Connections to and from Broca’s region successfully predict functional connectivity in humans: a new perspective on ‘language’ networks? (Commentary on Kelly et al.)

Brain Behavior and Cognition Program and Program In Neurosciences Boston University, 64 Cummington St., Boston 02215, MA,USAIn this issue of EJN, Kelly et al. succeeded in demonstrating that autoradiographic anatomical tracing studies in the macaque monkey predictedpatterns of connectivity into and out of Broca’s ‘language’ region in man. Resting state connectivity during functional magnetic resonanceimaging was measured in humans, as anatomical tracing cannot be done and diffusion tensor imaging cannot delineate the exact cortical originsand terminations of pathways.The Kelly et al. (2010) study was executed with great rigor. The human regions of interest were mapped on the basis of individuals’ uniquesulcal and gyral morphology, which were precisely deﬁned and translated from the monkey into human cytoarchitectural nomenclature. Thisindividualized method was then followed by a seed-based analysis and a data-driven spectral clustering analysis. Great methodologicaltransparency was provided (e.g. by illustrating how the number of clusters designated to be found (e.g. 2 vs. 4) affected the structure of theﬁndings). The monkey target regions were BA 44 and 45 (traditionally considered Broca’s Area) and BA 6 (which subserves orofacial movements). However, recent research suggest that BA 47 (pars orbitalis) should now be included in ‘Broca’s Complex’ (Hagoort et al., 2004; Hagoort, 2005)as it is activated during both semantic processing (Bookheimer, 2002) and in the extraction of structural order or ‘syntax’ from oral (Friedericiet al., 2006) and signed (Petitto et al., 2000) speech.Many of the projections from Broca’s area (Kelly et al., 2010) and from Broca’s complex (Xiang et al., 2010) are not with regions traditionallyconsidered linguistic. Indeed, BA 47 has been implicated in the extraction of temporal coherence from music (Levitin & Menon, 2003). Takentogether these ﬁndings may help to liberate Broca’s complex from being primarily a language-speciﬁc node. Instead, consistent with the cognitiveneuroscience perspective, regions inside of and outside of Broca’s complex participate in variety of functional networks beyond just ‘language’. In terms of future research, it would be good to validate the relationship between anatomical tracing and resting state functional connectivity ofBroca’s Complex within at least one species of monkey. To my knowledge this has not been done even though resting state activity in man andmonkey have been compared (Rilling et al., 2007). After that, it would be interesting to compare the hypothesis–driven ﬁndings guided by the new anatomical tracings of ‘Broca’s complex’ in themonkey to a recent resting state functional connectivity analysis of ‘Broca’s complex’ in man. This would help to assess the extent to which data-driven predictions from the monkey affect data analysis in the human.Another suggestion may be to move away from just measuring connectivity of the default brain at rest and, instead, examine resting stateconnectivity during the immediate period before a trial has begun but while the individual is preparing for a speciﬁc cognitive task (such as wordrhyming). Frye et al. (2008, 2010) have performed such a connectivity analysis with magnetoencephalographic data analyzed by means ofGranger Causality. This method computes not only the strength of connectivity between regions but also the strength of the direction of activity inor out of a speciﬁc cortical area.