SCIENCE DISCUSSION TOPIC STRATEGIES OF LESION LOCALIZATION – Reply to Marshall, Fink, Halligan and Vallar

Much to our regret we recognise, that our recently published data and considerations based on these facts were substantially misunderstood in the present comment of John Marshall and colleagues (this volume). First, we must reject the assumption, that our work “confirms that unilateral visuo-spatial neglect can result from lesions of right temporal cortex and from lesion of right parietal cortex”. In fact, we published an analysis of the cortical anatomy of 25 patients with spatial neglect demonstrating a significant area of lesion overlap, that was located in the middle part of the superior temporal gyrus and not in the parietal cortex or the temporo-parieto-occipital (TPO) junction area (Karnath et al., 2001). This outcome is fundamentally different from the hitherto known findings of previous studies on the same topic, recently reviewed by Vallar (2001). Second, and even more important, we never intended to distinguish between several subgroups of neglect patients. A differentiation between “pure spatial neglect” on the one hand and “impure spatial neglect” on the other hand representing two different types of neglect, as put forward here by John Marshall and his colleagues (this volume), is misleading and does not exist in our conclusions and considerations. The term “pure” spatial neglect, that we used in our recent article (Karnath et al., 2001), simply refered to the fact, that patients with neglect included in that study did not suffer from hemianopia, a neurological symptom that is frequently observed in association with hemispatial neglect. Our work was motivated by the fact, that preceding studies on the same topic included a considerable proportion of neglect patients with additional hemianopia. Although hemianopia and hemispatial neglect frequently co-occur, hemianopia obviously represents an unique disorder and cannot be regarded as an integral part of the neglect syndrome. Following an infarct in the vascular territory of the middle cerebral artery (MCA), hemianopia results from damage to the optic radiation. Including a considerable number of neglect patients with additional hemianopia in anatomical studies thus will bias the region of overlap to those areas associated with the occurence of hemianopia, i.e. the subcortical and cortical neural tissue supplied by the posterior branch territory of the MCA. (The cortical tissue that mortifies with such lesions is located in the inferior parietal lobe and the TPO junction area as can be taken, for example, from our recent study that illustrated the lesion overlap in four patients with “pure” hemianopia, i.e. who had only hemianopia after a right MCA infarct without additional spatial neglect.)