Habitual Lines of Thought

Physiologists tell us of the adaptation of brain structure to habitual lines of thought––i.e. to our habits.

from Charlotte Mason's Preface to the Home Education Series.

Neurophysiology has advanced much since the day when she wrote this, but the field still seems to support her thoughts on this matter. I found one example yesterday when I was looking for the information on the prefrontal cortex. From Brain Development and the Development of Executive Function:

Changes in the brain appear to be dependent on experience. For example, stress appears to slow down the creation of new neurons in the hippocampus, whereas using particular parts of the brain appears to make those parts grow. In one study by researchers in London, England, cab drivers (who have to pass a rigorous test demonstrating their knowledge of London streets) were found to have larger posterior hippocampi than other men of the same age. Moreover, the size of their posterior hippocampi corresponded closely to the number of years that they had been driving a cab. This finding suggests that relying heavily on spatial memory (and engaging regularly in navigation) leads to an increase in the size of the relevant brain areas—in this case the posterior hippocampus.

Another study makes the same point. This study, by researchers in Germany, examined the sensorimotor cortices of violin players—specifically the part that is associated with the complex fingering movements involved in playing the violin. Results indicated that this part of the brain was larger in the violin players than it was in people who don’t play stringed instruments.

Evidently, you can grow your own brain by using it! Whether this growth involves the creation of new neurons is unknown, but it almost certainly involves changes that affect the connections among neurons (for instance, thickening of dendrites). ...

Of course, this is mostly concentrated on professional habits, while Charlotte Mason was talking about habits involving "lines of thought". Still, I would imagine the principle would be somewhat the same.