Tuesday, March 3, 2009

Luigi Galvani

Here are some notes on Luigi Galvani that I've collected, mostly from Clarke and Jacyna's book Nineteenth-Century Origins of Neuroscience Concepts.

Luigi Galvani (1737-1798) was an Italian scientist interested in the role that electrical forces play in animal physiology. Toward the end of the 18th century, Galvani showed that applying electric current to the nerves of frog legs could get the legs to kick. Galvani was not the first to have shown that electric current could induce contractions in skeletal muscles. In fact, he was repeating experiments that had already been performed. But his interpretation of the experiments earned him his place in the history of science (Clarke and Jacyna 164). The word "galvanized" finds its origin in Galvani's name.

Galvani's work with frogs branched into work on other animals, which later, through the work of Emile du Bois-Reymond spawned the field of electrophysiology.

It appears that Galvani's discovery was interpreted against the background of the hollow nerve theory, which had been espoused by such distinguished scientists as Rene Descartes. According to the hollow nerve theory, nerves are like pipes that generate muscular actions by channeling fluids around the body. The "hollow nerve" theory can be traced back to Erasistratus (c.260 BCE) and was endorsed by Galen four centuries later (Clarke and Jacyna 160). It seems that Galvani did not question the hollow nerve theory. Instead, he questioned preceding theories of what flowed through the hollows, and how that flow created muscle actions.

Based on his own experimental results, Galvani claimed to demonstrate that animals run on a special kind of electricity, so-called "animal electricity". Animal electricity was supposed to be a kind of fluid in Galvani's mind. The flow of the fluid through the nerves was what accounted for muscle flexion. Galvani's position stood in stark contrast with competing views on muscle flexion. According to these other views, the muscle actions were caused by effervescence, explosion, or ethereal oscillation (Clarke and Jacyna 161). (Personally, I find the explosion theory most compelling...joke.) Though a sound physical theory of electricity had not yet been found, Galvani's work tipped the scales in favor of the electrical theory of nerve conduction.

Neuroscience was revolutionized as a result of Galvani's work, but the revolution did not happen overnight. Not until the mid-19th century did consistent interest in electrophysiology emerge. Though he had nothing nice to say about Galvani or his work, Emil du Bois-Reymond carried Galvani's torch.

An interesting epistemological point:

Alessandro Volta (1745-1827) famously challenged Galvani's claim that nerve actions were normally driven by electricity. According to Volta, Galvani had not shown that electrical stimulation generated muscle contractions by the natural causal pathway (Clarke and Jacyna 171). Rather, he had shown that the actions of the metals used to stimulate the nerves were effective. Galvani met Volta's challenge with subsequent stimulation experiments without metals. It is pretty standard fare in contemporary neurosciece textbooks to delimit a class of experiments that mimic normal neural processes (you can find this notion in David Sweatt's textbook and Yadin Dudai's textbook).

The basic epistemic point: If your methods don't to some extent approximate typical causal forces working on the nervous system, your capacity to generalize from your studies will be limited. I wonder if there are prior discussions of "mimic" experiments in the neuroscience literature...