The Seduction of Reduction

So, sensory nerve cells (neurons) in the California sea hare increase their signal strength after they are exposed to serotonin, thereby causing sensitization. Finding this out several decades ago started a furious research effort by a bunch of competing and collaborating laboratories. This discovery is the portal into what Eric Kandel (Nobel Prize, 2000) refers to as the seduction of the reductionist program. Because the next question is how does serotonin do this to sensory neurons? Well there are a slew of special “receptor” proteins all over the outer membrane of sensory neurons, receptors that bind to the serotonin and activate a signal INSIDE the neurons. What kind of a signal? A second messenger called cyclic AMP. On and on this reductionist program meanders, asking more and more mechanistic questions to uncover each of the diverse links that lead to the ultimate increase in signaling that causes the increased withdrawal behavior that is sensitization.

Now many of you have probably glazed over by now, but if you did you’d be making a big mistake. It turns out that a huge number of these links are very similar or identical in YOUR neurons when YOU learn (but if you glazed over, it didn’t happen, so go back and read it again!). Neurobiological research on Aplysia has really pushed forward our understanding of learning and memory. So much so, that the really big researchers in this field are patenting “memory” drugs, based to some extent on the knowledge gleaned from work on this California sea hare.

But here I am in Costa Rica, far from the insanity of biomedically motivated research wanting to know something far more fundamental: How do learning mechanisms change across evolution? This particular example is the disappearance of learning. How did that come to be? To do this we have to go inside the neurons of Dolabrifera and search around for a smoking gun. A difference between Dolabrifera and Aplysia, that can account for the difference in the response of their sensory neurons to serotonin. Or a difference, totally unrelated to the sensory neuron difference, that is the real cause of their lack of sensitization.

This is where Leonid comes in.

Driving into the biological station, San Miguel