The Excitable Membrane

“The restitution of (brain) function” is James’ phrase, and it’s a somewhat cumbersome one. Today we’d just refer to the underlying idea as the brain’s “plasticity.” James is a phenomenal writer, so I’m inclined to believe that if he could have gotten his intent across with a two dollar word instead of a ten dollar phrase he would have. I suspect he chose the ‘restitution’ phrasing to give more of a notion of a telos at work — something that gives a suggestion of a process sitting outside of ‘mere’ biology. Ideas around plasticity can definitely shade into neuromysticism about our seemingly endless capacity for recovery and reinvention.

Anyway, James gives us two theories to choose from to explain the recovery of function after brain (specifically cortical) injury. It’s either the case that: 1) lower centers pick up the slack, and quickly go about the business of learning the new tasks that higher centers are no longer doing, or 2) after injury, the native talents of the lower centers are released from habitual suppression (inhibition) by the higher centers. It’s like if your boss retired, and you stepped up and did a fine job. You either learned very quickly from scratch, or you always kind of were a boss, deep down, but only had to show it when the occasion called for it.

If you’re not a neuroscientist, idea #2 might sound a little exotic and implausible. But it turns out that this kind of “release from inhibition”, or ‘disinhibition’ is actually a really common motif in the brain. Rather than cooking up whole behaviors de-novo, in the moment, the brain often opts for the solution of keeping complex behaviors muffled and unexpressed, and simply releasing them, selectively, as needed. James reviews some of the evidence for inhibition and disinhibition, and sees little reason to doubt that the latter explains some of what’s observed when behaviors are recovered after injury. The important question to him is one of degree. Does all recovery result from the release of already extant capacities from inhibition, or is there also genuinely new learning, and formation of new compensatory paths after injury? (Note: we definitely know new paths form today. I’m just fleshing out James’ line of argument below since it’s logically sound, still relevant, and well worth thinking through)

James finds the extreme case of all recovery being the result of disinhibition unlikely. For starters, if it were true, that would imply that there’s “an almost incredible number of functions natively lodged in [sub cortical structures]”. In other words, it’s more likely that if you regain a lost ability to read after a brain injury it’s because a new brain area has learned how to read, rather than an already skilled but slumbering reader has been awakened.

The deeper questions here for James are about potential and predestination: are new things possible in the brain, and by extension, are we capable of real personal change? When we rise to the occasion, is that because we’ve learned a new trick through sweat and toil, or is it just the inexorable release of talents that are fixed at birth, and repurposed as needed?