Utility dependent plasticity
When we say that experience shapes our brain’s circuitry, a fundamental question to ask is ‘what kind of experiences?’ A very simple answer is that experience relevant to us renders our neural networks in a heightened state of plasticity. Every time a stimulus is meaningful to us, we attend to it. But how do we then know if a stimulus would indeed be worth attending to? Here is when we need to talk about the way we learn from the environment.
The environment around us bombards us with millions of stimuli at every time point. But thankfully there is some kind of pattern in all of these stimuli and we are able to statistically track frequency, co-occurrence of stimuli, and the transitional probability of one stimulus following another. In that sense, we are all statistical learners. Every behavioral response that is classified as innate, that is the stimulus-response circuitry being genetically determined was probably learned at some point during the course of evolution from a single-celled to complex multi-cellular creatures. With repeated exposure, it was learned that responding reflexively to certain kinds of stimuli became necessary for survival. Since they were useful characteristics, they became genetically encoded and hence we innately exhibit reflexive behavior from the moment we are born. Apart from such pre-determined circuitry most of it is shaped during the life-span of an individual based on the experiences that one receives. Infants do not have any prior knowledge of what stimuli are important and what are nothing but irrelevant noise. But they are great statistical learners. Based on the frequency of occurrence of a stimulus, they learn that something is important. Eventually, they track the co-occurrence of other stimuli that occur with it and perceive them to be relevant as well. To sum up, we can say that relevance of the stimuli is learned from the environment itself, at least during the early stages of infancy.
The famous Hebbian learning rule which says, ‘Neurons that fire together, wire together’ is crucial to understand how the brain organizes itself. As mentioned previously, temporally co-occurring stimuli are tracked and represented together in the cortex. These co-incidentally firing neuronal networks get wired together. The fate of these networks depends on their utility. They are further strengthened or weakened based on the relevance of experience during development. Thus, it is essential to note that mere exposure to stimuli alone does not determine the extent to which it re-organizes the neuronal networks, but is determined by the meaningfulness and the value that it encodes.
Hence the experiences that shape our brain the most, are the ones that matter to us the most!
