Decreased inhibitory control in mental fatigue, and meditation as a tool for recovery and prevention

Abstract

No widely accepted model for understanding mental fatigue exists. Consequently, researchers have opted to treat time spent on any mental activity as an index of fatigue, resulting in inconsistent findings. A solution to this problem may lie in Kaplan's (1995) thesis that mental fatigue is the result of prolonged directed attention, which relies on inhibition, a supposedly limited resource. However, empirical investigation of Kaplan's thesis has been lacking, with particular difficulties in inducing a fatigued state. Nevertheless, work on attentional restoration, typically through exposure to natural settings, has provided some useful information. Addressing concerns about the availability, accessibility, and convenience of environmental-based interventions, Kaplan (2001) has also outlined the specific utility of meditation as a portable restorative technique. Meditation induces a state that minimises unnecessary directed attention and actively deconstructs cognitive processes that require inhibitory control. Additionally, experienced meditators may benefit from strengthened inhibitory mechanisms and/or superior attentional regulation strategies that protect against the onset of mental fatigue. However, there is an ongoing question regarding the differences between two common meditative practices, concentrative (single-pointed awareness on focal object) and mindfulness (open awareness of all mental objects). Valentine and Sweet (1999) reported that mindfulness practitioners were superior at a mental shift task, suggesting improved mental flexibility. Given that restoration and prevention of mental fatigue is based on the capacity to flexibly move between, and let go of, different thoughts/schemas, mindfulness may be a preferred intervention strategy. Another specific issue is that without empirical observation of the mechanisms of mental fatigue, and in particular the decrements associated with theoretically fatiguing activities, it is impossible to conduct a compelling research programme. Thus, before investigating the recovery and prevention of mental fatigue, two preliminary studies were conducted: First, a modified replication of Valentine and Sweet's (1999) study, and then development of an activity for inducing inhibitory control decrement. After four weeks of training, novice concentrative (n = 9) and mindfulness (n = 9) practitioners displayed equivalent performance on the mental shift task employed by Valentine and Sweet. However, meditators showed superior performance compared to a progressive muscle relaxation (PMR) control group (n = 8). The challenge of developing a fatigue induction procedure was approached by modifying an existing unsuccessful induction procedure based on a Stroop activity interspersed with a number categorisation task (Hartig, Mang, and Evans, 1991). Inhibitory demands were intensified primarily through incorporating a distracting stimulus and employing a more complex interspersed activity, while a low-demand condition more closely resembled the original procedure (n = 18 in each condition). Participants in the high-demand condition displayed comparatively decreased inhibitory control performance from pre- to post-test and gave subjective reports of being fatigued. Given the preliminary findings, a mental fatigue intervention program was developed, consisting of five weeks of training in meditation (n = 31), PMR (n = 32), or passive/intuitive relaxation (n = 34). Supporting guidebooks presented information on fatigue and restoration and provided a diary format for recording sessions throughout training. After training, pre/post-fatigue and intervention testing showed meditation to be uniquely effective at restoring inhibitory control, and participant feedback indicated positive experiences with the program format. Finally, an investigation of long-term meditators and matched non-meditating controls (N = 14) showed resistance to the objective cognitive effects of the fatiguing task. Moreover, interviews revealed an awareness of and capacity to avoid ongoing attentional demands amongst the long-term meditators, both in the testing situation and in everyday life. The present results are somewhat preliminary and further research on the intersection between laboratory-induced and naturally occurring mental fatigue is particularly needed. Nevertheless, the effectiveness of meditation as a recovery tool after brief training warrants consideration of applied intervention. In this regard, mental health professionals are of primary interest as the nature of their work requires ongoing inhibition of immediate sympathetic responses and maintenance of a constructive and objective approach in the therapeutic relationship. Thus the main practical outcome of the foregoing work is a basis for adapting and implementing the prototype intervention program in such a population.

Date of Award	2010
Original language	English