Experience-dependent brain development
The last several decades have seen numerous debates on the extent of genetically determined neural circuitry and experience-dependent modifications. In this argument, the period in which the brain is most influenced by the environment, also known as the critical period, is highly talked about given the inconclusive evidence. Studying congenitally blind individuals who regained sight after several years, has proved to be a boon in understanding the role of experience in the development of the brain.
Infants are born with a preliminary architecture which is mostly under genetic control. After birth, these circuits are constantly shaped by the individuals’ experiences with the world. It is important to note that the modifications that take place as a result of experience are constrained by the infant’s genome as the environment entails plasticity by gene expression. In the early years, the infant’s brain is highly sensitive and the neural circuitry re-organizes and wires itself up to the patterns of the environment. The sensitive period demonstrates the importance of the right environmental exposure for proper brain development.
Having said this, it is interesting to envision a brain that never received these environmental stimuli in order for proper brain development. Several case studies of congenitally blind individuals who gained vision during the later years of their life have given us insights into the role of the environment. Immediately after gaining vision, they seem to have difficulties in object perception but do improve with time. The question that arises here is what happened to the neuron networks of their visual cortex? Since they never got any input, did they go into a developmental arrest and picked up once their vision was restored? In this case, it seems as if the brain remains plastic until appropriate inputs are re-established. The other argument is that the visual cortex took up inputs from other modalities such as haptic or auditory and got shaped by their inputs. In such a case, the immediate significant performance of the individuals with a restored vision does not seem to fit in well. We could argue that not all of the visual cortex performed other functions and some of it still remained sensitive to visual input. With time and experience using vision to perceive the world, their ability improves.
Several questions are yet to be answered with regard to the mechanisms behind the brain’s plasticity. For now, harnessing the brain’s ability to remain sensitive to the environmental stimuli even after the early years, has opened up great potential for rehabilitation after the restoration of vision.
