Frequency domain identification of proprioceptive evoked potentials in compliant kinematic experiments

Proprioception is a critical component of closed-loop motor control with sensory information being used to dynamically adjust and correct movement. We mapped brain responses in healthy adults to proprioceptive stimulation at different steady state frequencies. A haptic robotic device generated small, short, recurrent force pulses producing displacements of approximately 1 cm of the subject´s index finger. Four stimulation frequencies were used: 2 Hz, 3 Hz, 5 Hz and 7 Hz. Finger displacement and high resolution 63 channel EEG were simultaneously recorded. The resulting proprioceptive steady state evoked potentials (PSSEPs) and the compliant kinematics of the subject´s index finger were analyzed in the frequency domain. The harmonics of the input force pulse were used to interpolate and extrapolate the estimated kinematic and proprioceptive linear transfer functions beyond the fundamental frequencies of stimulation experiments. We used the relative SNR of the EEG channels to rank and identify the most important components of the spatial and frequency response. A physiologic, task-free, quantification of proprioceptive ability could have applications to diagnose and rehabilitate people with neurodegenerative and motor disorders.