block, and can even monitor our
speed, but we haven't a clue when it comes to how the thing works.

When I took your question, I understood you to mean, "What causes
rhythmic 'detectable' brainwaves" "Detectable" being the key word I
made my decision to answer on. Had the question been simply "What
causes brainwaves" I wouldn't have touched it, because we don't know
what "causes" them. Many theories exist, some plausible, some out
there on the cosmic end of things (which some studies with Richard
Dawson PhD might prove are not so far fetched as they first appeared a
few years ago).

http://www.psychiatry.wisc.edu/Faculty/FacultyPages/Davidson.htm
http://www.mnet.co.za/CarteBlanche/Display/Display.asp?Id=2678
http://www.wchstv.com/newsroom/healthyforlife/1849.shtml
http://www.theage.com.au/articles/2005/01/08/1104832349658.html?from=top5&oneclick=true

We also now have some ideas that every breath the body takes, alters
these brain waves.

"University of Michigan Health System (UMHS) researchers found the
first evidence that on average, brain waves change with each breath,
not just the short periods of the night when a person experiences
sleep apnea."
http://www.hon.ch/News/HSN/517312.html
http://www.ninds.nih.gov/disorders/brain_basics/understanding_sleep_brain_basic.htm

We also now have a greater understanding that the brain can change the
way it uses its own paths to make up for injuries
http://www.medterms.com/script/main/art.asp?articlekey=40362
http://www.ucp.org/ucp_generaldoc.cfm/1/4/24/24-6610/465


I can offer you a site, which you might be interested in, and a group,
which is a great source of information in this area. That group is the
OpenSource EEG project on Source Forge.

http://openeeg.sourceforge.net/doc/

http://openeeg.sourceforge.net/doc/links.html

http://qeeg.com/EEGorigin.html

http://www.maps.org/news-letters/v13n1/13115fre.html

In a nut shell here is what we know about what Causes EEG detectable Brain waves

"What causes the EEG?

The electrical waves we can record on the surface of the scalp reflect
the activity of many thousands of brain cells. These waves represent
the sum of waves of excitation and inhibition that are happening to
the individual cells. So this is a summed image of many thousands of
cells being coordinated and getting almost ready to fire, then not
ready at all, then almost ready again, etc., as they ride the waves up
and down. This coordination of being ready to fire sets up the
possibility of the mass reaction of billions of neurons that underlies
our conscious awareness."
http://qeeg.com/qeegfact.html


That is, I am sorry to report at this point, the extent of our
knowledge, other than some more detailed papers on "what more we don't
know about the root cause of brain waves in the humans", or any other
animal for that matter.

webadept-ga

Thanks for this clarification. Even though, ultimately, brain waves
are not completely understood, your quotes and linked websites
provided information that I found interesting and enlightening. So I'm
glad you took the question; otherwise I would never have learned
whether it was a question that doesn't have an easy answer, or if I
just hadn't put up enough $ to have it answered!

In effect, mega slow, quasi-synchronous clocks. Parallel processing compensates.

Best

If you can solve your question, there is a Nobel Prize waiting for
you. However, though I said clock (slightly tongue in cheek) the
analogy is rather poor. I would suggest it is more a sympathetic
handshake which results in rhythmic firing. This is indeed more
closely related to asynchronous systems which regularly rise to
intellectual prominence. There is a lot to be said for it because it
largely avoids race conditions and allows things to run at their
optimum speed. Notable failure (in humans) is a stutter where things
get out of order and can sometimes be ameliorated by introducing a
clock. Many years ago I threw together an electronic metronome for a
psychiatric nurse, the intent being to assist a patient with music. In
practice, its contribution proved limited, but he serendipitously
found dramatic improvement with a severely stutter handicapped
patient.

I hope you don?t mind that aside, but if brains are your thing you may
find it of interest.

As concerns *why* the oscillations, you likely know the condition in
epilepsy where everything just keeps firing. This would seem to
indicate that for things to function correctly, cascades must also
initiate suppression. Hence oscillations. The system could of course
be ?designed? differently but that is just the way it has evolved. The
reason for the different frequencies is likely to be related to the
what they are associated with -- speed of input and output data,
complexity of required processing, neural path-lengths etc. In all
cases though the cascade has to be terminated. One often has to
address this sort of situation in electronics where the loop response
time is critical and has to be tailored to these parameters. Yes of
course the brain is not simply a breadboard, but models can shed
light. Sometimes indeed, consideration of how the brain / body
interacts can give inspiration into how to design circuits!

Is that all reasonable?

Best

Yes, I know of these things to varying degrees: race conditions,
response times, handshakes, avoiding runaway positive feedback,
psychiatric nurses.... Your aside was indeed interesting. I've heard
of rhythm and music helping people who stutter.

webadept helpfully mentions the role of different neurotransmitters in
excitatory and inhibitory actions on neurons. One of the references
cited also mentions that there's a minimum refractory period after a
neuron fires before it's able to fire again.

So my attempt to summarize: Vastly interconnected neurons allow for
cascade effects. Cascade effects allow for almost synchronous firing
of a good-enough number of neurons to produce a signal detectable by
EEG. Excitatory and inhibitory processes in/across those neurons
likely alternate (or something similar) to keep the firing in a
moderate balance. The cascades don't emanate one-way from some
centrally-located neuronal "clock driver", but in more of a roughly
resonant-like action. The 4 brainwave frequency ranges (delta, theta,
alpha, beta) for different levels of consciousness/alertness remind me
of a car with 4 gears for different speeds.

That is all reasonable. Thanks!

Agreed. Good luck with the Nobel Prize :-)