Have you ever felt your brain transforming to a lump of jelly when you encountered something contradicting all prior knowledge and experience? Well, maybe then you can imagine how my brain felt when it digested the following statement in Jordan Peterson's book 12 Rules for Life1:
If a dominant lobster is badly defeated, its brain basically dissolves. Then it grows a new, subordinate’s brain--one more appropriate to its new, lowly position.[ed: cites Yeh et al. 1996 here] Its original brain just isn’t sophisticated to manage the transformation from king to bottom dog without virtually complete dissolution and regrowth.
Woah, that gives a new meaning to brain washing.
The point is: How can that happen?
Conceded, there is the phenomenon known as metamorphosis, where certain species undergo an abrupt change in the structure of their bodies. This involves cell growth and differentiation. Lobsters actually have a larval stage that undergoes metamorphosis and develops into an adult specimen, which molts from time to time.
But metamorphosis of the brain (even if one would consider this likely) would take time. The learning effect on the other hand is almost instantaneous. The experiments show that Lobsters remember very well who they are dealing with if they encounter the same foe an hour or less later. No time for metamorphosis.
Another idea would be something similar to the regeneration of limbs crustaceans are known to be capable of. But limbs are somewhat peripheral appendices, whereas the "brain" of lobsters is likely the single most organ of the organism with the most complex connections inside the body. Look at this image of the ladder-like central nervous system of crayfish (Katsushi Kagaya CC:BY-NC-SA). No way, that it is able to dissolve and regrow in minutes (or at all).
We conclude that social experience can modulate neural circuit function by controlling the effect of a neuromodulator on the response of an identified neuron. Presumahly this type of neural plasticity mediates the animal's social adaptation by producing experience- and context-dependent changes in the relative excitability of neural circuits.
So, Yeh et al. refer to the well known mechanism of neural plasticity. No dissolving and magically regrowing brains here. Yeh et al. don't even mention the word "brain" once.
If anybody got some information about Peterson's dissolving lobster brains, I'd be genuinely interested. It's kind of a miracle and probably worth a Nobel price.