London, January 31 : An animal study by researchers at the Salk Institute for Biological Studies has revealed that a process by which neural stem cells remain in proliferative state, known as neurogenesis, modulates learning and memory.
During the study, mice were genetically engineered to stop neurogenesis - literally the "birth of neurons" - and that turned them into "slow learners".
The troubles faced by them while navigating a water maze and remembering the location of a submerged platform evidenced that the mice had reduced their learning ability and memory.
The findings attain significance as, one day, they may enable scientists to stimulate neurogenesis with orally active drugs to influence memory function.
"Our study directly establishes that neurogenesis plays an important role in a defined process, the acquisition and storage of spatial memory," Howard Hughes Medical Investigator Ronald M. Evans a professor in the Salk Institute's Gene Expression Laboratory, was quoted as saying by Nature magazine in its online edition.
"This finding puts us in a new and important position to exploit the potential of stem cell-based therapies to improve brain function in neurodegenerative diseases such as Alzheimer's that are accompanied by a loss of memory," Evans added.
In a previous study, the same research team had found that a so-called orphan receptor, TLX, is crucial for maintaining adult neural stem cell in an undifferentiated, proliferative state.
Postdoctoral fellow Chun-Li Zhang combined mouse genetics and gene transfer techniques to genetically engineer mice, something that allowed him to specifically delete TLX in the brains of adult mice, and, thus, shut down neurogenesis.
The researcher then put the mice through a battery of standard behavioural tests.
The mice passed with flying colours in all but one test: the Morris water maze, a common behavioural test in which mice have to rely on visual cues on the surrounding walls to find and remember the location of a submerged platform hidden in a pool of milky water.
The task was designed in such a manner as would help researchers to observe the subjects' cognitive abilities such as analytical skills, learning and memory, and the ability to form strategies.
The more challenging the test was made, the more difficult the altered mice found it to navigate the maze and remember the location of the platform.
"The mice showed both learning and memory deficits. It's not that they didn't learn, they were just slower at learning the task and didn't retain as much as their normal counterparts," Zhang said.
Fred H. Gage, a professor in the Laboratory of Genetics, said: "Whatever these new neurons are doing it is not controlling whether or not these animals learn. But these new cells are regulating the efficiency and the strategy that they using to solve the problem."