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H Scheich

Publications and source records attributed to H Scheich.

At least 19 recordsLinked to original sources
PubMed2000

New insights into the hemodynamic blood oxygenation level-dependent response through combination of functional magnetic resonance imaging and optical recording in gerbil barrel cortex.

Fast, low-angle shoot functional magnetic resonance imaging (fMRI), based on the blood oxygenation level-dependent (BOLD) effect, was combined with optical recording of intrinsic signals (ORIS) and 2-deoxyglucose labeling in gerbil barrel cortex. We observed over the activated barrel a positive BOLD signal and increased levels of deoxyhemoglobin and total hemoglobin during each period of prolonged (30 sec) D2 vibrissal stimulation. These data show that the hemodynamic basis of this fMRI signal is not necessarily a washout of deoxyhemoglobin, as generally assumed. Instead, they suggest that a positive BOLD signal can also be caused by a local increase of blood volume, even if deoxyhemoglobin levels are persistently elevated. We also show that this alternative interpretation is consistent with theoretical models of the BOLD signal. The changes in BOLD signal and blood volume, which are most tightly correlated with the periodic stimulation, peak at the site of neuronal activation. These results contribute to the understanding of the hemodynamic mechanisms underlying the BOLD signal and also suggest analysis methods, which improve the spatial localization of neuronal activation with both fMRI and ORIS.

Animals↗
PubMed2000

The inhibitory influence of an acquired escape strategy on subsequent avoidance learning in gerbils.

In gerbils an acquired non-avoidance strategy as pre-experience in a shuttle-box was studied in its influence on the learning of a standard avoidance paradigm. Thereby the same cue stimuli, frequency modulated tones (CS) and electric footshocks (US) were used in different behavioral paradigms. In the preexperience sessions the interstimulus interval between CS and US and on the other hand the escapability or inescapability of the US was varied. It was found that the experience with a relatively long interstimulus interval led to a prolonged maintenance of an acquired escape strategy during subsequent standard avoidance learning. This effect increased with the preexperience of an inescapable US. Additional insights into the temporal inhibition of avoidance learning by the pre-experience were provided by behavioral events like attention responses and orienting responses reflecting components of information processing.

Acoustic Stimulation↗
PubMed2000

An interspike interval method for computing phase locking from neural firing.

Inner hair cells (IHCs) transform the mechanical movements of the basilar membrane into electrical impulses. The impulse coding of the IHCs is the main information carrier in the auditory process and is the basis for improvements of cochlea implants as well as for low rate, high-quality speech processing and compression. This paper shows how to compute the speech signal from the neural firing based on the analysis of the interspike interval histogram. This new approach solves problems that other standard analysis methods do not solve sufficiently well.

Action Potentials↗
PubMed2000

Early unilateral auditory deprivation increases 2-deoxyglucose uptake in contralateral auditory cortex of juvenile Mongolian gerbils.

The effects of early onset, unilateral conductive hearing loss on tone-induced 2-deoxyglucose (2-DG) uptake in the auditory cortex of juvenile Mongolian gerbils (Meriones unguiculatus) were studied. Atresia of the left ear canal was induced at postnatal day 9 (P9) to achieve reversible auditory deprivation prior to onset of hearing (around P12). Atresia either persisted (ATR, n=4) or the canal was opened 15 min before the 2-DG experiments (RE, n=4) at P27. Control animals were either non-deprived (CON, n=4), or their left ears were plugged acutely (PAX, n=4). In PAX, 2-DG uptake in primary auditory cortex (AI) and anterior auditory field (AAF) was lower in right than in left AI and AAF. In contrast, in ATR and RE, uptake was significantly higher on the right side contralateral to the atresia. Hence, atresia during early development leads to plastic changes resulting in an interhemispheric imbalance of functional metabolism in favor of the auditory cortex contralateral to the manipulated ear. Distances between tone-induced 2-DG labeling in AI and AAF were increased in PAX, but smaller in ATR in the right compared to the left hemisphere, suggesting effects of atresia also on spatial relations in cortical tonotopic maps.

Acoustic Stimulation↗
PubMed2000

Functional dissociation between medial and lateral prefrontal cortical spatiotemporal activation in negative and positive emotions: a combined fMRI/MEG study.

The orbitofrontal cortex has been cytoarchitectonically and connectionally subdivided into a medial and a lateral part which are assumed to subserve distinct functions in emotional processing. However the exact spatiotemporal mechanisms of negative and positive emotional processing in medial and lateral orbitofrontal cortex remain unclear. We therefore investigated spatiotemporal orbitofrontal and prefrontal cortical activation patterns during emotional stimulation in a combined fMRI/MEG study. We investigated 10 healthy subjects, 5 women and 5 men. Positive and negative pictures from the International Affective Picture system (IAPS) were used for emotional stimulation, whereas neutral and gray pictures were taken as control conditions. fMRI/MEG measurements covered the whole frontal lobe and a time window between -2000 and +200 ms around motor responses (right index finger extension) associated with each picture. Positively and negatively correlated activities were determined in various prefrontal/frontal cortical regions in fMRI. Isocontour maps and single dipoles in MEG were analyzed in 50 ms time windows ranging from -2000 to +200 ms. Dipoles and fMR images were mapped on three-dimensional anatomical MRI so that anatomical localization of single dipoles and regional fMRI activity could be compared. Both negative and positive emotional conditions differed from non-emotional control conditions by strong orbitofrontal and lateral prefrontal activation as well as by the presence of early magnetic fields (-1700 to +1100 ms). Negative emotional processing was characterized by strong medial orbitofrontal activation and earlier (-1700 ms), stronger and more medially oriented orbitofrontal dipoles. In contrast positive emotional processing showed a rather strong activation in lateral prefrontal cortex with later (-1500 ms), weaker and more laterally oriented orbito and prefrontal dipoles. Negative emotional processing can be characterized by strong and early medial orbitofrontal cortical activation, whereas positive emotional processing showed rather later and weaker activation in lateral orbitofrontal/prefrontal cortex. Such a functional dissociation between medial and lateral orbito-frontal/prefrontal cortex during negative and positive emotional processing lends further support to the assumption of a functional subdivision in the orbitofrontal cortex.

Adult↗
PubMed2000

Topographic analysis of epidural pure-tone-evoked potentials in gerbil auditory cortex.

This study investigated the tonotopic organization of pure-tone-evoked middle latency auditory evoked potentials (MAEPs) recorded at the auditory cortical surface in unanesthetized gerbils. Multielectrode array recording and multiple linear regression analysis of the MAEP demonstrated different degrees of tonotopic organization of early and late MAEP components. The early MAEP components P1 and N1 showed focal topography and clear dependence in location and size of cortical area covered on pure-tone frequency. The later components P2 and N2 showed a widespread topography which was largely unaffected in location and size of cortical area covered by pure-tone frequency. These results allow delimitation of the neural generators of the early and late MAEP components in terms of the spectral properties of functionally defined neural populations.

Acoustic Stimulation↗
PubMed1999

Functional mapping of transsynaptic effects of local manipulation of inhibition in gerbil auditory cortex.

Cortical networks are under the tonic influence of inhibition which is mainly mediated by GABA. The state of inhibition of small neuronal populations in the auditory cortex (AC) field AI of gerbils was altered by local microinjection of GABA, of the GABA(A)-receptor agonist 4-piperidine-sulfonic acid (P4S) and the GABA(A)-receptor antagonists bicuculline methiodide (BMI) and SR-95531. In order to elucidate direct and transsynaptic effects of the alterations of inhibition produced by these substances we used the 2-fluoro-2-deoxy-D-[(14)C(U)] glucose (FDG) mapping method. The injection of GABA (10 mM) caused no significant changes in FDG labeling but P4S caused a marked decrease of local FDG uptake in a small region surrounding the injection site but in no other region. The injection of the GABA(A)-receptor antagonists caused massive increases of FDG uptake within the entire ipsilateral AC, whereas the contralateral AC was not significantly affected in spite of prominent callosal connections. However, disinhibited excitatory output from the ipsilateral AC is suggested by a strong increase in FDG labeling of the corticothalamic fiber tract and ipsilateral structures like medial geniculate nucleus, caudal striatum, and lateral amygdaloid nucleus and a structure at the caudoventral margin of the thalamic reticular nucleus, presumably the subgeniculate nucleus, a structure with hitherto unknown connections and function. No alteration of FDG uptake could be detected in the inferior colliculus, another main descending target structure of the AC. In summary, the effects resulting from microinjection of GABA(A)-receptor antagonists reflect a differential influence of the AC on its anatomically connected target regions. The findings demonstrate the potential of the method of focal application of neuroactive substances in combination with the FDG technique for mapping their transsynaptic influences which are hard to derive from anatomical tracing studies alone.

Animals↗
PubMed1999

Presynaptic cytomatrix protein bassoon is localized at both excitatory and inhibitory synapses of rat brain.

Bassoon is a 420-kDa protein specifically localized at the active zone of presynaptic nerve terminals. It is thought to be involved in the structural organization of the neurotransmitter release site. We studied the distribution of Bassoon transcripts and protein in rat brain and assessed which types of presynaptic terminals contain the protein. As shown by in situ hybridization, Bassoon transcripts are widely distributed in the brain and occur primarily in excitatory neurons. In addition, examples of gamma-aminobutyric acid (GABA)-ergic neurons expressing Bassoon are detected. At the light microscopic level, Bassoon immunoreactivity is found in synaptic neuropil regions throughout the brain, with the strongest expression in the hippocampus, the cerebellar cortex, and the olfactory bulb. Immunoelectron microscopy showed that Bassoon immunoreactivity is found in both asymmetric type 1 and symmetric type 2 synapses. Immunopositive asymmetric synapses include mossy fiber boutons and various spine and shaft synapses in the hippocampus and mossy fiber terminals and parallel fiber terminals in the cerebellum. Bassoon-containing symmetric synapses are observed, e.g., between basket and granule cells in the hippocampus, between Golgi cells and granule cells, and between basket cells and Purkinje cells in the cerebellum. Within synaptic terminals, Bassoon appears highly concentrated at sites opposite to postsynaptic densities. In cultured hippocampal neurons, Bassoon was found to colocalize with GABA(A) and glutamate (GluR1) receptors. These data indicate that Bassoon is a component of the presynaptic apparatus of both excitatory glutamatergic and inhibitory GABAergic synapses.

Animals↗
PubMed1999

Increase of extracellular dopamine in prefrontal cortex of gerbils during acquisition of the avoidance strategy in the shuttle-box.

We examined whether extracellular dopamine (DA) increase in medial prefrontal cortex is correlated with the establishment or with the retrieval of an auditory avoidance strategy in a shuttle-box. Using microdialysis from right medial prefrontal cortex (mPFC) in combination with behavioral measures, gerbils were trained on a tone-footshock combination in two sessions on two successive days. Sessions in each animal involving avoidance strategy formation and avoidance strategy retrieval were differentiated post hoc by using the percentage of conditioned responses (CR) and other behavioral measures of training sessions. It was found that exclusively strategy formation correlated with high DA levels in mPFC.

Acoustic Stimulation↗
PubMed1999

Task-related and item-related brain processes of memory retrieval.

In all cognitive tasks, general task-related processes operate throughout a given task on all items, whereas specific item-related processes operate differentially on individual items. In typical functional neuroimaging experiments, these two sets of processes have usually been confounded. Herein we report a combined positron emission tomography and event-related potential (ERP) experiment that was designed to distinguish between neural correlates of task-related and item-related processes of memory retrieval. Two retrieval tasks, episodic and semantic, were crossed with episodic (old/new) and semantic (living/nonliving) properties of individual items to yield evidence of regional brain activity associated with task-related processes, item-related processes, and their interaction. The results showed that episodic retrieval task was associated with increased blood flow in right prefrontal and posterior cingulate cortex, as well as with a sustained right-frontopolar-positive ERP, but that the semantic retrieval task was associated with left frontal and temporal lobe activity. Retrieval of old items was associated with increased blood flow in the left medial temporal lobe and with a brief late positive ERP component. The results provide converging hemodynamic and electrophysiological evidence for the distinction of task- and item-related processes, show that they map onto spatially and temporally distinct patterns of brain activity, and clarify the hemispheric encoding/retrieval asymmetry (HERA) model of prefrontal encoding and retrieval asymmetry.

Adult↗
PubMed1999

Discrimination learning of amplitude modulated tones in Mongolian gerbils.

Discrimination learning of 100% sinusoidal amplitude modulated tones (AM) was investigated in adult Mongolian gerbils using a footshock motivated shuttle box avoidance go/no go paradigm. AM stimuli to be discriminated had identical carrier frequency (2 kHz) but differed in modulation frequency (fm) by one octave. Six groups of gerbils were trained to discriminate AM-pairs with fm ranging from 10 to 640 Hz. Learning proceeded faster and discrimination performance was slightly better for low fm, up to 80 Hz, than for high fm, above 80 Hz. These results may be related to cortical AM encoding (Schulze, H. and Langner, G., J. Comp. Physiol. A, 181 (1997) 651-663), which is temporal for low fm (synchrony code) and spatial for high fm (rate-place code). This may implicate different neuronal learning strategies or distinct behavioral meanings influencing the discrimination training.

Acoustic Stimulation↗
PubMed1999

Processing of sound sequences in macaque auditory cortex: response enhancement.

It is well established that the tone-evoked response of neurons in auditory cortex can be attenuated if another tone is presented several hundred milliseconds before. The present study explores in detail a complementary phenomenon in which the tone-evoked response is enhanced by a preceding tone. Action potentials from multiunit groups and single units were recorded from primary and caudomedial auditory cortical fields in lightly anesthetized macaque monkeys. Stimuli were two suprathreshold tones of 100-ms duration, presented in succession. The frequency of the first tone and the stimulus onset asynchrony (SOA) between the two tones were varied systematically, whereas the second tone was fixed. Compared with presenting the second tone in isolation, the response to the second tone was enhanced significantly when it was preceded by the first tone. This was observed in 87 of 130 multiunit groups and in 29 of 69 single units with no obvious difference between different auditory fields. Response enhancement occurred for a wide range of SOA (110-329 ms) and for a wide range of frequencies of the first tone. Most of the first tones that enhanced the response to the second tone evoked responses themselves. The stimulus, which on average produced maximal enhancement, was a pair with a SOA of 120 ms and with a frequency separation of about one octave. The frequency/SOA combinations that induced response enhancement were mostly different from the ones that induced response attenuation. Results suggest that response enhancement, in addition to response attenuation, provides a basic neural mechanism involved in the cortical processing of the temporal structure of sounds.

Acoustic Stimulation↗
PubMed1999

Lateralized auditory spatial perception and the contralaterality of cortical processing as studied with functional magnetic resonance imaging and magnetoencephalography.

Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were used to study the relationships between lateralized auditory perception in humans and the contralaterality of processing in auditory cortex. Subjects listened to rapidly presented streams of short FM-sweep tone bursts to detect infrequent, slightly deviant tone bursts. The stimulus streams consisted of either monaural stimuli to one ear or the other or binaural stimuli with brief interaural onset delays. The onset delay gives the binaural sounds a lateralized auditory perception and is thought to be a key component of how our brains localize sounds in space. For the monaural stimuli, fMRI revealed a clear contralaterality in auditory cortex, with a contralaterality index (contralateral activity divided by the sum of contralateral and ipsilateral activity) of 67%. In contrast, the fMRI activations from the laterally perceived binaural stimuli indicated little or no contralaterality (index of 51%). The MEG recordings from the same subjects performing the same task converged qualitatively with the fMRI data, confirming a clear monaural contralaterality, with no contralaterality for the laterally perceived binaurals. However, the MEG monaural contralaterality (55%) was less than the fMRI and decreased across the several hundred millisecond poststimulus time period, going from 57% in the M50 latency range (20-70 ms) to 53% in the M200 range (170-250 ms). These data sets provide both quantification of the degree of contralaterality in the auditory pathways and insight into the locus and mechanism of the lateralized perception of spatially lateralized sounds.

Acoustic Stimulation↗
PubMed1998

A new method for reliable and efficient reconstruction of 3-dimensional images from autoradiographs of brain sections.

Valuable information on metabolism and function of distinct brain regions can be extracted from autoradiographs of 2D brain sections, e.g. after labelling with the non-metabolisable sugar derivate [14C]-2-fluoro-deoxyglucose (2-FDG). For a more complete comprehension of the data and for a comparison with information obtained by modern functional imaging techniques it is essential to have a reliable and efficient method for the 3D reconstruction of autoradiographs of serial sections. This paper describes a new method for the alignment of 2D 2-FDG images, that combines two established algorithms, i.e. principal axes alignment followed by consistent matrix transformation. The power and efficiency of this new 2-step method is compared to those of various previously described procedures.

Algorithms↗
PubMed1998

BrainView: a computer program for reconstruction and interactive visualization of 3D data sets.

A computer program, BrainView, is presented which has been developed to reconstruct, visualize, and evaluate three dimensional (3D) biological and medical imaging data, such as images from histological sections, confocal microscopy, or magnetic resonance tomography. The program allows the simultaneous display of three orthogonal sectional planes, i.e. the horizontal, frontal, and sagittal planes, of reconstructed data and to move interactively through the brain to optimally assess the 3D data set. Furthermore, any arbitrary sectioning plane through a data set can be visualized. Implemented warping algorithms allow the geometric normalization of data sets of different animals, modalities or developmental stages as a preprocessing for the comparative evaluation of the data. For a quantitative analysis, data sets can be segmented based on equal grey levels and the corresponding equidensities were calculated. The program works on Apple-Macintosh computers and has a user-friendly graphical interface. The BrainView program is discussed in comparison to related programs.

Animals↗
PubMed1998

Right auditory cortex lesion in Mongolian gerbils impairs discrimination of rising and falling frequency-modulated tones.

Mongolian gerbils (Meriones unguiculatus) were trained in a shuttle box to discriminate the direction in frequency-modulated tones (FM). Whereas control animals easily acquired FM discrimination, animals with auditory cortex lesion on the right side showed considerable difficulties in learning this task. The discrimination performance of gerbils with left auditory cortex lesion, however, was not different from controls. This study, suggesting that the right auditory cortex plays a dominant role in FM discrimination learning in gerbils, describes a useful animal model for investigation of the basic mechanisms underlying hemispheric asymmetries in auditory perception.

Acoustic Stimulation↗