Please cite this article in press as: Carreiras, M., et al. Broca’s area plays a causal role in morphosyntactic processing. Neuropsychologia (2012), doi:10.1016/j.neuropsychologia.2012.01.016 ARTICLE IN PRESS G Model NSY-4380; No. of Pages 5 Neuropsychologia xxx (2012) xxx–xxx Contents lists available at SciVerse ScienceDirect Neuropsychologia jo u rn al hom epa ge : www.elsevier.com/locate/neuropsychologia Broca’s area plays a causal role in morphosyntactic processing Manuel Carreiras a,b,∗ , Chotiga Pattamadilok c , Enrique Meseguer d , Horacio Barber d , Joseph T. Devlin e a Basque Center on Cognition Brain and Language, Donostia-San Sebastian 20009, Spain b IKERBASQUE. Basque Foundation for Science, Bilbao 48011, Spain c Unite de Recherche en Neurosciences Cognitives, Universite Libre de Bruxelles, B-1050 Brussels, Belgium d University of La Laguna, Tenerife 28205, Spain e Cognitive, Perceptual & Brain Sciences, UCL, London, UK a r t i c l e i n f o Article history: Received 20 August 2011 Received in revised form 25 November 2011 Accepted 12 January 2012 Available online xxx Keywords: TMS LIFG Syntax Gender and number a b s t r a c t Although there is strong evidence that Broca’s area is important for syntax, this may simply be a by- product of greater working memory and/or cognitive control demands for more complex syntactic structures. Here we report an experiment with event-related transcranial magnetic stimulation (TMS) to investigate whether Broca’s area plays a causal role in morphosyntactic processing when both working memory and cognitive control demands are low. Participants were presented with word pairs that could either agree or disagree in grammatical number or gender while receiving stimulation to Broca’s area or to the right intraparietal sulcus (a control site). Stimulation of Broca’s area significantly reduced the advantage for grammatical relative to ungrammatical word pairs. In contrast, stimulation of control site left this grammaticality advantage unchanged. The interaction between grammaticality and stimulation was specific to Broca’s area, suggesting a clear involvement of the region in morphosyntactic processing. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Broca’s area is an important hub for language processing, how- ever, its specific role is still unclear and under ongoing debate (see Rogalsky & Hickok, 2011). In the sixties it was conceptualized as the syntactic core for comprehension and production processes tak- ing into account the performance of the so-called Broca’s aphasics (Bradley, Garret & Zurif, 1980; Caramazza & Zurif, 1976; Gleason, Goodglass, Green, Ackerman, & Hyde, 1975; Goodglass, 1968, 1976; Goodglass & Berko, 1960; Goodglass & Kaplan, 1972; Kean, 1977, 1995). However, this view was challenged when it was discovered that a) Broca’s aphasics were able to make syntactic judgments (Linebarger, 1990; Linebarger, Schwartz, & Saffran, 1983; Martin, 2003; Wulfeck, 1988), and b) the relationship between Broca’s aphasia and damage to Broca’s area was not so simple, revealing a very complex relationship between the behavioral deficit and the anatomy. In fact, it has been reported that damage to Broca’s area alone does not necessarily result in Broca’s aphasia (Mohr et al., 1978). Evidence from functional neuroimaging studies added fuel to the debate, but did not helped to settle it. Many fMRI studies, ∗ Corresponding author at: Basque Center on Cognition, Brain, and Language, Paseo Mikeletegi, 69, 20009 Donostia-San Sebastián, Spain. E-mail address: m.carreiras@bcbl.eu (M. Carreiras). using different tasks, stimuli, languages, and paradigms have found activation of left inferior frontal areas during syntactic process- ing (e.g., Indefrey, Hagoort, Herzog, Seitz, & Brown, 2001; Indefrey et al., 2004). In particular, some experiments showed that activity in Broca’s area was greater during the comprehension of com- plex structures (Caplan, Alpert, & Waters, 1998; Caplan, Alpert, & Waters, 1999; Dapretto & Bookheimer, 1999; Just, Carpenter, Keller, Eddy, & Thulborn, 1996; Stromswold, Caplan, Alpert, & Rauch, 1996) and in particular when manipulating syntactic com- plexity, such was when comparing long versus short distance movement dependencies (Cooke et al., 2002; Fiebach, Schlesewsky, Lohmann, von Cramon, & Friederici, 2005; Grodzinsky & Santi, 2008; Grodzinsky, 1986, 2000; Rogalsky, Matchin, & Hickok, 2008; Santi & Grodzinsky, 2007a,b). However, long distance movement dependencies involve heavier working memory load. Thus, the greater activity in Broca’s area attributed to the movement distance effect could be just triggered by domain-general working memory load (Just et al., 1996; King & Just, 1991; Rogalsky et al., 2008). In fact, it is known that Broca’s area is activated in verbal working memory tasks (Awh et al., 1996; Buchsbaum & D’Esposito, 2008; Buchsbaum, Olsen, Koch, & Berman, 2005; Hickok, Buchsbaum, Humphries, & Muftuler, 2003; Smith & Jonides, 1997; Smith, Jonides, & Koeppe, 1996). Broca’s area has also been suggested to be involved in cognitive control and conflict monitoring (Duncan & Owen, 2000). Although both functions are critical for language processing, neither is 0028-3932/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.neuropsychologia.2012.01.016