Grace Lindsay, a neuroscience graduate student from Columbia University, is guest blogging about neuroplasticity for our “Tales from the Lab” series. This is Grace’s third and final blog post.
Adaptation is crucial to survival: in a world where only the fittest survive, changing circumstances call for changing responses. While some bodily adaptations to the environment occur over long, evolutionary timescales, the brain has two key features that allow for behavioral adaptations to occur much faster: complexity and plasticity. The immense number of cells in the brain means that there are many ways that those cells could connect to each other, and plasticity allows for re-wiring that can sample some of these connection possibilities. When inputs to the brain cause re-wiring, the brain's response to a future input will be different—and hopefully more beneficial to the animal–than it was before. Acquiring a new physical skill, learning to avoid places associated with danger, and figuring out how to extract relevant information in a new environment are all adaptive behaviors that rely on this ability.
So what situations allow for this remarkable process, and what occurs in the brain? In order to study this, researchers take “before and after” shots of brain activity centered around exposure to a new environment, object, or behavioral demand. For example, human fMRI studies have shown how finger dexterity training increases activation in motor cortex, which correlates with increased performance over time.
Animal experiments allow us to investigate this plasticity more complexly and on a finer level. For example, researchers from Stanford fitted owls with prism glasses that shifted their field of vision. With the prisms, the visual information they received about the location of prey in their environment no longer lined up with the location information they received via auditory cues. Ordinarily, each cell in an area called optic tectum (OT) receives visual and auditory inputs representing the same location (the outputs of these cells help to create a cohesive map of the world), but the prisms created an offset in the two inputs. After 10 weeks of wearing the prisms, plasticity in the owls’ auditory synapses brought the inputs slightly back in line. The more remarkable finding, however, comes from a second group of owls given the same prisms. This group, unlike the first which was fed dead mice, was allowed to hunt for their food for one hour a day. At the end of 10 weeks, the auditory plasticity in this group was five times greater than that of the first, restoring the visual-auditory alignment in OT to almost pre-prism levels. This demonstrates the important role of relevant inputs in the plasticity process.
In certain situations, however, 10 weeks may be too long to wait for adaptation. Luckily, not all plasticity requires this much time. It has long been known that animals can learn to avoid aversive stimuli, and their predictors, after only one exposure. Researchers in the UK studied this in chicks. The researchers showed that after just one exposure to a chemically-coated bead, the chicks learned to avoid the bead. And the number of synapses onto cells in a forebrain area associated with memory formation increased significantly after just one hour post-exposure (when compared to chicks who were exposed to a water-coated bead). Thus, stimuli that are immediately relevant to the animal's well-being can exert a strong and quick influence on neural plasticity. And luckily so, since our ability to adapt on short timescales is what has ensured our survival.
Grace Lindsay is a first-year Ph.D. student in the Neurobiology and Behavior Program at Columbia University. She got her BS in neuroscience from the University of Pittsburgh in 2011 and then spent a year doing research at the Bernstein Center in Freiburg, Germany. She blogs about all things neuroscience at neurdiness.wordpress.com.