LETTER TO THE EDITOR Reply: ‘The anatomy underlying acute versus chronic spatial neglect’ also depends on clinical tests

Sir, earlier this year we published the first longitudinal study of spatial neglect in your journal (Karnath et al., 2011). Longitudinal studies of this profoundly debilitating disorder are crucial to unlock one of the great mysteries of this disorder: some individuals spontaneously recover while others are left with long-term deficits. Recently, Saj et al. (2011) responded to our work, noting that there are actually a variety of attentional deficits that are common following right hemisphere brain injury. Saj et al. (2011) warn that scientists need to be careful that they do not pool across different underlying syndromes, which may each rely on different anatomy and exhibit different patterns of recovery. We think their recent work adds to a growing consensus regarding the complex interaction of anatomy, recovery phase and symptoms observed following right hemisphere injury. While we believe this type of work will prove theoretically crucial (demonstrating the unique functional roles of different anatomical nodes) and clinically vital (providing improved long-term prognosis based on acute behaviour and acute imaging), we do think it is appropriate to fully describe the historical precedence for Saj et al.’s (2011) work. Further, we describe some of the methodological advances required in order to accurately address the issues raised by these authors. Saj et al.’s (2011) work hinges on the idea that there is not a single, unitary perceptual deficit associated with right hemisphere damage, but rather a series of relatively independent syndromes. Indeed, one of the striking features of right hemisphere injury is the variability of the symptoms observed. For example, stimuli might be missed on the left side of the patient’s space (egocentric neglect) or the left side of individual stimuli might be ignored regardless of position with respect to the body (object-centred or allocentric neglect). There is now compelling evidence that consolidating all symptoms under the catch-all term ‘spatial neglect’ is a misguided approach. Instead, a clear framework for core and satellite symptoms exists (Karnath and Rorden, 2011) based on the observation that individual symptoms correlate with specific anatomy. While Saj et al. (2011) describe some of the recent findings, it should be noted that these behavioural–anatomical dissociations have a long history. For example, Binder et al.’s (1992) seminal work noted that individuals with neglect who had difficulty accurately determining the midpoint of a line (a measure of allocentric deficits) had more posterior lesions than individuals who only had errors on cancellation tasks (a measure of egocentric neglect). This effect has been replicated (Rorden et al., 2006; Verdon et al., 2010; Vossel et al., 2011), and this behavioural distinction can even be used retrospectively to explain anatomy in individual patients in prior studies (cf. Mort et al., 2003). While much early work relied solely on the line bisection task to measure allocentric neglect, other tasks that attempt to dissociate egocentric and allocentric deficits appear to support the same anatomical dichotomy (Grimsen et al., 2008; Medina et al., 2009; Chechlacz et al., 2010; Verdon et al., 2010; however, see Hillis et al., 2005). doi:10.1093/brain/awr230 Brain 2011: Page 1 of 3 | 1