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The EEG frequency architecture, coupled oscillations and consciousness
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Physics of Life Reviews 9 (2012) 295–296 www.elsevier.com/locate/plrev
Comment
The EEG frequency architecture, coupled oscillations and consciousness Comment on ‘Consciousness, biology and quantum hypotheses’ by Baars and Edelman Wolfgang Klimesch ∗ , Aditi Arora Division of Physiological Psychology and Doctorate College Imaging the Mind, DK+, Department of Psychology, University of Salzburg, Austria Received 20 July 2012; accepted 23 July 2012 Available online 25 July 2012 Communicated by L. Perlovsky
In their insightful review, Baars and Edelman [1] emphasize that conscious mentation is critically dependent on specific brain structures, but only if they ‘constitute a unified oscillatory machine displaying different spontaneous rhythms’. Here, we suggest in addition that a certain frequency architecture, enabling a balanced coupling and decoupling between oscillations, is closely related to – or even enables – conscious functions. Research on brain oscillations suggests that different frequency domains are associated with different classes of cognitive processes. As an example, theta oscillations appear to be related to the processing of new (episodic) information, whereas alpha is associated with the access to semantic information that represents knowledge of our environment (for reviews see e.g. [2,3]). A crucial implication is that different frequency domains interact in terms of cross frequency (CF) coupling. The problem, however, is that spurious (‘unwanted’, ‘erroneous’) CF synchronization may cause considerable interference between oscillatory processing domains. Depending on their numerical ratio, the excitatory phases of two frequencies, f1 and f2, will either meet frequently and regularly as for harmonic frequency relationships or infrequently and irregularly as for non-harmonic relationships. Harmonic coupling provides an optimal basis for a functional interchange between two oscillatory systems. Non-harmonic coupling, blocks an interchange only to some extent because of spurious CF synchronization. Pletzer, Kerschbaum and Klimesch [4] could demonstrate that in a mathematical sense two frequencies f1 and f2 will never synchronize if the frequency relationship for f1, f2 (f2 > f1) equals the golden mean (which is 1.618) and that there is no other frequency relationship that is better capable of avoiding spurious CF synchronization. These findings suggest that a dynamically changing frequency architecture reflects a state of conscious processing. The dynamic change is seen between a harmonic and a golden mean relationship between neighbouring frequencies either enabling co-activation or blocking co-activation between assemblies. As an example, the typical harmonic relationships for slow frequencies would be Delta : Theta : Upper Alpha = 3 : 6 : 12 Hz. This relationship may change to 3 : 4.85 (= 3 × 1.618) : 7.85 (= 4.85 × 1.618) if the frequencies should be separated functionally. Note that the DOI of original article: http://dx.doi.org/10.1016/j.plrev.2012.07.001. * Corresponding author.
E-mail address: [email protected] (W. Klimesch). 1571-0645/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.plrev.2012.07.010
296
W. Klimesch, A. Arora / Physics of Life Reviews 9 (2012) 295–296
traditional frequency range of alpha of about 7–13 Hz is nicely mirrored by this example ranging here from 7.85 to 12 Hz. The general idea is that conscious processes are reflected by a dynamic change of coupling and de-coupling which e.g., is absent during slow wave sleep. Investigating the world of multiple coupled oscillators with a dynamic change in their frequency ratios may open a new dimension for understanding brain processes and conscious processes in particular. On this abstract level, quantum hypotheses may indeed have a place in the ‘world of multiple coupled oscillators’. References [1] [2] [3] [4]
Baars B, Edelman DB. Consciousness, biology and quantum hypotheses. Physics of Live Reviews 2012;9(3):285–94 [this issue]. Klimesch W. Evoked alpha and early access to the knowledge system: the P1 inhibition timing hypothesis. Brain Research 2011;1408:52–71. Klimesch W, Sauseng P, Hanslmayr S. EEG alpha oscillations: the inhibition timing hypothesis. Brain Research Reviews 2007;53:63–88. Pletzer B, Kerschbaum H, Klimesch W. When frequencies never synchronize: the golden mean and the resting EEG. Brain Research 2010;1335:91–102.
Physics of Life Reviews 9 (2012) 295–296 www.elsevier.com/locate/plrev
Comment
The EEG frequency architecture, coupled oscillations and consciousness Comment on ‘Consciousness, biology and quantum hypotheses’ by Baars and Edelman Wolfgang Klimesch ∗ , Aditi Arora Division of Physiological Psychology and Doctorate College Imaging the Mind, DK+, Department of Psychology, University of Salzburg, Austria Received 20 July 2012; accepted 23 July 2012 Available online 25 July 2012 Communicated by L. Perlovsky
In their insightful review, Baars and Edelman [1] emphasize that conscious mentation is critically dependent on specific brain structures, but only if they ‘constitute a unified oscillatory machine displaying different spontaneous rhythms’. Here, we suggest in addition that a certain frequency architecture, enabling a balanced coupling and decoupling between oscillations, is closely related to – or even enables – conscious functions. Research on brain oscillations suggests that different frequency domains are associated with different classes of cognitive processes. As an example, theta oscillations appear to be related to the processing of new (episodic) information, whereas alpha is associated with the access to semantic information that represents knowledge of our environment (for reviews see e.g. [2,3]). A crucial implication is that different frequency domains interact in terms of cross frequency (CF) coupling. The problem, however, is that spurious (‘unwanted’, ‘erroneous’) CF synchronization may cause considerable interference between oscillatory processing domains. Depending on their numerical ratio, the excitatory phases of two frequencies, f1 and f2, will either meet frequently and regularly as for harmonic frequency relationships or infrequently and irregularly as for non-harmonic relationships. Harmonic coupling provides an optimal basis for a functional interchange between two oscillatory systems. Non-harmonic coupling, blocks an interchange only to some extent because of spurious CF synchronization. Pletzer, Kerschbaum and Klimesch [4] could demonstrate that in a mathematical sense two frequencies f1 and f2 will never synchronize if the frequency relationship for f1, f2 (f2 > f1) equals the golden mean (which is 1.618) and that there is no other frequency relationship that is better capable of avoiding spurious CF synchronization. These findings suggest that a dynamically changing frequency architecture reflects a state of conscious processing. The dynamic change is seen between a harmonic and a golden mean relationship between neighbouring frequencies either enabling co-activation or blocking co-activation between assemblies. As an example, the typical harmonic relationships for slow frequencies would be Delta : Theta : Upper Alpha = 3 : 6 : 12 Hz. This relationship may change to 3 : 4.85 (= 3 × 1.618) : 7.85 (= 4.85 × 1.618) if the frequencies should be separated functionally. Note that the DOI of original article: http://dx.doi.org/10.1016/j.plrev.2012.07.001. * Corresponding author.
E-mail address: [email protected] (W. Klimesch). 1571-0645/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.plrev.2012.07.010
296
W. Klimesch, A. Arora / Physics of Life Reviews 9 (2012) 295–296
traditional frequency range of alpha of about 7–13 Hz is nicely mirrored by this example ranging here from 7.85 to 12 Hz. The general idea is that conscious processes are reflected by a dynamic change of coupling and de-coupling which e.g., is absent during slow wave sleep. Investigating the world of multiple coupled oscillators with a dynamic change in their frequency ratios may open a new dimension for understanding brain processes and conscious processes in particular. On this abstract level, quantum hypotheses may indeed have a place in the ‘world of multiple coupled oscillators’. References [1] [2] [3] [4]
Baars B, Edelman DB. Consciousness, biology and quantum hypotheses. Physics of Live Reviews 2012;9(3):285–94 [this issue]. Klimesch W. Evoked alpha and early access to the knowledge system: the P1 inhibition timing hypothesis. Brain Research 2011;1408:52–71. Klimesch W, Sauseng P, Hanslmayr S. EEG alpha oscillations: the inhibition timing hypothesis. Brain Research Reviews 2007;53:63–88. Pletzer B, Kerschbaum H, Klimesch W. When frequencies never synchronize: the golden mean and the resting EEG. Brain Research 2010;1335:91–102.