CIHM research findings
Theta phase synchrony and conscious target perception: Impact of intensive mental training
Slagter et al., 2009, Journal of Cognitive Neuroscience
The information-processing capacity of the human mind is limited, as is evidenced by the attentional blink – a deficit in identifying the second of two targets (T1 and T2) presented in close succession. This deficit is thought to result from an overinvestment of limited resources in T1 processing. We previously reported that intensive mental training in a style of meditation aimed at reducing elaborate object processing, reduced brain resource allocation to T1 and improved T2 accuracy (Slagter et al., 2007). Here we report EEG spectral analyses to examine the possibility that this reduction in elaborate T1 processing rendered the system more available to process new target information, as indexed by T2-locked phase variability. Intensive mental training was associated with decreased cross-trial variability in the phase of oscillatory theta activity after successfully detected T2s, in particular for those individuals who showed the greatest reduction in brain resource allocation to T1. These data implicate theta phase locking in conscious target perception, and suggest that after mental training the cognitive system is more rapidly available to process new target information. Mental training was not associated with changes in the amplitude of T2-induced responses or oscillatory activity before task onset. In combination, these findings illustrate the usefulness of systematic mental training in the study of the human mind by revealing the neural mechanisms that enable the brain to successfully represent target information.
Neural correlates of attentional expertise in long-term meditation practitioners Brefczynski-Lewis et al., 2007, Proceedings of the National Academy of Sciences
Concentration meditation is a way to increase attentional focus and concentration. In this meditation one tries to focus all one's attention upon one object, keep it on that object, and bring it back to that object when one finds that one has been distracted (i.e. by outer perceptions or inner thoughts).
As scientists, we wondered whether the brain activation patterns during concentration meditation would be different in experienced Buddhist practitioners compared to normal people without prior meditation experience, and also whether practitioners with different levels of training would show different activation patterns. We hoped that our results would tell us some important things about what brain regions are involved in this meditation, and what brain regions might show effects of training. The first thing we did was to choose participants that were “the crème de la crème” of Buddhist practitioners. These participants had at least 10,000 hours of meditation retreat practice, and some had more than 50,000 hours of practice. These were Buddhist monks and lamas who were often flown in from Nepal, India, the U.S., Europe and Canada. For comparison, the “novice” participants were normal people who had an interest in meditation, but no prior meditative training. We worked only with volunteers who were well motivated to learn the meditation techniques, and willing to practice them every day for a week before the actual scan.
Both the experienced practitioners and the newly trained novices performed the same meditation task while undergoing functional Magnetic Resonance Imaging (fMRI) scans. The fMRI scan is sensitive to changes in blood flow, and can thus detect active brain regions. In addition to just looking at the meditation vs. a normal resting state, we presented sounds in order to test how distractible participants were during the meditation vs. rest. The object of focus in the fMRI scanner was a small dot on the computer screen that the participants could view with special goggles. Participants were to focus all their attention, without distraction on this dot during the meditation blocks. If participants were drowsy or distracted either by the distracting sounds or own thoughts, they were instructed to simply bring the focus back to the dot.
What we found is that both the expert and the novice meditators were using the same brain regions (regions related to attention) during the concentration meditation. However, the degree of expertise made a difference in the amount of activation. Experts as a group had more activation than the novices, which might be expected since novices were likely to struggle with concentration. There was also a delay in activation such that novices often took 10 seconds or more to show significant activation. In contrast, experts with the most hours of practice (over 40,000 hours of retreat practice) had only about 20 seconds of activation in some brain regions at the beginning of the meditation that then dropped back to zero. This decreased activation was possibly due to reduced effort necessary to maintain concentration for these very seasoned practitioners. This “inverted u-shaped curve” is similar to that seen in other learning-related studies such as when one learns a second language.
As for the distracting sounds presented in the meditation, we investigated how brain response to the sounds differed between novices and experts, and how brain response in certain regions varied with hours of practice among the experts. For an emotionally disturbing sound (a woman screaming) there was less activation in regions related to emotion and cognitive discursiveness in experts vs. novices. Those with the most hours of practice showed the least activation suggesting that they were the least disturbed by these sounds.
In sum, concentration meditation activated attention-related brain regions in both expert meditation practitioners and novices. Meditators with more practice initially recruited stronger activation in attention regions, but those with the most practice (over 40,000 hours) had activity drop after less than half a minute, when their concentration may have settled into a tranquil but alert awareness, as is the goal of the meditation practice. Furthermore, the most practiced meditators showed the least reaction to distracting sounds presented during medititation. The results from this study give promising evidence that concentration meditation may be an effective way to train attention, with results that one can see in brain scans. Since concentration meditation itself can be a secular practice done completely outside of a religious context, it has broad applications for training attention. Those with attentional deficits as well as those with attentionally demanding jobs such as surgeons and air traffic controllers may find benefits from this type of meditation.
Mental training affects distribution of limited brain resources
Slagter et al., 2007, PLoS Biology
Meditation includes the mental training of attention, which involves the selection of goal-relevant information from the array of inputs that bombard our sensory systems. One of the major limitations of the attentional system concerns the ability to process two temporally close, task-relevant stimuli. When the second of two target stimuli is presented within a half second of the first one in a rapid sequence of events, it is often not detected. This so-called ‘‘attentional-blink’’ deficit is thought to result from competition between stimuli for limited attentional resources. We measured the effects of intense meditation on performance and scalp-recorded brain potentials in an attentional-blink task. We found that three months of intensive Vipassana meditation reduced brain-resource allocation to the first target, enabling practitioners to more often detect the second target with no compromise in their ability to detect the first target. These findings demonstrate that meditative training can improve performance on a novel task that requires the trained attentional abilities. Furthermore, they support the idea that plasticity in brain and mental function exists throughout life and illustrates the usefulness of systematic mental training in the study of the human mind.
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