Deafferentation in thalamic and pontine areas in severe traumatic brain injury.

PURPOSE: Severe traumatic brain injury (TBI) is characterized mainly by diffuse axonal injuries (DAI). The cortico-subcortical disconnections induced by such fiber disruption play a central role in consciousness recovery. We hypothesized that these cortico-subcortical deafferentations inferred from diffusion MRI data could differentiate between TBI patients with favorable or unfavorable (death, vegetative state, or minimally conscious state) outcome one year after injury. METHODS: Cortico-subcortical fiber density maps were derived by using probabilistic tractography from diffusion tensor imaging data acquired in 24 severe TBI patients and 9 healthy controls. These maps were compared between patients and controls as well as between patients with favorable (FO) and unfavorable (UFO) 1-year outcome to identify the thalamo-cortical and ponto-thalamo-cortical pathways involved in the maintenance of consciousness. RESULTS: Thalamo-cortical and ponto-thalamo-cortical fiber density was significantly lower in TBI patients than in healthy controls. Comparing FO and UFO TBI patients showed thalamo-cortical deafferentation associated with unfavorable outcome for projections from ventral posterior and intermediate thalamic nuclei to the associative frontal, sensorimotor and associative temporal cortices. Specific ponto-thalamic deafferentation in projections from the upper dorsal pons (including the reticular formation) was also associated with unfavorable outcome. CONCLUSION: Fiber density of cortico-subcortical pathways as measured from diffusion MRI tractography is a relevant candidate biomarker for early prediction of one-year favorable outcome in severe TBI.

The multimodal connectivity of the hippocampal complex in auditory and visual hallucinations.

Hallucinations constitute one of the most representative and disabling symptoms of schizophrenia. Several Magnetic Resonance Imaging (MRI) findings support the hypothesis that distinct patterns of connectivity, particularly within networks involving the hippocampal complex (HC), could be associated with different hallucinatory modalities. The aim of this study was to investigate HC connectivity as a function of the hallucinatory modality, that is, auditory or visual. Two carefully selected subgroups of schizophrenia patients with only auditory hallucinations (AH) or with audio-visual hallucinations (A+VH) were compared using the following three complementary multimodal MRI methods: resting state functional MRI, diffusion MRI and structural MRI were used to analyze seed-based Functional Connectivity (sb-FC), Tract-Based Spatial Statistics (TBSS) and shape analysis, respectively. Sb-FC was significantly higher between the HC, the medial prefrontal cortex (mPFC) and the caudate nuclei in A+VH patients compared with the AH group. Conversely, AH patients exhibited a higher sb-FC between the HC and the thalamus in comparison with the A+VH group. In the A+VH group, TBSS showed specific higher white matter connectivity in the pathways connecting the HC with visual areas, such as the forceps major and the inferior-fronto-occipital fasciculus than in the AH group. Finally, shape analysis showed localized hippocampal hypertrophy in the A+VH group. Functional results support the fronto-limbic dysconnectivity hypothesis of schizophrenia, while specific structural findings indicate that plastic changes are associated with hallucinations. Together, these results suggest that there are distinct connectivity patterns in patients with schizophrenia that depend on the sensory-modality, with specific involvement of the HC in visual hallucinations.

Structural abnormalities in the cerebellum and sensorimotor circuit in writer's cramp.

BACKGROUND: Structural abnormalities were detected in bilateral primary sensorimotor areas in writer's cramp. Evidence in other primary dystonia, including blepharospasm and cervical dystonia, suggest that structural abnormalities may be observed in other brain areas such as the cerebellum in writer's cramp. OBJECTIVE: To test the hypothesis that structural abnormalities are present along the sensorimotor and cerebellar circuits in patients with writer's cramp. METHODS: Using voxel-based morphometry, the authors compared the brain structure of 30 right-handed patients with writer's cramp with that of 30 healthy control subjects matched for gender, age, and handedness. RESULTS: Gray matter decrease was found in the hand area of the left primary sensorimotor cortex, bilateral thalamus, and cerebellum (height threshold p < 0.01, cluster significant at p < 0.05 corrected for multiple comparisons). CONCLUSIONS: These results demonstrate in writer's cramp the presence of structural abnormalities in brain structures interconnected within the sensorimotor network including the cerebellum and the cortical representation of the affected hand. These abnormalities may be related to the pathophysiology of writer's cramp, questioning the role of the cerebellum, or to maladaptive plasticity in a task-related dystonia.