Electroencephalography

Alpha phase synchronization predicts P1 and N1 latency and amplitude size. Gruber, W. R. et al. Cereb. Cortex 15, 371–377 (2005)

There are two possible mechanisms for the generation of event-related evoked potentials (ERPs) — phase resetting of existing oscillations in the brain, or the imposition of stimulus-locked activity on random oscillations. Gruber and colleagues used several methods of analysis and found that the ERP components P1 and N1 are probably produced by phase resetting and synchronization between frequencies.

Neurodevelopment

A centrosomal mechanism involving CDK5RAP2 and CENPJ controls brain size. Bond, J. et al. Nature Genet. 37, 353–355 (2005)

Autosomal recessive primary microcephaly (MCPH) causes a reduction in the size of the cerebral cortex with reduced cognitive functions. The authors describe two mutations that can cause this disorder, in the genes CDK5RAP2 and CENPJ. In mouse embryos, these genes are expressed in the developing neuroepithelium and are localized at the centrosome during mitosis, which indicates that MCPH might be caused by an abnormality in the number of neurons generated that results from a centrosomal mechanism.

Neural Coding

Identification of network-level coding units for real-time representation of episodic experiences in the hippocampus. Lin, L. et al. Proc. Natl Acad. Sci. USA 102, 6125–6130 (2005)

Individual neurons in the brain show considerable variability in their responses to stimuli, and this variability makes it difficult to investigate how experiences are encoded in the brain. Lin and colleagues used a 96-channel array to record from neurons in the mouse hippocampus during episodes of 'startling', and identified network-level functional coding units that can represent these experiences in real time. The neurons within these units show 'co-spiking' dynamics that allow the variability of individual responses to be overcome.

Glia

Resting microglial cells are highly dynamic surveillants of brain parenchyma in vivo. Nimmerjahn, A. et al. Science 14 April 2005 (10.1126/science.11106471)

The authors used in vivo two-photon microscopy to study microglia in the uninjured neocortex of mutant mice that showed specific expression of enhanced green fluorescent protein in brain microglia. They found that 'resting' microglia, far from being dormant, are highly active. The cells extend motile protrusions into the surrounding environment and respond immediately to disruption of the blood–brain barrier with local activation and a switch to a 'shielding' role.