Biomedical subjects

H Scheich

Publications and source records attributed to H Scheich.

At least 55 records · Page 3Linked to original sources

PubMed1997

Statistical methods in functional magnetic resonance imaging with respect to nonstationary time-series: auditory cortex activity.

In awake animal and human auditory cortices, it is a common experience with electrophysiological and suitable imaging methods for responses to steady stimulation to be strongly state-dependent and to exhibit nonstationarities, even over short periods of observation. If such nonstationary behavior is also reflected by hemodynamic responses in the human auditory cortex, conventional methods of analysis of fMRI data, although applicable for instance to largely stationary responses in visual and other cortices, may be misleading in attempts to parcellate auditory cortex into fields and to demonstrate functional maps. Time-Windows, described in this article as a convenient tool for the detection and analysis of time-variant brain activities, solves some of these problems. Time-Windows demonstrates that activity is evoked reliably in three separate territories of human auditory cortex, parts of which may show nonstationary behavior, depending on the auditory stimuli and tasks.

Adult↗

PubMed1997

Lateralized processing of speech prosodies in the temporal cortex: a 3-T functional magnetic resonance imaging study.

Prosodic modulation of speech provides information about emotional states of speakers (affective prosodies) or serves as syntactic markers to change linguistic aspects of speech (linguistic prosodies). Previous electrophysiological investigations and studies on patients with right or left hemisphere damage showed nonuniform results with respect to lateralization of prosodic processing. In this study 20 healthy right-handed volunteers were investigated with functional magnetic resonance imaging of the acoustically responsive areas on the supratemporal plane while detecting phonemes as control targets or prosodies in strings of nonsense syllables and adjectives, the latter randomly intonated in a declarative, interrogative, commanding, happy, or sad fashion. In control task A the phoneme /a/ was detected in the syllables. In control task B the phoneme /a/ was detected in the adjectives, and in the experimental task C the sad intonations (affective) and in the experimental task D the interrogative intonations (linguistic) had to be detected in the same material. In task A intensity-weighted volumes of activated voxels were not different in the two hemispheres (laterality index 0). In task B with an irrelevant phoneme detection with respect to prosodic material, the population split into two subgroups with similar right or left hemispheric lateralization of activity leading to an absolute laterality index of 26.8 across all subjects. During detection of affective prosodies (task C), lateralization was maintained yet the absolute laterality index reduced to 14.5, while there was no lateralization during detection of linguistic prosodies. The sum of activations in the two hemispheres was the same across all tasks and subgroups, which suggests that the lateralizations occurring with presentation and detection of prosodic material depend on a redistribution of activity between hemispheres.

Adolescent↗

PubMed1997

Field-specific responses in the auditory cortex of the unanaesthetized Mongolian gerbil to tones and slow frequency modulations.

Responses of multi-units in the auditory cortex (AC) of unanaesthetized Mongolian gerbils to pure tones and to linearly frequency modulated (FM) sounds were analysed. Three types of responses to pure tones could be clearly distinguished on the basis of spectral tuning properties, response latencies and overall temporal response pattern. In response to FM sweeps these three types discharged in a temporal pattern similar to tone responses. However, for all type-1 units the latencies of some phasic response components shifted systematically as a function of range and/or speed of modulation. Measurements of response latencies to FMs revealed that such responses were evoked whenever the modulation reached a particular instantaneous frequency (Fi). Effective Fi was: (1) independent of modulation range and speed, (2) always reached before the modulation arrived at a local maximum of the frequency response function (FRF) and consequently differed for downward and upward sweeps, and (3) was correlated with the steepest slope of that FRF maximum. The three different types of units were found in discrete and separate fields or regions of the AC. It is concluded that gross temporal response properties are one of the key features distinguishing auditory cortical regions in the Mongolian gerbil.

Acoustic Stimulation↗

PubMed1997

Learning-induced dynamic receptive field changes in primary auditory cortex of the unanaesthetized Mongolian gerbil.

Learning-induced changes of the spectro-temporal characteristics of primary auditory cortex (AI) units were studied by response plane analysis of recordings from the AI in unanaesthetized Mongolian gerbils. Using response planes obtained prior to and after auditory discrimination training bins of significant change were identified and their spectro-temporal distribution was studied. Bins of significant changes were generally found to be distributed over the entire spectro-temporal receptive field but occurred most frequently within the first 100 ms of response in the spectral neighbourhood (1.5 octaves) of the frequency of the reinforced conditioned stimulus. Training-induced response decreases occurred early after 10 ms for reinforced conditioned tones and tones in the frequency neighbourhood. Response increases occurred so early only for non-reinforced tones in the neighbourhood of the reinforced frequency and occurred later (after 40 ms) for the reinforced tones. The results are discussed in the light of dynamic disinhibition.

Animals↗

PubMed1997

Influence of experience on the representation of the "mothering call" in frontoparietal and auditory cortex of pups of the rodent Octodon degus: FDG mapping.

Several types and subtypes of vocalizations which have a behavioral impact on degu pups were identified. Among these the complex "mothering call" which is exclusively uttered by females and first during extensive nursing periods in the nest is a candidate for filial learning. In 14C-2-fluoro-2-deoxyglucose (FDG) experiments two-weeks-old pups raised by normal mothers showed higher metabolic activity in somatosensory frontoparietal and frontal cortex upon play back of a mothering call than pups raised by muted mothers. It is suggested that pups learn to associate the mothering call with close body contact with their mother early in life. In addition, FDG representation of the call, of its components and of tone and noise stimuli were studied in degu auditory cortex. Five fields and some aspects of tonotopic organization were identified. The mothering call activated all fields, but with more spatial extent of labeling in normally raised pups. A rostral field was activated by play-back of the mothering call, noise, and two-tone sequences, but hardly by single-frequency tones and the narrow-band component of the mothering call.

Acoustic Stimulation↗

PubMed1997

Artificial implementation of auditory neurons: a comparison of biologically motivated models and a new transfer function oriented model.

Auditory perception neurons, also called inner hair cells (IHCs) because of their physical shape, transform the mechanical movements of the basilar membrane into electrical impulses. The impulse coding of the IHC is the main information carrier in the auditory process and is the basis for improvements in cochlear implants as well as for low-rate, high-quality speech processing and compression. This paper compares biologically motivated models (Meddis, Cooke, Payton) with a newly developed model which is transfer function oriented. The new model has only three reservoirs and the parameters can be controlled through five small ROM tables. This model is compared with the often used Meddis model in terms of accuracy, system parameter flexibility, and hardware effort in an FPGA implementation.

Auditory Pathways↗

PubMed1997

Dopaminergic and serotonergic neurotransmission systems are differentially involved in auditory cortex learning: a long-term microdialysis study of metabolites.

Auditory cortex has been shown to be a site of widespread neuronal learning processes even in the context of simple auditory conditioning behavior. In view of their presumed role in determining behavioral and motivational relevance of incoming information we investigated whether the dopaminergic and serotonergic systems are involved in auditory cortex learning. Using a chronic brain microdialysis technique over 4 days, samples from auditory cortex were obtained before, during, and after daily footshock avoidance training simultaneously from trained gerbils and passive control animals or pseudotrained animals. Because of detection limits of dopamine and serotonin in auditory cortex, the response profiles of extracellular homovanillic acid as the metabolite of the dopaminergic system and of 5-hydroxyindoleacetic acid as the metabolite of the serotonergic system were determined from consecutive dialysis samples each day. The response of the dopaminergic system appeared to reflect the initial formation of the behaviorally relevant association exclusively during the first training day, whereas the serotonergic response appeared to correlate with the stress level of animals.

Animals↗

PubMed1997

Differentiation of hypoglycaemia induced cognitive impairments. An electrophysiological approach.

Effects of hypoglycaemia on distinct cognitive processes were assessed with event-related brain-potential (ERP) measures and reaction times in a hybrid selective-attention/response-choice task. One group of subjects received a euglycaemia-hypoglycaemia-euglycaemia treatment order and a second group a euglycaemia-placebo(euglycaemia)-euglycaemia sequence of treatments. During hypoglycaemia, ERP measures of selective attention (selection negativity), response choice (lateralized readiness potential) and reaction time were delayed compared with baseline performance. After restoration of euglycaemia, the onset of the selection negativity returned to baseline, whereas the lateralized readiness potential was still delayed, and error frequencies remained elevated. These results suggest that hypoglycaemia delays both the stimulus selection and the motor-response selection. They further suggest that the stimulus-selection process recovers quickly after restoration of euglycaemia, but that the response-selection process does not. Slow shifts in cortical potentials with a broad frontal distribution that occurred during hypoglycaemia, are discussed in relation to frontal lobe mechanisms involved in the control of subordinate, modality-specific selection mechanisms.

Adult↗

PubMed1997

Some functions of primary auditory cortex in learning and memory formation.

In the primary auditory field AI of gerbil auditory cortex, aversive tone conditioning paradigms reshaped frequency receptive fields of single units and also changed the spatial representation of tones in fluoro-2-deoxyglucose (FDG) experiments. As another aspect of learning-induced plasticity in gerbil AI, antibodies against the immediate early gene product c-Fos identified an unusual spatial pattern of neurons in terms of a "macrocolumn." The pattern resulted from repeated short exposure of the animals to a tone in a new environment. The search for transmitters that may mediate this gene activation is carried out by microdialysis through chronically implanted probes in auditory cortex. So far, dopamine transmission was found to reflect specific aspects of auditory learning in cortex. The results suggest that spectral features of sounds as well as aspects of learned behavioral meaning of the sounds may be represented in AI.

Animals↗

PubMed1997

Auditory event-related potentials in post- and prelingually deaf cochlear implant recipients.

The development of central auditory functions in cochlear implant (CI) patients was studied over six months of rehabilitation. Examinations were performed beginning with the first week after processor calibration, and in monthly follow-up sessions thereafter. The subjects were given a simple auditory perception task (detection of a 400 Hz and a 1450 Hz tone), as well as an oddball-paradigm (detection of one of the tones as a rare deviant). Auditory evoked potentials, reaction time and errors were recorded. Results from five patients, two postlingually deaf and three prelingually deaf CI recipients are shown. Generally, in the auditory evoked potentials of patients a shortening of N100 latency towards those of subjects with normal hearing was seen from month to month. However, in the prelingually deaf patients this effect was weaker and more variable over time. Three CI recipients showed a P300 component in the oddball-paradigm in correlation with their performance. Two prelingually deaf patients failed to show a P300 in the oddball-paradigm. For both components, the N100 and the P300 we found a larger spreading over the skull in the patients compared to a normal hearing person. The results show that from the very first days after initial processor fitting prelingually and postlingually deaf CI recipients may show cortical correlates of stimulus processing and discrimination. For some components of the auditory evoked potentials an initial temporal change but a maintained larger spreading over the skull was seen.

Cochlear Implantation↗

PubMed1996

Singular perturbation analysis of competitive neural networks with different time scales.

The dynamics of complex neural networks must include the aspects of long- and short-term memory. The behavior of the network is characterized by an equation of neural activity as a fast phenomenon and an equation of synaptic modification as a slow part of the neural system. The main idea of this paper is to apply a stability analysis method of fixed points of the combined activity and weight dynamics for a special class of competitive neural networks. We present a quadratic-type Lyapunov function for the flow of a competitive neural system with fast and slow dynamic variables as a global stability method and a modality of detecting the local stability behavior around individual equilibrium points.

Algorithms↗

PubMed1996

Optical and FDG mapping of frequency-specific activity in auditory cortex.

With optical recording of intrinsic signals (ORIS) and tone stimulation, we analysed frequency- and intensity-dependent spatio-temporal activity in primary auditory cortex AE of awake Mongolian gerbils. We found a two-dimensional and assymetric propagation of ORIS activity (1) from ventral to dorsal along isofrequency contours at all frequencies and (2) from the low-frequency end across the complete tonotopic gradient at low frequencies. High-frequency representations remained tonotopic. Tonotopic asymmetries were independent of stimulus intensity. By contrast, in fluoro-2-deoxyglucose images from the same animals metabolic activity was tonotopically confined at high and low frequencies. The assymetric tonotopic propagation of ORIS activity suggests subthreshold directional interaction mechanisms in the cortical network which may serve to relate low- to high-frequency components of complex sounds.

Acoustic Stimulation↗

PubMed1996

LTD and LTP induced by transcranial magnetic stimulation in auditory cortex.

Using a system capable of relatively localized and rapidrate transcranial magnetic stimulation (rTMS), evoked trains of complex spikes were studied in rodent auditory cortex. Low rate rTMS from 1 to 10Hz produced a frequency-dependent increase in spike rate. Iterations of rTMS resulted in long-term potentiation (LTP)-like, and more durable long-term depression (LTD)-like changes in evoked spike rate. These observations generate new perspectives for studying mechanisms of learning and memory non-invasively as well as introducing some caveats for use of rTMS in humans.

Animals↗

PubMed1996

Ultrastructural localization of glycogen phosphorylase predominantly in astrocytes of the gerbil brain.

The localization of glycogen phosphorylase in gerbil brain was determined by immunoelectron microscopy using the pre-embedding peroxidase technique. Electron-dense granular reaction product of peroxidase activity was observed in astrocytes of all brain regions examined (cerebral cortex, striatum, cerebellar cortex, hippocampal formation, corpus callosum, mesencephalic trigeminal nucleus). The reaction product was distributed in a diffuse pattern throughout the cytoplasmic matrix of perikarya and processes; sometimes the nucleus of labeled astrocytes also contains immunopositive material. The light microscopically visible glycogen phosphorylase immunoreactivity associated with capillaries could be characterized as a staining of astrocytic endfeet ensheathing capillaries. Endothelial cells and pericytes were never labeled. In addition to astrocytes, ependymal cells also presented immunopositive material in their cytoplasm. On the other hand, no reaction product was observed in cells identified as oligodendroglia or microglia. Neurons (with the exception of neurons of the mesencephalic trigeminal nucleus), their processes, and their synaptic endings were free of reaction product. In the neuropil we frequently observed immunopositive glial processes adjacent to synaptic structures. This intimate spatial relationship may be interpreted as a morphological sign of a metabolic interaction. The data support the hypothesis that astroglia play a key role in glycogen metabolism and energization of the brain.

Animals↗

PubMed1996

Alteration of auditory cortex activity with a visual stimulus through conditioning: a 2-deoxyglucose analysis.

In two experiments, the 2-deoxyglucose metabolic mapping technique was used to examine the hypothesis that a stimulus of one modality (a light) will begin to activate the sensory cortex of a stimulus of another modality (a tone) with which it has been repeatedly paired. Adult gerbils received repeated presentations of either a light or the light paired with a tone known to affect 2DG labeling patterns in the auditory cortex. Intermittent footshock was included on a pseudo-random basis to maintain arousal in the subjects. One day after training, each gerbil was injected with 2DG and either received repeated presentations of the light only or was simply exposed to the training context. Analysis of the auditory cortex revealed no differences in overall metabolic activity of the auditory cortex between the groups. However, in both experiments, the light that was previously paired with the tone changed the relative activity of the cortical subfields compared to the light not previously paired with the tone. Specifically, the results indicate greater activity in the anterior auditory field (AAF-Experiments 1 and 2) and the posterior fields (DPVP-Experiment 2) relative to the primary field AI in response to the light that was previously paired with the tone during training. Gerbils either only placed in the context during the 2DG session or that received unpaired presentations of the light and tone during training did not show this shift in relative labeling between the subfields. Because no differences in overall activity of the auditory cortex were found, we conclude that the shift in relative labeling between the subfields reflects, on average, both an increase in activity of fields AAF and DPVP and a concomitant decrease in AI activity in response to the light stimulus. The results have implications for our understanding both of brain learning mechanisms in general and the potential functions of auditory cortex subfields in particular.

Animals↗

PubMed1996

Differential frequency conditioning enhances spectral contrast sensitivity of units in auditory cortex (field Al) of the alert Mongolian gerbil.

Differential aversive auditory conditioning in the awake Mongolian gerbil was performed during single- and multi-unit recording in field Al of the primary auditory cortex. Presentations of pure tone stimuli of a given frequency (reinforced conditioned stimulus; CS+) paired with electrocutaneous stimulation (unconditioned stimulus) were combined with several other non-reinforced tone stimuli (non-reinforced conditioned stimulus; CS-). Stimulus presentation during training and testing was optimized for constancy of the probability of occurrence of both the CS+ and the CS- stimulus. The paradigm led to a reorganization of both the spectral and temporal response characteristics of auditory cortical neurons with the following basic results. First, tone-evoked responses of Al neurons recorded after multiple acoustic stimulation under these conditions varied statistically around a mean value (stationarity). Conditioning produced a shift in mean values of evoked responses. The altered tone responses were also stationary (stability of the plastic effects). Second, the frequency-receptive fields (FRFs) of neurons were reorganized in a frequency-specific way such that the CS+ frequency became located in a local minimum of the FRF after training. This resulted from a training-induced increase in the responses to frequencies adjacent to the CS+ frequency in the FRF relative to the CS+ response. The effect can be interpreted as an enhancement of the 'spectral contrast' sensitivity of the unit in the CS+ neighbourhood. Third, apart from this frequency-specific plastic effect, responses to other frequencies also underwent changes during training. The non-frequency-specific changes were not generally predictable but the post-trial responses were stationary. Fourth, the analysis of the long-term behaviour of FRF reorganization revealed the stability of plastic effects under retention training and the gradual re-establishment of the pretrial FRF during extinction training. Fifth, not only the spectral characteristics but also the temporal structure of the tone-evoked responses could be affected by the training. In most cases the training-induced changes measured within the first tens of milliseconds of the response corresponded to the response changes obtained by integration over the total response period. There were some cases, however, in which the direction of the response change varied with time, indicating that excitatory and inhibitory influences on the temporal response pattern were differently affected by training.

Acoustic Stimulation↗

PubMed1995

Comparison of frequency-specific c-Fos expression and fluoro-2-deoxyglucose uptake in auditory cortex of gerbils (Meriones unguiculatus).

Induction of c-Fos in the auditory cortex of gerbils was investigated immunocytochemically 1 h after single, triple or 1 h continuous stimulation with a series of narrow band frequency-modulated tone bursts. With single stimulation c-Fos immunoreactive neurons were chiefly found in the primary auditory field (AI), where they formed a narrow frequency-specific column across layers II-VI. Side-band-like patterns adjacent to this column appeared characteristically with triple stimulation. Immunoreactive cell density in the anterior auditory field and the caudal fields was sparse and location not frequency specific with single or triple stimulation. Spatial comparisons of c-Fos immunoreactive neuron density with 2-deoxy-2-fluoro-D-glucose (FDG) autoradiography in the same animals after 1 h of stimulation revealed spreading of c-Fos expression in neurons across the tonotopic maps of the AI and in the rostral and caudal fields of the auditory cortex. The pattern of the highest density of c-Fos labelled cells in the AI still matched the peak labelling of FDG autoradiographs. The results show that the postsynaptic marker c-Fos reflects the frequency representation in the AI with single or triple stimulation yet with a higher spatial resolution than the deoxyglucose technique. Longer stimulation causes nontonotopic intracortical spreading of the c-Fos-inducing message, a phenomenon potentially reflecting the effects of cooperativity in the maps.

Animals↗

PubMed1995

Mapping of stimulus features and meaning in gerbil auditory cortex with 2-deoxyglucose and c-Fos antibodies.

The basic functional organization of gerbil auditory cortex was previously mapped with unit recording of best frequency and with the fluoro-2-deoxyglucose mapping (FDG) technique. Among at least seven subfields in this cortex the primary auditory cortex (AI) and the anterior auditory field (AAF) showed prominent tonotopic organization with parallel dorsoventral iso-frequency contours (electrophysiology) in correspondence to FDG labelling of frequency band laminae. In an approach to mechanisms of learning aversive tone conditioning paradigms were found to reshape frequency receptive fields of single units in AI and also produced spatial shifts of tone representation in the tonotopic maps of AI and AAF. Both results suggest that spectral features as well as aspects of behavioural meaning of sounds may be represented even in primary auditory cortex. General meaningfulness in terms of occurrence of novel and salient stimuli may be reflected by expression of immediate early genes. Mapping with an antibody against the immediate early gene product c-Fos was performed in order to identify the spatial distribution of neurons in auditory cortex which change metabolism as a result of stimulation with auditory signals in a new environment. Very short e.g. less than 3 min repetitive stimulation with a tone led to frequency-specific columnar expression of c-Fos in AI and to spare non-tonotopic expression in other fields. Longer stimulation or longer aversive conditioning with the same tone led to spreading of expression, i.e. to accessory non-tonotopic labelling in AI and other fields, particularly pronounced in the output layers V and VI. It is assumed that this spreading relates to the formation of output schemes from auditory cortex in terms of implicit behavioural meaning of stimuli.

Animals↗