Deploying such a mechanism might be possible but comes at a cost. STN stimulation in Parkinson’s disease – which may PD0332991 mw affect the hyperdirect/reactive pathway – improves performance on STOP and Go-NoGo tasks (Van den Wildenberg et al., 2006), but also results in cortical inhibition-related activity which persists for up to 400 msec (Baker, Montgomery, Rezai, Burgess, & Lüders, 2002). Suppression of motor output over a similar timescale due to global inhibition has also been observed using MEPs (Badry et al., 2009). These data suggest that although the CHANGE

task could be performed using the reactive inhibitory pathway, this would come at the cost of a delay due to the duration of the post-stimulus suppression. Thus, caudal pre-SMA may not be necessary for stopping per se, but might be more important for selectively inhibiting an action

plan in order to switch to an alternative response. This possibility is supported by evidence from studies of neurons in monkey pre-SMA and functional imaging in humans which suggest that pre-SMA may be crucial for switching between controlled and automatic behaviour ( Forstmann et al., 2008b and Isoda and Hikosaka, 2007). Thus, it is likely that this patient might also exhibit elongated reaction times on tasks which specifically test the ability to switch between response plans. Unfortunately, we did not have the INCB018424 solubility dmso opportunity to test this. As there is evidence to suggest that focal lesions can also result in disruption of network activity (Gratton et al., 2012), and since pre-SMA is thought to form a part of a right-lateralised inhibitory network (Aron et al., 2007), to what extent can it be reasonably argued that these findings are attributable to deficits solely in pre-SMA function? First, the lesion is a consequence of a resection, rather than vascular pathology, and is highly constrained within the grey matter, therefore it is unlikely that the observed behaviour is the result of a pure disconnection syndrome. Second, this distinct deficit in switching between responses is consistent MRIP with previous electrophysiological recordings in monkey pre-SMA

( Isoda and Hikosaka, 2007 and Isoda and Hikosaka, 2008), whereas the function of the other regions involved in this inhibitory network, IFC and STN, has been more consistently associated with either stopping responses or attentional capture ( Aron and Poldrack, 2006, Sharp et al., 2010 and Swann et al., 2012), behaviours in which we observed no deficit at all. However, future studies may still wish to consider employing functional or structural neuroimaging – such as DTI or resting state – in order to test for possible differences in network function following such lesions. The lateralisation of the lesion to the right hemisphere raises the question of whether a patient presenting with a left hemisphere lesion would demonstrate a similar deficit.