An RPi doesn't seem appropriate - firstly due to its high power demand. "Bio-signal" pickups have to be double-insulated from the grid to prevent accidental electrocution, thus some battery-powered low-power device (e.g. an ESP* controller continuously transmitting the measured values) might be a better choice.

Anyway I'd recommend to use an "Analog Front End" (AFE) targeting EEG applications, which I'd expect to deliver better results than some combination of external amplifiers and multiplexers and the use of the microcontroller's ADC(s).

Mr Dreher is right regarding the electric insulation. All medical devices have a quite restrict requirements for insulation, you may pay attention on this.

but, apart from this problem, you first need to know about this signal you want to acquire: how many channels? dynamic range? what resolution is necessary? sampling frequency? acquisition time? is simultaneously sampling necessary?

RPi doesn't not have analog-to-digital converter (ADC) embedded, it means you need to do it yourself. I recently developed a system for data acquisition with RPi for 45 channels.

For this I used 3 ADC with multiplexed input and 16 channels each with SPI (serial data bus) to talk to the RPi.

You should pay attention that: data acquisition when it comes to time series data, for example, sound recording, or your EEG signal, you need a precise clock to trigger the converters. For example, you need each of your sample equally spaced 100ms in time. This is usually made by dedicaded hardware, and almost impossible by RPi's software (in fact this is more or less like real time).

anyways: you can maybe use RPi to receive a data from some dedicaded ADC system and store it, but, I don't see advantages of this instead a normal computer. If your idea is to develop something portable, RPi isn't the right approach, maybe as an auxiliar device, not as the main controller.

Best,

thank you so much for response