Alpha synchronization and anxiety: Implications for inhibition vs. alertness hypotheses Gennady G. Knyazev * , Alexander N. Savostyanov, Evgenij A. Levin State Research Institute of Physiology, Siberian Branch of the Russian Academy of Medical Sciences, Timakova str., 4, Novosibirsk 630117, Russia Received 6 December 2004; received in revised form 8 February 2005; accepted 18 March 2005 Available online 14 June 2005 Abstract Although there is much evidence that alpha oscillations are linked with processes of perception, attention and semantic memory, their functional significance remains uncertain. Synchronization in the alpha frequency range is taken to be a marker of cognitive inactivity, active inhibition of sensory information, or a means of inhibition of non-task relevant cortical areas. Here we propose an alternative interpretation which posits that higher alpha power during reference interval signifies higher readiness of alpha system to information processing. Predictions derived from the inhibition and alertness hypotheses were tested during presentation of acoustic stimuli (tone 1000 Hz) and neutral words to 30 males (18–25 years) with different levels of trait anxiety. On the whole, predictions derived from the inhibition theory were not confirmed and findings more corresponded to the alertness hypothesis. High-anxiety subjects showed higher alpha power during reference interval simultaneously with higher magnitude of event-related desynchronization and higher amplitude of phase-locked alpha responses. These findings are discussed in terms of functional significance of alpha band synchronization and desynchronization. D 2005 Elsevier B.V. All rights reserved. Keywords: EEG; Alpha oscillations; Anxiety; Event-related desynchronization; Averaged evoked potential 1. Introduction Some data indicate that alpha oscillations are enhanced in anxious individuals particularly in anxiogenic environment (Bell et al., 1998; Herrmann and Winterer, 1996; Knyazev et al., 2002, 2003, 2004a,b; Knyazev and Slobodskaya, 2003). This enhancement has been interpreted as a sign of higher readiness of alpha system for information processing (Knyazev and Slobodskaya, 2003). Prima facie, this interpretation seems dubious since enhanced alpha oscil- lations have long been considered as an attribute of relaxation. Indeed, starting from Berger’s (1929) pioneering works, many studies have noted a task-related decrease in alpha power. This finding was so pervasive that alpha power has come to be considered as a reverse measure of activation. More recently this idea has been reconceptual- ized to propose alpha as a mechanism for increasing signal to noise ratios within the cortex by means of inhibition of unnecessary or conflicting processes to the task in hand (Klimesch et al., 1999, 2000)—the greater the task demands, the more inhibition needed, the greater the synchronization. Klimesch’s proposals are compatible with the notion of ‘‘surround inhibition’’ wherein active cortical areas, indexed by alpha desynchronization are surrounded by a ‘‘doughnut’’ of alpha synchronization or inhibition (Suffczynski et al., 2001; Pfurtscheller, 2003) in keeping with Crick’s (1984) spotlight of attention hypothesis. The idea of inhibitory function for alpha synchronization is appealing but it raises some doubts. First, it is not clear how the same mechanism might be linked with perceptual activation, as in the case of phase-locked evoked alpha oscillations (Basar, 1998, 1999), and perceptual inhibition (as proposed for event-related alpha synchronization, ERS). Next, if ERS served a function of selective attention (e.g. inhibition of non-task-relevant perception), one would expect that relatively small cortical area within a task- 0167-8760/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.ijpsycho.2005.03.025 * Corresponding author. Tel.: +7 383 2 33 48 65; fax: +7 383 2 32 42 54. E-mail address: G.G.Knyazev@iph.ma.nsc.ru (G.G. Knyazev). International Journal of Psychophysiology 59 (2006) 151 – 158 www.elsevier.com/locate/ijpsycho