Large-Scale Functional Brain Network Reorganization During Taoist Meditation.

Meditation induces a distinct and reversible mental state that provides insights into brain correlates of consciousness. We explored brain network changes related to meditation by graph theoretical analysis of resting-state functional magnetic resonance imaging data. Eighteen Taoist meditators with varying levels of expertise were scanned using a within-subjects counterbalanced design during resting and meditation states. State-related differences in network topology were measured globally and at the level of individual nodes and edges. Although measures of global network topology, such as small-worldness, were unchanged, meditation was characterized by an extensive and expertise-dependent reorganization of the hubs (highly connected nodes) and edges (functional connections). Areas of sensory cortex, especially the bilateral primary visual and auditory cortices, and the bilateral temporopolar areas, which had the highest degree (or connectivity) during the resting state, showed the biggest decrease during meditation. Conversely, bilateral thalamus and components of the default mode network, mainly the bilateral precuneus and posterior cingulate cortex, had low degree in the resting state but increased degree during meditation. Additionally, these changes in nodal degree were accompanied by reorganization of anatomical orientation of the edges. During meditation, long-distance longitudinal (antero-posterior) edges increased proportionally, whereas orthogonal long-distance transverse (right-left) edges connecting bilaterally homologous cortices decreased. Our findings suggest that transient changes in consciousness associated with meditation introduce convergent changes in the topological and spatial properties of brain functional networks, and the anatomical pattern of integration might be as important as the global level of integration when considering the network basis for human consciousness.

Dissection of the posterior inferior cerebellar artery in a young adult with cerebellar infarct.

The posterior inferior cerebellar artery (PICA) is frequently involved in dissection of the vertebral artery (VA); however, isolated PICA dissection has rarely been reported. A 37-year-old man experienced acute and progressive drowsiness, vertigo, occipital headache, vomiting, and ataxia. There was no precedent trauma or chiropractic manipulation. Neurologically, he had dysmetria of the left extremities. His NIHSS score was 3. Brain magnetic resonance imaging showed an acute cerebellar infarct in the left PICA territory. Magnetic resonance angiography showed a faint signal adjacent to the junction of the left VA and PICA, suggesting a vascular shadow. Catheter angiography showed focal stenosis with a post-stenotic fusiform aneurysmal dilatation of the left proximal PICA that was highly suggestive of dissection with pseudoaneurysm formation. He was treated with clopidogrel and was free of neurological symptoms 3 months after the stroke event. Isolated PICA dissection may be considered in patients with PICA territory infarct or subarachnoid hemorrhage. Treatment depends on the manifestations; ruptured dissecting aneurysms are often treated with surgery or embolization, and infarcts are usually treated with antithrombotic agents.