NIVEL DE LAS COMPETENCIAS DE LOS PRACTICANTES Y SU VALORACIÓN DADA POR LOS EMPRESARIOS

Study 1 provided the first evidence for a new category-selective area in the human visual system (Bracci, et al., 2010). The anterior end of the left lateral occipital sulcus (LOS) showed a highly selective response to the visual presentation of human hands and was consistently localised in all 14 participants. This LOS hand-selective area partially overlaps with the left EBA, but is functionally and anatomically dissociated from it. Indeed, not only is the hand-selective region strongly lateralised in the left hemisphere (in right handers) relative to other well documented right- dominant selective areas for bodies (Downing, et al., 2001) and faces (Kanwisher, et al., 1997), but it is also characterised by a unique functional profile. The LOS hand-selective area responds most strongly to hands, but also partially to robotic hands, fingers and feet, while its response to depictions of various body parts did not significantly differ from baseline. By contrast, EBA responds most strongly to body parts, followed by hands and feet, and did not significantly respond

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to robotic hands or fingers. Finally, and most importantly, in contrast to the body-selective area, the hand-selective region responds to the inanimate category of tools but not to inanimate objects in general (see also Study 2 and Study 3). The two experiments reported in Study 1 provided strong evidence for a new category-selective area in the human visual system. Similar to other socially relevant object categories such as faces and bodies, hands continually play an important role in our daily life: hands are the primary way we interact with the external world (e.g., action execution) and visual processing of other people‟s hands mediates social interaction (e.g., action understanding, gestural communication, etc.). These occurrences might be a key factor in the evolution and specialisation of selective neural substrates to process visual information of hands (see Figure 6.1).

In Study 2, I reported evidence for a possible organising principle regarding the distribution of category-selective responses across human high-order visual cortex. In two independent fMRI studies, I investigated the distribution of selective responses to hands, tools, whole bodies, body parts, objects and visual motion. The results show a striking similarity between the response distribution of hands and tools, but not between tools (or hands) and other selective responses (e.g., to whole bodies). Both hands and tools, relative to various control categories, selectively activated the LOS hand region (Study 1) in left lateral occipitotemporal cortex (LOTC) in 27 of the 28 participants tested. Furthermore, multivoxel activity patterns across LOTC were highly similar to hands and tools, but were distinct from other categories including non-hand body parts. These results provide the first evidence for shared selectivity for hands and tools in higher-level visual cortex. Finally, functional connectivity analysis showed that the tool/hand region was selectively connected, relative to neighbouring regions, with regions in the left parietal and premotor cortex that have been implicated in tool-use execution and observation. The overlap between hand and tool responses indicates that the functional organisation of LOTC partly follows non-visual object dimensions (given that hands and tools differ in visual appearance and object domain). I propose that this is due to the constraint to connect object information encoded in LOTC to functionally specialised networks elsewhere in the brain (e.g., frontoparietal action network).

In Study 3, I tested whether hands and tools activate other areas beside LOTC. Interestingly, results provided evidence for correspondence between hand and tool representations in a left lateralised functional network that interconnects two regions: the left LOTC in the ventral „visual‟ stream (see also Study 2) with the left aIPSv in the dorsal „action‟ stream. Anatomical and functional correspondence between hand and tool representations was tested in 16 participants

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using block-design fMRI. Using a different set of stimuli and testing a different group of participants, we replicated the finding reported in Study 2 showing spatial (anatomical overlap) and functional (response profile similarities) binding between hands and tools in the left LOTC. Moreover, these results revealed new evidence for a similar hand-tool coupling in the left aIPSv. Furthermore, connectivity analysis showing patterns of mutual functional connectivity between the ventral left LOTC and the dorsal left aIPSv hand/tool regions brings additional support to the proposition that these regions are part of a common functional network devoted to hand/tool processing. In addition, hand responses (but not tool responses) were also found in the opposite ventral right aIPS and in the dorsal aspect of aIPS in both hemispheres. I advance the hypothesis that the aIPSd might be important to convey visual feedback during online visuomotor transformations of visually guided hand movements. Finally, the fusiform gyrus was found to encode representations of tools and hands in a distinct manner: whereas tools and non-graspable objects (inanimate domain in general) are encoded in the medial portion of the fusiform gyrus, hands and bodies (animate domain in general) are represented in the lateral portion of the fusiform gyrus. This latter result is in line with previous reports showing differential medial to lateral specificity with respect to inanimate and animate category domains (e.g., Mahon, et al., 2009). Taken together, these results further support the hypothesis that the LOTC and aIPSv hand/tool regions in the left hemisphere are part of a network that processes representations of both hands and tools to subserve common hand/tool computational processing (e.g., hand-tool visual- processing and action-representations).

In Study 4, I reported results showing that visually-evoked and motor-evoked hand-tool action-related responses are encoded within segregated neural substrates in the left LOTC and left aIPSv, despite the finding that group-level activation maps for execution and observation show consistent anatomical overlap within these regions. In this fMRI study, 16 participants were tested using a combination of conventional univariate whole-brain group-level activation analysis (GLM), as well as multivoxel pattern analyses (MVPA). The results of the whole-brain group-level analyses revealed consistent overlap between motor-evoked and visually-evoked responses for hand/tool actions in the left LOTC and the left aIPSv. However, more detailed investigation using MVPA revealed that motor-evoked and visually-evoked information is primarily encoded by spatially interleaved but functionally independent neural populations within these regions. These results show that, contrary to the largely accepted account of shared representations between action and perception (for reviews on the human mirror system: Agnew, et al., 2007; Rizzolatti &

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Craighero, 2004), the left LOTC and the left aIPSv appear to primarily encode hand-tool action- related motor and visual information in a distinct manner.

Figure 6.1. Schematic representation of the principal visual category-selective areas in the human visual cortex. The left hemisphere is portrayed from lateral view (left side). Brain areas are shown according to their category-selective preference: the object area (LOC), motion area (MT/MST), tool area (MTG), multisensory area (STG), extrastriate body area (EBA), occipital face area (OFA). The hand area (LOS) reported in this thesis is shown in the anterior part of the lateral occipital sulcus.