Not to blame somebody for trying any kind of experiments in the absence of any secure knowledge, in, say, 1920's or 1930's. However, caution may be in order when interpreting the history of such discoveries as the following :

"Cerletti came to the first use of electroshock for therapeutic purposes in human beings by way of his experiments with animals on the neuropathological consequences of repeated epilepsy attacks. In Genoa, and later in Rome, he used an electroshock apparatus to provoke repeatable, reliable epileptic fits in dogs and other animals. The idea to use ECT in humans came first to him by watching pigs being anesthetised with electroshock before being butchered, in Rome." (Internet)

This seems fairly clear, the electroshock would provoke reliable, repeatable epileptic fits in dogs and other animals. As a matter of common sense estimation : what would you expect of some kind of animal or other being hit with high-voltage electric current ?

I am also quite willing to believe in "pigs being anesthetised with electroshock before being butchered". This might be, as a matter of common sense observation, the natural reaction of the pig, or any more or less sentient being, to having been exposed to high-voltage electricity.

The pigs were successfully anesthetised. That, in other words, means loss of feeling (an-aesthesia). So far so good ; but this is a far way from anything like 'therapy', which implies not loss of feeling but strenghtening the individual.

Note : "Following its introduction in 1930's by Cerletti and Bini", etc. ("Electroconvulsive Therapy", Washington : Am. Psychiatric Association, 1978, p. 13).

Electroconvulsive therapy : report of the Task Force on Electroconvulsive Therapy of the American Psychiatric Association / Fred H. Frankel, chairperson ... [et al.]. Publisher Washington : The Association, 1978. Paging xi, 200 p. : ill. ; 23 cm. Series Task force report (American Psychiatric Association) ; 14 Notes Includes bibliographical references. Subject Headings Electroconvulsive therapy.