The Behavioural Activation System: lateralization of the BAS and its role in mediating approach motivation

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The Behavioural Activation System: lateralization of the BAS and its role in mediating approach motivation

The location and role of the Behavioural Activation System have been extensively debated. The present research attempted to extend support for theory which suggests that the BAS is an approach motivation mediator. Additionally, clarification of past debate on motivational lateralisation, as opposed to emotional lateralisation, of the brain was examined. Measures of BAS strength were taken to identify high or low levels of BAS sensitivity between individuals. A hand-contraction task was used to direct activation to the contralateral hemisphere and an approach motivation measure was taken after completion of this task. Scores on the approach motivation measure were hypothesized to be affected by BAS level, hemispheric activation, and an interaction of the two. Two conceptualisations of approach motivation were measured: intrinsic and success motivation. Results were mixed, with a significant effect of BAS strength demonstrated on intrinsic motivation and a significant effect of unilateral hemispheric activation demonstrated on success motivation.

        Reinforcement Sensitivity Theory (RST) has been developed in the quest to understand a biological basis to personality. A multitude of research has been dedicated to investigating variation in sensitivity to punishment and reward and the effect these variations have on individuals. RST is now widely conceptualised as consisting of two central systems, within which individual differences are understood to exist which affect behaviour. The Behavioural Activation System (BAS) and the Behavioural Inhibition System (BIS) mediate punishment and reward experiences, and patterns in the variation of these experiences ultimately lead to trait differences in personality (Ryan, 2006). The BAS has been defined as a predominantly dopaminergic system whose neural basis is not entirely clear, and which is sensitive to signals of reward. The BIS is comprised within the septohippocampal system and its neocortical projection in the frontal lobe and is sensitive to signals of punishment (Carver and White, 1994). Sensitivity of both systems has traditionally been measured using self-report questionnaires. A person can be understood to be ‘high’ or ‘low’ in strength of either system and these differences are understood to function with the same consistency as traits of personality (Pickering and Smillie, 2008). An individual, based on the subjective strengths of these two systems, can thus be described in the same way other theories would have classified them as being high or low in extroversion. Across all individuals, different combinations of BIS and BAS strength exist, creating rich variation within the population.

        The BAS has traditionally been understood to regulate positive affect. However, more recent research has begun to challenge this conceptualisation and suggest that the BAS is not solely, or even predominantly, a mediator of positive affect. Research has demonstrated BAS strength to be predictive of aggressive emotional experiences, a finding at striking odds with traditional conceptions of the BAS (Harmon-Jones, 2003). The BAS’s more contemporary conceptualisation is as a facilitator of behaviour. Individuals identified as high in trait BAS are considered as being more likely to experience approach motivation, regardless of affective experience (Carver and White, 1994; Sutton and Richard, 1997). Elliot and Thrash (2002) demonstrated levels of BAS to be consistent with high or low achievement motivation towards goals. They posited that this indicates a motivational, and not affective, model of the BAS. The present research looked to demonstrate support for this model of the BAS as an approach mediator by measuring approach motivation within high and low BAS individuals. Carver and White (1994) suggested that individuals measured as being high in BAS by their BIS/BAS Scale would be predisposed to high motivation toward goal-directed tasks. This suggests that individuals who are high in BAS will score more highly on a measure of approach motivation to an upcoming task, providing support for the BAS as a motivational system.  

        Examination of the BAS has extended beyond measuring the effect of variations in strength and the effect this has on behaviour. Along with creating a more specific understanding of its role in emotive or approach motivation, locating the BAS within the brain has become a focal point of reserach. Traditionally, an emotive model of hemispheric lateralisation has dominated the literature. Positive affect has generally been understood to be controlled by the left hemisphere and negative affect by the right hemisphere (Schutter, de Weijer, Meuwese, Morgan, and van Honk, 2008; Richard, 1992). However much like the BAS, more recent research has begun to re-examine hemispheric specificity to be more strongly associated with motivational direction than with positive or negative affect. The motivational direction model of frontal asymmetry suggests that differences between the hemispheres are not specific to affective valence, but are responsible for controlling motivation, as distinct from emotion (Petersen, Shackman, and Harmon-Jones, 2008; Harmon-Jones and Allen, 1998). It is this model which the present research sought to explore. Electroencephalogram (EEG) research has demonstrated greater bilateral frontal cortical activity to be associated with higher scores of BAS sensitivity (Hewig, Hagemann, Seifert, Naumann, and Bartussek, 2006). EEG research has also revealed individuals rated high in BAS to have higher levels of left hemisphere resting alpha activity (Harmon-Jones, 1997). Harmon-Jones (2006) looked to extend understanding of motivational lateralisation using a hand-contraction task where participants were asked to squeeze a ball in either their left or right hand to direct activation to the contralateral hemisphere. After the hand-contraction exercise, a measure of approach motivation was taken using self-report measures. Participants who had directed activation towards the left hemisphere were demonstrated to experience higher levels of motivation. This suggests the left hemisphere controls motivation, and that when it is active, individuals are more likely to produce higher scores on approach motivation measures.

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To examine both the lateralisation of motivational processes and the BAS as a key player in this process, the present research examined BAS levels among participants, and attempted to manipulate cortical activity before measuring approach motivation. Approach motivation has many conceptualisations. However, previous research does not dictate that any specific concept would not be affected by the independent variables of this methodology. Therefore, a questionnaire was used which measures two concepts of motivation (intrinsic and success) in an attempt to gain as complete a picture as possible of any affects of the independent variables. For the first independent variable, a ...

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