Draganski et al (2004) conducted experiments to determine if learning a new motor skill is associated with structural/functional changes in the brain. fMRI scans were used in a cohort of individuals learning to juggle. The study presents fMRI data in the context of procedural learning. Results indicate a significant increase in bilateral gray matter density within the mid-temporal lobe that is associated with visual memory. Over time, however, densities decreased. The conclusion offered is that of neuroplasticity that involves neural networks and axonal pruning.
What is important to understand is that procedural learning has been shown to involve building new neural connections and neural network associations in the cortex termed, parallel distributed processing. As learning progresses, many connections become redundant and are eliminated, resulting in the phenomenon termed synaptic pruning. These events are part of synaptic plasticity.
Another way to look at this is to understand what normally happens in the infant brain during postnatal development. Many synaptic connections become redundant during development and are pruned away, leading to more specific structure/function behaviors. As synaptic pruning continues, dendritic trees become more connected and form dendritic bundles. The synaptic arrangement within these bundles often is represented by ephaptic connections termed gap junctions. These dendrodendritic connections are electrotonic, not neurochemical, providing fast synchronized transmission via ion channels between dendritis bundles within a network.
The result is a new hard-wired structure/function correlate in learning and behavior. Admittedly, this is a broad overview of neural plasticity, but important to understand.
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