Simulation of background neuronal activity and noise in human intracranial microwire recordings.

BACKGROUND: Human intracranial microwire recordings allow measurement of neuronal activity in human subjects at a fine temporal and spatial scale. The recorded extracellular potentials represent a mixture of action potentials from nearby neurons, local field potentials, and other noise sources. Signal processing of these recordings is used to separate the activity of putative single neurons from other background and noise. To better understand the separation of single neuron activity, one approach is to simulate the signals produced by neurons firing action potentials combined with background activity and noise. NEW METHOD: This paper characterizes the background activity and noise in human intracranial microwire recordings and presents an accurate and efficient method of simulation using an infinite impulse response filter to color white noise. RESULTS AND COMPARISON: This method reproduces the power spectral density of the background activity and noise over a frequency range of 1-5000 Hz and is over 200 times faster than previously used methods. It thus facilitates large scale studies of variation of noise sources, field potentials, and processing parameters. It performs equivalently in terms of spike sorting to simulation using white noise. Another advantage is that the simulated signals are known to arise from a pseudorandom number generator and cannot be the result of detecting simulated background spiking activity. CONCLUSIONS: This approach provides a rapid and accurate method of simulating background noise and neural activity in human intracranial microwire recordings. It is suitable for use in large scale simulations to study spike sorting in this type of recording.

International consensus conference recommendations on ultrasound education for undergraduate medical students.

OBJECTIVES: The purpose of this study is to provide expert consensus recommendations to establish a global ultrasound curriculum for undergraduate medical students. METHODS: 64 multi-disciplinary ultrasound experts from 16 countries, 50 multi-disciplinary ultrasound consultants, and 21 medical students and residents contributed to these recommendations. A modified Delphi consensus method was used that included a systematic literature search, evaluation of the quality of literature by the GRADE system, and the RAND appropriateness method for panel judgment and consensus decisions. The process included four in-person international discussion sessions and two rounds of online voting. RESULTS: A total of 332 consensus conference statements in four curricular domains were considered: (1) curricular scope (4 statements), (2) curricular rationale (10 statements), (3) curricular characteristics (14 statements), and (4) curricular content (304 statements). Of these 332 statements, 145 were recommended, 126 were strongly recommended, and 61 were not recommended. Important aspects of an undergraduate ultrasound curriculum identified include curricular integration across the basic and clinical sciences and a competency and entrustable professional activity-based model. The curriculum should form the foundation of a life-long continuum of ultrasound education that prepares students for advanced training and patient care. In addition, the curriculum should complement and support the medical school curriculum as a whole with enhanced understanding of anatomy, physiology, pathophysiological processes and clinical practice without displacing other important undergraduate learning. The content of the curriculum should be appropriate for the medical student level of training, evidence and expert opinion based, and include ongoing collaborative research and development to ensure optimum educational value and patient care. CONCLUSIONS: The international consensus conference has provided the first comprehensive document of recommendations for a basic ultrasound curriculum. The document reflects the opinion of a diverse and representative group of international expert ultrasound practitioners, educators, and learners. These recommendations can standardize undergraduate medical student ultrasound education while serving as a basis for additional research in medical education and the application of ultrasound in clinical practice.

Two kinds of memory signals in neurons of the human hippocampus.

Prior studies of the neural representation of episodic memory in the human hippocampus have identified generic memory signals representing the categorical status of test items (novel vs. repeated), whereas other studies have identified item specific memory signals representing individual test items. Here, we report that both kinds of memory signals can be detected in hippocampal neurons in the same experiment. We recorded single-unit activity from four brain regions (hippocampus, amygdala, anterior cingulate, and prefrontal cortex) of epilepsy patients as they completed a continuous recognition task. The generic signal was found in all four brain regions, whereas the item-specific memory signal was detected only in the hippocampus and reflected sparse coding. That is, for the item-specific signal, each hippocampal neuron responded strongly to a small fraction of repeated words, and each repeated word elicited strong responding in a small fraction of neurons. The neural code was sparse, pattern-separated, and limited to the hippocampus, consistent with longstanding computational models. We suggest that the item-specific episodic memory signal in the hippocampus is fundamental, whereas the more widespread generic memory signal is derivative and is likely used by different areas of the brain to perform memory-related functions that do not require item-specific information.

3D Printed Heart Models Illustrating Myocardial Perfusion Territories to Augment Echocardiography and Electrocardiography Interpretation.

Visualizing the vascular territories of coronary arteries during echocardiography or electrocardiography (ECG) requires trainees to mentally relate and overlay 2D sonographic images or cardiac lead projections with 3D anatomical representations of the ventricular walls and their respective blood supply. To facilitate the acquisition of these competencies, this study focuses on the feasibility of developing low-cost, open-sourced 3D printed heart models with standard ultrasound views or ECG lead projections illustrating the myocardial perfusion territories. A 3D digital heart model was cut to reflect the typical cardiac ultrasound views. The 4-chamber view model was further punctured for the paths of the precordial and limb leads of an ECG. Painting coronary arteries on the surface and internal views of the 3D prints illustrated vessel territories. Students, residents, and staff were surveyed during bedside ultrasound simulation sessions and ECG teaching half-days. Results demonstrated clear appreciation of 3D printed models, which suggests such models can easily be implemented by other institutions to augment trainees' experience during skill acquisition.

Spiking activity in the human hippocampus prior to encoding predicts subsequent memory.

Encoding activity in the medial temporal lobe, presumably evoked by the presentation of stimuli (postonset activity), is known to predict subsequent memory. However, several independent lines of research suggest that preonset activity also affects subsequent memory. We investigated the role of preonset and postonset single-unit and multiunit activity recorded from epilepsy patients as they completed a continuous recognition task. In this task, words were presented in a continuous series and eventually began to repeat. For each word, the patient's task was to decide whether it was novel or repeated. We found that preonset spiking activity in the hippocampus (when the word was novel) predicted subsequent memory (when the word was later repeated). Postonset activity during encoding also predicted subsequent memory, but was simply a continuation of preonset activity. The predictive effect of preonset spiking activity was much stronger in the hippocampus than in three other brain regions (amygdala, anterior cingulate, and prefrontal cortex). In addition, preonset and postonset activity around the encoding of novel words did not predict memory performance for novel words (i.e., correctly classifying the word as novel), and preonset and postonset activity around the time of retrieval did not predict memory performance for repeated words (i.e., correctly classifying the word as repeated). Thus, the only predictive effect was between preonset activity (along with its postonset continuation) at the time of encoding and subsequent memory. Taken together, these findings indicate that preonset hippocampal activity does not reflect general arousal/attention but instead reflects what we term "attention to encoding."

The Canadian Medical Student Ultrasound Curriculum: A Statement From the Canadian Ultrasound Consensus for Undergraduate Medical Education Group.

OBJECTIVES: This study sought to establish by expert review a consensus-based, focused ultrasound curriculum, consisting of a foundational set of focused ultrasound skills that all Canadian medical students would be expected to attain at the end of the medical school program. METHODS: An expert panel of 21 point-of-care ultrasound and educational leaders representing 15 of 17 (88%) Canadian medical schools was formed and participated in a modified Delphi consensus method. Experts anonymously rated 195 curricular elements on their appropriateness to include in a medical school curriculum using a 5-point Likert scale. The group defined consensus as 70% or more experts agreeing to include or exclude an element. We determined a priori that no more than 3 rounds of voting would be performed. RESULTS: Of the 195 curricular elements considered in the first round of voting, the group reached consensus to include 78 and exclude 24. In the second round, consensus was reached to include 4 and exclude 63 elements. In our final round, with 1 additional item added to the survey, the group reached consensus to include an additional 3 and exclude 8 elements. A total of 85 curricular elements reached consensus to be included, with 95 to be excluded. Sixteen elements did not reach consensus to be included or excluded. CONCLUSIONS: By expert opinion-based consensus, the Canadian Ultrasound Consensus for Undergraduate Medical Education Group recommends that 85 curricular elements be considered for inclusion for teaching in the Canadian medical school focused ultrasound curricula.

Estimates of distributed coding of visual objects by single neurons in the human brain depend on which spike sorting technique is used.

OBJECTIVE: To determine whether the estimated fraction and degree of distribution of visual responsive neurons in human intracranial microwire recordings depends upon the spike sorting method used. APPROACH: A large dataset of human intracranial microwire recordings from four brain areas was sorted into single unit activity (SUA) and multiunit activity (MUA) using 4 spike sorting methods previously applied to this type of recording. The responses were examined for visual responses to 33 objects which were presented. MAIN RESULTS: The 4 spike sorting techniques examined here yielded fractions of responsive SUA varying from 8% in the left anterior cingulate cortex to 27% in the right amgdala. The fraction of responsive SUA and MUA depended on the type of spike sorting being used as well as brain area and side being recorded from. Agreement between spike sorting techniques was low (0.04-0.16 on the 0-1 AMIall scale). SIGNIFICANCE: Prior estimates of the fraction of single neurons in the human medial temporal lobe coding semantic memory of visual objects have yielded fractions ranging from 0.04% by very strict response criteria to 47% by other criteria. A variety of explanations of these differences have been posited, including differences in the type of memory being tested, differences in visual stimuli, as well as technical differences such as spike sorting techniques. This study shows the dependence of the reported fraction of neurons encoding visual objects on the spike sorting technique employed and confirms a distributed representation of visual objects by single neurons in the human brain. Both the variation in the responsive fractions with spike sorting technique and low levels of agreement between techniques highlight the need for better understanding of the signals being extracted in human intracranial microwire recordings.

Canadian national survey of family medicine residents on point-of-care ultrasound training.

OBJECTIVE: To assess the quality of point-of-care ultrasound (POCUS) training in family medicine residency programs and to obtain the opinions of current family medicine residents on the role of ultrasound in primary care. DESIGN: A 23-question online survey conducted using SurveyMonkey between March 15 and June 30, 2017. SETTING: Canada. PARTICIPANTS: All family medicine residents of the 17 Canadian family medicine residency programs were included in the study but all enhanced skills residents were excluded. MAIN OUTCOME MEASURES: The quality and relevance of POCUS to primary care as perceived by residents and reported in the survey. RESULTS: A total of 854 Canadian family medicine residents responded, for a national response rate of 32.3%. Most respondents (94.3%) believe that POCUS training should be included in family medicine residency programs; however, only 18.4% of respondents currently receive formal training within their residency. Among those without POCUS training, 91.7% are interested in receiving formal training and 29.7% resorted to taking external POCUS courses. Most (77.5%) would consider using ultrasound in their future practice if they were competent in POCUS. The most useful applications for family medicine were considered to be the FAST (Focused Assessment with Sonography in Trauma) examination for free fluid and ascites (95.1%), procedural guidance (92.4%), and identifying an intrauterine pregnancy (88.6%). CONCLUSION: This is the largest survey identifying the perceived needs of family medicine residents for POCUS. Very few Canadian family medicine residents currently receive POCUS training. Consistent with our recent family medicine program director survey, there is overwhelming interest by family medicine residents to begin incorporating POCUS training into the family medicine curriculum.

The Use of Ultrasound Simulators to Strengthen Scanning Skills in Medical Students: A Randomized Controlled Trial.

OBJECTIVES: This study evaluates the use of ultrasound simulators for retaining and improving ultrasound skills acquired in undergraduate ultrasound training. METHODS: Fourth-year medical students (n = 19) with prior training in point-of-care sonography for shock assessment were recruited for this study. Students were randomly assigned to a study group (n = 10) that followed an undergraduate ultrasound training curriculum, then used a simulator to complete 2 self-directed practice ultrasound sessions over 4 weeks. The control group (n = 9) followed the same undergraduate ultrasound training curriculum and received no additional access to a simulator or ultrasound training. A blinded assessment of the students was performed before and after the 4-week study period to evaluate their image acquisition skills on standardized patients (practical examination). To evaluate the student's clinical understanding of pathological ultrasound images, students watched short videos of prerecorded ultrasound scans and were asked to complete a 22-point questionnaire to identify their findings (visual examination). RESULTS: All results were adjusted to pretest performance. The students in the study group performed better than those in the control group on the visual examination (80.1% versus 58.9%; P = .003) and on the practical examination (77.7% versus 57.0%; P = .105) after the 4-week study period. The score difference on the postintervention practical examinations was significantly better for the study group compared to the control group (11.6% versus -9.9%; P = .0007). CONCLUSION: The use of ultrasound simulators may be a useful tool to help previously trained medical students retain and improve point-of-care ultrasound skills and knowledge.

Canadian national survey of point-of-care ultrasound training in family medicine residency programs.

OBJECTIVE: To assess the current state of point-of-care ultrasound (POCUS) training in Canadian family medicine residency programs. DESIGN: Cross-sectional survey to evaluate POCUS education in accredited Canadian family medicine residency programs; only 1 completed survey was accepted per residency program. SETTING: Seventeen accredited Canadian family medicine residency programs. PARTICIPANTS: Fourteen directors of family medicine programs across Canada. MAIN OUTCOME MEASURES: Opinions of program directors in family medicine education on the relevance of POCUS in family medicine, and the role of POCUS training in family medicine residency programs. RESULTS: The Web-based, anonymous survey, which was completed during the months of March and April 2016, achieved a response rate of 82% (14 out of 17 program directors). About one-fifth (21%) of program directors reported having an established ultrasound curriculum. Almost all directors (93%) believed that POCUS teaching should be integrated into family medicine residency curricula. Barriers to establishing training included the following: lack of adequate equipment (57%), lack of instructors (57%), lack of available time in the curriculum (57%), and lack of funding available to support training (71%). Seventy-one percent of respondents believed that POCUS could be used in outpatient family medicine clinics to alter clinical decision making. Some potential benefits associated with POCUS in primary care include more rapid diagnosis, improved patient outcomes, and potential to reduce health care costs. CONCLUSION: Although only a few Canadian family medicine residency program directors reported actually having an established ultrasound curriculum, most of them believed that POCUS training should be offered to family medicine residents and that its use could positively affect primary care. A growing number of family medicine residency programs are considering incorporating ultrasound training into their curricula, but resource availability remains a considerable barrier to implementation.

Accuracy of Medical Students in Detecting Pleural Effusion Using Lung Ultrasound as an Adjunct to the Physical Examination.

OBJECTIVES: This study compared the accuracy of medical students in identifying pleural effusion in hospitalized patients using the physical examination versus lung ultrasound (US). METHODS: Fourth-year medical students (n = 14) received 20 hours of general practical US training (including 2 hours of specialized lung US training) plus theoretical and video documentation. The students used the physical examination alone versus the physical examination plus lung US to document the presence or absence of pleural effusion in the right and left hemithoraces of hospitalized patients (n = 11 patients; 22 hemithoraces examined 544 times in total). The reference standard for identification of pleural effusion was a lung US examination by 2 expert point-of-care sonographers. RESULTS: The odds of correctly identifying the presence versus absence of pleural effusion was 5 times greater with lung US as an adjunct to the physical examination compared to the physical examination alone (odds ratio [OR], 5.1 from multivariate logistic regression; 95% confidence interval, 3.3-8.0). The addition of lung US to the physical examination resulted in an increase in sensitivity from 48% to 90%, in specificity from 73% to 86%, and in accuracy from 60% to 88%. The benefits of using US were greater when pleural effusion was present versus absent (OR, 10.8 versus 2.4) and when examining older versus younger patients (OR, 10.2 versus 2.8). CONCLUSIONS: These results demonstrate that medical students' ability to detect the presence or absence of pleural effusion is superior when using lung US as an adjunct to the physical examination than when using the physical examination alone.

Coding of episodic memory in the human hippocampus.

Neurocomputational models have long posited that episodic memories in the human hippocampus are represented by sparse, stimulus-specific neural codes. A concomitant proposal is that when sparse-distributed neural assemblies become active, they suppress the activity of competing neurons (neural sharpening). We investigated episodic memory coding in the hippocampus and amygdala by measuring single-neuron responses from 20 epilepsy patients (12 female) undergoing intracranial monitoring while they completed a continuous recognition memory task. In the left hippocampus, the distribution of single-neuron activity indicated that only a small fraction of neurons exhibited strong responding to a given repeated word and that each repeated word elicited strong responding in a different small fraction of neurons. This finding reflects sparse distributed coding. The remaining large fraction of neurons exhibited a concurrent reduction in firing rates relative to novel words. The observed pattern accords with longstanding predictions that have previously received scant support from single-cell recordings from human hippocampus.

Single neuron recordings of bilinguals performing in a continuous recognition memory task.

We report the results of a bilingual continuous recognition memory task during which single- and multi-neuron activity was recorded in human subjects with intracranial microwire implants. Subjects (n = 5) were right-handed Spanish-English bilinguals who were undergoing evaluation prior to surgery for severe epilepsy. Subjects were presented with Spanish and English words and the task was to determine whether any given word had been seen earlier in the testing session, irrespective of the language in which it had appeared. Recordings in the left and right hippocampus revealed notable laterality, whereby both Spanish and English items that had been seen previously in the other language (switch trials) triggered increased neural firing in the left hippocampus. Items that had been seen previously in the same language (repeat trials) triggered increased neural firings in the right hippocampus. These results are consistent with theories that propose roles of both the left- and right-hemisphere in real-time linguistic processing. Importantly, this experiment presents the first instance of intracranial recordings in bilinguals performing a task with switching demands.

Comparison of combined spike detection and clustering using mutual information.

BACKGROUND: Spike sorting techniques involve both detection of spike waveform events and classification of those events into clusters of similar waveform shape. The one existing method of evaluating the combined effects of both detection and classification depends on assignment of cluster correspondence. Other methods of evaluation have focused on either clustering or detection, but not both, although these two steps may interact. NEW METHOD: This paper develops an information theoretic measure of agreement between the output of two spike sorting techniques, AMIall, which can be used even when the number of waveform events detected by the two techniques differs. RESULTS: AMIall is shown to be a useful measure for studying variations of parameters of spike sorting techniques in two examples: comparing outputs for simulated noisy spike sorting and spike sorting of human single neuron recordings. Comparison with existing methods Computing AMIall does not require an explicit assignment of cluster correspondence, thereby eliminating a potential source of variation. By providing a single measure of performance, computing AMIall is very useful when comparing large numbers of algorithmic or parametric variations of spike sorting techniques; prior comparison techniques have often required multiple measures of performance which complicates large scale comparisons. CONCLUSIONS: The use of AMIall to measure agreement between spike sorting techniques facilitates the comparison of the outputs of those techniques, including variations in both spike detection and waveform clustering. This measure should be useful for broad based and large scale comparisons between spike sorting techniques.

The benefits of doing ultrasound exams in your office.

Family medicine ultrasound is more accurate, more cost-effective, and less time-consuming than you might imagine. Here's how it can improve your care.

Acquisition and Long-term Retention of Bedside Ultrasound Skills in First-Year Medical Students.

OBJECTIVES: The purpose of this study was to assess bedside ultrasound skill acquisition and retention in medical students after completion of the first year of a new undergraduate bedside ultrasound curriculum at McGill University. METHODS: Skill acquisition was assessed in first-year medical students (n = 195) on completion of their bedside ultrasound instruction. Instruction included 6 clinically based 60-minute practical teaching sessions evenly spaced throughout the academic year. Students' ability to meet course objectives was measured according to a 4-point Likert rating scale. Evaluations were performed by both instructors and the students themselves. Retention of skill acquisition was evaluated 8 months later on a year-end practical examination. RESULTS: The mean percentage ± SD of students assigned a rating of "strongly agree" or "agree" by instructors was 98% ± 0.4% for all 6 teaching sessions (strongly agree, 52% ± 3%; agree, 46% ± 3%). According to student self-evaluations, the mean percentage of students assigned a rating of strongly agree was significantly greater than the percentage assigned by instructors for all teaching sessions (86% ± 2% versus 52% ± 3%; P < .0005). Evaluation of skill retention on the year-end examination showed that 91% ± 2% of students were assigned a rating of strongly agree or agree for their ability to demonstrate skills learned 8 months previously. Ninety-five percent of students reported that bedside ultrasound improved their understanding of anatomy for all 6 teaching sessions (mean, 95% ± 0.01%). CONCLUSIONS: These results demonstrate that first-year medical students show acquisition and long-term retention of basic ultrasound skills on completion of newly implemented bedside ultrasound instruction.

Bedside ultrasound education in Canadian medical schools: A national survey.

BACKGROUND: This study was carried out to determine the extent and characteristics of bedside ultrasound teaching in medical schools across Canada. METHODS: A cross-sectional, survey-based study was used to assess undergraduate bedside ultrasound education in the 17 accredited medical schools in Canada. The survey, consisting of 19 questions was pilot-tested, web-based, and completed over a period of seven months in 2014. RESULTS: Approximately half of the 13 responding medical schools had integrated bedside ultrasound teaching into their undergraduate curriculum. The most common trends in undergraduate ultrasound teaching related to duration (1-5 hours/year in 50% of schools), format (practical and theoretical in 67% of schools), and logistics (1:4 instructor to student ratio in 67% of schools). The majority of responding vice-deans indicated that bedside ultrasound education should be integrated into the medical school curriculum (77%), and cited a lack of ultrasound machines and infrastructure as barriers to integration. CONCLUSIONS: This study documents the current characteristics of undergraduate ultrasound education in Canada.

Gender differences in human single neuron responses to male emotional faces.

Well-documented differences in the psychology and behavior of men and women have spurred extensive exploration of gender's role within the brain, particularly regarding emotional processing. While neuroanatomical studies clearly show differences between the sexes, the functional effects of these differences are less understood. Neuroimaging studies have shown inconsistent locations and magnitudes of gender differences in brain hemodynamic responses to emotion. To better understand the neurophysiology of these gender differences, we analyzed recordings of single neuron activity in the human brain as subjects of both genders viewed emotional expressions. This study included recordings of single-neuron activity of 14 (6 male) epileptic patients in four brain areas: amygdala (236 neurons), hippocampus (n = 270), anterior cingulate cortex (n = 256), and ventromedial prefrontal cortex (n = 174). Neural activity was recorded while participants viewed a series of avatar male faces portraying positive, negative or neutral expressions. Significant gender differences were found in the left amygdala, where 23% (n = 15∕66) of neurons in men were significantly affected by facial emotion, vs. 8% (n = 6∕76) of neurons in women. A Fisher's exact test comparing the two ratios found a highly significant difference between the two (p < 0.01). These results show specific differences between genders at the single-neuron level in the human amygdala. These differences may reflect gender-based distinctions in evolved capacities for emotional processing and also demonstrate the importance of including subject gender as an independent factor in future studies of emotional processing by single neurons in the human amygdala.

Distributed representation of visual objects by single neurons in the human brain.

It remains unclear how single neurons in the human brain represent whole-object visual stimuli. While recordings in both human and nonhuman primates have shown distributed representations of objects (many neurons encoding multiple objects), recordings of single neurons in the human medial temporal lobe, taken as subjects' discriminated objects during multiple presentations, have shown gnostic representations (single neurons encoding one object). Because some studies suggest that repeated viewing may enhance neural selectivity for objects, we had human subjects discriminate objects in a single, more naturalistic viewing session. We found that, across 432 well isolated neurons recorded in the hippocampus and amygdala, the average fraction of objects encoded was 26%. We also found that more neurons encoded several objects versus only one object in the hippocampus (28 vs 18%, p < 0.001) and in the amygdala (30 vs 19%, p < 0.001). Thus, during realistic viewing experiences, typical neurons in the human medial temporal lobe code for a considerable range of objects, across multiple semantic categories.

A comparison of telemedicine teaching to in-person teaching for the acquisition of an ultrasound skill - a pilot project.

Telemedicine is widely used for medical education but few studies directly investigate how telemedicine teaching compares to conventional in-person teaching. Here we determine whether telemedicine teaching is as effective as in-person teaching for the acquisition of an ultrasound skill important in trauma care. Nurses with no prior ultrasound experience (n = 10) received study material and a teaching session on how to locate and image the hepatorenal space (Morison's pouch). One group of nurses was taught in-person (In-person Group) and the other group was taught via telemedicine (Telemedicine Group). Telemedicine allowed two-way audio and visual communication between the instructor and the nurses. A comparison of the teaching techniques showed that telemedicine teaching was equivalent to in-person teaching for the acquisition of practical and theoretical skills required to locate Morison's pouch. The average time required to locate Morison's pouch after teaching was similar between both groups. The results demonstrate that telemedicine teaching is as effective as in-person teaching for the acquisition of bedside ultrasound skills necessary to identify Morison's pouch. Remote teaching of these bedside ultrasound skills may help in the diagnosis of intra-abdominal bleeding in rural healthcare centers.