Neuroplasticity

The existence of neural plasticity does not mean the brain is a blob of clay pounded into shape by experience. Neuroplasticity or cortical plasticity is a concept in neuroscience referring to the fact that the brain can actually "re-wire" itself as a result of environmental inputs. This can occur in a number of ways. For instance, a neuron may change the number of neurotransmitters it releases and re-uptakes. Hebbian learning is a common form of neuroplasticity, which, informally, states that "neurons that fire together wire together." In the mid 1990s, neuroscientists in Europe, led by Herta Flor, were able to demonstrate that phantom limb pain can be associated with plastic changes in the cortex. This phenomenon is known as maladaptive plasticity.

Another example is a famous series of studies often informally referred to as the "London cabbie studies," in which the size of London taxi drivers' hippocampi (a brain structure responsible for spatial memory) were found to be significantly larger than those of the rest of the population and to have grown proportional to their time on the job. This is only one example of how environmental factors can influence brain structure.

So why does it matter?
The media and pop psychology absolutely love fMRI and other brain scanning techniques. Studies using one of these techniques are often snapped up by the press and get slapped with the headline "Brain differences in 'x' may be hard-wired!" The problem with this is simple: Because of neuroplasticity, the direction of causality in these studies cannot be determined. The differences may be due to "nature," "nurture," or (most likely) some mix of both, but it is impossible to tell from a single, one-time scan. So, no, a single scan does not magically reveal "hard-wired differences." Developmental and longitudinal studies may be undertaken to sort out some of these effects, however, they are less common than studies using single scans.

The "hard-wired" fetish has been variously dubbed "blobology," "neo-phrenology," "neuro-essentialism," "neuro-mysticism," and "neuro-bollocks." This sort of thinking tends to reduce neuroscience to a crude biological determinism. In addition, due to the popularity of evolutionary psychology, the authors of a perfectly fine neuroscientific study may be asked to speculate on the "evolutionary origins" of whatever effect they may have found, leading to a "just-so story" pop evo psych soundbyte mixed in with legitimate science.

Furthermore, what may end up being spurious results are often trumpeted as definitive findings. Due to the cost of using technology like fMRI, many of these studies must rely on small sample sizes and alleged differences may disappear in meta-analyses. Statistical analyses without correction for multiple comparisons may also skew the results. In addition, bad psychological models sound much more convincing with some neuro-babble chucked in, and that's ScienceTM. One claim that has entered the canon of neuro-mythology is the supposed larger female corpus callosum, which was variously reported on as being the "seat of women's intuition" or some other such nonsense. However, a meta-analysis demonstrated that the largest differences were found in studies with the smallest sample sizes and the differences were likely due to statistical noise.

Of course, the brain is not infinitely plastic or malleable and to what degree it is plastic is an open subject of debate in neuroscience. However, the basic concept of neuroplasticity often debunks the mis-representation of "hard-wired" differences reported in the media. On the flip side, "neuroplasticity" itself has become a buzzword wherein studies that show any changes in brain imaging are reported as "X can re-wire the brain!" This is true but trivial, as just about everything can "re-wire" the brain in some way. The question is how does it re-wire the brain? Neuroplasticity is a catch-all term for various processes, including synaptic plasticity (changes in the strength of synaptic connections), neurogenesis (the creation of new neurons), synaptic genesis/pruning (the creation and destruction of synapses), and neuronal migration (the movement of neurons away from where they are formed). Just bandying about the terms "neuroplasticity" and "re-wired" doesn't really say anything in terms of specific claims about the brain. Social media sites like Facebook have become popular targets for claims about how the internet is "re-wiring" our brains, and the world will subsequently go to hell in a hand-basket for some unspecified reason relating to neurotransmitters.

As always, it's probably a bit more complicated than that.