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Research Synthesis I
Consciousness: Operational Definition and Implication
Consciousness is the fundamental, unifying characteristic of the human experience.
Despite of its crucial importance, or perhaps because of it, consciousness’s role as the lens
through which we interact with the world continues to elude definition and measurement for
philosophers and scientists, as it has for millennia. These attempts have historically been framed
by the technological limitations of the time. The famed mathematician and philosopher René
Descartes infamously pinpointed the pineal gland as the mind-body interface, and therefore, seat
of consciousness. Scientists have since relegated the pineal gland to the no less important, if less
glamorous, role of endocrine regulation, but a rational, cohesive theory of consciousness
continues to defy classification, particularly by the neurobiologists who typically balk at the idea
of objectively classifying such a subjective experience. Recently, philosopher John Earle has
somewhat cheekily related the opinion of a neurobiologist that, “It’s okay to be interested in
consciousness, but [first] get tenure...”
That said, the goal of operationally defining consciousness continues to attract attention.
Traditionally, there have existed two modalities with which scientists can try applying
definitions to consciousness. The first tries to examine the relationship between the content of
consciousness with the experiences that are reported verbally by human subjects. This may
involve such psychological tools as priming and illusory ambiguities, in order to tease apart
salient of cognition. The second attempts to conceptualize consciousness via a subtractive
approach informed by the knowledge that some behaviors are impaired by injuries to the brain,
by developmental deficits, by or intoxication by various drugs or toxins. The advents of EEG and
fMRI neuroimaging have given researchers incredible tools with which to farm insights into
locating the alleged neural correlates of consciousness.
The hope is to find an activity, pattern, or process in a localized region of the brain,
whose presence predicts conscious awareness and that is both necessary and sufficient for it. One
can appreciate the difficulties in finding any singular neuronal entity from which consciousness
emanates; in fact it seems a hopeless to try and pin something so high-order, so emergent, and so
irreducible on one neuron or class of neuron, as you can with shape-sensing or brightnesssensing. However, one idea that has drawn considerable attention is that of associating
consciousness with rhythmic oscillations of brain activity. This idea arose first in the 1980s from
the work of Christof von der Malsburg and Wolf Singer, who showed that a particular frequency
of oscillations, around the 40 Hz area (referred to as gamma oscillations), may evoke the
conscious experience by linking information represented in different parts of the brain into a
unified experience.
This theory is promising because it presents consciousness as the emanation of higher
order processes working in tandem rhythmicity, an attractive characteristic when one considers
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the free-flowing nature of consciousness. Additionally, it’s reliance on an electrical substrate as
opposed to a neurological substrate fits with the accepted ideas that no morphological changes
occur in the brains during sleep, the most accessible, recoverable, unconscious state. We can all
appreciate that when tired, we fall asleep very quickly, and that if we are asleep and the alarm
rings, we can jolt awaken. The speed of these transitions, between such disparate states of
consciousness and unconsciousness implicate that substrate capable of supporting consciousness
must be electrical in nature.
In 2002, Rodolfo Llinás proposed that the aforementioned oscillations, characterized by
repeating resonances between the thalamus and the cortex, bind what are referred to as the
specific thalamocortical systems, which are responsible for content, and the non-specific or
centromedial thalamocortical systems, which are responsible for context. More recently,
magnetoencephalography, which is the magnetic neuroimaging of electrical brain signaling, has
been used to show that during conscious perception, gamma-band frequency electrical activity
and thalamocortical resonance prominently occurs in the conscious human brain, whereas their
absence is correlated with nonconscious states, such as dreamless, non-REM sleep.
Because this activity is present during REM sleep, the dream-filled, conscious state, it
was theorized that the thalamocortical resonances are modulated by the brainstem and would be
given content by sensory input in the ‘awake’ state and by inner brain activity during dreaming.
In support of this theory, gamma oscillations do not reset by sensory input during REM sleep
(they do during wakefulness), though responses indicate that other parts of the brain are sensitive
to the sensory input, like the alarm clock. These results suggest that we do not perceive the
external world during REM sleep because the intrinsic activity of the nervous system does not
place sensory input in the context of the functional state being generated by the brain.
This evolves further alongside the idea that when two feature-neurons, which are neurons
or groups of neurons which encode for perceptual stimuli (such as edges or shapes), fire
synchronously their percepts are bound, or associated, and fire out of synchrony when they are
unbound. This binding of feature-neurons, as synchronization oscillates segregates features of
individual objects based on the activity across the cortex of many different neurons, and links
them with corresponding perceptual entities.
The question remained whether this gamma band activity could offer an adequate tool for
studying cortical activation patterns during different modes of conscious emotional faceinformation processing. In one study, brain oscillations were analyzed in response to facial
expression of emotions. Specifically, the gamma resonances were measured in a number of
subjects looking at emotional (angry, fearful, happy, and sad) faces or neutral faces. The results
showed that both consciousness and significance of the stimulus in terms of arousal can
modulate the power of synchronization of the gamma oscillations, and that this proxy of
consciousness in the subjects were enhanced more by high conscious arousal (anger and fear)
than low conscious arousal (happiness and sadness) emotions.
Consciousness continues to be an elusive target. However, the most promising theories
have come from the idea that instead of any one neural entity, the emergent feature of
consciousness is evoked by high frequency electrical oscillations between content and context
thalamocortical circuits. And as neuroimaging becomes more and more exact, it is feasible to
believe we will move closer and closer to a rational, unified theory on consciousness.
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Citations
Balconi, M. & Lucchiari, C. (2008) Consciousness and arousal effects on emotional face
processing as revealed by brain oscillations. A gamma band analysis, International Journal of
Psychophysiology, Volume 67 (1): 41-46
Bollimunta, Anil (2011). Neuronal Mechanisms and Attentional Modulation of Corticothalamic
Alpha Oscillations. The Journal of Neuroscience. Society for Neuroscience. 31 (13): 4935–4943.
Crick, Francis and Koch, Christoph (2003). A framework for consciousness. Nature
Neuroscience. 6 (2): 119–126.
Koch, C. (2004). The Quest for Consciousness. Englewood CO: Roberts & Company. pp. 16–19.
Horst Hendriks-Jansen (1996). Catching ourselves in the act: situated activity, interactive
emergence, evolution, and human thought. Massachusetts Institute of Technology. p. 114.
Llinas, R. (1998). The neuronal basis for consciousness. Phil. Tran. R. Soc. Lond. The Royal
Society. 353: 1841–1849.
Llinas, R. & Sugimori, M. (1981) Electrophysiological properties of in vitro Purkinje cell somata
in mammalian cerebellar slices. J. Physiol. 305: 171-195.
Llinás R. (2002). I of the Vortex. From Neurons to Self. MIT Press
Miltner, W (1999). Coherence of gamma-band EEG activity as a basis for associative learning.
Nature. Nature Publishing Group. 397: 434–436.
Ryle G. (1949). The Concept of Mind. University of Chicago Press. pp. 156–163
Singer, W. "Binding by synchrony". Scholarpedia.
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Research Synthesis II
Neurology of Meditation
Meditation is an umbrella term for a broad spectrum of practices whose pursuit is
intended to induce an altered mode of consciousness, either for the direct realization of
therapeutic mental affect or simply to address some otherwise hidden or elusive aspect of the
mind. Its goals have ranged from the mundane and modest to the incredible: practitioners have
credited meditation with increasing compassion and dampening egoism, as far as with pervading
everyday life with an invincible and cosmic sense of peace, or nirvana.
And while allopathic (Western) medicine has a history of skepticism with regard to
treatments originating in spiritual or metaphysical concepts, the popularity and therapeutic
success of meditation in any number of fields and forms has motivated research into how and
why it works.
In a longitudinal study, researchers using neuroimaging techniques found that long-term
mindfulness meditation increases neuronal grey-matter concentration in several regions of the
hippocampus in the brain, as well as in the posterior cingulate cortex, temporo-parietal junction,
and cerebellum. This information becomes particularly exciting when synthesized alongside the
knowledge that several categories of mental disorders (i.e.: severe depression, stress & anxiety
disorders, and possibly schizophrenia) are mediated by the loss of pyramidal neurons in the very
same hippocampal regions. The regrowth of these neurons, and the alleviation of the disabling
effects of their impairment or injury, may be the proximate cause of the happiness or positive
alterations that meditators report.
Mindfulness meditation–based interventions have been shown to improve pain across a
wide spectrum of pain-related disorders, including fibromyalgia, migraines, chronic pelvic pain,
irritable bowel syndrome, and even back pain. Meditation produced a 40% reduction in pain
intensity and 57% reduction in pain unpleasantness ratings in one study using heat as a noxious
stimulant. In that experiment, greater activation of certain brain areas, including the anterior
cingulate cortex, orbitofrontal cortex, and the right anterior insula, was associated with the loss
of pain, or analgesia. The ACC in particular is understood to be critically involved in the
cognition and affective control of pain, while the OFC has been implicated in evaluating the
context of sensory events, and the right anterior insula is associated with the modulation of
afferent nociceptive (pain-sensing) processing and awareness. It was also found that mindfulness
meditation–based pain relief was associated with greater deactivation of the thalamus. Thus,
meditation may reduce pain by fine-tuning the amplification of pain-sensing sensory events
through top-down control processes (OFC/ACC/right anterior insula to thalamus). This suggests
that the cognitive state of meditation–based analgesia does not reduce pain through one avenue
but rather many unique neural mechanisms.
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Lutz in 2008 found that during meditation, empathic activation in the insula was greater
for expert meditators than for novice meditators during presentation of negative sounds than
positive or neutral. Similarly, strength of activation was correlated with self-reported intensity of
the meditation for both groups. The comparison between meditation and rest states between
experts and novices also showed greater activation in the amygdala, right temporo-parietal
junction, and right posterior superior temporal sulcus for experts than novices during meditation.
The data combined indicate that meditation alters the activation of circuits linked with empathy
and theory of mind in response to emotional stimuli, and enhances the empathic effects in a way
that might emerge as outward-facing positive regard.
A set of experiments by Barnes, Ditto, and Kok can be synthesized to see how rhythmic
breathing meditation and positivity mediation can therapeutically induce vagal tone changes. In
the Barnes-lead experiment, the impact of breathing awareness meditation program was found to
be ameliorative to ambulatory blood pressure and sodium handling in adolescents with highnormal systolic blood pressure levels. Significant changes before and after the intervention were
observed between meditative and control groups, highlighting the potential beneficial impact of
BAM on blood pressure control in the natural environment in youth at risk for hypertension.
In the Ditto paper, the vagus nerve was investigated to associate myoelectrical activity
and vagal activity with stress. Using electrogastrography and electrocardiograms to measure
activity, a meal was found to result in an increase electrical activity in a number of metrics,
except a slow-wave waveform. Similar responses were found during sessions of relaxation.
Stress inhibited all these normal responses and reduced the regularity of gastric slow waves.
Stress also impaired vagal activity, and therefore inhibited healthy myoelectric activity as
implicated to be mediated by the vagal pathway.
Kok hypothesized that an “upward-spiral dynamic” reinforces the connection between
positive emotions and physical health. This idea was tested in an experiment in which subjects
either self-generated positive emotions via loving-kindness meditation or did not, as a control.
Participants in the intervention group increased in positive emotions relative to those in the
control group, moderated by and measured with baseline vagal tone. Increased positive
emotions, in turn, produced increases in vagal tone. This experimental evidence identifies a
mechanism by which perceptions of positive social emotion are able to build physical health, as
mediated by the vagus nerve, seen above to be implicated when impaired with stress-related
electrical activity. The researchers suggested furthermore, that the results indicate that positive
meditative emotions, positive social connections brought about by the emotive positivity, and
physical health all influence one another in a constructive, sustaining upward-spiral dynamic.
Despite the breadth of the term, many types and practices of meditation have shown
convincing results in providing therapies otherwise expensive or elusive. As more forms of
meditation come under greater and more inventive scrutiny, we will likely gain greater and
greater pictures of how it is that they provide ameliorative effects to our hectic, stressful lives.
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Citations
Barnes, V. A., Pendergrast, R. A., Harshfield, G. A., & Treiber, F. A. (2008). Impact of
Breathing Awareness Meditation on Ambulatory Blood Pressure and Sodium Handling in
Prehypertensive African American Adolescents. Ethnicity & Disease, 18(1), 1–5.
Ditto, B., Eclache, M. & Goldman, N. (2006) Short-term autonomic and cardiovascular effects of
mindfulness body scan meditation. Ann. Behav. Med. 32: 227.
Hölzel, B. K., Carmody, J., Vangel, M., Congleton, C., Yerramsetti, S. M., Gard, T., & Lazar, S.
W. (2011). Mindfulness practice leads to increases in regional brain gray matter density.
Psychiatry Research, 191(1): 36–43.
Karl A, Schaefer M, Malta LS, Dörfel D, Rohleder N, Werner A (2006). "A meta-analysis of
structural brain abnormalities in PTSD". Neuroscience and Biobehavioral Reviews. 30 (7):
1004–31.
Kempton MJ, Salvador Z, Munafò MR, Geddes JR, Simmons A, Frangou S, Williams SC
(2011). Structural neuroimaging studies in major depressive disorder. Meta-analysis and
comparison with bipolar disorder. Archives of General Psychiatry. 68 (7): 675–90.
Kok, B. et al (2013) How Positive Emotions Build Physical Health. Psychological Science. Vol
24 (7): 1123 - 1132
Lutz, A. et al. 2013. Altered anterior insula activation during anticipation and experience of
painful stimuli in expert meditators. Neuroimage 64: 538–546.
Lutz et. al; Slagter, HA; Dunne, JD; Davidson, RJ (2008). "Attention regulation and monitoring
in meditation". Trends in Cognitive Sciences. 12 (4): 163–9.
Murphy, Michael. "1". The Physical and Psychological Effects of Meditation: Scientific Studies
of Contemplative Experience: An Overview. Archived from the original on June 15, 2010.
Wright IC, Rabe-Hesketh S, Woodruff PW, David AS, Murray RM, Bullmore ET (January
2000). "Meta-analysis of regional brain volumes in schizophrenia". The American Journal of
Psychiatry. 157 (1): 16–25. doi
Zeidan F, Vago DR (Jun 2016). "Mindfulness meditation-based pain relief: a mechanistic
account". Ann N Y Acad Sci. 1373 (1): 114–27.