Clinical Handbook of Mindfulness (19 page)

given moment, and has also been proposed as a key region involved in pro-

cessing transient bodily sensations, thereby contributing to our experience

of “selfness”
(Craig, 2004).
One hypothesis for the increased activation of the insula during meditation is that it reflects the mediator’s careful attention to

the rising and falling of internal sensations. The sub-region of insula identi-

fied in these studies is also strongly implicated in several psychopathologies

(Phillips, Drevets, Rauch, & Lane, 2003).
The gray matter in this region is significantly smaller among schizophrenic patients as compared to controls

(Crespo-Facorro et al., 2000;
Wright et al., 2000).
Insular activity has also been found among depressed and healthy subjects during the induction of

sad mood
(Liotti, Mayberg, McGinnis, Brannan, & Jerabek, 2002),
experience of pain
(Casey, Minoshima, Morrow, & Koeppe, 1996)
or disgust (Wright, He, Shapira, Goodman, & Liu,
2004).
Studies have also highlighted the role of the insula in internally generated emotions
(Reiman, Lane, Ahern, & Scwartz,

1997)
as well as during guilt
(Shin et al., 2000).
These findings suggest that abnormalities in insular function may play a critical role in various psychiatric

disorders.

In addition to brain regions that become active during meditation, neu-

roimaging techniques can also be used to identify specific differences in

brain structure. In 2005, our group published a study that strongly supports

the hypothesis that mindfulness practice has long-term effects on brain struc-

ture. Twenty long-term mindfulness meditators and 15 controls participated

in a comparison of cortical thickness using high-resolution MRI images. Med-

itators and controls were matched for gender, age, race, and years of edu-

cation. It was found that long-term meditators had increased cortical thick-

ness in the anterior insula, sensory cortex, and prefrontal cortex. Given the

emphasis on observing internal sensations that occurs during meditation,

thickening in these regions is consistent with reports of mindfulness prac-

tice (Lazar et al., 2005). A more recent study confirmed and extended the

results from our group, reporting increased gray matter density in the right

anterior insula, as well as the hippocampus and left temporal gyrus among

mindfulness meditators as compared to non-meditators (Hözel et al., 2008).

52

Michael T. Treadway and Sara W. Lazar

Mechanisms of Action

As more information regarding the underlying neural networks involved in

meditation have been published, researchers are now beginning to investi-

gate the neural mechanisms that may explain how these networks promote

the reported behavioral and clinical effects of mindfulness practice. In so

doing, scientists hope to better understand mindfulness by exploring how it

is related to other types of mental activities.

Although this work is very much in its nascent stages, two recent stud-

ies deserve special note. The first study examined how MBSR training

may impact neural networks involved in self-referential experience. Self-

reference has historically been divided into two distinct forms: momentary

self-awareness focused on present experience, and extended self-reference in

terms of enduring characteristics (e.g., I am tall, I am generally upbeat, etc.).

Farb et al. (2007) hypothesized that mindfulness training may help individu-

als to better discriminate between these two forms of self-reference. Using

fMRI, the authors investigated the neural networks that became active dur-

ing an experiential focus condition in which subjects focused on present-

moment experiences as compared to a narrative focus condition in which

subjects considered their personality traits. Farb et al. found that while the

control group showed significant overlap in brain regions that activated

between the experiential and narrative focus conditions, the mindfulness

group did not. This data suggests that one possible mechanism of action

for mindfulness meditation is a decoupling of two self-referential neural net-

works that are normally integrated, and a strengthening of the experiential

network, consistent with the goals of MBSR training.

A second study explored the relationship between self-reported mind-

fulness and identifying emotions expressed in facial stimuli in healthy col-

lege students who were non-meditators (Creswell, Way, Eisenberger, &

Lieberman,
2007).
This study is unique, in that it focused on mindfulness as a skill/trait outside of the context of meditation practice. The authors

found that trait mindfulness as measured by self-report was correlated with

increases in activity in the medial prefrontal cortex (mPFC) as well as simulta-

neous decreases in activity in the amygdala during an affect-labeling task. The

authors propose that mindfulness may therefore be associated with improved

prefrontal regulation of limbic responses and may help explain part of why

mindfulness is a useful component of therapy.

While these studies are encouraging, they are preliminary. Significantly

more research will be required to elucidate the means by which mindfulness

practices may provide its putative cognitive, emotional, and psychological

benefits. In the final section, we will briefly touch on some of the clinical

implications of the studies that have thus far been reviewed.

Clinical Implications

The goal of this section is not to review the clinical literature of mindfulness-

based interventions. Rather, we wish to explore how recent neurobiological

studies of meditation and mindfulness may be relevant to clinical applica-

tions. A summary of important clinical findings is provided below.

Chapter 3 The Neurobiology of Mindfulness

53

Increased time “Living in the Moment”

One of the hallmarks of expert meditators is their ability to experience

negative emotions without necessarily “getting caught up” in them. This

skill has significant implications for the treatment of common forms of

psychopathology, particularly mood and anxiety disorders. Both families of

disorders involve excessive forms of rumination on negative thoughts. Mind-

fulness training incorporates a set of techniques that helps individuals reduce

their tendency to ruminate
(Jain et al., 2007).
If mindfulness can indeed help individuals decouple their present moment experience from their long-term

sense of narrative self as suggested by Farb et al. (2007), then this may explain

how it helps individuals focus on their current experience rather than nega-

tive thoughts relating to past experiences or future worries.

Increased Positive Affect

Although many long-term practitioners have reported high levels of equa-

nimity and contentment as a result of their meditation practice, objective

measurement of the tantalizing link between mindfulness and positive affect

is difficult to quantify. However, a few studies have offered some hints that

mindfulness practices may help to foment positive affect, inclusive of clinical

populations.

Richard Davidson and colleagues measured resting EEG patterns in healthy

subjects before and after an 8-week MBSR intervention as compared to a

control group
(Davidson et al., 2003).
Davidson had previously shown that patients suffering from depression and anxiety have increased EEG power

in the right half of the brain while resting quietly, while psychologically

healthy subjects have greater activity on the left. Although the study was

small, the results indicated that a leftward shift in resting EEG patterns could

be detected after 8 weeks of practice and persisted for 3 months following

the study completion. More importantly, the observed changes were corre-

lated with improved immune function.

Additionally, a recent EEG study of MBCT using a group of 22 acutely sui-

cidal patients found that positive affective style as measured by EEG activity

increased significantly in the MBCT condition as compared to treatment as

usual. This suggests that the success of MBCT may in part be attributable to

helping individuals to maintain an emotionally stable pattern of brain activity

(Barhofer et al., 2007).

Reduced Stress Reactivity

Cultivation of equanimity increases the practitioner’s ability to experience

negative events with less reactivity.
Goleman and Schwartz (1976)
hypoth-

esized that meditators should demonstrate less physiological reactivity to

unpleasant stimuli compared to controls. To test this hypothesis, they

measured skin conductance responses (SCR) from meditators and controls

while the subjects viewed re-enacted wood-shop accidents. SCR measure

the amount of sweat produced as an indicator of autonomic arousal. Com-

pared to controls, the meditation subjects experienced a slightly larger initial

increase in SCR, but then returned to baseline levels more quickly, indicat-

ing that the meditation subjects had heightened responses to the negative

54

Michael T. Treadway and Sara W. Lazar

images, but were then able to quickly “let go” of the images and return to

a state of mental calm and equilibrium. Presumably these subjects are less

engaged in ruminative thoughts that would prolong their autonomic arousal.

Enhanced Cognitive Vitality

Another potentially important benefit of regular meditation is the protection

against cortical thinning that normally occurs in old age. In our 2005 study,

it was found that among meditators, one small region of prefrontal cortex

appeared to be spared from normal age-related cortical thinning. This sug-

gests that meditation may protect against cortical thinning that is typically

associated with aging. A similar recent study comparing the cortical thick-

ness of a group of Zen practitioners with non-meditators also found that

age was correlated with decreased cortical thickness in the control group

but not for the meditator group (Pagnoni, personal communication) 2007.

Future studies will be required to verify whether this is indeed the case. If

so, meditation could be a potentially powerful intervention against some of

the age-dependent cognitive declines in older adults.

Summary

The purpose of this chapter has been to provide an overview of the recent

neurobiological literature on mindfulness meditation, as well as some of the

clinical applications of this work. We now possess sufficient evidence to

demonstrate that meditation is a unique mental state—distinct from resting

states—and that it appears to promote long-term structural and functional

changes in brain regions important for performing clinically relevant func-

tions. By identifying these neurobiological changes and connecting them to

behavioral and clinical benefits, we will be able to better understand how

meditation and mindfulness practice work at the brain level, which may help

validate their use and help identify those conditions that are more likely to

respond favorably to mindfulness-based interventions.

Given the heterogeneity of meditation techniques, future comparative

studies are needed to elucidate both common mechanisms and differential

effects that are associated with different styles of meditation practice. Par-

ticularly when working with a clinical population, we are likely to find that

different forms of meditation are more or less well-suited to help individu-

als with a specific type of disorder. Learning how to select the right form of

meditation practice to best match an individual patient is a critical next step

in the clinical application of mindfulness-based treatment. Of crucial impor-

tance in this effort will be the use of longitudinal study designs, in which

scientists can compare clinical and neurobiological changes in individuals at

pre- and post-treatment time points.

Overall, clinicians should be encouraged by the results of the neurobio-

logical research on meditation. While there is still much that we have yet to

understand, research findings generally support the use of meditation as a

powerful technique in clinical practice.

Chapter 3 The Neurobiology of Mindfulness

55

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