A frequency-position function for the human cochlear spiral ganglion

Greenwood's frequency-position function for the organ of Corti (OC) is commonly used to estimate represented frequencies for cochlear implant (CI) electrodes, both in temporal bone studies and in imaging studies of living CI recipients. However, many contemporary CIs position stimulating electrodes near the modiolus, directly targeting the spiral ganglion (SG) cells within Rosenthal's canal. At the extreme base and apex, the SG does not extend as far as the OC, and the radial nerve fibers take a tangential course into the modiolus resulting in a potential offset between the frequency maps of the OC and SG. In this investigation, human cadaveric cochleae (n = 7) were studied in surface preparations after osmium staining. The OC and SG lengths were measured and radial fiber trajectories traced to identify frequency-matched points on each structure. These data allowed derivation of a mathematical function correlating represented frequency along the OC to position along the SG. A cubic function fit the data with a very high intersubject correlation. Better knowledge of the human SG 'neural frequency map' may help to refine electrode design, and to more accurately map CI channel filter bands to the appropriate cochlear place along the SG, which may be advantageous for more sophisticated CI outcomes, such as music appreciation. These data also could be valuable for electroacoustic stimulation, by defining the insertion distance of a CI electrode required to reach specific frequencies (based upon preoperative imaging) in an individual subject, thus helping to avoid trauma to cochlear regions with residual hearing.

External calibration of the spectral coverage for three-dimensional multispectral MRI

PURPOSE

By combining images created at distinct frequency offsets from the Larmor frequency, three-dimensional (3D) multispectral imaging (3D-MSI) sequences help overcome the large spatial frequency dispersion caused by metal implants. This frequency dispersion, however, varies with the implant size, orientation, and composition. Using a MAVRIC 3D-MSI acquisition, we sought to prospectively calibrate the spectral coverage needed for 3D-MSI scans. This calibration should offer a significant improvement to image quality, and reduce the scan time.

METHODS

The 24 spectral bins from the calibration scan were used to generate a map of frequency offsets around the implant. The magnitude image was used to remove any outliers in the associated frequency offset map, and this processed map was used to determine the cutoff frequency offset and, hence, number of spectral bins. This approach was tested in 13 subjects, by retrospectively reconstructing MAVRIC-SL images with fewer spectral bins. Subsequently, the spectral coverage for MAVRIC-SL images was prospectively calibrated in six subjects, and based on the cutoff frequency offset, these images were acquired with fewer spectral bins.

RESULTS

With fewer spectral bins, both retrospectively and prospectively calibrated MAVRIC-SL images adequately delineated the implant boundary.

CONCLUSION

Incorporating this calibration procedure into future 3D-MSI exams will help improve image signal-to-noise ratio, reduce scan time, and significantly improve clinical workflow when imaging near orthopedic implants. Magn Reson Med 76:1494-1503, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Blast Exposure Disrupts the Tonotopic Frequency Map in the Primary Auditory Cortex

Blast exposure can cause various auditory disorders including tinnitus, hyperacusis, and other central auditory processing disorders. While this is suggestive of pathologies in the central auditory system, the impact of blast exposure on central auditory processing remains poorly understood. Here we examined the effects of blast shockwaves on acoustic response properties and the tonotopic frequency map in the auditory cortex. We found that multiunits recorded from the auditory cortex exhibited higher acoustic thresholds and broader frequency tuning in blast-exposed animals. Furthermore, the frequency map in the primary auditory cortex was distorted. These changes may contribute to central auditory processing disorders.

The organization of frequency and binaural cues in the gerbil inferior colliculus

The inferior colliculus (IC) is the common target of separate pathways that transmit different types of auditory information. Beyond tonotopy, little is known about the organization of response properties within the 3-dimensional layout of the auditory midbrain in most species. Through study of interaural time difference (ITD) processing, the functional properties of neurons can be readily characterized and related to specific pathways. To characterize the representation of ITDs relative to the frequency and hodological organization of the IC, the properties of neurons were recorded and the sites recovered histologically. Subdivisions of the IC were identified based on cytochrome oxidase (CO) histochemistry. The results were plotted within a framework formed by an MRI atlas of the gerbil brain. The central nucleus was composed of two parts, and lateral and dorsal cortical areas were identified. The lateral part of the central nucleus had the highest CO activity in the IC and a high proportion of neurons sensitive to ITDs. The medial portion had lower CO activity and fewer ITD-sensitive neurons. A common tonotopy with a dorsolateral to ventromedial gradient of low to high frequencies spanned the two regions. The distribution of physiological responses was in close agreement with known patterns of ascending inputs. An understanding of the 3-dimensional organization of the IC is needed to specify how the single tonotopic representation in the IC central nucleus leads to the multiple tonotopic representations in core areas of the auditory cortex.

Tibial plateau fractures: Fracture patterns and computed tomography evaluation of tibial plateau fractures in winter sports

The purpose was to analyze tibial plateau fractures (TPF) by computed tomography (CT) by creating a frequency map (FM). We hypothesized that a FM shows clinically important aspects of involvement that are not expressed in classic classifications. 185 TPF were retrospectively evaluated in this single center study. We created a FM onto an axial template of an intact subarticular tibial plateau and separated the joint surface in 9 areas, counted the frequency of involvement. The FM gives information of location and grade of damage and expressed three major fracture areas in 76%. 5 specific fracture types add up to 51%. The dorsal parts of the tibial plateau are involved in a higher percentage (+8%). True lateral fractures are less often than plane radiographs suggest. An impression was found in 50%. The complexity of TPFs is high, but 5 specific types could be identified in >50%. The complexity is not sufficiently covered in common classifications, especially the dorsal involvement. The FM is a simple and useful tool that complements common classifications and can be used as guideline for surgical treatment.

New insights into glioma frequency maps: From genetic and transcriptomic correlate to survival prediction

Increasing evidence indicates that glioma topographic location is linked to the cellular origin, molecular alterations and genetic profile. This research aims to (a) reveal the underlying mechanisms of tumor location predilection in glioblastoma multiforme (GBM) and lower-grade glioma (LGG) and (b) leverage glioma location features to predict prognosis. MRI images from 396 GBM and 190 LGG (115 astrocytoma and 75 oligodendroglioma) patients were standardized to construct frequency maps and analyzed by voxel-based lesion-symptom mapping. We then investigated the spatial correlation between glioma distribution with gene expression in healthy brains. We also evaluated transcriptomic differences in tumor tissue from predilection and nonpredilection sites. Furthermore, we quantitively characterized tumor anatomical localization and explored whether it was significantly related to overall survival. Finally, we employed a support vector machine to build a survival prediction model for GBM patients. GBMs exhibited a distinct location predilection from LGGs. GBMs were nearer to the subventricular zone and more likely to be localized to regions enriched with synaptic signaling, whereas astrocytoma and oligodendroglioma tended to occur in areas associated with the immune response. Synapse, neurotransmitters and calcium ion channel-related genes were all activated in GBM tissues coming from predilection regions. Furthermore, we characterized tumor location features in terms of a series of tumor-to-predilection distance metrics, which were able to predict GBM 1-year survival status with an accuracy of 0.71. These findings provide new perspectives on our understanding of tumor anatomic localization. The spatial features of glioma are of great value in individual therapy and prognosis prediction.

Multi-scale brain attributes contribute to the distribution of diffuse glioma subtypes

Gliomas are primary brain tumors and are among the most malignant types. Adult-type diffuse gliomas can be classified based on their histological and molecular signatures as IDH-wildtype glioblastoma, IDH-mutant astrocytoma, and IDH-mutant and 1p/19q-codeleted oligodendroglioma. Recent studies have shown that each subtype of glioma has its own specific distribution pattern. However, the mechanisms underlying the specific distributions of glioma subtypes are not entirely clear despite partial explanations such as cell origin. To investigate the impact of multi-scale brain attributes on glioma distribution, we constructed cumulative frequency maps for diffuse glioma subtypes based on T1w structural images and evaluated the spatial correlation between tumor frequency and diverse brain attributes, including postmortem gene expression, functional connectivity metrics, cerebral perfusion, glucose metabolism, and neurotransmitter signaling. Regression models were constructed to evaluate the contribution of these factors to the anatomic distribution of different glioma subtypes. Our findings revealed that the three different subtypes of gliomas had distinct distribution patterns, showing spatial preferences toward different brain environmental attributes. Glioblastomas were especially likely to occur in regions enriched with synapse-related pathways and diverse neurotransmitter receptors. Astrocytomas and oligodendrogliomas preferentially occurred in areas enriched with genes associated with neutrophil-mediated immune responses. The functional network characteristics and neurotransmitter distribution also contributed to oligodendroglioma distribution. Our results suggest that different brain transcriptomic, neurotransmitter, and connectomic attributes are the factors that determine the specific distributions of glioma subtypes. These findings highlight the importance of bridging diverse scales of biological organization when studying neurological dysfunction.

Correlating Cochlear Morphometrics from Parnell's Mustached Bat (Pteronotus parnellii) with Hearing

Morphometric analysis of the inner ear of mammals can provide information for cochlear frequency mapping, a species-specific designation of locations in the cochlea at which different sound frequencies are encoded. Morphometric variation occurs in the hair cells of the organ of Corti along the cochlea, with the base encoding the highest frequency sounds and the apex encoding the lowest frequencies. Changes in cell shape and spacing can yield additional information about the biophysical basis of cochlear tuning mechanisms. Here, we investigate how morphometric analysis of hair cells in mammals can be used to predict the relationship between frequency and cochlear location. We used linear and geometric morphometrics to analyze scanning electron micrographs of the hair cells of the cochleae in Parnell's mustached bat (Pteronotus parnellii) and Wistar rat (Rattus norvegicus) and determined a relationship between cochlear morphometrics and their frequency map. Sixteen of twenty-two of the morphometric parameters analyzed showed a significant change along the cochlea, including the distance between the rows of hair cells, outer hair cell width, and gap width between hair cells. A multiple linear regression model revealed that nine of these parameters are responsible for 86.9 % of the variation in these morphometric data. Determining the most biologically relevant measurements related to frequency detection can give us a greater understanding of the essential biomechanical characteristics for frequency selectivity during sound transduction in a diversity of animals.

The Spatial Distribution of Brain Metastasis Is Determined by the Heterogeneity of the Brain Microenvironment

It is now understood that brain metastases do not occur randomly but have distinct spatial patterns depending on the origin of the cancer. According to the "seed and soil" hypothesis, the final colonization of metastatic cells is the result of their adaptation to the altered environment. To investigate the most favorable microenvironment for brain metastasis, we analyzed neuroimaging data from 177 patients with breast cancer brain metastasis and 548 patients with lung cancer brain metastasis to create a replicable probabilistic map of metastatic locations. Additionally, we used population-based data from open repositories to generate brain atlases of diverse microenvironment features, including gene expression, functional connectivity, glucose metabolism, and neurotransmitter transporters/receptors. We then compared the spatial correlation between brain metastasis frequency and these features, after which we constructed a general linear model to identify the most significant variables that contributed to tumor location predilection. Our findings revealed that brain metastases from breast cancer and lung cancer had distinct radiographic characteristics and distribution patterns. Breast cancer tended to metastasize in brain regions with decreased expression of genes associated with immunity and metabolism and reduced levels of connectomic hubness and glucose metabolism. In contrast, lung cancer had a higher probability of metastasizing in regions with active metabolism. Moreover, neurotransmitter systems play various roles in determining tumor location. These results provide new insights into the adaptation of metastatic cells to the brain microenvironment and illustrate how factors on diverse biological scales can affect the colonization of brain metastases.