Volume 8 Issue 9, September 2005

Choosing to accept enough risk, but not too much, is an important survival skill, and depending on the circumstances, animals may either seek or avoid risk. Given the choice between a sure bet and a larger but uncertain reward, a paper in this issue reports macaques consistently take the riskier option, and posterior cingulate cortex neurons represent the riskiness of those choices.

Certain Wnts attract ascending somatosensory axons up the spinal cord toward the brain. A study in this issue shows that other Wnts guide corticospinal axons down the spinal cord, not by an attractive mechanism but by repulsion through the receptor Ryk.

In the adult brain, new neurons are generated from neural stem cells residing in the subventricular zone. Newborn neuroblasts release the transmitter GABA, which reduces the proliferation of stem cells—and thereby neurogenesis—by a nonsynaptic mechanism.

Object identification improves with repeated presentation, but neural activity decreases. In a new study, disrupting inferior frontal activity with transcranial magnetic stimulation during initial exposure to an object blocks later behavioral and neural changes.

Neurofibrillary tangles, composed of tau protein, are a central feature of Alzheimer disease. A new paper challenges the idea that these tau inclusions alone cause disease by showing that they can be dissociated from memory impairment and neuronal loss.