Nature Neuroscience

Language is classically considered a function of the left side of the brain, but there is actually a continuum of language lateralization from purely left-sided (common) to purely right-sided (rare) in the population. This individual variability is functionally important, report Knecht and colleagues in the July issue of Nature Neuroscience. The authors temporarily interrupted activity in language regions on each side of the brain and found that, in some people, both sides can support language processing; this work may explain why certain patients recover language abilities more quickly than others after brain damage.

The authors used brain imaging to select normal subjects with a range of language lateralization from left- to right-hemisphere dominance. While the subjects performed a task that required language skills, the authors delivered transcranial magnetic stimulation (TMS) to one side of the brain; they stimulated a region involved in language processing on the left side, or a homologous region on the right side. Such 'virtual lesions' disrupt the function of a targeted brain region for several minutes. In subjects with language dominance on one side, TMS over the dominant side slowed verbal processing, but TMS over the other side did not. Subjects with language representations on both sides of the brain were less affected by inactivation of either side. While functional imaging studies can monitor brain activity during different tasks, TMS experiments offer an important complement, as they can help to determine whether identified regions are indeed functionally relevant.

Nature Neuroscience

A paradoxical feature of drug addiction is that users work harder and harder, as the addiction progresses, to obtain drugs that they find less and less rewarding. Rats who experienced repeated withdrawals from prolonged cocaine self-administration showed a similar long-lasting decrease in brain reward function, correlated with increasing cocaine intake, says a study in the July issue of Nature Neuroscience. The authors speculate that treatments that block this decrease might prevent escalation of cocaine use, and thus may be promising therapies for addiction.

Serge Ahmed and colleagues implanted rats with electrodes that allowed them to press a lever to stimulate their own brains in a way that they find pleasurable. Previous work had shown that withdrawal from a single dose of cocaine briefly reduces the amount of work that rats are willing to do to obtain such brain stimulation, suggesting that they are not enjoying it as much. Now the authors report that this depression of the rewarding effect of brain stimulation became progressively worse with repeated cocaine exposure, but only in rats who had access to cocaine for six hours per day. Even after the availability of cocaine was reduced, the decrease in brain reward function lasted more than a week. The authors propose that this deficit in the ability to experience rewarding sensations during cocaine withdrawal may motivate animals to seek more drug to reverse the effect.

Nature Neuroscience

Those of us with little musical ability may wonder how professional musicians can make sense of the complex music that they play. The answer may lie in the finding that an area involved in auditory processing is larger and more responsive in professional musicians than in non-musicians, reported in the July issue of Nature Neuroscience. These results provide new insight into how musical ability is represented in the brain.

Peter Schneider and colleagues at the University of Heidelberg in Germany studied professional musicians, amateur musicians and non-musicians. Subjects heard tones of varying frequencies while brain responses were recorded within a region called Heschl's gyrus, part of the auditory cortex. Professional musicians showed greater responses to the tones than non-musicians; amateurs showed an intermediate response. Furthermore, when brain imaging techniques were used to measure Heschl's gyrus, the researchers found the structure to be larger in professional musicians. It remains unclear, however, whether such differences are due to a genetic predisposition or to increased exposure of professional musicians to musical training in early life.

Nature Neuroscience

Replacing the dopaminergic neurons that are damaged in Parkinson's disease with transplanted cells can improve symptoms. Last year, however, Curt Freed and colleagues showed that this treatment causes some patients to develop severe involuntary movement disorders. In the July issue of Nature Neuroscience, Olle Lindvall and colleagues now report that symptom relief is not correlated with the severity of movement disorders after such transplants, suggesting that it may be possible to prevent the development of side effects while maintaining the desired effects of this treatment.

The authors confirmed that dopaminergic transplants did increase the severity of movement disorders. In most patients, the movement disorders were mild and caused little distress, but one of the fourteen patients in the study was disabled by the side effects of the transplant. Patients whose dopaminergic neurons were most damaged before the transplant were the ones who suffered the most serious movement disorders afterward. Side effects were not predicted by how well the transplanted neurons survived and grew. The authors conclude that their findings provide no evidence that this side effect should stop further efforts to develop cell transplantation therapy for Parkinson's disease, and instead encourage more investigation into the causes of these undesirable effects.