Adjacent Fiber Tracts Research Articles

Deciphering the frontostriatal circuitry through the fiber dissection technique: direct structural evidence on the morphology and axonal connectivity of the fronto-caudate tract.

The authors sought to investigate the very existence and map the topography, morphology, and axonal connectivity of a thus far ill-defined subcortical pathway known as the fronto-caudate tract (FCT) since there is a paucity of direct structural evidence regarding this pathway in the relevant literature. Twenty normal adult cadaveric formalin-fixed cerebral hemispheres (10 left and 10 right) were explored through the fiber microdissection technique. Lateral to medial and medial to lateral dissections were carried out in a tandem manner in all hemispheres. Attention was focused on the prefrontal area and central core since previous diffusion tensor imaging studies have recorded the tract to reside in this territory. In all cases, the authors readily identified the FCT as a fan-shaped pathway lying in the most medial layer of the corona radiata and traveling across the subependymal plane before terminating on the superolateral margin of the head and anterior part of the body of the caudate nucleus. The FCT could be adequately differentiated from adjacent fiber tracts and was consistently recorded to terminate in Brodmann areas 8, 9, 10, and 11 (anterior pre-supplementary motor area and the dorsolateral, frontopolar, and fronto-orbital prefrontal cortices). The authors were also able to divide the tract into a ventral and a dorsal segment according to the respective topography and connectivity observed. Hemispheric asymmetries were not observed, but instead the authors disclosed asymmetry within the FCT, with the ventral segment always being thicker and bulkier than the dorsal one. By using the fiber microdissection technique, the authors provide sound structural evidence on the topography, morphology, and connectional anatomy of the FCT as a distinct part of a wider frontostriatal circuitry. The findings are in line with the tract's putative functional implications in high-order motor and behavioral processes and can potentially inform current surgical practice in the fields of neuro-oncology and functional neurosurgery.

Risks of postoperative paresis in motor eloquently and non-eloquently located brain metastases

BackgroundWhen treating cerebral metastases all involved multidisciplinary oncological specialists have to cooperate closely to provide the best care for these patients. For the resection of brain metastasis several studies reported a considerable risk of new postoperative paresis. Pre- and perioperative chemotherapy (Ctx) or radiotherapy (Rtx) alter vasculature and adjacent fiber tracts on the one hand, and many patients already present with paresis prior to surgery on the other hand. As such factors were repeatedly considered risk factors for perioperative complications, we designed this study to also identify risk factors for brain metastases resection.MethodsBetween 2006 and 2011, we resected 206 brain metastases consecutively, 56 in eloquent motor areas and 150 in non-eloquent ones. We evaluated the influences of preoperative paresis, previous Rtx or Ctx as well as recursive partitioning analysis (RPA) class on postoperative outcome.ResultsIn general, 8.7% of all patients postoperatively developed a new permanent paresis. In contrast to preoperative Ctx, previous Rtx as a single or combined treatment strategy was a significant risk factor for postoperative motor weakness. This risk was even increased in perirolandic and rolandic lesions. Our data show significantly increased risk of new deficits for patients assigned to RPA class 3. Even in non-eloquently located brain metastases the risk of new postoperative paresis has not to be underestimated. Despite the microsurgical approach, our cohort shows a high rate of unexpected residual tumors in postoperative MRI, which supports recent data on brain metastases’ infiltrative nature but might also be the result of our strict study protocol.ConclusionsSurgical resection is a safe treatment of brain metastases. However, preoperative Rtx and RPA score 3 have to be taken into account when surgical resection is considered.

Long-term time course of affective lability after subthalamic deep brain stimulation electrode implantation

The mechanism and time course of emotional side effects of subthalamic deep brain stimulation in Parkinson's disease are a matter for discussion. We report a 53-month follow-up of a patient with affective lability. Postoperative lesion plus bilateral stimulation strongly influenced mood in the first week in terms of laughing behavior, while voltage changes had only minor long-term impact up to 37 months on negative emotion, possibly caused by the right electrode stimulating the subthalamic nucleus and adjacent fiber tracts involving the internal capsule. Thus we conclude that affective lability can occur with different temporal dynamics of microlesion, and early and chronic stimulation.

Nonrigid Point Set Matching of White Matter Tracts for Diffusion Tensor Image Analysis

Patient studies based on diffusion tensor images (DTI) require spatial correspondence between subjects. We propose to obtain the correspondence from white matter tracts, by introducing a new method for nonrigid matching of white matter fiber tracts in DTI. The method boils down to point set registration that involves simultaneously clustering and matching of the data points. The tracts are implicitly warped to a common frame of reference to avoid the potential bias toward one of the datasets. The algorithm gradually refines from global to local registration, which is implemented through deterministic annealing. Special care was taken to incorporate the spatial relation between fiber points and the uncertainty in principal diffusion orientation. As a result, the computed clusters are oriented along the fiber tracts and discriminate between adjacent but distinct fiber tracts. This is validated on synthetic and clinical data. The root-mean-squared distance with respect to expert-annotated landmarks is low (3 mm). In contrast to a state-of-the-art nonrigid registration technique, the proposed method is more robust to residual misalignments in terms of measured fractional anisotropy values.

Disconnection's renaissance takes shape: Formal incorporation in group-level lesion studies

Group-level voxelwise statistical analyses of lesion-deficit relationships have been used to implicate brain structures critical for specific aspects of human cognition and behavior. Current approaches fail to account for the role of fiber tract disruptions in causing deficit, and confound cortical damage with damage to fibers of passage. Here, we develop a framework, Generalized Lesion-Symptom Mapping (GLSM), to integrate fiber tract information from DTI-based tractographic atlases in tractwise and voxelwise lesion-deficit analyses. First, we used the geniculo-calcarine system as a validation testbed. Using logistic regressions we predicted right homonymous visual field deficits in 149 subjects with focal brain damage based on lesion location, with and without incorporating fiber tract information. A probabilistic fiber tract atlas [Wakana S, Jiang H, Nagae-Poetscher LM, Van Zijl PC, Mori S. Fiber tract-based atlas of human white matter anatomy. Radiology 2004;230:77–87] coregistered to our reference brain was used to estimate disconnection to the optic radiations and adjacent fiber tracts. When tract information was not incorporated, lesions in multiple sectors of the temporal lobe were associated with visual field defects. When the optic radiations were incorporated, this artifactual association was eliminated and the calcarine cortex was correctly isolated. Among the incorporated tracts, only the optic radiations significantly predicted visual field defects. Second, we applied the approach to impairments of higher visuoperceptual functions in 111 subjects who were administered the Hooper Visual Organization Test. We included all six association fiber tracts available in the atlas, plus the optic radiations. Tract inclusion narrowed the cortical sectors associated with impaired performance in a manner consistent with recent fMRI findings. The left cingulum and inferior longitudinal fasciculus, significantly predicted impairments. The results demonstrate the viability, validity and value of incorporating fiber tract information in lesion-deficit analyses. The enhanced analysis framework opens a new avenue for studying neural systems, with the potential to facilitate identification of both cortical sectors and fiber tracts critical for cognitive functioning.

Preserved structural integrity of white matter adjacent to low-grade tumors

Brain tumors may dislocate, infiltrate, or disrupt the adjacent fiber tracts. We examined (1) microstructural changes of white matter (WM) adjacent to supratentorial low grade tumors in children and (2) WM tracts of the affected hemisphere using diffusion tensor imaging (DTI). We hypothesized that the structural integrity of the adjacent WM tracts would be preserved in these slow-growing tumors. DTI was performed in 11 children with low grade tumors diagnosed by magnetic resonance imaging (MRI). Regions of interest were placed in the tumor, in WM adjacent to tumor, and on the normal contralateral side. Fractional anisotropy (FA), trace, and eigenvalues were measured. Color-coded maps and tractography were used to grade the WM tracts: Grade one was normal tract size and color hue; grade two was reduced tract size but preserved color hue; and grade three was loss of color hue or failure to track on tractography. Grades one and two were subcategorized as "a" or "b," depending on the absence or presence of tract displacement. There were no significant differences in FA, trace, and eigenvalues between WM adjacent to tumor and the contralateral side. One patient had grade 1a changes, six grade 1b, and four grade 2b. We found preserved microstructural integrity of WM adjacent to low grade tumors in children. Color vector maps and tractography demonstrated displacement of the WM tracts in all but one patient. Our findings could be useful for neurosurgical planning to minimize injury to the WM tracts and improve preoperative risk analysis.

The effect of cytotoxic lesions of the hippocampus on recognition memory in the rat: effects of stimulus size.

Rats with excitotoxic hippocampal lesions were trained on delayed nonmatching-to-sample (DNMS) with small goal boxes, containing complex objects, presented on a pseudo trial-unique schedule. A series of experiments then tested performance on repeated presentation of either the small object or large empty goal boxes. All rats acquired the nonmatching rule, but hippocampal-lesioned rats performed less well than controls on choice accuracy for the final 2 blocks of acquisition. In the study's main phase, the lesions impaired choice accuracy when the large empty boxes were used as stimuli. This deficit was ameliorated when the rats were tested with the small object boxes, although the performance of the hippocampal-lesioned rats was still below that of controls. These results extend previous reports of box size-dependent effects of hippocampal aspiration lesions on DNMS and suggest that selective damage to the hippocampus, not neuronal loss in adjacent structures or fiber tracts, is critical for the effect.

Storage, metabolism, and processing of 125I-fibroblast growth factor-2 after intracerebral injection

Basic fibroblast growth factor (FGF-2) is a potent trophic agent for both neuronal and non-neuronal cells of the mammalian CNS. It can enhance survival and neurite outgrowth of a variety of neuronal types in vitro and in vivo, and recently has been shown to stimulate neuroblast proliferation in culture. To determine the most effective means of introducing FGF-2 into the brain, and to further our understanding of the behavior of exogenous FGF-2 following intracerebral injection, we examined the diffusion and degradation of 125I-FGF-2 following intraventricular or intraparenchymal injection. SDS-PAGE and autoradiography show that when radiolabelled FGF-2 is injected into the parenchyma of the rat brain, it remains at the site of injection where it is detectable for several days. During this time, it is slowly metabolized to 2 specific heparin-binding metabolic fragments that are virtually identical to the ones described for its metabolism by neurons and astrocytes in vitro. Microscopic examination and autoradiography of these tissue sections show that within these areas, FGF-2 diffuses throughout the site of injection. Initially, it migrates along adjacent fiber tracts, binds to specific cells and to basement membranes of the microvasculare, but later on it remains associated to basement membranes and non-neuronal cells. Based on its slow clearance and slow rate metabolic degradation, this FGF-2 is presumed to be in a sequestered form and to have limited activity. In contrast, the intraventricular injection of 125I-FGF leads to a rapid clearance, with some binding to ependymal cells lining the ventricles and little translocation into the parenchyma. Based on these studies, we conclude that the distribution, half life, and activities of FGF-2 can be dramatically affected by the mode selected for its administration. This may derive from its high affinity for immobilized heparan sulfate related proteoglycans. Accordingly, in the design of strategies to test the neurotrophic potential of FGF-2, the ideal delivery protocol will require more than a slow release of locally acting growth factor and also a mechanism that retains the molecule at the desired site of action, to avoid sequestration in compartments adjacent to or distal from target cells.

Functional characteristics of spontaneously active neurons in rat dorsal cochlear nucleus in vitro.

1. The cochlear nucleus of rat brain stem slices was explored with extracellular microelectrodes to determine the distribution and characteristics of spontaneously active neurons. 2. In mapping experiments few spontaneously active neurons were found in anteroventral or posteroventral divisions of the cochlear nucleus. In contrast, spontaneously active neurons (N = 648) were widely distributed in the dorsal cochlear nucleus (DCN), especially its more superficial part. The density (neurons per penetration) was greatest 100-400 microns from the lateral surface of DCN, corresponding approximately to the fusiform soma layer and closely adjacent portions of the molecular and deeper regions. In penetrations with active neurons as many as 13 were found, with a mean of 4.3 neurons per penetration. Activity was found along the entire dorsomedial-ventrolateral extent of the nucleus, across the tonotopic representation. 3. Most neurons were readily categorized according to the spike interval pattern as regular (40%), bursting (30%), or irregular (30%). Regular and bursting patterns were highly stable, but few bursting neurons were found in relatively inactive slices. Although there was extensive overlap in location, bursting neurons were significantly closer to the lateral edge of the slice. Also, they were more likely to have initially negative action potentials than regular or irregular neurons. 4. A high density of spontaneous firing, including regular, bursting, and irregular patterns, was observed in slices containing only DCN and adjacent fiber tracts, with other nuclear structures trimmed away. 5. When the K+ concentration of the perfusion medium was decreased from 6.25 to 3.25 mM firing rates of regular neurons decreased moderately without changes in pattern. In contrast, firing rates of most bursting and irregular neurons showed large increases, and bursts were prolonged. 6. When the K+ concentration was increased from 6.25 to 9.25 or 12.25 mM regular neurons showed moderate increases in rate without changes in pattern. Effects on firing rates differed among bursting and irregular neurons, but bursts usually increased in frequency and decreased in duration, and irregular neurons showed some burst firing. 7. When Ca2+ was decreased to 0.2 mM and Mg2+ increased to 3.8 or 7.8 mM regular neurons did not change in pattern of firing although firing rates increased or decreased moderately. Bursting neurons showed large increases in the durations of the bursts. Firing rates of bursting neurons usually increased during 0.2 mM Ca2+ -3.8 mM Mg2+ but typically decreased, after an initial rise, during 0.2 mM Ca2+ -7.8 mM Mg2+.(ABSTRACT TRUNCATED AT 400 WORDS)

Topography of the uncinate fascicle and adjacent temporal fiber tracts

Neurosurgical procedures in the anterior temporal lobe are common, in which different postoperative neuropsychological deficits may occur. For the refinement of the surgical approach 10 human hemispheres were dissected using the method of dissection by Klinger, to gain more data about the fiber tracts in the anterior temporal lobe, respectively the temporal stem. The uncinate fascicle has a form like a curved dumb-bell with a thin (about 2 mm thick), fan-like arrangement of fibers in the frontal and temporal lobe. The solid portion runs in the extreme and external capsule through the limen insulae. The topography of adjacent important fiber tracts (inferior occipito-frontal fascicle, Meyer's loop, anterior commissure, inferior thalamic bundle) could be displayed. According to the results possible neuropsychological deficits and surgical considerations are discussed.

Temporal relationship between single unit activity in superior olivary complex and scalp-derived auditory brainstem response in guinea pig

Single unit activities in the region of the superior olivary complex were recorded from 8 guinea pigs concurrently with the recording of auditory brainstem potentials from the scalp. At any one anatomical site, be it a fiber tract (e.g. trapezoid body) or a nucleus (e.g. medial nucleus of the trapezoid body), the modal latency of the onset discharge of the units encountered corresponded in time with the latencies of several different waves (waves P2–P5) of the auditory brainstem response (ABR). Moreover, at the time of occurrence of just one of the ABR waves, single units in several diverse anatomical sites in and around the superior olive were found with modal latencies of onset discharge at that same time period. The slopes of the latency/intensity functions for both the peaks of the ABR and the modal latency of the onset discharge for most of the single units studied in the superior olive and its adjacent fiber tracts were remarkably similar. These data support the hypothesis of multiple rather than single generator site(s) for components of the ABR, at least, for waves P2–P5 in the guinea pig. These data do not distinguish whether the ABR are generated in part by travelling nerve action potentials or graded synaptic events.

Catenoid shape of the interventricular septum: possible cause of idiopathic hypertrophic subaortic stenosis.

Previous studies have shown that asymmetric septal hypertrophy (ASH) may occur in embryonic and malformed hearts and that muscle cell disarray is found in myocardium that contracts isometrically. To account for the characteristic ASH and septal muscle fiber disarray of idiopathic hypertrophic subaortic stenosis (IHSS), we postulated that a catenoid shape of the septum, i.e., net zero curvature, would have the mechanics required to produce IHSS. Accordingly, hearts from eight autopsied patients with IHSS were studied for curvature and thickness of free walls and septum, and they were compared to similar measurements in 80 other hearts. In all eight hearts with IHSS the septum was concave to the left in the transverse plane but convex to the left in the apex-to-base plane. Such a catenoid configuration of the septum was not observed in any of the other 80 hearts. The distinctive shape of the septum in IHSS would account for isometric contraction, since adjacent fiber tracts with opposite curvatures would develop maximum tension but would not have motion. Fiber disarray and local hypertrophy would result from such isometric contraction. Since ventricular configuration is acquired early in cardiogenesis, IHSS might therefore result from a genetic or embryonic determination of a catenoid septum.

Acetylcholinesterase and pseudocholinesterase in neural and non-neural tissue in the medial geniculate body of the cat

The technique of retrograde degeneration has shown that acetylcholine esterase is present in both pre- and post-synaptic neurons in the medial geniculate body of cat. In sensory systems the enzyme activity is higher in cell groups than in adjacent fiber tracts. Butyrylcholine esterase is probably present in glial and vascular tissue as well as in neural tissue of the medial geniculate body, and is higher in the fiber tracts of the central nervous system than in most of the adjacent cell groups.