A 'Total Unique Variation Analysis' for Brain-Machine Interfaces.

When designing a fully implantable brain-machine interface (BMI), the primary aim is to detect as much neural information as possible with as few channels as possible. In this paper, we present a total unique variance analysis (TUVA) for evaluating the signal unique to each channel that cannot be predicted by linear combination of signals on other channels. TUVA is a statistical method for determining the total unique variance in multidimensional data, ordering channels from most to least informative, to aid in the design of maximally-efficacious BMIs. We demonstrate how this method can be applied to the design of BMIs by comparing TUVA values computed for simulated lead-field maps for high-channel-count electrocorticography (ECoG) with values computed for recordings in the interictal period in the context of surgery planning for epileptic resection.Clinical Relevance- This paper introduces a new statistical method for comparison of neural interface designs, focused on quantifying recording efficiency by minimizing channel crosstalk, which may help improve the risk-benefit profile of invasive neural recording.

Cortical Auditory Evoked Potentials Recorded Directly Through the Cochlear Implant in Cochlear Implant Recipients: a Feasibility Study.

OBJECTIVES: The use of objective measures in cochlear implant (CI) mapping, has greatly contributed to the refinement of the setting of audible and comfortable stimulation levels, which serve as the basis of the mapping process, especially in cases of infants and young children. In addition, objective measures can also confirm the integrity of the CI system. Current CI objective measures mainly reflect neural activity from the auditory nerve and brainstem site. An objective cortical CI measure that reflects directly central auditory activity is greatly needed, especially since it is closely related to CI outcomes in both children and adults. Recording the brain activity currently requires an external evoked potential (EP) system including scalp electrodes, rendering it impractical for widespread clinical use. This study aimed to assess the feasibility of recording cortical auditory evoked potentials (CAEPs) directly and solely through the cochlear implant in response to external acoustic stimulation in the non-implanted ear. DESIGN: A total of nine CI users (four females and five males) participated, including seven post-lingual adults (23 to 72 years), and two pediatric cases, one teenager (15 years), and one child (8 years)-both pre-lingual. All participants had a residual hearing in the ear contralateral to the ear with CI. CAEPs were recorded in the implanted ear in response to acoustic stimulation of the non-implanted ear, consisting of a brief tonal stimulus at comfortable listening levels. Recordings used an intracranial montage consisting of an intracochlear apical electrode (active) and one of the two ( case and ring ) extra-cochlear implanted electrodes serving as reference electrodes. The CI CAEPs were compared with a single-channel conventional CAEP recording obtained simultaneously via scalp electrodes (Fz-mastoid) using a standard EP system and an external trigger from the CI system. Statistical comparisons were made between the CI and the scalp recorded CAEPs and for differences between the CI CAEP measures acquired using the ring and the case as the reference electrode. RESULTS: CAEPs recorded directly and solely through the CI were equivalent to the standard scalp recorded CAEP responses. CAEP responses acquired using the case electrode as the reference were highly correlated in terms of morphology, latencies, and amplitudes of the CAEP components. The CI CAEP latencies of the two pediatric cases were consistent with their normal developed age group and delayed relative to adult CAEP latencies, as expected. CONCLUSIONS: This study demonstrated the feasibility of recording long latency CAEPs directly and solely through CI in adults with residual hearing, in response to acoustic stimulation of the non-implanted ear. The CI CAEPs closely resembled the CAEPs recorded simultaneously by an external EP system and via scalp electrodes. The ability to record directly from the implant, without the need of an external recording system, presents an innovative method with many clinical and research implications.