The present invention includes a responsive neural stimulator having electrodes, a filter, a processor, a recording medium, an extractor for extracting instantaneous voltage amplitudes of biased oscillatory activity with asymmetrically distributed peak/trough amplitudes, and a neural stimulator connected to the processor configured to apply neural stimulation via the neural stimulator when a predetermined state of neuronal excitability is detected, a state of relatively higher neuronal excitability corresponding to a relatively lower instantaneous voltage amplitude extracted by the extractor. Also provided is a system for providing neurofeedback including electrodes, a filter, a processor, a recording medium, an extractor for extracting instantaneous voltage amplitudes of biased oscillatory activity with asymmetrically distributed peak/trough amplitudes, and an output device configured to communicate changes in, increases in, decreases in, or maintenance of instantaneous voltage amplitudes, or any combination, to a participant in a neurofeedback session.
IMPROVED MEASUREMENT OF CORTICAL EXCITABILITY