Where Equilibrium Backfires: Allostasis Explained
Anyone who has tried to lose weight knows that the body has a maddening way of defeating our intentions by magically resetting back to “normal.”
The process is broadly referred to as “homeostasis,” where our biology finds a way of maintaining the body's equilibrium. Closely related is “allostasis.”
Homeostasis assumes an unchanging environment, say where you’re not trying to lose weight. Various biological feedback loops insure you don’t wake up 20 pounds heavier in the morning, though it may seem that way to some.
Go on a diet, though, and your body automatically assumes you’re in sub-Saharan Africa in the middle of a twenty-year famine. Suddenly, everything gets stored as fat, even - seemingly - that baby spinach leaf salad that has replaced your double-cheese pizzas.
This is allostasis, “stability through change.” Typically, allostasis is about anticipation. Say, if you are about to engage in physical activity, you will experience a temporary spike in glucose levels. This spike is perfectly normal, even if the reading raises diabetes alarm bells.
Later, the glucose will recede to its standard “set point.” Stability through change.
As you may have guessed, homeostasis and allostasis apply to every process in our body, including brain function. Thus, in reaction to unanticipated pleasure, a particular brain circuit may deliver a pulse of dopamine, plus other neurochemicals, to the striatum and frontal cortex.
In the context of bipolar, equilibrium tends to be where we want to be - or at least where the people around us wish we were, and here we run into a major problem.
Where equilibrium backfires ...
According to a commentary (paid access) in the October JAMA Psychiatry by Peter Sterling of the University of Pennsylvania, psychiatry misses the whole point of allostasis.
Let’s start with the premise that psychiatric drugs influence synaptic transmission in a variety of ways, such as by inhibiting reuptake of certain neurotransmitters. This leads to the idea that psychiatric disorders are essentially disorders of the synapse.
From there, psychiatry assumes that synaptic activity needs to be maintained within certain set parameters, equivalent to maintaining steady glucose levels in patients with diabetes.
Thus, neurotransmitter flow is expected to remain constant - not too high, not too low, not too strong, not too weak. This, in essence, is a homeostatic view of the brain.
Perhaps you have already guessed the catch, two of them, actually: For one, unlike glucose levels, we have no magic numbers to indicate “normal” synaptic flow. Our brain is way too complex for that.
The big one, though, is that wild fluctuations in synaptic activity are perfectly normal. Think of that sudden pulse of dopamine in response to pleasure.
The pleasure you experience, in turn, may be a response to something you are trying to learn, such as a musical passage on an instrument.
The last thing we need is our meds interfering with all this. Equilibrium may be fine, but not at the expense of messing the brain’s ability to adapt to its environment.
Says Dr Sterling:
Mental health is the capacity to choose among thoughts and shift flexibly between them; it is the capacity to match mood and affective expression to the immediate situation.
Mental illness, on the other hand is the very opposite. We may find ourselves stuck in one thought or emotion or mood. This suggests, says Dr Sterling, that the goal of therapy is to restore our brain’s responsiveness to the full range of signals.
Not surprisingly, on meds we feel blunted. According to Dr Sterling, this blunting should not be regarded as a side effect, as such. Rather blunting should be seen as the predictable outcome of interfering with allostasis.
Allostatic overload ...
So far, so good, but this is the point in the discussion where we need to raise our hands and ask about “allostatic overload.” Dr Sterling doesn’t talk about this, so let's fill in the blanks.
Allostatic overload is essentially a failure of allostasis. Thus, it is normal for the body and brain to enter into a state of “fight or flight” in response to a stressful event. In due course, our circuits will reset to normal.
But constant exposure to stress may sabotage the brain's ability to appropriately respond and to readjust. In this context and in similar ones, a pharmaceutical assist is certainly appropriate.
The homeostasis complication ...
Robert Whitaker’s book, Anatomy of an Epidemic, is largely based on the premise that homeostasis-allostasis ultimately defeats the purpose of long-term meds use. Thus, if you are on a med that blocks dopamine from attaching to certain receptors, the brain’s neurons may grow more receptors to compensate.
This is still a hotly debated subject, but Mr Whitaker certainly raises a case to be answered.
Keep your eye on the prize ...
The long term goal of any therapy or treatment or recovery plan is to restore the brain to what Dr Sterling refers to as a process of “predictive regulation.” This involves:
... continual remodeling of neural circuits. The adult brain continues to grow new synapses, and it makes space for them by pruning old ones. Thus mental health—responsiveness—involves both learning and forgetting.
According to Dr Sperling, this boils down to “practice plus plasticity.” To learn a new behavior, for instance, we need to repeat it. But remodeling a circuit also requires our synapses being sensitive to chemical signals.
Does your doctor understand this?