Strategy and suppression impairments after right lateral prefrontal and orbito-frontal lesions

Sir,We read with interest the scientific commentary by Hornberger and Bertoux (2015) on our study on the specificity of prefrontal cortex subregions for strategy use, verbal initiation and suppression (Robinson et al. , 2015). We administered Section 1 and 2 of the Hayling sentence completion task (Burgess and Shallice, 1997) to a large group of frontal and posterior patients. Section 1, assessing verbal initiation, requires the subject to complete sentences with an appropriate word (e.g. ‘ The captain stayed with the sinking …’ could be completed by saying ‘ ship ’). Section 2, assessing inhibition/suppression, requires the completion of sentences with an unconnected word (e.g. ‘ London is a very busy …’, could be completed by saying…‘ banana ’). This section also assesses the ability to adopt appropriate strategies. Healthy subjects are known to use heuristics in order to generate words unrelated to the sentence frame. Frontal patients may produce suppression errors (e.g. ‘ London is a very busy …’ may be completed with ‘… city ’). We found that right lateral (RL) patients were impaired on three critical variables, whereas patients with left lateral (LL) or superior medial lesions were not. Right lateral patients produced a significantly greater number of Suppression Errors, fewer Number of Correct Answers in Section 2 and had a larger Response Time difference (RTs Section 2 − RTs Section 1), a measure taken to indicate the additional ‘thinking time’ required to generate unconnected rather than appropriate words. We suggested that the right lateral region has a key role in generating or implementing an effective strategy. Other studies have previously documented that lesions in right rostral prefrontal cortex or right inferior frontal gyrus are linked to suppression impairments (Roca et al. , 2010). However, our study was the first to link these deficits to impairment …