The shallow-lakes analogy
What Scheffer's lakes can teach us about depression — and about the limits of thinking in causes.
One of the most beautiful analogies from the work of Marten Scheffer concerns the shallow lakes of the Netherlands. Many of them are turbid, polluted and poor in biodiversity. But it need not be so. The same lake may also be clear — with a diverse fish population, water plants and visibility down to the bottom. What determines which state the lake is in? And, more importantly: how do we bring a turbid lake back to the clear state?
The obvious reasoning is that the phosphorus load is the determining factor. Much phosphorus (from agriculture, from wastewater) leads to algal bloom, leads to disturbance of the ecosystem, leads to turbid water. So: lower the phosphorus load, and you get your clear lake back.
When this was seriously tried a few decades ago — in various places in Europe and beyond — it turned out not to work. The phosphorus load was lowered far below the level at which the lake was still clear in earlier years, and yet the clarity did not return.
Hysteresis: there and back are not the same
What ecologists discovered is that such a lake is a complex system with two stable states — clear and turbid — and with a hysteresis effect between these states. The tipping point from clear to turbid lies at a far higher phosphorus load than the return tipping point. Stronger still: the return point can lie so low that it is no longer in fact feasible in an urbanised landscape.
The thinking in linear dose-response relations — more phosphorus, more turbid; less phosphorus, less turbid — falls short of reality here. The lake is not a linear system. It is a complex system with two attractors. Once in the turbid attractor, it takes more than merely removing the cause to come out.
"The dogma that the cause of the problem is the key to its solution does not necessarily hold for complex systems." — Han van der Maas, after Marten Scheffer
What did work: catching the fish
The breakthrough came when ecologists in the 1980s began with a radical intervention: in winter they netted nearly all the fish out. At first glance entirely illogical — what has fish to do with phosphorus? But it worked. In spring a new equilibrium arose, with other fish species, water plants and clear water. And this new clear state proved often to be stable, sometimes for many years.
The analysis of the cause — phosphorus — was not the key to the solution. The key was an intervention on a quite other variable, at a different level of the system, that pushed the system enough out of its equilibrium to tip into the other attractor.
From lakes to depression
Han van der Maas draws this parallel explicitly in his book. A depression has much in common with a turbid lake. Two stable states — healthy and depressed. A tipping that can come suddenly, often after a stressor that is "the last straw". And subsequently a peculiarly persistent phenomenon: the stressor disappears, life improves, and the depression remains. The return road does not run by the same route as the road out.
That lowering the original stressor does not automatically lead to recovery is not a treatment failure. It is a property of complex systems with hysteresis. We must dig deeper than the cause — or, better, we must search for the "fish" that we can catch to break the attractor.
What is the "fish" in depression?
That is precisely the question to which we have as yet no clean answer. But the thought itself is useful. Which interventions, which on the face of it have nothing to do with the original cause of a depression, may nevertheless disturb the system enough to make tipping possible?
A few candidates, with varying strength of evidence:
- Behavioural activation — not waiting until one feels better in order to do things, but doing things in order to be able to feel better. An intervention on behaviour, not on the "cause"
- Sleep restoration — often an early and powerful tipping moment, even when the original stressor had nothing to do with it
- Social reconnection — not as "treatment" of the depression, but as a change of the context in which the depression lives
- Sport — strikingly powerful, with effects reaching the neurophysiological level
- A radically different setting — an admission, a retreat, a stay abroad. Sometimes a disruption of routine is what the system needs
None of this is guaranteed. But it is a worthier line of thought than ever again trying to take away "the cause". For patients who hear for years "you must work on your trauma, then it will get better" — while the trauma does not yield and the depression remains — this may be a relief. It is not their fault that the linear model fails. The system works differently.
Inspiration for the consulting room
The shallow-lakes analogy invites a different gaze on a stuck patient. First of all, to some restraint towards the automatism that cause and solution should be each other's mirror image. Sometimes that is so; sometimes not at all. It is a hypothesis, not a given.
Next, to a certain creativity regarding interventions. Which "fish" could be caught here? Which variables in this life have perhaps not been "the cause", but may yet be capable of disturbing the system — or precisely of helping it reorganise?
And finally, to patience with patients who have been in their "turbid" state for years. There is no unwillingness at work there, and no weakness. What is at work is the persistence of an attractor in a complex system, and the wait for the right moment, the right intervention, the right conjunction of circumstances.
The shallow-lakes analogy is not everything. But for those who see the image, much clinical experience falls suddenly into better place. It is a metaphor with a scientific backbone — and that combination makes it useful.