Elsevier Editorial(Tm) for Neuroimage Manuscript Draft
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Elsevier Editorial(tm) for NeuroImage Manuscript Draft Manuscript Number: NIMG-04-81R1 Title: Distinct unimodal and multimodal regions for word processing in the left temporal cortex Article Type: Regular Article Keywords: Corresponding Author: Dr. Laurent Cohen Hôpital de la Salpêtrière Other Authors: Antoinette Jobert; Denis Le Bihan, MD, PhD; Stanislas Dehaene, PhD , , * Cover Letter Dear Sir, Thank you for giving us the opportunity to submit a revised version of our paper. We include a detailed cover letter with our responses to all the reviewers’ comments and suggestions. Sincerely Laurent COHEN Service de Neurologie 1 Hôpital de la Salpêtrière 47/83 Bd de l’Hôpital 75651 Paris CEDEX 13, France Tel: 01 42 16 18 49 / 01 42 16 18 02 Fax: 01 44 24 52 47 E-mail: [email protected] * Response to Reviews Response to Reviews Reviewer #2 1. The reviewer observes that our use of the terms “multimodal” and “crossmodal” was somewhat fuzzy and inaccurate. We basically agree, and we therefore modified the text accordingly. We no longer use the word “crossmodal” with reference to cortical areas, but only to effects such as “crossmodal priming”, which reveal the existence of shared representations for auditory and visual words. The word “multimodal” now applies uniformly to anatomical regions activated by both auditory and visual words. Accordingly, we modified the title, checked the entire text, and suppressed from the introduction our initial attempt to define the respective meaning of the two terms when applied to anatomical regions. Note that this terminology conforms to a common usage, and should not be taken to imply any strong theoretical commitment on functional brain organization. 2. The reviewer suggests that the introduction of a new anatomical label (the LILA, for lateral inferotemporal language area) may lead to useless rhetorical controversies without adding any substance to the scientific content of the data. He/she proposes that we should stick to more general labels such as BTLA (basal temporal language area). However, we think that whenever a brain system with defined functional properties is identified on sound empirical bases, the attribution of a distinctive label is not only legitimate but also quite useful. In the present case, as accepted by the reviewer, the identification of the LILA is based upon its original functional properties in terms of modality and task, and upon its anatomical localization, distinct from other systems such as the Visual Word Form Area. Moreover, we show that those functional and anatomical properties are reproducible across individual subjects. It therefore seems useful, in further work, to systematically distinguish the two regions. Giving them distinct names can only help further research, even before their complete functional characterization. As an example of a laudable outcome, we revisited in the discussion some of the neuroimaging literature on dyslexia, pointing to the clarifying role of the distinction between the VWFA and the LILA. In contrast, the exclusive use of the BTLA, a term which was initially proposed to label anterior inferotemporal regions in which direct stimulation yielded speech arrest in epilepsy patients, would yield more confusion, by pooling under a single term a variety of regions with distinct functional properties. 3. We prefer to leave the methodological considerations on conscious vs subliminal priming partly in the introduction and partly in the discussion. Presenting some possible drawbacks of conscious priming in the introduction allows to formulate more balanced predictions, and should help readers to understand word repetition effects as they appear in the results. 4. As suggested, we report more precisely the findings by Belin and Zatorre (2003) on the respective properties of the left and right STS. 5. The reviewer suggests that in Figure 5 we could indicate sulci by simple black lines. However in this figure we try to show not only the localization of inferotemporal activations, but also to illustrate their systematic relationship with specific sulci (the lateral occipitotemporal and inferior temporal sulci). In order to make this relationship visible across variations of individual anatomy, it was important that individual sulci be clearly identified. Therefore, using a different color code for the two main relevant sulci seemed preferable, rather that depicting them uniformly in black. Moreover, activations are mostly visible on translucid brain views, on which the whole surface of sulci is visible. Showing sulcal surface in black on those pictures would make them very difficult to grasp visually. Reviewer #3 1. The use of a combined threshold, with a requirement of statistical significance both for individual voxels and for the size of activated clusters (with the the appropriate correction for multiple tests) is standard practice. 2. The interaction of task and modality is presented by the end of the section titled “Task-related activations within each modality” (p. 15), and detailed activation data are provided at the bottom of Table 2. * Manuscript 1 Distinct unimodal and multimodal regions for word processing in the left temporal cortex 1,2Laurent Cohen, 2Antoinette Jobert, Denis Le Bihan,3 and 2,3 Stanislas Dehaene 1 Institut de Neurologie, Hôpital de la Salpêtrière, AP-HP, Paris, France 2 INSERM U562 « Cognitive Neuroimaging », Service Hospitalier Frédéric Joliot, CEA/DSV, Orsay, France 3 Anatomical and functional neuroimaging unit (UNAF), Service Hospitalier Frédéric Joliot, CEA/DSV, Orsay, France Correspondence : Laurent COHEN Service de Neurologie 1 Hôpital de la Salpêtrière 47/83 Bd de l’Hôpital 75651 Paris CEDEX 13, France Tel: 01 42 16 18 49 / 01 42 16 18 02 Fax: 01 44 24 52 47 E-mail: [email protected] 2 Abstract How are word recognition circuits organized in the left temporal lobe? We used functional magnetic resonance imaging to dissect cortical word-processing circuits using three diagnostic criteria: the capacity of an area (1) to respond to words in a single modality (visual or auditory) or in both modalities; (2) to modulate its response in a top-down manner as a function of the graphemic or phonemic emphasis of the task; and (3) to show repetition suppression in response to the conscious repetition of the target word within the same sensory modality or across different modalities. The results clarify the organization of visual and auditory word processing streams. In particular the visual word form area (VWFA) in the left occipito-temporal sulcus appears strictly as a visual unimodal area. It is, however, bordered by a second lateral inferotemporal language area (LILA) which is multimodal. Both areas might have been confounded in past work. Our results also suggest a possible homolog of the VWFA in the auditory stream, the auditory word form area, located in the left anterior superior temporal sulcus. 3 Introduction In literate adults, the perception of a written word gives access, within half a second, to a wide variety of representations and processes, ranging from orthography and phonology to semantics and articulation (Marinkovic et al., 2003). Accordingly, word reading is correlated with the activation of extensive bilateral cerebral networks, with left-sided predominance (for reviews, see e.g. Fiez and Petersen, 1998; Jobard et al., 2003; Price et al., 2003a). However, the efficacy of all those processing stages first depends on the fast and parallel identification of strings of letters by the visual system, which may be seen as the gateway into the reading network (Besner, 1989; Nazir, 2000; Paap et al., 1984; Pelli et al., 2003). Among the visual areas that are consistently activated during reading, we proposed that a region of the left inferotemporal cortex plays a crucial role in this perceptual expertise (Cohen et al., 2000). On the basis of imaging and neuropsychological data, we suggested that this region (the Visual Word Form Area or VWFA) computes a representation of abstract letter identities from visual input, a representation invariant for irrelevant parameters such as size, location, font or case (for reviews, see Cohen and Dehaene, in press; McCandliss et al., 2003). There are still ongoing controversies about the functional properties of the VWFA, and particularly about its involvement in the processing of auditory or even Braille words (Büchel et al., 1998; Cohen and Dehaene, in press; Price et al., 2003b). In a recent study using fMRI, we contrasted the processing of written and spoken words while subjects performed a same- different task on consecutive words (Dehaene et al., 2002). In agreement with our hypotheses, the left inferotemporal cortex was activated by visual words in every subject, while there was no activation by spoken words. However, a number of other studies have demonstrated left inferotemporal activations during the perception of auditory words (e.g. Binder et al., 1996; Büchel et al., 1998; Buckner et al., 2000; Chee et al., 1999; Démonet et al., 1992; Démonet et 4 al., 1994; D'Esposito et al., 1997; Giraud and Price, 2001; Perani et al., 1998; Pihlajamäki et al., 2000; Vandenberghe et al., 1996; Wise et al., 2000). As discussed in Cohen et al. (2002), this apparent discrepancy may result from at least two causes. First, the left inferotemporal cortex may encompass several distinct areas involved in word processing, each area having distinctive patterns of activation to written or spoken words. Due to their close proximity, such regions may be difficult to distinguish, particularly when comparing the coordinates of activations across subjects and across studies, including group PET studies with a relatively low spatial resolution. Notwithstanding those methodological limitations, a review of ventral temporal activations suggests that words in non-visual modalities yield activations more anterior (average y = -43) than the visual activations typical of the VWFA (average y = -60) (Cohen et al., 2002). Furthermore, the anterior activations are more sensitive to the semantic demands of the task, whereas posterior activations were observed even for visual pseudowords relative to random letter strings.