News & Views in 2005

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.

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.

Voluntarily paying attention to one object in a crowded scene enhances perception of that object and increases the activity of neurons representing it. Attention can also be drawn involuntarily by salient objects—for example, by the sudden onset of a bright stimulus. A study now shows how this involuntary type of attention may mediate competition between representations in human visual cortex.

Aβ peptide is linked to Alzheimer pathology, but its toxic mechanism remains unclear. New work shows that Aβ leads to internalization of NMDA receptors, reducing their availability at synapses. The authors also suggest a molecular mechanism for this endocytosis.

Cerebral cortex size in individuals and species is determined by cortical progenitor mitosis and death during embryogenesis. EphA signaling—important in axon guidance and patterning—also seems to be critical in regulating the survival of cortex progenitors.

A new paper shows that the transcription factor Dlx1, known to be involved in neuronal migration, is also necessary for interneuron survival. Mice lacking Dlx1 show subtype-specific loss of interneurons, a reduction in inhibitory currents and generalized seizures.

Reward-sensitive neurons are present throughout the brain. A report in Science now shows that a subset of thalamic neurons respond selectively to the smaller of two rewards, as opposed to just reflecting reward magnitude, as do neurons in other brain areas.

Empathy refers to our ability to share emotions and sensations such as pain with others. Imaging studies on pain showed that the affective but not sensory component of our pain experience is involved in empathy for pain. In contrast, a new study using transcranial magnetic stimulation highlights for the first time the role of sensorimotor components in empathy for pain in other people.

Although we hear sounds throughout their duration, studies on anesthetized animals have suggested that auditory cortex neurons primarily detect changes in sound. New evidence in a report in Nature from awake animals is forcing us to reconsider this view.

The rodent brain constantly generates new granule and periglomerular interneurons to replenish the olfactory bulb. New work shows that the two subtypes are derived from distinct progenitor populations, revealing unexpected diversity among adult neural stem cells.

Illusions of spatial vision can occur during rapid eye movements known as saccades. A new report shows that temporal judgments are also distorted around the time of saccades, suggesting that the neural representations of time and space may be linked.

The postsynaptic protein GRIP1 is now shown to work with the receptor tyrosine kinase EphB2 to bind a kinesin microtubule motor protein. This causes dendritic transport of EphB2, triggering a pathway critical for establishment and maintenance of dendritic arbors.

Hormonal changes during the estrous cycle have profound effects on synaptic transmission, from altering the density of synapses to changing receptor composition. A new paper shows that neurons express different subsets of GABA_A receptor subunits during different phases of the estrous cycle, and that this alters tonic inhibition, seizure susceptibility and anxiety in female mice.

A study in this issue describes the first multipotent stem cell identified in the postnatal cerebellum. These cells can generate inhibitory interneurons, astrocytes and oligodendrocytes. They may also be responsible for a class of childhood brain tumors.

How do genes act in the brain to influence susceptibility to mental illness? An imaging study suggests that healthy carriers of a gene variant associated with depression risk have decreased brain volume and neural coupling in affective circuitry involved in depression.

Sleep deprivation causes all too familiar behavioral impairments and increased need for sleep. A new Drosophila mutant with alterations in the Shaker potassium channel sleeps less than normal but does not show the usual effects of sleep deprivation.

How do we form arbitrary associations, such as 'stop at red' or 'go at green'? A report in Nature suggests that these associations are first formed in the striatum but that activity changes in the prefrontal cortex are more closely related to improved performance.