Saturday, September 25, 2010

Trade Off #10: Plasticity vs Specialization

In college, I was constantly reading neuro lit extolling the virtues of neural plasticity, which is the ability of neurons to change based on feedback from the environment. Plasticity certainly has huge benefits. Specifically, plasticity allows for a better match between phenotype and environment across variable environments than a single, constant phenotype would.

But after a while, the idolatry of plasticity began to annoy me, in part because much of the lit discussed plasticity as if it had no downsides, which seems impossible. (If there really were no costs to plasticity, then evolution should have selected for it like woah).

The general downside seems to be that plasticity hinders specialization. That is, if a system has the ability to change easily (i.e. it has high plasticity), then it will tend to expend resources on a wide range of trait values, and will have fewer resources to focus on the most important and relevant traits. A few examples:
  • Synaptic pruning and other mechanisms for synaptic plasticity allow for learning and memory, but they are energetically costly. Indeed, one hypothesis holds that sleep is the price we have to pay for plasticity the previous day. (see here)
  • In an evolutionary framework, the major costs to more plasticity are 1) actually sensing the current environmental conditions, and 2) producing the actual trait in a less efficient way. Both of these divert resources from other tasks. (see here and here)
  • People with autism spectrum disorders often find it difficult to parse novel stimuli, but can sometimes concentrate for especially long periods of time on specific niches. So one might think of the autistic cognitive style as shifted towards the specialization side of this trade off. (see here)
Despite the many applications, the members of the committee and I are a bit wary about this trade off. First, its status depends largely on one's particular definitions of plasticity and specialization. Also, some think it might just be a specific case of trade off #3, switching costs vs change gains.

But given our current working definitions (plasticity = the ability, which is highly correlated with the tendency, for context-dependent change; specialization = funneling energy expenditures to a narrow purpose), and because it is sort of one level "meta" to switching costs vs change gains, we are granting this trade off its own place in the canon.

(Above photo taken by flickr user uncle beast. Plants are often studied w/r/t genetic plasticity because they can't simply pack up shop and move if the environment changes, like an animal or insect could.)