Individual differences in resting asymmetrical frontal brain activity have been found to predict subsequent emotional responses. The question of whether frontal brain asymmetry can cause emotional responses has yet to be addressed. Biofeedback training designed to alter the asymmetry of frontal brain activity was therefore examined. Eighteen right-handed female participants were randomly assigned to receive biofeedback training designed to increase right frontal alpha relative to left frontal alpha~n ϭ 9! or to receive training in the opposite direction~n ϭ 9!. Five consecutive days of biofeedback training provided signals of reward or nonreward depending on whether the difference between right~F4! and left~F3! frontal alpha exceeded a criterion value in the specified direction. Systematic alterations of frontal EEG asymmetry were observed as a function of biofeedback training. Moreover, subsequent self-reported affect and facial muscle activity in response to emotionally evocative film clips were influenced by the direction of biofeedback training.Descriptors: Frontal EEG asymmetry, Biofeedback, Emotion, Approach-withdrawal model Asymmetrical activation of the anterior cortical regions appears to influence emotional responding, with left hemisphere activity relating to approach-related emotional responses and right hemisphere activity relating to withdrawal-related emotional responses. This observation is based on studies that have examined relationships between individual difference measures and resting cortical electroencephalographic~EEG! activity-particularly in the alpha frequency band, which is inversely associated with cortical activation. To illustrate, less right than left frontal alpha~i.e. increased relative right activity! is seen in depression and those with a history of depression~Allen, Iacono, Depue, & Arbisi, 1993;Gotlib, Ranganath, & Rosenfeld, 1998; Davidson, 1990, 1991!, and Davidson, 1993Davidson, , 1998 HarmonJones & Allen, 1997;Sutton & Davidson, 1997!, and that the asymmetry-depending on its magnitude and direction-taps a propensity to respond to emotionally evocative events with predictable emotional responses.Although the neurophysiological underpinnings of this model remain to be fully elucidated, individual differences in and alterations of asymmetrical frontal brain activity are likely to be functional, and not the result of underlying structural differences Davidson, 1998!. Several authors~e.g. Davidson, 1998 HarmonJones & Allen, 1997, 1998Sutton & Davidson, 1997;Wiedemann et al., 1999! have suggested that these frontal asymmetries tap not positive or negative affect per se, but a broader motivational tendency towards approach-related or withdrawal-related behaviors and emotions. In this view, depression and sad states represent a reduction in the left-frontally mediated propensity to approach and engage with the environment, and panic and fear represent a

Individual differences in resting asymmetrical frontal brain activity have been found to predict subsequent emotional responses. The question of whether frontal brain asymmetry can cause emotional responses has yet to be addressed. Biofeedback training designed to alter the asymmetry of frontal brain activity was therefore examined. Eighteen right-handed female participants were randomly assigned to receive biofeedback training designed to increase right frontal alpha relative to left frontal alpha ~n 9! or to receive training in the opposite direction ~n 9!. Five consecutive days of biofeedback training provided signals of reward or nonreward depending on whether the difference between right ~F4! and left ~F3! frontal alpha exceeded a criterion value in the specified direction. Systematic alterations of frontal EEG asymmetry were observed as a function of biofeedback training. Moreover, subsequent self-reported affect and facial muscle activity in response to emotionally evocative film clips were influenced by the direction of biofeedback training.