Bioamplifier, how?

Question

Electronics

Once I saw a circuit with 3-4 transistors, which was a bioamplifier. That book talked about a children's railway that could be controlled through 2 of these amplifiers (by the movement of the fingers or the wrist, I do not remember exactly).
Prompt links or books with similar material (capturing muscle currents). Perhaps there are materials on capturing brain currents, but I think there will be very little on this topic.

Answer 1

A little offtopic. In my small library I found such books on your subject:
Berezovsky, Kolotilov - Biophysical characteristics of tissues
Smolyaninov - Mathematical models of biological tissues
Nikolaev - Workshop on clinical medicine
- On a superficial examination, I did not seem to see bioamplifiers. Only graphs/characteristics of currents, voltages, frequencies, etc.

Answer 2

Look for the book Gurfinkel V.S., Malkin V.B. Bioelectric control, there are device schematics.