Dear Yashaswee! The Creator created a dream for scientists who are engaged in this problem never slept during the operation. Please refer to the articles that are in the annex to my letter.

Vladimir

Dear  Yashswee,

please check the links

https://web.mst.edu/~psyworld/sleep_stages.htm

www.end-your-sleep-deprivation.com/stages-of-sleep.htm

emedicine.medscape.com/article/1188226-overview

www.healthcommunities.com › Health Topics › Sleep

Hi Yashaswee,

 Your questions are very stimulating. I will try to answer some:

1.      Interpretability of delta activity as well as other EEG activity that is captured by conventional EEG is complex . While what we record by scalp EEG are brain waves generated by cerebral cortex, cerebral cortex itself receives inputs from subcortical structures (i.e., thalamus (thalamocortical projections), brainstem etc. Therefore, it is possible that sleep EEG (and its waves throughout various sleep stages) reflects the tendency of specific parts of the brain to generate electrical oscillations or modify them.  In human, delta power in sleep, for example, can be more profoundly seen in parietooccipital or occipitotemporal (posterior delta),  or temporal, be associated with eye movements, or be mostly observed in anterior derivations. This observation points to various brain regions potentially involved in generation of these delta electrical fields recorded by cortical EEG. To troubleshoot, clinicians assess the significance of delta activity in relation to its derivation, voltage, frequency/voltage ratio, complexity and variability of waveform, synchrony, and symmetry. Any of these factors and their degree of expression is used then for clinical judgement (i.e., normality vs abnormality), taking into account clinical history of a patient.  

2.      Theta, Beta and Alpha waves which are hallmark for their corresponding stages, but their pattern and proportion are not stage specific, why? This can be related to antagonistic work of specific brain structures that are responsible for the regular alternation between various sleep stages (different levels of sleep depth), either producing or regulating more inhibitory and more excitatory inputs in firing groups of neurons at a given timepoint. Good thing is that in human the EEG of an adult shows stability over time (i.e., person can be recognized by his/her EEG spectral pattern with a confidence of 90%). This suggests that despite the complexity of brain waves in sleep, oscillatory sites at the level of the organism are reasonably fixed.

3.      Is there any certain values for theta, delta and beta ratio which signifies the corresponding sleep or wake stage?  I did not come across such ratios, however given that the presence and the character of alpha rhythm is indicative of one’s affective state and the level of arousal; beta activity enhanced during stage 1 and 2 tends to variably decrease during deeper stages of sleep (subject to decline with age, too); theta activity can be present or absent when fully awake; and the complexity of delta waves, such ratios would be very difficult to establish experimentally. Hope this helps. Kind regards.

Some relevant readings:

1.      Berkhout J, Walter D. Temporal stability and individual differences in the human EEG: An analysis of variance of spectral values.1968. IEEE Trans Biomed Eng, 15:165-68.

2.      Gloor P. Ball G, Schaul N. Brain lesions that produce delta waves in EEG. 1977. Neurology, 27:326-33.