Striatum gray matter reduction in males with an overactive behavioral activation system A. Barro ´ s-Loscertales, 1 V. Meseguer, 1 A. Sanjua ´n, 1 V. Belloch, 1,2 M. A. Parcet, 1 R. Torrubia 3 and C. A ´ vila 1 1 Department of Psychology, Campus Riu Sec, Faculty Ciencies Humanes i Socials, Universitat Jaume I, e-12071 Castello ´, Spain 2 Department Radiology, ERESA, Valencia, Spain 3 Department of Psychiatry and Forensic Medicine and Neurosciences Institute, Universitat Auto ` noma de Barcelona, Spain Keywords: basal ganglia, behavioral activation system, caudate, Gray’s model, sensitivity to reward, striatum Abstract Using optimized voxel-based morphometry, we studied the relationship between gray matter volume in brain areas associated with reward and scores on a behavioral activation system measure (the Sensitivity to Reward scale) in a sample of 50 male undergraduates. Voxel-based morphometry analysis revealed a negative correlation between Sensitivity to Reward scores and gray matter volume in the dorsal striatum and prefrontal cortex. Results indicate that a reduced volume in the striatum might be associated with enhanced reward sensitivity and deficits in inhibitory control. Introduction Rewards play an important role in motivated behavior. The hedonic properties of a potential reward can lead to approach behavior and a sense of pleasure after consumption, serving to reinforce such behavior (Schultz et al., 2000). Thus, it is important to consider how the human brain perceives different properties of a salient stimulus, such as valence and magnitude. Reward is processed in the brain using a network that includes the orbitofrontal system, medial prefrontal cortex, striatum and amygdala (McClure et al., 2004). Personality research has proposed the existence of stable individual differences in the functioning of the brain areas involved in the reward system, known as the behavioral activation (Depue & Collins, 1999) or approach (Pickering & Gray, 2001) system [behavioral activation system (BAS)]. A recent review of the model has emphasized that this reward system responds to both conditioned and unconditioned reinforcers (Corr, 2004). Some theoretical pro- posals have related high BAS activity with disinhibitory disorders such as psychopathy (see Gorenstein & Newman, 1980), attention- deficit ⁄ hyperactivity disorder (ADHD) (Newman & Wallace, 1993; Nigg, 2001; Mitchell & Nelson-Gray, 2006) or alcoholism (Sher & Trull, 1994). Dopaminergic neurotransmission has been proposed as playing a central role in BAS functioning because of the implication of mesolimbic and mesocortical pathways in reward-directed behav- ior (Pickering & Gray, 2001). The BAS is specifically activated in the presence of stimuli previously associated with reward, thus promoting approach to the stimulus in order to achieve the positive features associated with it. This system then generates feelings of hope, which intervene in the learning of rewarded behaviors. Individuals with an overactive BAS usually detect more appetitive stimuli and, once detected, have a greater probability of engaging in approach behavior. One of the most frequently used scales to measure individual differences in functioning of the BAS is the Sensitivity to Reward (SR) scale of the Sensitivity to Punishment and Sensitivity to Reward Questionnaire, which has proved its validity in different psychometric (Torrubia et al., 2001), psychopathological (Newman et al., 2005), behavioral (A ´ vila, 2001) and psychophysiological studies (De Pascalis et al., 2005). Despite the acceptance of Gray’s model, little evidence exists about the relationship between BAS self-reported measures and the involvement of brain areas associated with the BAS. The aim of the present study was to analyse in a group of males the relationship between individual differences in the activity of the BAS as measured by the SR scale and gray matter volume in brain areas associated with reward (i.e. striatum, orbitofrontal cortex and amygd- ala) using a voxel-based morphometry (VBM) analysis. We only studied males as previous research has shown gender differences in gray matter volume (Good et al., 2001) and SR scores (Torrubia et al., 2001). Materials and methods Participants Fifty male undergraduates (mean age 22.43 years, range 18–34 years) were studied, each having given prior informed consent. The experi- ment was approved by the Ethical Committee of the University Jaume I and complied with code of ethics of the World Medical Association. All subjects were right-handed and did not report any neurological or psychiatric disorders. All participants completed the SR scale of the Sensitivity to Punishment and Sensitivity to Reward Questionnaire (Torrubia et al., 2001). The mean score was 10.84 (SD 4.62). MRI acquisition and voxel-based morphometry Images were acquired with a 1.5-T Sonata scanner (Siemens). Contiguous 1-mm sagittal images were acquired across the entire brain with a T1-weighted fast-field echo sequence (TE, 4.2 ms; TR, 11.3 ms; flip angle, 90; FOV, 24 cm; matrix, 256 · 224 · 176 mm). Correspondence: Dr Ce ´sar A ´ vila, as above. Email: avila@psb.uji.es Received 16 January 2006, revised 26 July 2006, accepted 1 August 2006 European Journal of Neuroscience, Vol. 24, pp. 2071–2074, 2006 doi:10.1111/j.1460-9568.2006.05084.x ª The Authors (2006). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd