Neuroimaging of Single Cases: Benefits and Pitfalls

Abstract

Single case studies of neurological patients has a long and storied history (Zillmer & Spiers, 2001). First used as a teaching tool (Haas, 2001), the method of thoroughly exploring the cognitive and motor functions of a unique individual patient has led to extraordinary advances in our understanding of structure-function relationships in the human brain. Single cases have led to important advances in many fields, including pioneering work on language (Broca, 1861; see also Ryalls & Lecours, 1996) and visual perception (Poppelreuter, 1917/1990; see also Humphreys & Riddoch, 1996) to more recent work on memory systems (Scoville & Milner, 1957; Milner & Penfield, 1955-1956; see Milner, 2005 for a recent review) where one patient (HM) has arguably done more to advance that field than any other single case study in history. Prior to the advent of x-rays and eventually computerised axial tomography (CT scans), the method of studying single cases was the only way to determine the location of a patient's pathology. The advent of CT scans in the 1970's obviated, to some degree, the need for detailed neuropsychological testing, at least as it was needed to determine the location of pathology (Banich, 2004; Lezak, et al., 2004; Kolb & Wishaw, 2009). A few decades later and the advent of functional MRI (fMRI) provides an even more powerful tool for examining the nature of structure-function relationships in humans and in non-human primates (Ogawa et al., 1992; Ford et al., 2009). Indeed, the rapid rise of fMRI studies (Fox, 1997; Raichle, 1994) has outstripped the pace of single case studies in the past few decades (Figure 1). By 2005 the proportion of neuroimaging abstracts accepted for presentation at the Cognitive Neuroscience Society meeting was around 35% compared to only 15% for patient studies (which included group and single case methods; Chatterjee, 20051). There are a range of reasons behind the rise of functional neuroimaging studies including the ease and relatively low cost with which these studies can be carried out (Chatterjee, 2005). Although per hour imaging costs seem high to most, the cost of patient research is undoubtedly far higher both in time committed and real costs related to screening and following patients over longer periods of time (Chatterjee, 2005). In addition, each method