Subcortical damage and white matter disconnection associated with non-fluent speech

In a recent paper published in Brain, Dronkers and colleagues (2007) re-examined the brain damage in two historic patients of P. Paul Broca, Leborgne and Lelong, who had lost the ability to speak following brain damage.The observation of these cases lead Broca to suggest that the left inferior frontal lobe (later coined Broca's area) is the crucial lesion location associated with acquired motor speech impairment.Utilizing high resolution MRI, Dronkers and colleagues observed that the brain damage in both of Broca's cases extend further subcortically than Broca could have observed, therefore, suggesting that the critical lesion location for motor speech production is not restricted to the inferior frontal gyrus.In particular, the authors demonstrated that the superior longitudinal fasciculus was damaged in both cases, arguing that this lesion may also have affected Broca's patients' speech production.This timely examination by Dronkers et al. combines a historical perspective and the current debate regarding the critical lesion location associated with non-fluent speech.In an earlier study employing lesion mapping in chronic stroke patients, Dronkers (1996) suggested that damage to the left anterior insula, but not to Broca's area, is the crucial lesion location associated with non-fluent speech.Until then, Broca's initial findings were largely undisputed by tangible evidence.These observations, however, were contrasted in a controlled study by Hillis and colleagues (2004) which investigated acute patients and observed that, indeed, Broca's area, as opposed to left anterior insular damage, is strongly associated with non-fluent speech.In support of these findings, numerous studies utilizing functional MRI in normal participants have demonstrated a strong relationship between Broca's area activity and speech production (Bonilha et al., 2006;Ozdemir et al., 2006;Guenther et al., 2006).For example, our group showed that the contrast between speech and nonspeech oral movements revealed Broca's area activity associated