ICMS detection threshold

The minimum stimulus a subject can reliably detect, usually estimated from a psychometric function relating detection probability to charge or amplitude and reported at a fixed criterion (for example the 50 percent-detected level). For single-electrode ICMS in human somatosensory cortex, thresholds are on the order of tens of microamperes, but this figure is not a fixed property of the electrode alone.

Detection threshold falls as pulse-train frequency rises and as train duration lengthens, reflecting temporal integration of charge, and it falls further when several electrodes are stimulated together through spatial summation. Thresholds also drift over the life of a chronic implant, tracking changes in interface impedance and the surrounding tissue, so periodic re-measurement is part of maintaining a stable write channel.