Alistair Jenkins

High-Frequency Network Oscillations in Cerebellar Cortex

Both cerebellum and neocortex receive input from the somatosensory system. Interaction between these regions has been proposed to underpin the correct selection and execution of motor commands, but it is not clear how such interactions occur. In neocortex, inputs give rise to population rhythms, providing a spatiotemporal coding strategy for inputs and consequent outputs. Here, we show that similar patterns of rhythm generation occur in cerebellum during nicotinic receptor subtype activation. Both gamma oscillations (30-80 Hz) and very fast oscillations (VFOs, 80-160 Hz) were generated by intrinsic cerebellar cortical circuitry in the absence of functional glutamatergic connections. As in neocortex, gamma rhythms were dependent on GABA(A) receptor-mediated inhibition, whereas VFOs required only nonsynaptically connected intercellular networks. The ability of cerebellar cortex to generate population rhythms within the same frequency bands as neocortex suggests that they act as a common spatiotemporal code within which corticocerebellar dialog may occur.

A nonsynaptic mechanism underlying interictal discharges in human epileptic neocortex

Very fast oscillations (VFOs, >80 Hz) are important for physiological brain processes and, in excess, with certain epilepsies. Putative mechanisms for VFO include interneuron spiking and network activity in coupled pyramidal cell axons. It is not known whether either, or both, of these apply in pathophysiological conditions. Spontaneously occurring interictal discharges occur in human tissue in vitro, resected from neocortical epileptic foci. VFO associated with these discharges was manifest in both field potential and, with phase delay, in excitatory synaptic inputs to fast spiking interneurons. Recruitment of somatic pyramidal cell and interneuron spiking was low, with no correlation between VFO power and synaptic inputs to principal cells. Reducing synaptic inhibition failed to affect VFO occurrence, but they were abolished by reduced gap junction conductance. These data suggest a lack of a causal role for interneurons, and favor a nonsynaptic pyramidal cell network origin for VFO in epileptic human neocortex.

Gap junction networks can generate both ripple-like and fast ripple-like oscillations

Fast ripples (FRs) are network oscillations, defined variously as having frequencies of > 150 to > 250 Hz, with a controversial mechanism. FRs appear to indicate a propensity of cortical tissue to originate seizures. Here, we demonstrate field oscillations, at up to 400 Hz, in spontaneously epileptic human cortical tissue in vitro, and present a network model that could explain FRs themselves, and their relation to ‘ordinary’ (slower) ripples. We performed network simulations with model pyramidal neurons, having axons electrically coupled. Ripples (< 250 Hz) were favored when conduction of action potentials, axon to axon, was reliable. Whereas ripple population activity was periodic, firing of individual axons varied in relative phase. A switch from ripples to FRs took place when an ectopic spike occurred in a cell coupled to another cell, itself multiply coupled to others. Propagation could then start in one direction only, a condition suitable for re‐entry. The resulting oscillations were > 250 Hz, were sustained or interrupted, and had little jitter in the firing of individual axons. The form of model FR was similar to spontaneously occurring FRs in excised human epileptic tissue. In vitro, FRs were suppressed by a gap junction blocker. Our data suggest that a given network can produce ripples, FRs, or both, via gap junctions, and that FRs are favored by clusters of axonal gap junctions. If axonal gap junctions indeed occur in epileptic tissue, and are mediated by connexin 26 (recently shown to mediate coupling between immature neocortical pyramidal cells), then this prediction is testable.

Glissandi: transient fast electrocorticographic oscillations of steadily increasing frequency, explained by temporally increasing gap junction conductance

Purpose:  We describe a form of very fast oscillation (VFO) in patient electrocorticography (ECoG) recordings, that can occur prior to ictal events, in which the frequency increases steadily from ∼30–40 to >120 Hz, over a period of seconds. We dub these events “glissandi” and describe a possible model for them.

Osteochondroma of the rib: An unusual cause of paraparesis

A case of extradural spinal cord compression secondary to invasion of the spinal canal by a costal osteochondroma is reported. The literature relating to osteochondromas of the thoracic region is reviewed.

Congenital glioblastoma multiforme: complete resection with long-term survival and a novel technique of contralateral cystoventriculostomy.

Congenital glioblastomas are rare primary tumours of the central nervous system with poor prognosis if left untreated. We report the case of a 4-week-old infant with such a tumour treated by surgical excision and a course of postoperative chemotherapy. After the chemotherapy, the patient displayed a neurological deterioration and follow-up magnetic resonance imaging (MRI) scans revealed no signs of recurrence, but showed entrapment and significant distension of the right lateral ventricle. A novel technique of contralateral cystoventriculostomy was performed to attempt to decompress the cyst and improve the infants neurological status. After surgery there was a significant neurological improvement, and 30 months after resection the child is alive, with mild hemiparesis and no signs of recurrence on follow-up MRI scan. The cystoventriculostomy is patent and continues to decompress the encapsulated ventricle.

Tethering of the cervico–medullary junction with central cord oedema after foramen magnum decompression for Chiari malformation

An unusual complication following foramen magnum decompression for Chiari malformation is described: adhesive tethering of the cervico–medullary junction with oedema of the upper spinal cord and lower medulla. Further surgery was required to correct this condition.

Trigeminal neuralgia from an Arteriovenous malformation: An intra-operative diagnosis

Abstract We report the case of a 72-year-old lady with a magnetic resonance imaging (MRI) occult arteriovenous malformation (AVM) causing trigeminal neuralgia (TN). The possibility of an AVM when managing patients with TN should be borne in mind. Where possible, decompression of the trigeminal nerve should be attempted, as first-line therapy.

National audits need more sensitive and specific outcome measures for quality improvement

We agree with Westaby’s views on publishing individual surgeons’ death rates.1 In April, the Society of British Neurological Surgeons launched the Neurosurgical National Audit Programme (NNAP)—a comprehensive audit of elective and non-elective neurosurgical services. The NNAP has been mandated by NHS England to publish surgeon and unit level death rates in the 2014 Consultant Outcome Publication. Through the NNAP, neurosurgeons have undertaken a …

Ventriculitis from a pituitary prolactinoma: bacterial or chemical?

Abstract We report the case of a 70-year-old man presenting with pituitary apoplexy from a macroprolactinoma and ventriculitis. It was not possible to distinguish a bacterial or chemical origin, on the basis of his clinical presentation, laboratory studies and imaging, highlighting the importance of prompt imaging and attainment of CSF cultures, in making the diagnosis.