Patch clamp headstages have traditionally passed current via a feedback resistor of typically 10 gigohms or more,but this component generates thermal noise, and distributed capacitance within it can distort the frequency response in ways that are difficult to correct. Capacitive (integrating) headstages, where current is supplied by charging a small feedback capacitor, are theoretically superior in respect of both noise and frquency response. Capacitors, however, must be discharged from time to time, and the necessary circuitry must be designed carefully to realise the full benefits of the technique.

Tthe headstage of the Optopatch generates the currents directly at the input by the controlled illumination of miniature photodiodes. The effective resistance of these devices is extremely high, giving the same theoretical advantages as a capacitive headstage, but without needing the capacitor and its associated discharge circuitry. Bandwidths in excess of 100KHz can be achieved, and we use the technique for whole-cell recording (currents up to 100nA) as well as for true patch-clamp recording (currents up to 1nA). Careful design has yielded a compact headstage, of body dimensions 62.5 x 30 x 20 mm