Theta Synchrony

[Guest guest]

Hi

Devidas,

You asked

about the concepts of polymorphic theta and 'good' theta. If the formatting

(below) doesn't line up, let me know and I will send a pdf.

In my

experience there are few more important references than Stern and Engels'

" Atlas of EEG Patterns " (Lippincott & Wilkins). It is a

highly regarded new classic in the field of raw EEG classification. In the

chapter of theta activity you will find excellent EEG charts that carefully

explain the differences between the important types of theta signatures, namely

frontal midline theta (Cigánek rhythm), polymorphic theta, and rhythmic

midtemporal theta.

First lets

recall that polymorphic comes from two roots. " Poly " means more than

one (maybe many) and " morphic " means shape (from Greek 'morphē').

Rhythmic

EEG forms: may look as

regular as the mathematical sine wave that looks something like this:

*

* *

* *

* *

*

*

* *

* *

* *

*

*

* *

*

*

* *

*

*-------*-------*-------*-------*-------*-------*-------*-

* *|

* *|

*

*

* * |

* * |

* *

* *

| * *

| *

*

|

|

*---------------*

period=250ms

time

->

Remember -

the peaks and troughs are as smooth as the movements of a horse going up and

down on a carnival merry-go-round. The horse slows at the top of its curve then

goes down faster and faster until it starts slowing at the trough and reversing

direction. This pattern is a fundamental pattern in most of mathematics and

physics. It is particularly important in heart rate variability. Only if the

HRV curve is very smooth on the peaks and troughs do you get rewarded at higher

challenge levels. There is only one form of pure sign wave, but there are an

infinite number of ways this pure form can be deformed. With 256 samples per

second, there are 256 different spots that can be distorted above or below the

line of the normal sine wave.

Note the

spacing between the above waves is uniform. If this were a 4 hz theta wave,

then 4 cycles fit into a second. One second is equal to 1000 milliseconds. If 4

identical cycles fit into 1000 ms then every wave has a " period "

of 1000 ms)/4 = 250 ms.

The

" period " of time taken to complete one cycle is often mistakenly

referred to as " wavelength " which is a unit of distance. This usual

only annoys physicists.

Polymorphic

EEG forms: See the

little symbols * in the above chart. Imagine there were several

hundred of them instead. Imagine how many ways an individual * could be raised

1 or many steps above or below normal. Please remember that the spacing between

the waves (the period or 'wavelength') for theta varies from 125-250 ms (do the

math as above). This means that in addition to raising the individual * points

up or down we can mix and match literally an infinite number of periods between

125-250 ms and it is still a theta wave, but clearly of multiple shapes

(polymorphic).

Do you see

that such distortions could easily lead to a wide variety of charts that are

barely recognizable. You can roughly see two forms below that have wavelengths

which identify them as theta. The concept is easy to see when you

recognize that these theta waves cross the zero voltage line. Sometimes a theta

wave only appears long enough to display 1/2 cycle. So anything that roughly trends

up then down over a period of, say, 125 ms, may represent 1/2 of a theta cycle.

*

* * * **

*

*** *

* ** ** * * *

* *

*-------*-*----**------*--------*---*---*

* |

*** * **| *** |

|

* * | *|

|

|

|

|

|

|

*---------------*-------*

p=250ms

p=100ms time ->

" Good

theta " vs " bad theta " as scientific terminology can only be seen

as emblems for phenomena not yet well characterized. This also applies to delta

waves as well.

" Good "

theta is usually the more rhythmic type found in frontal central distribution

('frontal midline theta'). But it is also absolutely essential over the entire

cortex and is involved one way or another in most cognitive and autonomic

functions. Polymorphic theta (except in non-REM sleep) is a potentially ominous

sign.

I will

illustrate from one of my qEEGs where polymophic delta was a component:

Findings:

Polymorphic Delta Activity:

The

increased delta activity in this recording was found to be diffusely

distributed, did not occur in bursts, and was without identifiable rhythmicity,

thus qualifying it as polymorphic delta activity (PDA). Stern & Engel,

2005, give the following comparison of normal versus abnormal PDA.

“PDA

is a common finding on electroencephalograms (EEGs) that may be distinguished

as either normal or abnormal based on features and circumstances. However,

abnormal PDA may have several features of normal PDA, including bilateral symmetry

in frequency and amplitude, superimposed faster frequencies, and an increase in

frequency with alerting stimulation such as noise or touch. Nevertheless,

abnormal PDA commonly and characteristically has consistent asymmetry,

asymmetrically superimposed faster frequencies, and lack of change with

alerting stimulation. Focal PDA that has a region of maximum slowing and

minimal faster frequencies is especially abnormal and indicates a focal lesion

in the white matter that is deep to the most abnormal region within the focal

slowing.â€

“Generalized

PDA indicates either encephalopathy or sleep, and encephalopathy in this

context is a nonspecific state of diffuse neuronal dysfunction that may be as

severe as coma.â€

“The

encephalopathy producing generalized PDA may be a reversible state due to

transient physiologic abnormality or due to endogenous or exogenous sedatives.

Physiologic abnormalities may occur during migraine, syncope, and ischemia and

after a seizure. [1, 2] Metabolic dysfunction is the principal source for

endogenous sedation and may be produced by hepatic and renal disease. Exogenous

sedatives are specific toxins and pharmaceuticals, such as narcotics.

Generalized PDA also may be irreversible as from a diffuse cerebral insult such

as anoxia, infection, hypoglycemia, and inflammation; developmental abnormality

usually with global cognitive impairment; or certain degenerative or dementing

illnesses such as stroke, advanced Alzheimer’s disease, and sometimes

schizophrenia. Specifically, PDA occurs when serum glucose is less than 35

mg/100 ml, and all other frequencies are absent when the glucose drops below 18

mg/100 ml. Lower serum glucose concentrations will produce generalized

attenuation. Inflammatory causes of PDA include encephalitis, purulent meningitis,

and some autoimmune diseases such as Sydenham’s disease and Behçet’s disease.â€

“Regardless

of its cause, generalized PDA is similar to focal PDA as a sign of cerebral

white matter abnormality [3 ,4]. This abnormality must be significant and include

either cellular toxicity or mechanical compression. Interstitial edema alone

does not appear to produce abnormal slowing. Often the pathology is accompanied

by cerebral cortical abnormality, but abnormality limited to the cerebral

cortex does not produce slowing. It produces attenuation and loss of the faster

frequencies.†[5]

With

respect to the above discussion it should be emphasized that this client has 1)

asymmetric PDA with 2) lack of change between eyes closed and eyes open, with

3) attenuation and loss of faster frequencies which are asymmetrically

superimposed. See also Figures 8 & 9.

Careful

attention to age-appropriate cognitive, nutritive and metabolic status may help

elucidate the significance of these findings.

This is

just my interpretation of the literature. I hope it makes some sense.

Best

wishes,

Dailey

[1]

Ramelli GP, Sturzenegger M, Donati F, Karbowski K. EEG findings during basilar

migraine attacks in children. Electroencephalogr Clin Neurophysiol 1998:

107:374-378.

[2]

Ammirati F, Colivicchi F, Di Battista G, Garelli FF, Santini M.

Electroencephalographic correlates of vasovagal syncope induced by head-up tilt

testing. Stroke 1998: 29: 2347-2351.

[3]

Sharbrough FW. Nonspecific abnormal EEG patterns. In: Niedermeyer E, Lopes da

Silva F, Eds. Electroencephalography, basic principles, clinical applications,

and related fields. Baltimore: & Wilkins, 1999:215-234.

[4] Zifkin

BG, Cracco RQ. An orderly approach to the abnormal EEG. In: Daly DD, Pedley TA,

eds. Current practice of clinical electroencephalography. 2nd ed. New York:

Raven Press. 1990: 253-267.

[5] Schaul

N. Pathogenesis and significance of abnormal nonepileptiform rhythms in the

EEG. J Clin Neurophysiol 1990:7:229-248.

-----Original

Message-----

From: [mailto: ] On

Behalf Of devidasbhonde

Sent: Sunday, May 20, 2012 7:02 AM

Subject: Re: Theta Synchrony

,

very thought provoking. thank you.

Can you please

elaborate polymorphic theta ? And Good theta ?

Is it that

presence of harmonics make it polymorphic ?

And

fundamental theta with harmonics makes it bad ?

Regards,

Devidas