Description:

Speaker: Lee Miller, Ph.D.

Loss of somatosensation has devastating effects on our ability to move. Replacing somatosensation through an afferent Brain Computer Interface (BCI) has become a new neuroengineering goal following the effort in the previous decade to produce efferent BCIs. The basic approach is to stimulate the cortex electrically in an effort to recreate the patterns of neural activity resulting from natural stimuli. The well localized, punctate activation in tactile regions of cortex produced by simple skin indentation can be mimicked relatively easily by intracortical microstimulation (ICMS). This is not the case for proprioception, the sense of limb position and movement. Even very simple limb movements cause widespread cortical activation, with no evidence of an organized map of limb movement direction. Consequently, neuroengineering efforts to replace proprioception via ICMS lag well behind those of touch. Our scientific understanding of proprioception also lags that of touch. 

Our conscious sense of proprioception is mostly focused on where our hands are with respect to our body. This is also the basis of the classic model of how single neurons in somatosensory cortex represent limb state. We used this model to design experiments testing ICMS as a means to convey a sense of limb movement to monkeys. While the experiment worked well in one monkey, we were subsequently unable to replicate it. This limited success has led us to re-evaluate the simple hand-based cortical model of arm movement. We have begun to test other models and more complex, multi-electrode stimulation paradigms with the hope that they may be more readily interpretable as a source of artificial afferent input than is single-electrode ICMS. It remains a work in progress…