Learning occurs at all stages of a lifetime. New skills are picked up by adults, just as they are by children. Thus, experience-dependent changes are persistent at all stages in life. Let us now zoom in to the molecular basis of this learning.
With frequent and strong correlated activation of neurons, the synaptic connections between them are strengthened. This use-dependent plasticity is due to the long-term potentiation of synapses. Similarly, the lack of correlated input leads to the weakening of the synaptic connections, resulting in long-term depression. Pre-natally, the presence of specific receptor molecules at the synaptic junctions are crucial in establishing the fundamental architecture of the neurons. Post-natal experiences further fine-tune this initial organization by the strengthening and weakening of synaptic connections. The neuronal dendrites have tiny protrusions known as dendritic spines. These spines are highly dynamic which have the potential to emerge and retract in presence of new learning.
The extracellular matrix in the brain is highly important for the stabilization of the neuronal circuitry. Interestingly, this stabilization takes place once it encounters relevant experiences. In animals deprived of vision during the critical period, this stabilization may not occur and hence we see the critical period extension into adulthood. In adults, the extra-cellular matrix has to be degraded in order for plasticity to happen. In presence of new experiences, learning necessitates plasticity and thus leads to the degradation of the matrix. This gives way to the motility of the dendritic spines. Spines are of various shapes and they synapse onto adjacent axons. Dendritic spines are initially transient with a high-turnover, but with days they pruned and only a few are stabilized. The spines are highly correlated to learning and memory. Memory requires consolidation, which takes place during sleep. It has been shown that sleep results in the stabilization of spines and pruning. Thus sleep, after a period of learning is necessary for the strengthening and weakening of the dendritic spines.
Zooming out, I realize that with every new skill I pick up, there is a cascade of molecular reactions that take place that enable the process of learning, encoding, and consolidation. Spines emerge in a matter of minutes with new learning, suggesting that our brain is indeed open to change. Why have we been fooling ourselves into thinking that change is impossible? The stubborn nature of mankind claimed that change is hard. But starting from tiny molecules to the neurons that make up the brain are ever-ready for change. We just have to open our minds and embrace it. The rest will take care of itself. Also, don’t forget to get a good night’s sleep!