Stephanie Clarke

Distinct Pathways Involved in Sound Recognition and Localization: A Human fMRI Study

Evidence from psychophysical studies in normal and brain-damaged subjects suggests that auditory information relevant to recognition and localization are processed by distinct neuronal populations. We report here on anatomical segregation of these populations. Brain activation associated with performance in sound identification and localization was investigated in 18 normal subjects using fMRI. Three conditions were used: (i) comparison of spatial stimuli simulated with interaural time differences; (ii) identification of environmental sounds; and (iii) rest. Conditions (i) and (ii) required acknowledgment of predefined targets by pressing a button. After coregistering, images were normalized and smoothed. Activation patterns were analyzed using SPM99 for individual subjects and for the whole group. Sound recognition and localization activated, as compared to rest, inferior colliculus, medial geniculate body, Heschl gyrus, and parts of the temporal, parietal, and frontal convexity bilaterally. The activation pattern on the fronto-temporo-parietal convexity differed in the two conditions. Middle temporal gyrus and precuneus bilaterally and the posterior part of left inferior frontal gyrus were more activated by recognition than by localization. Lower part of inferior parietal lobule and posterior parts of middle and inferior frontal gyri were more activated, bilaterally, by localization than by recognition. Regions selectively activated by sound recognition, but not those selectively activated by localization, were significantly larger in women. Passive listening paradigm revealed segregated pathways on superior temporal gyrus and inferior parietal lobule. Thus, anatomically distinct networks are involved in sound recognition and sound localization.

DTI mapping of human brain connectivity: statistical fibre tracking and virtual dissection

Several approaches have been used to trace axonal trajectories from diffusion MRI data. If such techniques were first developed in a deterministic framework reducing the diffusion information to one single main direction, more recent approaches emerged that were statistical in nature and that took into account the whole diffusion information. Based on diffusion tensor MRI data coming from normal brains, this paper presents how brain connectivity could be modelled globally by means of a random walk algorithm. The mass of connections thus generated was then virtually dissected to uncover different tracts. Corticospinal, corticobulbar, and corticothalamic tracts, the corpus callosum, the limbic system, several cortical association bundles, the cerebellar peduncles, and the medial lemniscus were all investigated. The results were then displayed in the form of an in vivo brain connectivity atlas. The connectivity pattern and the individual fibre tracts were then compared to known anatomical data; a good matching was found.

Cytochrome Oxidase, Acetylcholinesterase, and NADPH-Diaphorase Staining in Human Supratemporal and Insular Cortex: Evidence for Multiple Auditory Areas

The pattern of cytochrome oxidase, acetylcholinesterase, and NADPH-diaphorase activity was studied in the supratemporal plane, the posterior part of the superior temporal gyrus, and the insula of normal human brains. Five dark cytochrome oxidase regions were found: (i) on Heschls gyrus (area TC of von Economo and Koskinas); (ii) on the planum polare (area TC/TG); (iii) posterior to Heschls gyrus (within area TA); (iv) on the posterior convexity of the superior temporal gyrus (within area TA); and (v) on the posterosuperior insula (area IB). More lightly stained cortex separated these regions (areas IA, TD, and part of TB). The laminar distribution of cytochrome oxidase activity varied in different areas. Acetylcholinesterase-positive fibers predominated in area TC and pyramidal neurons in areas TA and IA and in parts of TB; a mixture of fiber and neuronal staining was found in TC/TG, TD, and IB. NADPH-diaphorase positive profiles included large darkly stained nonpyramidal neurons, mostly in infragranular layers and in subcortical white matter, small faintly stained cells, and a dense array of fibers. The NADPH-diaphorase staining pattern did not vary between areas. The present results suggest that the supratemporal plane, the posterior part of the superior temporal gyrus, and the insula contain at least eight putative cortical areas. Comparison with activation studies by others suggest that, apart from the primary auditory area, six other putative areas may be auditory whereas one putative area, on posterior insula, may be vestibular.

Auditory agnosia and auditory spatial deficits following left hemispheric lesions: evidence for distinct processing pathways

Auditory recognition and auditory spatial functions were studied in four patients with circumscribed left hemispheric lesions. Patient FD was severely deficient in recognition of environmental sounds but normal in auditory localisation and auditory motion perception. The lesion included the left superior, middle and inferior temporal gyri and lateral auditory areas (as identified in previous anatomical studies), but spared Heschls gyrus, the acoustic radiation and the thalamus. Patient SD had the same profile as FD, with deficient recognition of environmental sounds but normal auditory localisation and motion perception. The lesion comprised the postero-inferior part of the frontal convexity and the anterior third of the temporal lobe; data from non-human primates indicate that the latter are interconnected with lateral auditory areas. Patient MA was deficient in recognition of environmental sounds, auditory localisation and auditory motion perception, confirming that auditory spatial functions can be disturbed by left unilateral damage; the lesion involved the supratemporal region as well as the temporal, postero-inferior frontal and antero-inferior parietal convexities. Patient CZ was severely deficient in auditory motion perception and partially deficient in auditory localisation, but normal in recognition of environmental sounds; the lesion involved large parts of the parieto-frontal convexity and the supratemporal region. We propose that auditory information is processed in the human auditory cortex along two distinct pathways, one lateral devoted to auditory recognition and one medial and posterior devoted to auditory spatial functions.

NINETEENTH CENTURY RESEARCH ON NATURALLY OCCURRING CELL DEATH AND RELATED PHENOMENA

Research on naturally occurring cell death is older than current opinion gives credit. More than 100 nineteenth century publications deal with it, and we review most of these. Soon after the establishment of the cell theory by Schleiden and Schwann, Carl Vogt (1842) reported cell death in the notochord and adjacent cartilage of metamorphic toads. Subsequent landmark discoveries included the massive cell death that occurs in pupating diptera (Weismann 1864), chondrocyte death during endochondral ossification (Stieda 1872), phagocytosis associated with cell death in the muscles of metamorphic toads (Metschnikoff 1883), chromatolytic (apoptotic) cell death in ovarian follicles (Flemming 1885), the reinterpretation of “Sarkoplasten” as “Sarkolyten” in metamorphic amphibia (Mayer 1886), the programmed loss of an entire population of neurons in fish embryos (Beard 1889), the death of scattered myocytes and myofibres in mammalian muscle (Felix 1889), and the death of many motor and sensory neurons in chick embryos (Collin 1906). Other lines of nineteenth century research established concepts important for understanding cell death, notably trophic interactions between neurons and their targets, and intercellular competition.

Human Primary Auditory Cortex Follows the Shape of Heschl's Gyrus

The primary auditory cortex (PAC) is central to human auditory abilities, yet its location in the brain remains unclear. We measured the two largest tonotopic subfields of PAC (hA1 and hR) using high-resolution functional MRI at 7 T relative to the underlying anatomy of Heschls gyrus (HG) in 10 individual human subjects. The data reveals a clear anatomical–functional relationship that, for the first time, indicates the location of PAC across the range of common morphological variants of HG (single gyri, partial duplications, and complete duplications). In 20/20 individual hemispheres, two primary mirror-symmetric tonotopic maps were clearly observed with gradients perpendicular to HG. PAC spanned both divisions of HG in cases of partial and complete duplications (11/20 hemispheres), not only the anterior division as commonly assumed. Specifically, the central union of the two primary maps (the hA1–R border) was consistently centered on the full Heschls structure: on the gyral crown of single HGs and within the sulcal divide of duplicated HGs. The anatomical–functional variants of PAC appear to be part of a continuum, rather than distinct subtypes. These findings significantly revise HG as a marker for human PAC and suggest that tonotopic maps may have shaped HG during human evolution. Tonotopic mappings were based on only 16 min of fMRI data acquisition, so these methods can be used as an initial mapping step in future experiments designed to probe the function of specific auditory fields.

What and Where in human audition: selective deficits following focal hemispheric lesions

Abstract. A sound that we hear in a natural setting allows us to identify the sound source and localize it in space. The two aspects can be disrupted independently as shown in a study of 15 patients with focal right-hemispheric lesions. Four patients were normal in sound recognition but severely impaired in sound localization, whereas three other patients had difficulties in recognizing sounds but localized them well. The lesions involved the inferior parietal and frontal cortices, and the superior temporal gyrus in patients with selective sound localization deficit; and the temporal pole and anterior part of the fusiform, inferior and middle temporal gyri in patients with selective recognition deficit. These results suggest separate cortical processing pathways for auditory recognition and localization.

Rapid Brain Discrimination of Sounds of Objects

Electrical neuroimaging in humans identified the speed and spatiotemporal brain mechanism whereby sounds of living and man-made objects are discriminated. Subjects performed an “oddball” target detection task, selectively responding to sounds of either living or man-made objects on alternating blocks, which were controlled for in their spectrogram and harmonics-to-noise ratios between categories. Analyses were conducted on 64-channel auditory evoked potentials (AEPs) from nontarget trials. Comparing responses to sounds of living versus man-made objects, these analyses tested for modulations in local AEP waveforms, global response strength, and the topography of the electric field at the scalp. In addition, the local autoregressive average distributed linear inverse solution was applied to periods of observed modulations. Just 70 ms after stimulus onset, a common network of brain regions within the auditory “what” processing stream responded more strongly to sounds of man-made versus living objects, with differential activity within the right temporal and left inferior frontal cortices. Over the 155–257 ms period, the duration of activity of a brain network, including bilateral temporal and premotor cortices, differed between categories of sounds. Responses to sounds of living objects peaked ∼12 ms later and the activity of the brain network active over this period was prolonged relative to that in response to sounds of man-made objects. The earliest task-related effects were observed at ∼100 ms poststimulus onset, placing an upper limit on the speed of cortical auditory object discrimination. These results provide critical temporal constraints on human auditory object recognition and semantic discrimination processes.

Textbook of Neural Repair and Rehabilitation

Textbook of neural repair and rehabilitation / , Textbook of neural repair and rehabilitation / , کتابخانه دیجیتال جندی شاپور اهواز

Cortical regions contributing to the anterior commissure in man

Abstract The human anterior commissure is believed, by extrapolation from data obtained in macaque monkeys, to convey axons from the temporal and orbitofrontal cortex. Reports of interhemispheric transfer and sexual dimorphism related to the anterior commissure, however, make more precise data on the human anterior commissure desirable. We investigated the connectivity of the human anterior commissure in six adults (male and female) that had circumscribed hemispheric lesions in temporal, frontal, parietal or occipital cortices or in infrapallidal white matter using the Nauta for anterogradely degenerating axons. Axons originating in the inferior part of temporal or occipital lobes, occipital convexity and possibly central fissure and prefrontal convexity were found to cross the midsagittal plane in the anterior commissure. The largest contigent of commissural axons originated in the inferior part of the temporal lobe; it displayed a roughly topographic organization, preferentially running through the inferior part of the commissure. The inferior temporal contigent seemed to reach homotopic and heterotopic targets in the opposite hemisphere. Among the latter were the amygdala and possibly the orbitofrontal cortex. The present data suggest that the human anterior commissure conveys axons from much larger territories than expected from work on non-human primates. Similarly to the human and non-human primate corpus callosum, the anterior commissure is roughly topographically organized and participates in heterotopic connectivity.