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Volume 9 (2009), Pages 639-651
Research Article

Estimating Brain Load from the EEG

1Brain Work Research Centre, Finnish Institute of Occupational Health, Helsinki, Finland
2Agora Center, University of Jyväskylä, Finland

Received 10 October 2008; Revised 14 June 2009; Accepted 26 June 2009

Academic Editor: Michael Chee

Copyright © 2009 Anu Holm et al.


Modern work requires cognitively demanding multitasking and the need for sustained vigilance, which may result in work-related stress and may increase the possibility of human error. Objective methods for estimating cognitive overload and mental fatigue of the brain on-line, during work performance, are needed. We present a two-channel electroencephalography (EEG)–based index, theta Fz/alpha Pz ratio, potentially implementable into a compact wearable device. The index reacts to both acute external and cumulative internal load. The index increased with the number of tasks to be performed concurrently (p = 0.004) and with increased time awake, both after normal sleep (p = 0.002) and sleep restriction (p = 0.004). Moreover, the increase of the index was more pronounced in the afternoon after sleep restriction (p = 0.006). As a measure of brain state and its dynamics, the index can be considered equivalent to the heartbeat, an indicator of the cardiovascular state, thus inspiring the name "brainbeat".