Semantic attributes are encoded in human electrocorticographic signals during visual object recognition.

Non-invasive neuroimaging studies have shown that semantic category and attribute information are encoded in neural population activity. Electrocorticography (ECoG) offers several advantages over non-invasive approaches, but the degree to which semantic attribute information is encoded in ECoG responses is not known. We recorded ECoG while patients named objects from 12 semantic categories and then trained high-dimensional encoding models to map semantic attributes to spectral-temporal features of the task-related neural responses. Using these semantic attribute encoding models, untrained objects were decoded with accuracies comparable to whole-brain functional Magnetic Resonance Imaging (fMRI), and we observed that high-gamma activity (70-110Hz) at basal occipitotemporal electrodes was associated with specific semantic dimensions (manmade-animate, canonically large-small, and places-tools). Individual patient results were in close agreement with reports from other imaging modalities on the time course and functional organization of semantic processing along the ventral visual pathway during object recognition. The semantic attribute encoding model approach is critical for decoding objects absent from a training set, as well as for studying complex semantic encodings without artificially restricting stimuli to a small number of semantic categories.

Quality-of-life assessment as an outcomes measure in critical limb ischemia.

Critical limb ischemia (CLI) is a diagnosis plagued by significant comorbidity and high mortality rates. Overall survival remains poor in this population regardless of the procedure-related success as demonstrated by freedom from amputation, intervention, and patency. The literature has traditionally focused on physician-centered and lesion-centered outcomes with regards to limb salvage procedures, but there remains a relative paucity of studies of CLI patients describing patient-centered outcomes such as quality of life (QoL), independent living, and ambulation status. Review of the available literature indicates patients do not always experience significant gains in their QoL after limb salvage interventions, despite reasonable graft patency, amputation-free survival, and limb salvage rates. Further research is required using QoL tools in a measurable and clinically relevant fashion to guide optimal quality care that maximizes patient-centered outcomes.

Normal Lower Extremity Duplex Findings in Patients with Left Ventricular Assist Devices: A Basis for Vascular Laboratory Interpretation.

BACKGROUND: Left ventricular assist devices (LVADs) have been shown to cause changes in carotid artery duplex-derived flow velocity waveforms; however, possible effects on lower extremity arterial duplex (LEAD) findings have not been characterized. We sought to characterize LEAD findings in patients with LVADs to establish a basis for vascular laboratory interpretation of LEAD in patients with LVADs. METHODS: Retrospective single institution review of all patients with LEAD performed after LVAD implantation from 2003 to 2014. Peak systolic velocity (PSVs) of common femoral (CFA), superficial femoral (SFA), popliteal, and posterior tibial arteries (PTA) in asymptomatic extremities in patients with LVADs were compared to a control group of patients at our institution without LVADs who underwent LEAD for nonischemic indications. Arterial brachial index (ABIs) and CFA waveform acceleration times (ATs) and end diastolic velocity (EDV) were also measured. RESULTS: There were 248 LVAD patients, 29 had LEAD of at least 1 lower extremity (34 extremities, 22 asymptomatic, and 12 symptomatic) during the study period and 136 control limbs. Mean PSVs (cm/s) in the control CFA, mid SFA, popliteal, and PTA were 137 ± 4.8, 104.2 ± 4.5, 65.2 ± 2.8, and 64.6 ±3.2. Mean PSVs were significantly decreased in the LVAD patients: 49.5 ± 4.9, 40.6 ± 3.7, 27.2 ± 2.2, and 25.5 ± 2.3, P < 0.001 for each comparison. Average ABI for control limbs was 0.91 ± 0.05 compared to 1.17 ± 0.35 in LVAD extremities (P < 0.001). Mean CFA AT was 97 ms in the controls and 207 ms in LVAD patients, P < 0.001. Mean CFA EDV was 14.7 cm/s in the controls and 18.6 cm/s in the LVAD patients, P = 0.011. CONCLUSIONS: This is the first study characterizing LEAD in lower extremity arteries in LVAD patients. PSV is significantly decreased throughout lower extremity vessels, and common femoral artery acceleration time increased. Results can serve as a basis for identifying normal LEAD findings in LVAD patients.

The impact of multidisciplinary therapy in node-positive rectal cancer.

Multidisciplinary therapy (MDT) of node-positive rectal cancer is considered optimal. We performed a retrospective cohort study of node positive rectal cancer patients diagnosed between January 1, 1994 and December 31, 2003 in Region 5 of the California Cancer Registry to determine the impact of MDT on disease specific survival (DSS). During the study period, 398 patients with stage III rectal cancer were identified. Only 251 patients (63.1%) received radiation (XRT). Patients receiving XRT had significantly improved survival when compared with those who did not (5 year DSS 55% with XRT vs. 36% without XRT, median follow-up 43 months, P < 0.001). There was no statistically significant difference in Tstage (P = 0.41), the number of N1 patients (P = 0.45), or the number of positive nodes harvested (mean 11.5 w/o XRT vs. 12.8 w/XRT, P = 0.37) between patients receiving XRT and those who did not. Patients receiving XRT were far more likely to receive systemic chemotherapy (83% vs. 27%, P < 0.0001). Multidisciplinary therapy of node-positive rectal cancer is associated with improved DSS. However, substantial numbers of node positive rectal cancer patients are not receiving MDT. Greater efforts are needed to implement consistent multidisciplinary algorithms into rectal cancer management.

The role of broadband inhibition in the rate representation of spectral cues for sound localization in the inferior colliculus.

Previous investigations have shown that a subset of inferior colliculus neurons, which have been designated type O units, respond selectively to isolated features of the cat's head-related transfer functions (HRTFs: the directional transformation of a free-field sound as it propagates from the head to the eardrum). Based on those results, it was hypothesized that type O units would show enhanced spatial tuning in a virtual sound field that conveyed the full complement of HRTF-based localization cues. As anticipated, a number of neurons produced representations of virtual sound source locations that were spatially tuned, level tolerant, and effective under monaural conditions. Preferred locations were associated with spectral cues that complemented the highly individualized broadband inhibitory patterns of tuned neurons. That is, higher response magnitudes were achieved when spectral peaks coincided with excitatory influences at best frequency (BF: the most sensitive frequency) and spectral notches fell within flanking inhibitory regions. The directionally dependent modulation of narrowband ON-BF excitation by broadband OFF-BF inhibition was not a unique property of type O units.

Neural Reconstruction Integrity: A Metric for Assessing the Connectivity Accuracy of Reconstructed Neural Networks.

Neuroscientists are actively pursuing high-precision maps, or graphs consisting of networks of neurons and connecting synapses in mammalian and non-mammalian brains. Such graphs, when coupled with physiological and behavioral data, are likely to facilitate greater understanding of how circuits in these networks give rise to complex information processing capabilities. Given that the automated or semi-automated methods required to achieve the acquisition of these graphs are still evolving, we developed a metric for measuring the performance of such methods by comparing their output with those generated by human annotators ("ground truth" data). Whereas classic metrics for comparing annotated neural tissue reconstructions generally do so at the voxel level, the metric proposed here measures the "integrity" of neurons based on the degree to which a collection of synaptic terminals belonging to a single neuron of the reconstruction can be matched to those of a single neuron in the ground truth data. The metric is largely insensitive to small errors in segmentation and more directly measures accuracy of the generated brain graph. It is our hope that use of the metric will facilitate the broader community's efforts to improve upon existing methods for acquiring brain graphs. Herein we describe the metric in detail, provide demonstrative examples of the intuitive scores it generates, and apply it to a synthesized neural network with simulated reconstruction errors. Demonstration code is available.

Feature Selection Methods for Zero-Shot Learning of Neural Activity.

Dimensionality poses a serious challenge when making predictions from human neuroimaging data. Across imaging modalities, large pools of potential neural features (e.g., responses from particular voxels, electrodes, and temporal windows) have to be related to typically limited sets of stimuli and samples. In recent years, zero-shot prediction models have been introduced for mapping between neural signals and semantic attributes, which allows for classification of stimulus classes not explicitly included in the training set. While choices about feature selection can have a substantial impact when closed-set accuracy, open-set robustness, and runtime are competing design objectives, no systematic study of feature selection for these models has been reported. Instead, a relatively straightforward feature stability approach has been adopted and successfully applied across models and imaging modalities. To characterize the tradeoffs in feature selection for zero-shot learning, we compared correlation-based stability to several other feature selection techniques on comparable data sets from two distinct imaging modalities: functional Magnetic Resonance Imaging and Electrocorticography. While most of the feature selection methods resulted in similar zero-shot prediction accuracies and spatial/spectral patterns of selected features, there was one exception; A novel feature/attribute correlation approach was able to achieve those accuracies with far fewer features, suggesting the potential for simpler prediction models that yield high zero-shot classification accuracy.

Classification of unit types in the anteroventral cochlear nucleus of laboratory mice.

This report introduces a system for the objective physiological classification of single-unit activity in the anteroventral cochlear nucleus (AVCN) of anesthetized CBA/129 and CBA/CaJ mice. As in previous studies, the decision criteria are based on the temporal properties of responses to short tone bursts that are visualized in the form of peri-stimulus time histograms (PSTHs). Individual unit types are defined by the statistical distribution of quantifiable metrics that relate to the onset latency, regularity, and adaptation of sound-driven discharge rates. Variations of these properties reflect the unique synaptic organizations and intrinsic membrane properties that dictate the selective tuning of sound coding in the AVCN. When these metrics are applied to the mouse AVCN, responses to best frequency (BF) tones reproduce the major PSTH patterns that have been previously demonstrated in other mammalian species. The consistency of response types in two genetically diverse strains of laboratory mice suggests that the present classification system is appropriate for additional strains with normal peripheral function. The general agreement of present findings to established classifications validates laboratory mice as an adequate model for general principles of mammalian sound coding. Nevertheless, important differences are noted for the reliability of specialized endbulb transmission within the AVCN, suggesting less secure temporal coding in this high-frequency species.

Impairments of the medial olivocochlear system increase the risk of noise-induced auditory neuropathy in laboratory mice.

HYPOTHESIS: Impairments of the medial olivocochlear system (MOCS) increase the risk of environmentally induced auditory neuropathy spectrum disorder (ANSD). BACKGROUND: ANSD is a problem in the neural transmission of auditory information that accounts for 10% to 15% of the cases of pediatric hearing loss. The underlying mechanisms of the disorder remain poorly understood, but noise exposure is an important risk factor. The goal of this study was to identify environmental conditions and genetic predispositions that lead to ANSD. Our approach was based on the assumption that noise induces ANSD by impeding the functional maturation of the brain's sound coding pathways. Because the MOCS adjusts the sensitivity of the inner ear to noise, impairments of this feedback are predicted to increase the disruptive effects of environmental exposures. METHODS: An animal model of ANSD was created by rearing mice in noise. MOCS protection was assessed by comparing the incidence of noise-induced ANSD among knockout mice lacking feedback and wild-type (WT) controls. The mice were screened for ANSD with distortion product otoacoustic emissions, auditory brainstem responses, and behavioral measures of gap detection. Single-unit recording procedures were used to link these deficits to impaired synaptic transmission in the ventral cochlear nucleus. RESULTS: ANSD manifested in noise-reared mice as intact distortion product otoacoustic emissions, abnormal auditory brainstem responses, and impaired gap detection. The phenotype was not observed among quiet-reared WT mice but was occasionally noted among noise-reared WT mice. The incidence of ANSD significantly increased among knockout mice, especially when they were reared in noise. CONCLUSION: Noise promotes ANSD by altering the functional maturation of the brain's temporal pathways. Noise-induced impairments are reduced by the sound-attenuating effects of the MOCS. Noise levels do not need to be unnaturally loud to constitute significant risk in MOCS-compromised individuals.