A commentary on
Gamma band activity in the reticular acti-
vating system (RAS)
by Urbano, F. J., Kezunovic, N., Hyde, J. R.,
Dana Simon, C., Beck, P. B., and Garcia-Rill,
E. (2012). Front. Neur. 3:6. doi: 10.3389/
fneur.2012.00006.
Gamma waves are high frequency neural
oscillations in the range of 30–100 Hz, on
average ∼40 Hz. These waves have been
implicated in creating the unity of con-
scious perception, or binding, and are
related to awareness, problem solving, and
rapid eye movement (REM) sleep. Based
on our level of awareness, Sigmund Freud
and his followers have divided the mind
into three different parts, the preconscious
mind, the subconscious mind, and the
conscious mind. The preconscious mind
includes those things of which we are aware,
but to which we are not paying attention.
If we choose to pay attention, we bring
them to the conscious mind (Civin and
Lombardi, 1990). In this issue of Frontiers
in Sleep and Chronobiology, Urbano et al.
(2012) suggest that gamma band activity
in the reticular activating system (RAS)
mediates preconscious awareness, and that
it is the maintained high frequency activity
across various nuclei that keeps the “stream
of consciousness,” as William James called
it, flowing across our preconscious mind
(James, 2007). This mechanism allows us
to survive in a complex world, being aware
of the traffic and pedestrians around us
as we commute to work. When a stimulus
introduces potential danger, for example,
an oncoming bus, we instantly bring it into
conscious control in order to respond.
This review article is a collaboration
between Dr. Edgar Garcia-Rill’s lab at the
Center for Translational Neuroscience at the
University of Arkansas for Medical Sciences
and the lab of Dr. Francisco Urbano at the
University of Buenos Aires, Argentina. They
refer to a series of recent articles published
in excellent journals that convincingly
demonstrate the presence of gamma band
activity in cells of the pedunculopontine
tegmental nucleus (PPT), the intralami-
nar thalamic parafascicular nucleus (Pf),
and the pontine subcoeruleus nucleus
dorsalis (SubCD; Simon et al., 2010, 2011;
Kezunovic et al., 2011, 2012). The PPT is
involved in the modulation of waking and
REM sleep, while the Pf can affect corti-
cal arousal, and the SubCD controls phasic
pontine-wave (P-wave) activity of REM
sleep – all states marked by high frequency
activity (Datta, 2010). Using an in vitro
technique, Garcia-Rill’s group found high
threshold calcium channels in every PPT
and Pf cell, and activation of these channels
drives the cells to fire faster and faster, until
they plateau at gamma band frequencies.
The cells simply reach a point at which they
do not fire any faster, which is not the case
in many CNS regions. In addition, every
SubCD cell studied exhibited sodium-
dependent sub-threshold oscillations that
maintained firing in the beta/gamma range.
Classic in vivo studies by Mircea Steriade
had established that cells in the PPT and
intralaminar thalamus could fire in the
gamma band range (Steriade et al., 1990,
1991, 1993), and NMDA receptor-mediated
activation of PPT cells has been shown to
induce gamma wave activity in the cerebral
cortex (Datta et al., 2001), but the cellular
mechanisms had not yet been identified.
The key to manifesting gamma band
activity in vitro is that these observations
in Garcia-Rill’s laboratory used record-
ings at close to body temperature (∼37°C),
as opposed to the usual slice work that is
conducted at 30°C. Under such conditions,
there is a flourish of high frequency activity
in these key RAS nuclei, and we are then
inspired to ask, what is the function of this
high frequency activity? It is assumed that
the flow of information from the sensory
systems that is sent in parallel to the RAS
provides the continuous information that
maintains such activity. These authors con-
clude that the most parsimonious expla-
nation for their observations is that this
mechanism participates in the process of
preconscious awareness. Future studies will
need to demonstrate that this is indeed the
function of this mechanism, but already we
have some indications that this might be
the case. For example, knockout mice with-
out these calcium channels show very low
gamma band activity, have sleep dysregula-
tion, motor problems, and die (usually of
low frequency seizures) by 3 weeks of age
(Llinás et al., 2007). However, there is still
much information needed before behav-
ioral studies can be performed to demon-
strate this function, for example knowledge
about the other channels involved, how this
mechanism is modulated by local transmit-
ter systems, and how it is affected during
development.
This review (Urbano et al., 2012) takes
us on a ride through the literature, remind-
ing us of the considerable work it has taken
to piece together the cellular mechanisms
involved in generating gamma band activ-
ity in the cortex, and introducing us to
new work that documents the presence
of gamma waves in the hippocampus and
cerebellum. Given this background, it is
not surprising to find gamma band activ-
ity in the RAS. The authors call the RAS
a “gamma making machine” and explain
a concept that few of us realize: in order
to maintain a circuit firing at gamma band
frequencies (∼40 Hz), synaptic interac-
tions by themselves cannot maintain the
rhythm due to the likely failure of multiple
synapses at such high frequencies. That is,
it is probably the presence of both synaptic
interactions and intrinsic membrane prop-
erties (e.g., sub-threshold oscillations) that
enable the maintenance of such fast activity.
The discovery of these mechanisms behind
gamma band activity, therefore, is critical
to understanding the function of the RAS.
The preconscious mind and gamma band activity in the
reticular activating system
Subimal Datta
1,2
*
1
Department of Psychiatry, Boston University School of Medicine, Boston, MA, USA
2
Department of Neurology, Boston University School of Medicine, Boston, MA, USA
*Correspondence: [email protected]
www.frontiersin.org February 2012 | Volume 3 | Article 16 | 1
General Commentary
published: 08 February 2012
doi: 10.3389/fneur.2012.00016
linergic nuclei in the cat. Proc. Nat. Acad. Sci. U.S.A.
88, 4396–4400.
Steriade, M., Curro-Dossi, R., and Contreras, D. (1993).
Electrophysiological properties of intralaminar
thalamocortical cells discharging rhythmic (∼40Hz)
spike-bursts at ∼1000Hz during waking and rapid eye
movement sleep. Neuroscience 56, 1–9.
Steriade, M., Datta, S., Paré, D., Oakson, G., and Curro
Dossi, R. (1990). Neuronal activities in brainstem cho-
linergic nuclei related to tonic activation processes in
thalamocortical systems. J. Neurosci. 10, 2541–2559.
Urbano, F. J., Kezunovic, N., Hyde, J. R., Dana Simon, C.,
Beck, P. B., and Garcia-Rill, E. (2012). Gamma band
activity in the reticular activating system (RAS). Front.
Neurol. 3:6. doi: 10.3389/fneur.2012.00006.
Received: 23 January 2012; accepted: 25 January 2012;
published online: 08 February 2012.
Citation: Datta S (2012) The preconscious mind and
gamma band activity in the reticular activating system.
Front. Neur. 3:16. doi: 10.3389/fneur.2012.00016
This article was submitted to Frontiers in Sleep and
Chronobiology, a specialty of Frontiers in Neurology.
Copyright © 2012 Datta. This is an open-access article
distributed under the terms of the Creative Commons
Attribution Non Commercial License, which permits
non-commercial use, distribution, and reproduction in
other forums, provided the original authors and source
are credited.
NMDA receptors induces wakefulness and cortical
activation in the rat. J. Neurosci. Res. 66, 109–116.
James, W. (2007). The Principles of Psychology. New York:
Cosimo Classics.
Kezunovic, N., Hyde, J., Simon, C., Urbano, F. J., and
Garcia-Rill, E. (2012). Gamma band activity in
the developing parafascicular nucleus (Pf). J.
Neurophysiol. 107, 772–784.
Kezunovic, N., Urbano, F. J., Simon, C., Hyde, J., Smith,
K., and Garcia-Rill, E. (2011). Mechanism behind
gamma band activity in the pedunculopontine
nucleus (PPN). Eur. J. Neurosci. 34, 404–415.
Llinás, R. R., Choi, S., Urbano, F. J., and Shin, H. S. (2007).
Gamma-band deficiency and abnormal thalamocorti-
cal activity in P/Q-type channel mutant mice. Proc.
Natl. Acad. Sci. U.S.A. 104, 17819–17824.
Simon, C., Kezunovic, N., Williams, D. K., Urbano, F.
J., and Garcia-Rill, E. (2011). Cholinergic and gluta-
matergic agonists induce gamma frequency activity in
dorsal subcoeruleus nucleus neurons. Am. J. Physiol.
301, C327–C335.
Simon, C., Kezunovic, N., Ye, M., Hyde, J., Hayar,
A., Williams, D. K., and Garcia-Rill, E. (2010).
Gamma band unit and population responses in
the pedunculopontine nucleus. J. Neurophysiol.
104, 463–474.
Steriade, M., Curro Dossi, R., Paré, D., and Oakson, G.
(1991). Fast oscillations (20-40 Hz) in thalamocortical
systems and their potentiation by mesopontine cho-
As indicated in a recent study, one of the
mechanisms for gamma band activity could
be the activation of intracellular CaMKII
within the PPT (Datta et al., 2011). In
addition, a complete understanding of the
mechanisms behind gamma band activity
in the RAS should allow the development
of novel stimulants and anesthetics, as well
as agents that modulate awareness. The
implications of this work are profound, and
we should pay conscious attention to these
findings and their relevance to the precon-
scious mind.
RefeRences
Civin, M., and Lombardi, K. L. (1990). The preconscious
and potential space. Psychoanal. Rev. 77, 573–585.
Datta, S. (2010). Cellular and chemical neuroscience of
mammalian sleep. Sleep Med. 11, 431–440.
Datta, S., O’Malley, M. W., and Patterson, E. H. (2011).
Calcium/calmodulin kinase II in the pedunculo-
pontine tegmental nucleus modulates the initiation
and maintenance of wakefulness. J. Neurosci. 31,
17007–17016.
Datta, S., Patterson, E. H., and Spoley, E. E. (2001).
Excitation of the pedunculopontine tegmental
Frontiers in Neurology
| Sleep and Chronobiology February 2012 | Volume 3 | Article 16 | 2
Datta Consciousness and gamma band activity
