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Left frontal activation: the voice or the finger?
- Michael D Hunter, Sean A Spence (9 January 2005)
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Michael D Hunter, Wellcome Clinical Fellow University of Sheffield, Sean A Spence
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m.d.hunter{at}sheffield.ac.uk Michael D Hunter, et al.
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We read Shergill and colleagues’ (2004) paper about the temporal course of brain activity associated with auditory verbal hallucinations (AVH) with considerable interest. In that study, the researchers used functional magnetic resonance imaging to reveal those brain regions activated before, during and after AVH (the occurrence of which was indicated by patients pressing a button). They concluded that activation of the left inferior frontal gyrus some 9s prior to button pressing supports the theory that hallucinations originate in brain areas involved in the generation of ‘inner speech’. Given the importance of this question for future paradigm development, we wish to offer constructive comment. There is a difficulty associated with the experimental method as described. Because no control condition was included (in which, for example, subjects might self-initiate button presses, unrelated to the timing of AVH) we cannot ascertain whether the frontal activation reported by Shergill and colleagues (2004) was attributable to the presence of AVH or the procedure of button pressing itself; a problem which emerged in the interpretation of an earlier, similar study (McGuire et al, 1993; Krams et al, 1996). In healthy subjects, we have observed that the left frontal cortex also activates 9s prior to simple, self-initiated button pressing (Hunter et al, 2004). Obviously, in healthy subjects this observed effect has no relationship to AVH (it is a feature of the temporal evolution of normal voluntary motor behaviour). During such behaviour, maximal frontal activity is seen in the middle and inferior frontal gyri (9s prior to button pressing). The temporal sequence of frontal activation observed by Shergill and colleagues (2004) could be related to the occurrence of hallucinations or it could be attributable to the self-initiation of motor action (button pressing). This methodological consideration radically constrains the authors’ conclusions. The techniques of functional neuroimaging are complex and unfamiliar to most general readers. We hope that the concern we raise is helpful in elucidating the methodological issues inherent in studies such as those by Shergill and colleagues (2004). Hunter, M.D., Green, R.D.J., Wilkinson, I.D., et al (2004) Spatial and temporal dissociation in prefrontal cortex during action execution. NeuroImage, 23, 1186-1191. Krams, M., Deiber, M-P., Frackowiak, R.S.J., et al (1996) Broca’s area and mental preparation. NeuroImage, 3, S392. McGuire, P.K., Shah, G.M.S. & Murray, R.M. (1993) Increased blood flow in Broca’s area during auditory hallucinations in schizophrenia. Lancet, 342, 703-706. Shergill, S.S., Brammer, M.J., Amaro, E., et al (2004) Temporal course of auditory hallucinations. British Journal of Psychiatry, 185, 516 -517. M.D. Hunter, S.A. Spence Sheffield Cognition and Neuroimaging Laboratory (SCANLab), Academic Clinical Psychiatry, Division of Genomic Medicine, University of Sheffield, The Longley Centre, Norwood Grange Drive, Sheffield S5 7JT, UK. E-mail: m.d.hunter@sheffield.ac.uk |
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