Signal recovery from stimulation artifacts in intracranial recordings with dictionary learning.

OBJECTIVE: Electrical stimulation of the human brain is commonly used for eliciting and inhibiting neural activity for clinical diagnostics, modifying abnormal neural circuit function for therapeutics, and interrogating cortical connectivity. However, recording electrical signals with concurrent stimulation results in dominant electrical artifacts that mask the neural signals of interest. Here we develop a method to reproducibly and robustly recover neural activity during concurrent stimulation. We concentrate on signal recovery across an array of electrodes without channel-wise fine-tuning of the algorithm. Our goal includes signal recovery with trains of stimulation pulses, since repeated, high-frequency pulses are often required to induce desired effects in both therapeutic and research domains. We have made all of our code and data publicly available. APPROACH: We developed an algorithm that automatically detects templates of artifacts across many channels of recording, creating a dictionary of learned templates using unsupervised clustering. The artifact template that best matches each individual artifact pulse is subtracted to recover the underlying activity. To assess the success of our method, we focus on whether it extracts physiologically interpretable signals from real recordings. MAIN RESULTS: We demonstrate our signal recovery approach on invasive electrophysiologic recordings from human subjects during stimulation. We show the recovery of meaningful neural signatures in both electrocorticographic (ECoG) arrays and deep brain stimulation (DBS) recordings. In addition, we compared cortical responses induced by the stimulation of primary somatosensory (S1) by natural peripheral touch, as well as motor cortex activity with and without concurrent S1 stimulation. SIGNIFICANCE: Our work will enable future advances in neural engineering with simultaneous stimulation and recording.

Performance characteristics of rapid (30-second) prescreening. Implications for calculating the false-negative rate and comparison with other quality assurance techniques.

Rapid (30-second) prescreening of cervicovaginal smears can be used to detect false-negative cases and determine the false-negative rate of primary screening, but the performance characteristics have not been evaluated fully. A test set of 242 cases including 80 originally false-negative cases were rapidly screened by 4 different cytotechnologists on 2 occasions. Intraobserver and interobserver reproducibility were good. Median specificity for each round of observations was 89% (range, 30%-96%). Median sensitivity for all true-positive cases was 78% (range, 63%-97%); for all false-negative cases it was 59% (range, 38%-89%). The relative sensitivity of rapid screening for true-positive and false-negative cases varied with the diagnosis. Rapid screening detected almost the same percentage of false-negative cases of atypical squamous cells of uncertain significance (ASCUS) as true-positive ASCUS cases (median ratio, 1.12; range, 0.72-1.52). The median ratio of false-negative to true-positive ASCUS cases was significantly different than the ratio for low-grade plus high-grade squamous intraepithelial lesions (0.68; range, 0.50-0.96). Although performance varies between individuals, in this test population the reproducibility, specificity, and sensitivity were good. Because it detects more false-negative cases at a lower cost per case than routine rescreening, rapid prescreening should be considered as an alternative to current quality control measures.

Accuracy and reproducibility of estimating the adequacy of the squamous component of cervicovaginal smears.

In the Bethesda System for reporting cervicovaginal cytology results, 1 criterion for smear adequacy is an adequate squamous component. The accuracy of a cytologist's estimate that 10% of the slide is covered by squamous cells, the adequacy threshold, has not been determined. The percentage of the surface of a glass slide covered by squamous cells was independently estimated by 4 cytologists on 2 occasions by microscopic examination of 83 buccal smears prepared to display estimated coverage of 1% to 20% of the slide surface. The accuracy of visual estimates was compared with measurements by the TracCell System. Each observer made a third set of estimates after receiving 5 slides with known coverage. Median coverage by visual estimation ranged from 4% to 25%, but as measured by the TracCell system was 2%. Median estimated coverage was significantly different for 2 of 4 observers between first and second viewings and between all but 1 pair of observers. For all observers, it was significantly higher than the true coverage. A visual estimate of 10% coverage corresponded to a true median coverage of 3%. When provided with a physical standard, the median estimated coverage by 3 of 4 observers was not statistically different from the true coverage, and interobserver kappa values improved. Unaided visual estimation of the adequacy of squamous cell coverage is neither reproducible nor accurate. What most cytologists consider "adequate" coverage represents only 3% coverage. The availability of a physical standard dramatically increases reproducibility and accuracy.