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Objectives-Eleven patients with idiopathic normal pressure hydrocephalus (NPH) were selected from an initial cohort of 43 patients. The patients with NPH fell into two distinctive subgroups: preshunt, group 1 (n=5) scored less than 24 on the mini mental state examination (MMSE) and were classified as demented and group 2 (n=6) scored 24 or above on the MMSE and were classified as nondemented. Methods-All patients were neuropsychologically assessed on two occasions: preshunt and then again 6 months postshunt. Group 1 completed the mini mental state examination (MMSE) and the Kendrick object learning test (KOLT). In addition to the MMSE and KOLT, group 2 completed further tasks including verbal fluency and memory and attentional tasks from the CANTAB battery. Nine of the 11 patients also underwent postshunt MRI. Results-Group 1, who, preshunt, performed in the dementing range on both the MMSE and KOLT, showed a significant postoperative recovery, with all patients now scoring within the normal nondemented range. Group 2, although showing no signs of dementia according to the MMSE and KOLT either preshunt or postshunt, did show a specific pattern of impairment on tests sensitive to frontostriatal dysfunction compared with healthy volunteers, and this pattern remained postoperatively. Importantly, this pattern is distinct from that exhibited by patients with mild Alzheimer's disease. Eight of the nine patterns of structural damage corresponded well to cognitive performance. Conclusions-These findings are useful for three main reasons: (1) they detail the structural and functional profile of impairment seen in NPH, (2) they demonstrate the heterogeneity found in this population and show how severity of initial cognitive impairment can aVect outcome postshunt, and (3) they may inform and provide a means of monitoring the cognitive outcome of new procedures in shunt surgery. (J Neurol Neurosurg Psychiatry 1999;67:723-732)

The systemic administration of norepinephrine has minimal effects on the cerebral circulation, perhaps due to blood-brain barrier mechanisms. To test hypothesis, the cerebrovascular effects of norepinephrine beyond the blood-brain barrier were studied in anesthetized baboons, Intraventricular norepinephrine (40 mug/kg) resulted in significant increases in cerebral blood flow (40%), cerebral oxygen consumption (21%), and cerebral glucose uptake (153%). Intracarotid hypertonic urea opens the blood-brain barrier by osmotic disruption; Consequent to hypertonic urea, the intracarotid infusion of norepinephrine, 50 ng/kg-min, significantly increase cerebral blood flow (49%), cerebral oxygen consumption (21%), and cerebral glucose uptake (76%), It appears probable that the cerebrovascular responses to norepinephrine are dependent on the integrity of the blood-brain barrier; It is likely that the increase in cerebral blood flow, associated with norepinephrine when it bypasses the barrier, is secondary to an increase in cerebral metabolism.

Indices derived from ICP waveform analysis can be helpful for the interpretation of progressive intracranial hypertension in patients after brain trauma.

A central goal of neuroscience is to understand how the brain synthesises information from multiple inputs to give rise to a unified conscious experience. This process is widely believed to require integration of information. Here, we combine information theory and network science to address two fundamental questions: how is the human information-processing architecture functionally organised? And how does this organisation support human consciousness? To address these questions, we leverage the mathematical framework of Integrated Information Decomposition to delineate a cognitive architecture wherein specialised modules interact with a “synergistic global workspace,” comprising functionally distinct gateways and broadcasters. Gateway regions gather information from the specialised modules for processing in the synergistic workspace, whose contents are then further integrated to later be made widely available by broadcasters. Through data-driven analysis of resting-state functional MRI, we reveal that gateway regions correspond to the brain’s well-known default mode network, whereas broadcasters of information coincide with the executive control network. Demonstrating that this synergistic workspace supports human consciousness, we further apply Integrated Information Decomposition to BOLD signals to compute integrated information across the brain. By comparing changes due to propofol anaesthesia and severe brain injury, we demonstrate that most changes in integrated information happen within the synergistic workspace. Furthermore, it was found that loss of consciousness corresponds to reduced integrated information between gateway, but not broadcaster, regions of the synergistic workspace. Thus, loss of consciousness may coincide with breakdown of information integration by this synergistic workspace of the human brain. Together, these findings demonstrate that refining our understanding of information-processing in the human brain through Integrated Information Decomposition can provide powerful insights into the human neurocognitive architecture, and its role in supporting consciousness.

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Transmission of intracranial pressure (ICP) to the perilymph of the cochlea may occur via the cochlear aqueduct and possibly other routes. Indirect measurement of perilymphatic pressure may be investigated by observing tympanic membrane (TM) displacement during stapedial reflex contraction. In a previous study we investigated the effects of changes in ICP on perilymphatic fluid pressure in three patients who underwent ventriculo/lumbar-peritoneal shunt operations. The TM displacement technique proved extremely sensitive and revealed marked changes in cochlear fluid pressure brought about by changes in ICP (Marchbanks et al., 1987). The study has been extended to 58 patients with hydrocephalus, intracranial tumours and other neurological conditions associated with abnormal ICP. Significant differences in the TM displacement were found between patients with raised and normal ICP. We have shown that changes in ICP can affect the hydrostatic pressure of the cochlea and influence the peripheral auditory system. The finding that ICP can be correlated with TM displacement strengthens the association between an abnormal TM displacement and abnormal cochlear hydrostatic status, irrespective of cochlear aqueduct patency. We suggest that the TM displacement technique provides a useful non-invasive method for the assessment of perilymphatic fluid pressure.