Clinical Handbook of Mindfulness (18 page)

tation. In traditional Buddhist practice, novice meditators are first instructed

to concentrate on observing the breath. Over time, as a mediator’s ability

to sustain attention on breath increases, he or she is gradually instructed to

broaden his or her attention to other external and internal stimuli. For this

study, Valentine and Sweet classified all subjects as either mindfulness- or

concentration-style meditators depending on self-report as to their mental

focus during meditation. Meditation subjects and a control group were com-

pared on a task in which they had to count rapidly-presented beeps, which

is a measure of sustained attention. All meditators were significantly better

than controls in their ability to detect all stimuli, suggesting that both groups

had developed heightened attention as a result of their practice. However,

the mindfulness meditators were significantly better in their ability to detect

unexpected stimuli (tones with different repetition frequencies) compared

to the concentration group, consistent with the intention of each practice.

It should be noted, however, that the sample sizes were quite small (9–10

48

Michael T. Treadway and Sara W. Lazar

subjects per group), so this finding should be interpreted cautiously. Finally,

when the two meditation groups were subdivided based on total number

of years they had practiced, there were striking and significant differences

between novice and experienced subjects in their ability to detect the stim-

uli, with subjects having
more
than 2 years of practice able to detect approx-

imately 5% more of the stimuli than the subjects with less than 2 years of

practice, regardless of meditation style. This last finding strongly suggests

that the differences between the meditators and controls were due to prac-

tice effects and not due to personality differences between groups.

Habituation

An additional claim of experienced meditators is that increased open aware-

ness to all internal and external stimuli will result in a decreased tendency

toward habituation. Habituation is the tendency to exhibit reduced neural

activity in response to a given stimulus if the stimulus has been repeated

multiple times. A decreased tendency toward habituation is therefore reflec-

tive of what the Buddhist tradition calls “beginner’s mind.” An early study

by
Kasamatsu and Hirai (1973)
with four highly experienced Zen masters

demonstrated that their EEG patterns failed to habituate to repeated clicking

sounds, while the pattern of non-meditating controls did habituate. Becker

and Shapiro failed to replicate these findings 15 years later
(Becker & Shapiro
,

1981)
using three groups of meditators and two control groups—one con-

trol group was instructed to attend to the sound closely and one to ignore it.

However, the subjects in the different groups were not matched for age (Zen,

37.8 years old; yoga, 31.5 years old; TM, 28.7 years old; two control groups,

26.5 and 29.5 years old). Furthermore, the sound characteristics and method

in which the clicks were presented in the two studies differed, which might

account for the differences. In the Kasamatsu study the sounds were pre-

sented through stereo speakers, while in the Becker study the subjects wore

headphones. The physical sensations associated with the headphones would

likely draw more attention to the ears and make all subjects more attentive

to the clicks. Also, neither study reported the magnitude of the tones, so it is

possible that in the second study the sounds were louder or more intrusive,

overcoming the subtle effects observed in the first study.

These studies provide support for two central claims reported by experi-

enced meditators regarding the effects of their practice: Meditation practice

does appear to increase an individual’s attentional capacity and to decrease

habituation. As we will discuss later in this chapter, these effects may con-

tribute to the observed clinical benefits that accrue from mindfulness-based

interventions.

Effects of Mindfulness on Neural Activity

EEG Studies of Meditative States

Early in the history of the neuroscience of mindfulness and meditation,

researchers were primarily interested in determining the extent to which

meditative states represented a unique form of conscious experience. In

the first of these studies, scientists focused on evaluating physiological

Chapter 3 The Neurobiology of Mindfulness

49

and psychological changes that occurred during meditation (Cahn &

Polich,
2006).
It was not until the late 1960s, however, that scientists

began using EEG to examine changes in brain activity during the act

of meditation. An EEG recording measures changes in electrical activ-

ity within the brain and can distinguish between different frequencies

of electrical signals, which are associated with different types of brain

activity.

Despite a large number of studies, EEG findings have been inconsistent.

These differences are in part due to differences in the type of meditation

studied, as well as methodological differences. Therefore, a clear, concise

summary of EEG findings remains elusive
(Cahn & Polich, 2006).
Long-term meditators appear to have higher baseline levels of alpha and theta band

activity, which is associated with sleep and rest
(Aftanas & Golocheikine,

2005; Andresen, 2000;
J. M.
Davidson, 1976; Delmonte 1984;
Jevning, Wallace, & Beidebach,
1992;
Schuman, 1980; West, 1979; Woolfolk, 1975).
Some studies have reported that increases in alpha band power are associated

with entering a meditative state
(Banquet, 1973;
Hirai, 1974;
Kasamatsu & Hirai,
1966;
Taneli & Krahne, 1987),
while some have reported decreases of alpha band (G.D.
Jacobs & Lubar, 1989;
Pagano & Warrenburg, 1983),

and still other have reported no difference between meditation and non-

meditation within the same subjects (Cuthbert, Kriteller, Simons, Hodes,

Lang,
1981; Delmonte, 1985).
Increases in theta power during meditative

practice have also been widely reported and are somewhat more consistent

(Cahn & Polich
,
2006).

Lehmann et al.
(2001)
studied a highly advanced Buddhist lama while

he practiced five distinct exercises. Although all the exercises were of the

concentration type, the study clearly showed in a single subject that differ-

ent meditation practices elicit different patterns of brain activity. Further-

more, the regions activated were consistent with what was known about the

functions of those regions (i.e., use of mantra-activated language areas and

imagery-activated visual areas), which helps verify that the subject’s neural

activity was consistent with his subjective report.

One possible explanation of the discrepant results of EEG studies is that dif-

ferent meditation styles may produce unique patterns of activity. Meditation

practices that emphasize deep physical relaxation are more likely to produce

higher theta and delta activity (which are more closely associated with deep

sleep), while practices that focus more on intensive concentration and mind-

fulness will likely have higher alpha and beta power. This hypothesis has not

been thoroughly tested, as few studies have endeavored to compare differ-

ent meditation styles directly, a phenomenon likely due to the bias in favor

of studying expert mediators, who have significant experience in one partic-

ular style of meditation. However, one study using non-expert mediators was

able to contrast relaxation, concentration, and mindfulness meditation styles.

These researchers found that baseline relaxation was associated with higher

delta and theta increases as compared to both the concentration and mind-

fulness meditation styles, but that the two different meditation conditions

resulted in increased alpha and beta 1 power. Interestingly, mindfulness med-

itation was associated with higher alpha and beta 1 increases as compared

to concentration meditation
(Dunn, Hartigan, & Mikulas, 1999).
This study supports the interpretation that different meditation styles may significantly

50

Michael T. Treadway and Sara W. Lazar

affect the resulting EEG data, despite the fact that most, if not all, meditation

practices utilize overlapping techniques.

Finally, one recent study comparing Tibetan Buddhist monks to normal

controls reported that the ratio of gamma band activity as compared to

slow oscillatory activity was initially higher for the monks during the resting

baseline. This difference increased sharply once the monks began a loving-

kindness meditation. The authors concluded that these data support the pos-

sibility that meditation may promote short-term and long-term changes in

neural functioning
(Lutz et al., 2004).

Neuroimaging Studies of Meditative States

As both earlier EEG studies and more recent behavioral studies have con-

firmed, meditation and mindfulness appear to represent unique patterns of

neural functioning. Although EEG allows scientists to see rapid changes in

types of brain activity, the major drawback of this technique is the extremely

limited spatial information it provides. One cannot assert with much confi-

dence where in the brain the observed activity is emanating from.

Conversely, two neuroimaging techniques developed over the last 10 or

15 years, fMRI and PET, have excellent spatial resolution but give no informa-

tion as to different types of neuron firing. The wealth of information these

tools provide concerning specific brain regions has revolutionized neuro-

science, allowing scientists to identify activity inside the brain during a wide

variety of tasks. Following the growing interest in mindfulness techniques,

a handful of studies using these tools to investigate meditation have been

published.

As with the earlier EEG studies, neuroimaging studies have varied sig-

nificantly in their design and the type of meditation studied, and therefore

often present conflicting results. However, several consistent findings have

emerged. The first is the activation of the dorsolateral prefrontal cortex

(DLPFC), an area that has been associated with executive decision-making

and attention. This area was activated in 5 of the 14 studies and appeared

across a range of meditation styles, including Kundalini yoga
(Lazar et al.,

2000),
mindfulness meditation
(Baerentsen, 2001),
Tibetan Buddhist imagery meditation
(Newberg et al., 2001),
Psalm recitation
(Azari et al., 2001),
and Zen meditation (Ritskes, Ritskes-Hoitinga, Stodkilde-Jorgensen, Baerentsen,

& Hartman,
2003).
Our lab has found trait-like changes of increased cortical thickness in this area, consistent with increased usage (Lazar, 2005). Taken

together, these findings suggest that meditation produces state changes of

increased activation in the DLPFC.

Another frequent finding is that meditation leads to increased activation

in the cingulate cortex, particularly the anterior subdivision (ACC). The ACC

has been described as playing a primary role in the integration of attention,

motivation, and motor control
(Paus, 2001).
A functional subdivision of the ACC into dorsal and rostral areas has also been proposed, in which the rostral portion is more activated by emotionally charged tasks, and the dorsal

portion is more activated by cognitive tasks
(Bush, Luu, & Posner, 2000).

As the ACC is often associated with directing attention, it might be expected

Chapter 3 The Neurobiology of Mindfulness

51

that more experienced meditators would show greater activation than novice

meditators. Alternatively, as more experienced meditators often report that

they can sustain periods of uninterrupted attention longer than novice med-

itators, it may result in less need for ACC activity. This was recently reported

in a study by Brefczynski-Lewis et al. in 2007. In this study, novice medi-

tators were also found to show more activity in the ACC as compared to

Buddhist monks
(Brefczynski-Lewis, Lutz, Schaefer, Levinson, & Davidson,

2007).
However, when Hölzel et al. attempted to replicate these results

using experienced insight (mindfulness) practitioners, they instead found

that these participants showed
more
activity in the ACC as compared to

non-meditators
(H¨

olzel et al., 2007).
This discrepancy may result from the

fact that Brefczynski-Lewis et al. utilized highly trained monks, while Hölzel

et al. utilized experienced lay practitioners, whose ability to sustain attention

is undoubtedly less developed than in the monks.

Finally, the insula has also been shown to activate during meditation

(Brefczynski-Lewis et al., 2007).
The insula is associated with interoception, which is the sum of visceral and “gut” feelings that we experience at any