The location of the stroke lesion itself may predict PSP. The lesions that were predictive of PSP in one study included the middle cerebral artery I (MCA I; sphenoidal segment), multiple hemispheric lesions (>1 major vascular territory), vertebrobasilar stroke and multiple vertebrobasilar stroke i.e. additional cerebellum and brainstem compromise [6]. Dysphagia wasn't controlled for in this trial but we can hypothesise on a fundamental level. Swallowing is a complex physiological mechanism and strokes can affect the process at a number of levels. Lesions in the pre-central gyrus for example interrupt oral, facial and lingual motor co-ordination contralaterally [11]. Strokes may compromise elements of cognitive function including attention and concentration leading to inefficient execution of swallowing [17]. Brainstem strokes are renowned for their association with dysphagia [11]. This is due to the complex interconnection between facial musculature, bulbar nuclei, swallowing centres and innervating suprabulbar neurones. This damage may herald aspiration pneumonia; further study is warranted to identify any neuroanatomical risk factors by functional imaging.