The Durk Pearson & Sandy Shaw®
Life Extension NewsTM
Volume 19 No. 3 • April 2016


Gamma Oscillations — Key to Consciousness?

If one word were to describe the essence of a human life, that word might be conscious.

Serious research published in reputable peer-reviewed journals have studied the neural basis for consciousness. This work is closing in on what distinguishes the brain’s activity when we are conscious from that when it is operating unconsciously (which is most of what the brain does).

A little of the new research reveals:

1. Gamma oscillations may be importantly associated with and perhaps causal to consciousness (Singer, 1995) though there is no general agreement. In a 1999 paper (Engel, 1999), the author described the “gamma wave hypothesis” as follows: “[t]he hypothesis is that synchronization of neuronal discharges can serve for the integration of distributed neurons into cell assemblies and that this process may underlie the selection of perceptually and behaviorally relevant information.” “Gamma oscillations (y) [where y is the number of oscillations] (30-120 Hz), an emergent property of neuronal networks correlate with memory, cognition and encoding.” (Ferando, 2013).

2. GABA (gamma aminobutyric acid, an inhibitory neurotransmitter) appears to be involved in the creation of gamma oscillations. (Chen, 2014) “Among the rhythmic firing patterns observed in brain networks, gamma oscillations are generated by a specific class of inhibitory neurons with robust interconnectivity through fast GABA synapses.” (Proddutur, 2013) “...gamma oscillations may contribute to learning and memory...” (Proddutur, 2013) “We have previously shown how gamma oscillation frequency recorded in the CA3 [an area of the brain] in vitro is controlled by a delta-GABA(A)Rs-mediated tonic conductance of INs [inhibitory neurons], that is dynamically balanced by an NMDA-R mediated tonic excitation.” (Ferando, 2013)

3. Gamma oscillations may be important in working memory, a short term form of memory that is critical for complex thought. “During working memory tasks, increasing cognitive load is associated with an increase in gamma oscillations in healthy participants and epilepsy patients.” (Chen, 2014)

4. Gamma oscillations were shown to be associated with spontaneous recovery from depression in mice following chronic restraint stress (Khalid, 2016). When mice are subject to chronic restraint stress, they develop a depressive state that includes anhedonia, withdrawal from social interactions, reduced locomotor activity, much like the depression seen in humans. However, a few weeks after the chronic restraint stress is discontinued, most of the animals spontaneously recover from this depressive state. The recovery is associated with restoration of gamma activity at the network level.

5. In another paper (Rodriguez, 1999), researchers describe a new (as of that time) process in which “a transition between two distinct cognitive acts (such as face perception and motor response) should be punctuated by a transient stage of undoing the preceding synchrony and allowing for the emergence of a new ensemble...” (The gamma oscillations were associated with an increase in synchrony.)

PRODUCING GAMMA OSCILLATIONS

6. Lutz A, Greischar LL, Rawlings NB, Ricard M, Davidson RJ. Long-term meditators self-induce high-amplitude gamma synchrony during mental practice. Proc Natl Acad Sci U S A. 2004 Nov 16;101(46):16369-73.

References

  • Chen CM, Stanford AD, Mao X, Abi-Dargham A, Shungu DC, Lisanby SH, Schroeder CE, Kegeles LS. GABA level, gamma oscillation, and working memory performance in schizophrenia. Neuroimage Clin. Mar 20;4:531-9, 2014.; also see Bower B. Synchronized thinking. Brain activity linked to schizophrenia, skillful meditation. Science News. 166(20):310 (2004).
  • Engel AK, Fries P, König P, Brecht M, Singer W. Temporal binding, binocularrivalry, and consciousness. Conscious Cogn. 8(2):128-51 1999 Jun.
  • Ferando and Mody. Ferando I, Mody I. Altered gamma oscillations during pregnancy through loss of δ subunit-containing GABA(A) receptors on parvalbumin interneurons. Front Neural Circuits. 17;7:144 2013 Sep.
  • Khalid et al. Gamma oscillation in functional brain networks is involved in the spontaneous remission of depressive behavior induced by chronic restraint stress in mice. Bmc Neurosci. 17:4 (2016).
  • Lutz et al. Long-term meditators self-induce high amplitude gamma synchrony during mental practice. Proc Natl Acad Sci U S A. 101:16369-73 (2004).
  • Proddutur A, Yu J, Elgammal FS, Santhakumar V. Seizure-induced alterations in fast-spiking basket cell GABA currents modulate frequency and coherence of gamma oscillation in network simulations. Chaos. 23(4):046109. doi: 10.1063/1.4830138. PubMed PMID: 24387588; PubMed Central PMCID: PMC3855147 (2013 Dec).
  • Rodriguez E, George N, Lachaux JP, Martinerie J, Renault B, Varela FJ. Perception’s shadow: long-distance synchronization of human brain activity. Nature. 397(6718):430-3 (1999 Feb 4).
  • Singer and Gray, “Visual feature integration and the temporal correlation hypothesis,” Annu Rev Neurosci. 18:555-586 (1995).

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