Sensory Survey 3D: an open source utility for the annotation of projected fields for sensory neural interfaces

One goal of neuroprosthetics is to restore sensation to those who have lost it due to disease or injury. This is often accomplished with electrical stimulation of nervous tissue. Common approaches to quantifying evoked sensations for somatosensory prostheses involve asking participants to draw or annotate flattened, 2-dimensional (2D) representations of body parts, a process that can distort the true nature of the 3-dimensional (3D) projected fields. In particular, patches of skin between the fingers and toes or at the edge of the wrist often go unrepresented in 2D, leaving them unquantified. Here, we present a 3D annotation tool that allows participants to accurately report evoked sensations on any given body part. Patients implanted with either NeuroPort electrode arrays (Blackrock Neurotech) in Brodmann's Area 1 (N=2 male) or Composite Flat Interface Nerve Electrodes on the peripheral nerves of an amputated arm (N=2 male) were electrically stimulated and asked to annotate the location of the resulting sensations. In the first cohort, patients reported sensations on a generic hand using either a 2D or 3D interface. We found that participants reported consistent sensation locations between annotation methods when sensations were localized to central parts of the fingers and hand, visible in 2-dimensions. However, as expected, the 3-dimensional interface better captured sensations on the edges of or between fingers. In the second cohort, intact limbs were scanned and an iterative Procrustes alignment algorithm was used to warp and compare projected fields between patient-specific models. Our 3-dimensional annotation tool allows for more precise annotation of evoked sensations than 2-dimensional alternatives and facilitates rapid analysis across patients with different morphologies.