Mental training affects distribution of limited brain resources

Abstract

The information processing capacity of the human mind is limited, as is evidenced by the so-called "attentional-blink" deficit: When two targets (T1 and T2) embedded in a rapid stream of events are presented in close temporal proximity, the second target is often not seen. This deficit is believed to result from competition between the two targets for limited attentional resources. Here we show, using performance in an attentional-blink task and scalp-recorded brain potentials, that meditation, or mental training, affects the distribution of limited brain resources. Three months of intensive mental training resulted in a smaller attentional blink and reduced brain-resource allocation to the first target, as reflected by a smaller T1-elicited P3b, a brain-potential index of resource allocation. Furthermore, those individuals that showed the largest decrease in brain-resource allocation to T1 generally showed the greatest reduction in attentional-blink size. These observations provide novel support for the view that the ability to accurately identify T2 depends upon the efficient deployment of resources to T1. The results also demonstrate that mental training can result in increased control over the distribution of limited brain resources. Our study supports 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.

Figure 1. Attentional-Blink Task

On every trial, between 15 and 19 items were presented at the center of the screen, preceded by a 1,780-ms fixation cross. Most of the items were letters, presented for 50 ms each and followed by a 34-ms blank. On T2-present trials, there were two target numbers (T1 and T2) among the items, which participants had to detect and report at the end of the trial. The temporal distance between T1 and T2 could be short (336 ms) or long (672 ms).

Figure 2. Effects of Intensive Mental Training on the Attentional Blink

(A) T2 accuracy at time 1 (black bars) and the improvement (red bars) or deterioration (blue bars) in T2 accuracy at time 2, for each participant, separately for the short and long T1–T2 interval. (B) Average T2 accuracy (plus standard error) for each session, T1–T2 interval, and group (at-chance participants excluded). Note that both groups showed an attentional blink at time 1: lower T2 accuracy at short- compared to long-interval trials. Note further that, as predicted, the practitioner group (Pract) showed a significantly larger reduction in attentional-blink size over time than the novice group (Nov).

Figure 3. Effects of Intensive Mental Training on Brain-Resource Allocation to T1

(A) Brain potentials from electrode Pz, time-locked to T1 onset on short-interval trials as a function of T2 accuracy (no-blink vs. blink), session, and group. These data show that, as hypothesized, the practitioners showed a significantly greater reduction in T1-elicited P3b amplitude than the novices in no-blink versus blink trials at time 2 versus time 1. The scalp map shows electrode sites where this three-way interaction was significant between 420 and 440 ms. (B) Brain potentials from electrode Pz, time-locked to T1 onset on short-interval trials as a function of session, T2 accuracy, and group. This figure panel illustrates that intensive mental training was associated with a selective reduction in T1-elicited P3b amplitude in no-blink trials in the practitioner group.

Figure 4. The Ability to Accurately Identify T2 Depends upon the Efficient Processing of T1

Relationship between the change in attentional-blink magnitude over time and the corresponding change in T1-elicited P3b amplitude (for no-blink trials). Note that those individuals that showed the largest decrease in T1-elicited P3b amplitude over time generally showed the largest increase in T2 accuracy over time.

Figure 5. Mental Training Selectively Reduced Early T1-Evoked P3b Amplitude

(A–C) Brain potentials from electrode Pz, time-locked to T1 onset as a function of Session (time 1 or time 2) and Group (novices or practitioners), shown separately for (A) short-interval T2-present no-blink trials, (B) long-interval T2-present no-blink trials, and (C) short-interval T2-absent trials. Yellow bars indicate the time windows in which the reduction in brain potential over time was significant in the time window of the T1-elicited P3b (p < 0.05). (D) The T1-locked change in brain potentials over time in practitioners from electrode Pz, shown separately for short-interval T2-present no-blink trials, long-interval T2-present no-blink trials, and short-interval T2 absent trials. The scalp maps show electrode sites where the change in T1-evoked P3b over time was significant between 380 and 400 ms, separately for each trial type. These data confirm that intensive mental training was associated with a selective reduction in T1-evoked P3b amplitude around 400 ms.