Injecting Instructions in Cortical Association Areas
We recently found that instructions about which movement to perform, normally delivered with different light emitting diodes (LEDs), can be delivered instead with intracortical microstimulation (ICMS) in the premotor cortex (PM) [Mazurek & Schieber, Neuron 96(6):1292-1289, 2017; see also coverage in the New York Times]. After learning to use these novel PM-ICMS instructions, subjects reacted faster to PM-ICMS than to LED instructions. Each PM-ICMS instruction could be delivered through a different single electrode, producing no direct muscle activation at effective amplitudes of 18 - 25 µA. Not only was the initial assignment of ICMS at a given electrode as an instruction for a particular movement made arbitrarily, but after we shuffled the electrode-movement assignments the subjects relearned the new assignments. These observations indicate that low-amplitude PM-ICMS at different electrodes produces experiences that can be distinguished and used as instructions to perform arbitrarily-associated movements. Whereas work in other laboratories focusses on applying ICMS in the primary sensory receiving areas—somatosensory, auditory, or visual—to deliver feedback information, our findings raise the possibility that injecting arbitrary, specific information into association cortical areas may enable the development of cortico-cortical neuroprosthetic devices that bridge across injured brain regions by decoding neural signals from upstream areas and injecting the processed information downstream. We hope to identify more cortical association areas where ICMS can be used to inject instructions.
Left: Floating microelectrode arrays implanted in the premotor cortex. Right: ICMS artifacts (cyan) have waveforms that can be distinguished readily from neuron action potentials (yellow, green).
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