Zones in a specific brain area change size depending on whether rats experience a calm or stressful environment, suggests a paper online in Nature Neuroscience this week. The observed size changes happen in a brain area involved in producing avoidance and approach behaviour.
An area deep in the brain known as the nucleus accumbens shell is subdivided into zones -- stimulating a zone towards the front of the accumbens shell causes rats to seek out food and mates, known as appetitive behaviour. Stimulating a zone towards the back of the accumbens causes rats to behave as if they are scared.
Sheila Reynolds and Kent Berridge now show that the size of these zones can be changed by the kind of environment in which the rats live. Rats feel safe in quiet, dark places and when rats were placed in such an environment, the area where electrical stimulation later resulted in appetitive behaviour expanded from the front of the accumbens shell to cover the back as well. About 90% of the accumbens shell became an appetitive behaviour generating zone in this condition. The size of the area where stimulation resulted in fearful behaviour shrank considerably.
In comparison rats find loud and bright environments very stressful. When rats were placed in a well-lighted room and made to listen to loud music, about 90% of the accumbens shell became a fearful behaviour generating zone. Stimulation in most places in this area resulted in fearful behaviour, and the area where stimulation resulted in appetitive behaviour shrank to the very front of the accumbens shell.
These findings suggest an explanation for how animals adjust their behaviour to match their environments.
Kent Berridge, University of Michigan, Ann Arbor, MI, USA)
Abstract available online.
(C) Nature Neuroscience press release.
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