High resolution whole brain diffusion imaging at 7T for the Human Connectome Project.

Mapping structural connectivity in healthy adults for the Human Connectome Project (HCP) benefits from high quality, high resolution, multiband (MB)-accelerated whole brain diffusion MRI (dMRI). Acquiring such data at ultrahigh fields (7T and above) can improve intrinsic signal-to-noise ratio (SNR), but suffers from shorter T2 and T2(⁎) relaxation times, increased B1(+) inhomogeneity (resulting in signal loss in cerebellar and temporal lobe regions), and increased power deposition (i.e. specific absorption rate (SAR)), thereby limiting our ability to reduce the repetition time (TR). Here, we present recent developments and optimizations in 7T image acquisitions for the HCP that allow us to efficiently obtain high quality, high resolution whole brain in-vivo dMRI data at 7T. These data show spatial details typically seen only in ex-vivo studies and complement already very high quality 3T HCP data in the same subjects. The advances are the result of intensive pilot studies aimed at mitigating the limitations of dMRI at 7T. The data quality and methods described here are representative of the datasets that will be made freely available to the community in 2015.

Effects of image reconstruction on fiber orientation mapping from multichannel diffusion MRI: reducing the noise floor using SENSE.

PURPOSE: To examine the effects of the reconstruction algorithm of magnitude images from multichannel diffusion MRI on fiber orientation estimation. THEORY AND METHODS: It is well established that the method used to combine signals from different coil elements in multichannel MRI can have an impact on the properties of the reconstructed magnitude image. Using a root-sum-of-squares approach results in a magnitude signal that follows an effective noncentral-χ distribution. As a result, the noise floor, the minimum measurable in the absence of any true signal, is elevated. This is particularly relevant for diffusion-weighted MRI, where the signal attenuation is of interest. RESULTS: In this study, we illustrate problems that such image reconstruction characteristics may cause in the estimation of fiber orientations, both for model-based and model-free approaches, when modern 32-channel coils are used. We further propose an alternative image reconstruction method that is based on sensitivity encoding (SENSE) and preserves the Rician nature of the single-channel, magnitude MR signal. We show that for the same k-space data, root-sum-of-squares can cause excessive overfitting and reduced precision in orientation estimation compared with the SENSE-based approach. CONCLUSION: These results highlight the importance of choosing the appropriate image reconstruction method for tractography studies that use multichannel receiver coils for diffusion MRI acquisition.

The Human Connectome Project: a data acquisition perspective.

The Human Connectome Project (HCP) is an ambitious 5-year effort to characterize brain connectivity and function and their variability in healthy adults. This review summarizes the data acquisition plans being implemented by a consortium of HCP investigators who will study a population of 1200 subjects (twins and their non-twin siblings) using multiple imaging modalities along with extensive behavioral and genetic data. The imaging modalities will include diffusion imaging (dMRI), resting-state fMRI (R-fMRI), task-evoked fMRI (T-fMRI), T1- and T2-weighted MRI for structural and myelin mapping, plus combined magnetoencephalography and electroencephalography (MEG/EEG). Given the importance of obtaining the best possible data quality, we discuss the efforts underway during the first two years of the grant (Phase I) to refine and optimize many aspects of HCP data acquisition, including a new 7T scanner, a customized 3T scanner, and improved MR pulse sequences.

The relationship between visual sensitivity and rhodopsin density in retinitis pigmentosa.

Rhodopsin density and absolute threshold were determined in 11 patients with retinitis pigmentosa (RP) and nine normal subjects. In eight patients with familial histories suggesting recessive inheritance, the retinal areas studied showed marked decrease in sensitivity which was related to rhodopsin loss, probably via a log-linear relationship. The other three patients showed absolute thresholds that were linearly related to rhodopsin density, suggesting that sensitivity loss was determined by the decrease in quantal absorption resulting from rhodopsin loss. The results indicate that RP patients can be classified into two categories according to the effects of rhodopsin loss on rod sensitivity. These categories may correspond to different genetic groups. Furthermore, this differentiation may, in fact, reflect different underlying disease mechanisms.

Retinitis pigmentosa.

The authors review the symptomatic and genetic aspects of the various entities of isolated retinitis pigmentosa (R.P), both in its typical form and in the forms associated with the affection of other ocular tissues. Syndromes in which R. P. is associated with the affection of other organs and systemic disorders are also cconsidered. Origin, diagnosis and the course of the disease are discussed with regard to electrophysiology, histopathology, fluorescein angiography and biochemistry. Animal research has provided new realizations about the ultrastructure and physiological mechanisms of retinal photoreceptors, and better understanding of abnormal changes. The possible pathogenesis of the human disease, based on research findings, is onsidered. Although R.P. is generally thought to be to be an "untreatable" disease, therapy may be effective in several pathological entities. Methods and results of therapy with vitamins, light deprivation and vision aids are discussed.

Left-hemisphere processing of emotional connotation during word generation.

Areas of the brain's left hemisphere involved in retrieving words with emotional connotations were studied with fMRI. Participants silently generated words from different semantic categories which evoked either words with emotional connotations or emotionally neutral words. Participants repeated emotionally neutral words as a control task. Compared with generation of emotionally neutral words, generation of words with emotional connotations engaged cortices near the left frontal and temporal poles which are connected to the limbic system. Thus, emotional connotations of words are processed in or near cortices with access to emotional experience.

Behavioral sensitization to amphetamine is not accompanied by a decrease in the number of c-Fos containing cells in the striatum.

The expression of c-Fos-like immunoreactivity (FLI) and chronic Fos-related antigen-like immunoreactivity (FRALI) accompanying behavioral sensitization to amphetamine was assessed in male rat striatum. Animals were treated for four days with amphetamine (A; 5 mg/kg) or vehicle (V) and challenged with A or V on the fifth day. The number of FLI-positive cells in the striatum was enhanced in V-A and A-A groups as compared to control (V-V), while the number of FRALI-positive cells in the striatum was enhanced in the A-V and A-A groups as compared to control. These results suggest that the absence of a decrease in the number of striatal FLI-positive cells accompanying chronic amphetamine treatment is not due to antibody cross-reactivity with chronic FRAs, and that behavioral sensitization to amphetamine is not accompanied by a change in the number of striatal cells expressing c-Fos.

Interocular transfer and dark adaptation to long-wave test lights.

Extrafoveal thresholds for 660 nm test flashes were measured for the two eyes separately following 30 min of dark adaptation. Then, the right eye was exposed to red light while the left eye was covered. Thresholds in the adapted right eye recovered to a plateau raised about 0.3 log units above the level measured in the dark. In contrast, thresholds in the nonlight-adapted left eye dropped by about 0.3 log units. These effects persist for about 15 min. They may be accounted for in terms of a hypothetical interocular inhibitory mechanism. Results of changing the intensity, duration and wavelength of the light adaptation upon this effect are described.

Interocular sensitization to a rod-detected test.

Intense red light adaptation of one eye lowers the dark adapted ("absolute") threshold of a 661 nm, extrafoveal, 1.02 deg test flash in the other eye, by about 0.15 log units, for 10-15 min. This effect ("interocular sensitization") also occurs with an extrafoveal 491 nm test, but does not occur if the 661 nm test is foveal, or is made small and brief. Blue or green light adaptations, matched either photopically or scotopically to the red, do not produce interocular sensitization. Thus the conditions producing the effect include intense red light adaptation of one eye, and scotopically mediated detection in the other.

The delayed effects of phencyclidine (PCP) disrupt latent inhibition in a conditioned taste aversion paradigm.

The acute effects of a low dose of phencyclidine (PCP) and the delayed effects of a high dose of PCP on latent inhibition (LI) were assessed in a series of experiments using conditioned taste aversion paradigms. Each paradigm involved a preexposure phase in which water-deprived male rats were allowed access to either water (nonpreexposed; NPE) or 5% sucrose (preexposed; PE), followed by a conditioning phase in which animals were allowed access to sucrose and subsequently injected with the negative reinforcer lithium chloride, and a test phase in which animals were allowed access to both sucrose and water. LI was assessed by comparing the %-sucrose consumed in PE and NPE groups on the test day. The effects of low-dose PCP (2.5 mg/kg) were assessed by comparing LI in animals treated with vehicle or PCP 15 min prior to the onset of the preexposure and conditioning phases. A 4-day paradigm involved 2 days of preexposure followed by a day of conditioning and a test day. This paradigm produced comparable levels of LI in vehicle and PCP-treated animals. A 5-day extinction paradigm involved 2 days of preexposure followed by 2 days of conditioning and a test day. This paradigm abolished LI in vehicle and PCP-treated animals. A 3-day paradigm involved 1 day of preexposure followed by a day of conditioning and a test day. One day of preexposure induced a modified LI effect in both in vehicle and PCP-treated animals. The delayed effects of high dose PCP (8.6 mg/kg) were assessed by comparing LI in animals treated with vehicle or PCP 20 h prior to the onset of the preexposure and conditioning phases in the 4-day paradigm. PCP disrupted latent inhibition in this paradigm. The results are discussed in the context of their relevance to the ability for PCP to model schizophrenic symptomatology.

The delayed effects of DTG and MK-801 on latent inhibition in a conditioned taste-aversion paradigm.

The delayed effects of phencyclidine (PCP) have been shown to disrupt latent inhibition (LI) in a conditioned taste-aversion paradigm. In an attempt to understand the mechanism of this disruption, the delayed effects of the selective sigma receptor agonist 1,3-Di(2-tolyl)guanidine (DTG) and the selective NMDA receptor antagonist MK-801 on latent inhibition were assessed in the same paradigm. Water-deprived male rats were allowed access to either water (nonpreexposed; NPE) or 5% sucrose (preexposed; PE) for 30 min on 2 consecutive days. On the third day, animals were allowed access to sucrose and subsequently injected with lithium chloride. On the forth day, animals were allowed access to both sucrose and water. LI was assessed by comparing the percent sucrose consumed in PE and NPE groups on the fourth day. DTG (1.0, 5.0, or 10.0 mg/kg), MK-801 (0.5, 1.0, or 2.0 mg/kg), or vehicle was administered IP 20 h before preexposure (days 1 and 2) and conditioning (day 3). In vehicle-treated groups, PE animals consumed a significantly higher percent sucrose on the test day than NPE animals, indicating the presence of LI. DTG (10.0 mg/kg) and MK-801 (2.0 mg/kg) decreased the percent sucrose consumed by animals in the PE group to the level observed in the NPE group, indicating disrupted LI. However, this dose of MK-801 was found to produce a decrease in percent sucrose consumed in PE animals not treated with lithium chloride, indicating that the decrease observed in the LI paradigm could be due to MK-801-induced decrease in taste preference for sucrose rather than a disruption of LI. Lower doses of MK-801 that did not produce a decrease in taste preference for sucrose did not significantly disrupt LI. None of the doses of DTG tested altered taste preference for sucrose. These data suggest a role for sigma receptors in the previously observed PCP-induced disruption of LI. Published by Elsevier Science Inc., 2000

Chediak-Higashi syndrome: ocular findings.

A case of Chediak-Higashi syndrome diagnosed by its characteristic ocular findings is described. The appearance of the optic disc and the contrast between total (or nearly total) lack of pigment in the pigment epithelium and the relatively unaffected choroidal pigmentation are believed to be observations of paramount importance in the differential diagnosis by ophthalmoscopic examination. Electrophysiological tests of our case showed abnormal responses and a further deterioration of the ERG and VEP on repeated examinations. Electron microscopic study of a conjunctival biopsy revealed the presence of pathognomonic giant intracytoplasmic lysosomal granules in stromal fibroblasts and, thus, can be used as an adjunct test in suspected cases of Chediak-Higashi syndrome.