Observation after observation shows that complex interactions of genes and environment occur continuously and throughout the life of an organism. Within this context, how must we interpret the two papers recently published in Science on the development of place memory? (The papers are “Development of the Hippocampal Cognitive Map in Preweanling Rats” and “Development of the Spatial Representation System in the Rat” published June 18, 2010 in Science.)
The hippocampus and entorhinal cortex are important for an animal’s sense of where they are. Place cells in the hippocampus signal when an animal visits a particular place. Neurons in Entorhinal cortex known as grid cells, head-direction cells and border cells are also involved in animal navigation through space. (For these neurons’ relevance in humans see my recent blog post “Do You Know Where You Are? Place Memory.”)
The two research groups that published the papers asked how the responses of place cells, grid cells, and head-direction cells in animals exploring the environment outside their nests for the first time compared with responses in adults. Both teams showed that place cells exhibit adult responses from the earliest time points recorded. Both also observed head-direction cells with adult responses from the earliest ages recorded.
The teams disagreed on the appearance of grid cells. This seemed more due to different operational definitions of grid cells than differences in observations. To me the data look identical. The interpretations may be reconciled by working out the mechanisms that transform the immature (or less mature) grid cell to exhibit mature adult characteristics.
Nature versus nurture – is the system defined by genetics (nature) or is it sculpted through experience (nurture) – continues to stand as a useful and testable hypothesis that drives experimentation. However, we know that the environment, genetics, and the various systems at every level in between interact continuously and in complex ways.
Both research teams observed an increase in the number of cells exhibiting adult characteristics over time. One team observed environmental influences on characteristics of some cells but stated that aging without influence by the environment was dominant. These observations may be the key to going beyond the nature versus nurture debate. The genes and environment are in a continuous dance. Sometimes one leads. Sometimes the other.
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