Publications

Abstract

The field of neuroanatomy of language is moving forward at a fast pace. This
progression is partially due to the development of diffusion tractography, which
has been used to describe white matter connections in the living human brain.
For the field of neurolinguistics this advancement is timely and important for
two reasons. First, it allows clinical researchers to liberate themselves from
neuroanatomical models of language derived from animal studies. Second, for
the first time, it offers the possibility of testing network correlates of
neurolinguistic models directly in the human brain. This chapter introduces the
reader to general principles of diffusion imaging and tractography. Examples of
its applications, such as tract analysis, will be used to explicate its potentials and
limitations.

Abstract

Our understanding of the functioning of the brain is primarily based on an average model of the brain's functional organisation, and any deviation from the standard is considered as random noise or a pathological appearance. Studying pathologies has, however, greatly contributed to our understanding of brain functions. For instance, the study of naturally-occurring or surgically-induced brain lesions revealed that language is predominantly lateralised to the left hemisphere while perception/action and emotion are commonly lateralised to the right hemisphere. The lateralisation of function was subsequently replicated by task-related functional neuroimaging in the healthy population. Despite its high significance and reproducibility, this pattern of lateralisation of function is true for most, but not all participants. Bilateral and flipped representations of classically lateralised functions have been reported during development and in the healthy adult population for language, perception/action and emotion. Understanding these different functional representations at an individual level is crucial to improve the sophistication of our models and account for the variance in developmental trajectories, cognitive performance differences and clinical recovery. With the availability of in vivo neuroimaging, it has become feasible to study large numbers of participants and reliably characterise individual differences, also referred to as phenotypes. Yet, we are at the beginning of inter-individual variability modelling, and new theories of brain function will have to account for these differences across participants.

Abstract

Following right-hemisphere damage, a specific disorder of motor awareness can occur called anosognosia for hemiplegia, i.e. the denial of motor deficits contralateral to a brain lesion. The study of anosognosia can offer unique insights into the neurocognitive basis of awareness. Typically, however, awareness is assessed as a first person judgement and the ability of patients to think about their bodies in more ‘objective’ (third person) terms is not directly assessed. This may be important as right-hemisphere spatial abilities may underlie our ability to take third person perspectives. This possibility was assessed for the first time in the present study. We investigated third person perspective taking using both visuospatial and verbal tasks in right-hemisphere stroke patients with anosognosia ( n = 15) and without anosognosia ( n = 15), as well as neurologically healthy control subjects ( n = 15). The anosognosic group performed worse than both control groups when having to perform the tasks from a third versus a first person perspective. Individual analysis further revealed a classical dissociation between most anosognosic patients and control subjects in mental (but not visuospatial) third person perspective taking abilities. Finally, the severity of unawareness in anosognosia patients was correlated to greater impairments in such third person, mental perspective taking abilities (but not visuospatial perspective taking). In voxel-based lesion mapping we also identified the lesion sites linked with such deficits, including some brain areas previously associated with inhibition, perspective taking and mentalizing, such as the inferior and middle frontal gyri, as well as the supramarginal and superior temporal gyri. These results suggest that neurocognitive deficits in mental perspective taking may contribute to anosognosia and provide novel insights regarding the relation between self-awareness and social cognition.

Abstract

Background: Functional neuroimaging supports the hypothesis that auditory verbal hallucinations (AVH) in schizophrenia result from altered functional connectivity between perisylvian language regions, although the extent to which AVH are also associated with an altered tract anatomy is less clear.

Methods: Twenty-eight patients with schizophrenia subdivided into 17 subjects with a history of AVH and 11 without a history of hallucinations and 59 age- and IQ-matched healthy controls were recruited. The number of streamlines, fractional anisotropy (FA), and mean diffusivity were measured along the length of the arcuate fasciculus and its medial and lateral components.

Results: Patients with schizophrenia had bilateral reduction of FA relative to controls in the arcuate fasciculi (p < .001). Virtual dissection of the subcomponents of the arcuate fasciculi revealed that these reductions were specific to connections between posterior temporal and anterior regions in the inferior frontal and parietal lobe. Also, compared with controls, the reduction in FA of these tracts was highest, and bilateral, in patients with AVH, but in patients without AVH, this reduction was reported only on the left.

Conclusions: These findings point toward a supraregional network model of AVH in schizophrenia. They support the hypothesis that there may be selective vulnerability of specific anatomical connections to posterior temporal regions in schizophrenia and that extensive bilateral damage is associated with a greater vulnerability to AVH. If confirmed by further studies, these findings may advance our understanding of the anatomical factors that are protective against AVH and predictive of a treatment response.

Abstract

Right hemisphere dominance for visuospatial attention is characteristic of most humans, but its anatomical basis remains unknown. We report the first evidence in humans for a larger parieto-frontal network in the right than left hemisphere, and a significant correlation between the degree of anatomical lateralization and asymmetry of performance on visuospatial tasks. Our results suggest that hemispheric specialization is associated with an unbalanced speed of visuospatial processing.