Years ago, London neurobiologists discovered a way to visualize the structural dynamics of memory formation using just a laser, a microscope, and a window. To start, they vivisected the craniums of dozens of laboratory mice and surgically embedded tiny glass panels into the outer fleshy folds of the living, exposed brains.
The researchers specifically targeted an area of the brain known as the visual cortex; their goal was to define the relationship between vision and memory. These implanted bits of glass were to serve as physical windows to the branching, ductile neurons of the brain; when scanned by a laser, they would allow for capture of microscopic images of fluorescing neurons and provide a glimpse into the creation of memories.
In 2009, their laborious efforts paid off. Mark Hubener’s lab at University College reported in January’s issue of Nature magazine that they had found a link between distinct neural growths and memories of past experiences. Through miniscule peepholes, Hubener’s team saw bud-like spines emerging from the branches of the brain’s neurons. These spines seemed to sprout most in response to new experiences, implicating them as the brain’s physical storage areas for memory.
Because Hubener’s work is fairly visual in nature, it’s easiest to begin with a mental picture of the brain. Let’s start by imagining its most basic component, the neuron, as a tree in winter, leafless with many branches, or dendrites. If the neuron is a tree, then the brain, quite simply, would be the forest where it resides. Now, if you can imagine that forest with one hundred billion trees densely packed into a space the size of a grapefruit, then you’ve got a basic idea of what the human brain looks like.
Not impressed? Each tree in your brain forest physically contacts the branches of thousands of other trees; in children, these contacts, or synapses, number a quadrillion, in adults, this number decreases then stabilizes to a mere few hundred trillion. If synapses were dollars, we’d have enough money to pay for the Bush administration’s tax cuts… for two thousand years*.
So, what’s the purpose of all of these branching contacts? Synapses serve as conduits of communication between neurons- they allow information to race from dendritic branch to dendritic branch, relaying messages of sense, perception, reaction, and thought. But what about memory? Where are our recollections of past experiences stored among this vast network of neurons?