Biomedical subjects

Henning Scheich

Publications and source records attributed to Henning Scheich.

At least 19 recordsLinked to original sources

PubMed2007

Working memory specific activity in auditory cortex: potential correlates of sequential processing and maintenance.

Working memory (WM) tasks involve several interrelated processes during which past information must be transiently maintained, recalled, and compared with test items according to previously instructed rules. It is not clear whether the rule-specific comparisons of perceptual with memorized items are only performed in previously identified frontal and parietal WM areas or whether these areas orchestrate such comparisons by feedback to sensory cortex. We tested the latter hypothesis by focusing on auditory cortex (AC) areas with low-noise functional magnetic resonance imaging in a 2-back WM task involving frequency-modulated (FM) tones. The control condition was a 0-back task on the same stimuli. Analysis of the group data identified an area on right planum temporale equally activated by both tasks and an area on the left planum temporale specifically involved in the 2-back task. A region of interest analysis in each individual revealed that activation on the left planum temporale in the 2-back task positively correlated with the task performance of the subjects. This strongly suggests a prominent role of the AC in 2-back WM tasks. In conjunction with previous findings on FM processing, the left lateralized effect presumably reflects the complex sequential processing demand of the 2-back matching to sample task.

Adult↗

PubMed2006

Determining language laterality by fMRI and dichotic listening.

For imaging studies on hemispheric specialization of the human brain, data about known functional asymmetries other than handedness would be valuable for a reliable interpretation of lateralized activation in individuals or groups of subjects. As certain aspects of language processing are observed to be a function of primarily the left, it can be used as a reference for other asymmetric processes such as sensory or cognitive skills. For analyzing language laterality, there are a variety of methods, but these differ in application or accuracy. In this study, we tested the reliability of two widely used methods - dichotic listening and fMRI - to determine language dominance in 30 individual subjects. The German adaptation of a dichotic listening test (Hättig, H., Beier, M., 2000. FRWT: a dichotic listening test for clinical and scientific contexts, Zeitschr f Neuropsychologie 11. 233-245.) classified 54% of the 26 right-handed subjects as left hemispheric dominant. The results of the fMRI paradigm (Fernández, G., de Greiff, A., von Oertzen, J., et al., 2001. Language mapping in less than 15 min: real-time functional MRI during routine clinical investigation. Neuroimage 14, 585-594.) tested on the same subjects, however, classified 92% of the right-handed subjects as left dominant. The main reason for this discrepancy was that the ear dominance score of many subjects in the dichotic listening test was too low to determine a reliable ear advantage. As a consequence, this specific dichotic listening test cannot be used to determine language laterality in individual subjects. On the other hand, the fMRI results are consistent with numerous studies showing left dominant language processing in more than 90% of right-handers. In some subjects, however, language laterality critically depends on the areas used to determine the laterality index.

Acoustic Stimulation↗

PubMed2006

Dual time scales for categorical decision making in auditory cortex.

Category formation allows us to group perceptual objects into meaningful classes and is fundamental to cognition. Categories can be derived from similarity relationships of object features by using prototypes or multiple exemplars, or from abstract relationships of features and rules . A variety of brain areas have been implicated in categorization processes, but mechanistic insights on the single-cell and local-network level are still rare and limited to the matching of individual objects to categories . For directional categorization of tone steps, as in melody recognition , abstract relationships between sequential events (higher or lower in frequency) have to be formed. To explore the neuronal mechanisms of this categorical identification of step direction, we trained monkeys for more than two years on a contour-discrimination task with multiple tone sequences. In the auditory cortex of these highly trained monkeys, we identified two interrelated types of neuronal firing: Increased phasic responses to tones categorically represented the reward-predicting downward frequency steps and not upward steps; subsequently, slow modulations of tonic firing predicted the behavioral decisions of the monkeys, including errors. Our results on neuronal mechanisms of categorical stimulus identification and of decision making attribute a cognitive role to auditory cortex, in addition to its role in signal processing.

Acoustic Stimulation↗

PubMed2006

Spatial organization of EEG coherence during listening to consonant and dissonant chords.

Theories of harmony state that the contribution of both sensory and cognitive components is important for musical consonance perception. The aims of the present study were to analyze (a) functional intra- and inter-hemispheric connectivity associated with listening to consonant and dissonant chords using EEG coherence method; (b) relationships between affective responsiveness, sensory aspects of perceived consonance and associated brain connectivity. We identified two lines of inter-hemispheric connectivity in the theta band; one localized anterior being sensitive to consonance and one localized posterior sensitive to dissonance. Stronger right intra-hemispheric connectivity for consonance than dissonance in the theta band was associated with higher pleasantness ratings. The relationship between sensory aspects of perceived consonance and left intra-hemispheric connectivity found in theta-2 was interpreted as processing of vertical harmony without emotional involvement. The stronger connectivity along the axis "left anterior-right posterior" for dissonance than consonance in the alpha-1 band is discussed as a correlate of novelty processing. By introducing a "auditory object dissociation" hypothesis we suggest to extend the present concept of harmony perception. We believe that "auditory object dissociation" is a component of "sensory dissonance."

Acoustic Stimulation↗

PubMed2006

Influence of tone duration and intertone interval on the discrimination of frequency contours in a macaque monkey.

Behavioral studies have shown that non-human primates can categorically discriminate descending from ascending frequency steps in sequences of pure tones. Here we show that the performance of a long-tail macaque remains stable in such a task when the silent interval between the tones of a frequency step is varied between 0 and 1100 ms. Our finding suggests that: (1) some monkeys can keep frequency-specific information in their short-term memory for periods >1s, which can be used to make categorical decisions on the direction of frequency steps, and that (2) their ability to categorize the direction of frequency steps may be more similar to humans than previously assumed.

Acoustic Stimulation↗

PubMed2006

Cortical and subcortical sides of auditory rhythms and pitches.

It is commonly assumed that different perceptual qualities arising from sensory stimuli depend on their physical nature being transformed by specific peripheral receptors, for example, colour, vibration or heat. A notable unexplained exception is the low and high repetition rates of any sound perceived as rhythm or pitch, respectively. Using auditory discrimination learning in bilaterally auditory cortex ablated animals, we demonstrate that the perceptual quality of sounds depends on the way the brain processes stimuli rather than on their physical nature. In this context, cortical and subcortical processing steps have different roles in analysing different aspects of sounds with the complete analysis accomplished not before information converges in the auditory cortex.

Acoustic Stimulation↗

PubMed2006

In vivo quantification of spinal and bulbar motor neuron degeneration in the G93A-SOD1 transgenic mouse model of ALS by T2 relaxation time and apparent diffusion coefficient.

Magnetic resonance imaging (MRI) has provided important information in characterizing amyotrophic lateral sclerosis (ALS) in humans and in animal models. A frequently used animal model to study mechanisms of pathogenesis and the efficacy of drugs in ALS is a transgenic mouse over-expressing the human mutated G93A-superoxide dismutase 1 (G93A-SOD1). In our study, we applied MRI to find suitable progression markers, which can be used to monitor the development of ALS and to evaluate therapeutic approaches at early stages of the disease. Therefore, we generated parameter maps of the spin-spin relaxation time (T2) and the apparent diffusion coefficient (ADC) starting at day 70 after birth, i.e., before motor scores decline around day 90. Depending on the progression of the disease, G93A-SOD1 mice showed significantly increased values of T2 in the brain stem motor nuclei Nc. V (trigeminal nucleus), VII (facial nucleus), and XII (hypoglossal nucleus), and spinal cord compared to non-transgenic wild-type mice and transgenic mice over-expressing the non-mutated wild-type human SOD1 (tg-SOD1). Similar effects in these motor nuclei were revealed by ADC mapping. Furthermore, in the upper spinal cord, a dorsal-ventral difference with significantly higher T2 values in the ventral part was demonstrated by T2 mapping. While both T2 and ADC might prove useful as progression markers and enable the longitudinal non-invasive evaluation of ALS in G93A-SOD1 mice, the potential is limited by age-dependent effects in case of ADC mapping.

Amyotrophic Lateral Sclerosis↗

PubMed2006

Comparison of estimates for volumes of brain ablations derived from structural MRI and classical histology.

Estimates of auditory cortex ablation sizes in a rodent model as derived from classical histology (volume reconstructions from Nissl-stained brain sections) and structural magnetic resonance imaging (MRI) (T1-weighted whole-brain scans from a 4.7 T animal scanner) were compared in the same specimens (Mongolian gerbils). Estimates of lesion volumes obtained with the two methods were very similar, robust, highly correlated and not significantly different from each other. Hence, the general usefulness of structural MRI for the determination of brain lesion size in small animal models is demonstrated. MRI therefore seems to be well suited to determine proper size and location of an experimental brain ablation prior to (potentially extensive) behavioral testing.

Animals↗

PubMed2006

Manganese-enhanced MRI reveals structural and functional changes in the cortex of Bassoon mutant mice.

Manganese-enhanced magnetic resonance imaging (ME-MRI) was used to analyze the brain architecture in mice lacking the functional presynaptic active zone protein Bassoon. Anatomical characterization revealed a significant increase in the total brain volume in Bassoon mutants as compared with wild-type mice, which is mainly caused by changes in cortex and hippocampus volume. The measured enlargement in cortical volume coincides with an altered Mn2+ distribution within cortical layers as visualized by T1-weighted magnetic resonance imaging. Two days after manganese application, the cortex of Bassoon mutant mice appeared more laminated in ME-MRI, with an enhanced accumulation of manganese in deep, central, and superficial cortical cell layers. Whereas morphologically the cortical lamination is not affected by the absence of a functional Bassoon, an altered basal activation pattern was found in the cortex of the mutant mice both by metabolic labeling with [14C]-2-deoxyglucose and histochemical detection of the potassium analogue thallium uptake. Consequently, the results indicate that the absence of the functional presynaptic protein Bassoon causes disturbance in the formation of normal basal cortical activation patterns and thereby in the functional cortical architecture. Furthermore, this study shows that ME-MRI can become a valuable tool for a structural characterization of genetically modified mice.

Animals↗

PubMed2006

Differential effects of iontophoretic in vivo application of the GABA(A)-antagonists bicuculline and gabazine in sensory cortex.

We have compared the effects of microiontophoretic application of the GABA(A)-receptor antagonists bicuculline (BIC) and gabazine (SR95531) on responses to pure tones and to sinusoidally amplitude-modulated (AM) tones in cells recorded extracellularly from primary auditory cortex (AI) of Mongolian gerbils. Besides similar effects in increasing spontaneous and stimulus-evoked activity and their duration, both drugs elicited differential effects on spectral tuning and synchronized responses to AM tones. In contrast to gabazine, iontophoresis of the less potent GABA(A)-antagonist BIC often resulted in substantial broadening of frequency tuning for pure tones and an elimination of synchronized responses to AM tones, particularly with high ejecting currents. BIC-induced effects which could not be replicated by application of gabazine were presumably due to the well-documented, non-GABAergic side-effects of BIC on calcium-dependent potassium channels. Our results thus provide strong evidence that GABA(A)-mediated inhibition in AI does not sharpen frequency tuning for pure tones, but rather contributes to the processing of fast temporal modulations of sound envelopes. They also demonstrate that BIC can have effects on neuronal response selectivity which are not due to blockade of GABAergic inhibition. The results have profound implications for microiontophoretic studies of the role of intracortical inhibition in sensory cortex.

Acoustic Stimulation↗

PubMed2006

Contralateral white noise selectively changes left human auditory cortex activity in a lexical decision task.

In a previous study, we hypothesized that the approach of presenting information-bearing stimuli to one ear and noise to the other ear may be a general strategy to determine hemispheric specialization in auditory cortex (AC). In that study, we confirmed the dominant role of the right AC in directional categorization of frequency modulations by showing that fMRI activation of right but not left AC was sharply emphasized when masking noise was presented to the contralateral ear. Here, we tested this hypothesis using a lexical decision task supposed to be mainly processed in the left hemisphere. Subjects had to distinguish between pseudowords and natural words presented monaurally to the left or right ear either with or without white noise to the other ear. According to our hypothesis, we expected a strong effect of contralateral noise on fMRI activity in left AC. For the control conditions without noise, we found that activation in both auditory cortices was stronger on contralateral than on ipsilateral word stimulation consistent with a more influential contralateral than ipsilateral auditory pathway. Additional presentation of contralateral noise did not significantly change activation in right AC, whereas it led to a significant increase of activation in left AC compared with the condition without noise. This is consistent with a left hemispheric specialization for lexical decisions. Thus our results support the hypothesis that activation by ipsilateral information-bearing stimuli is upregulated mainly in the hemisphere specialized for a given task when noise is presented to the more influential contralateral ear.

Acoustic Stimulation↗

PubMed2006

Rapid-rate transcranial magnetic stimulation of animal auditory cortex impairs short-term but not long-term memory formation.

Bilateral rapid-rate transcranial magnetic stimulation (rTMS) of gerbil auditory cortex with a miniature coil device was used to study short-term and long-term effects on discrimination learning of frequency-modulated tones. We found previously that directional discrimination of frequency modulation (rising vs. falling) relies on auditory cortex processing and that formation of its memory depends on local protein synthesis. Here we show that, during training over 5 days, certain rTMS regimes contingent on training had differential effects on the time course of learning. When rTMS was applied several times per day, i.e. four blocks of 5 min rTMS each followed 5 min later by a 3-min training block and 15-min intervals between these blocks (experiment A), animals reached a high discrimination performance more slowly over 5 days than did controls. When rTMS preceded only the first two of four training blocks (experiment B), or when prolonged rTMS (20 min) preceded only the first block, or when blocks of experiment A had longer intervals (experiments C and D), no significant day-to-day effects were found. However, in experiment A, and to some extent in experiment B, rTMS reduced the within-session discrimination performance. Nevertheless the animals learned, as demonstrated by a higher performance the next day. Thus, our results indicate that rTMS treatments accumulate over a day but not strongly over successive days. We suggest that rTMS of sensory cortex, as used in our study, affects short-term memory but not long-term memory formation.

Analysis of Variance↗

PubMed2005

Nonauditory events of a behavioral procedure activate auditory cortex of highly trained monkeys.

A central tenet in brain research is that early sensory cortex is modality specific, and, only in exceptional cases, such as deaf and blind subjects or professional musicians, is influenced by other modalities. Here we describe extensive cross-modal activation in the auditory cortex of two monkeys while they performed a demanding auditory categorization task: after a cue light was turned on, monkeys could initiate a tone sequence by touching a bar and then earn a reward by releasing the bar on occurrence of a falling frequency contour in the sequence. In their primary auditory cortex and posterior belt areas, we found many acoustically responsive neurons whose firing was synchronized to the cue light or to the touch or release of the bar. Of 315 multiunits, 45 exhibited cue light-related firing, 194 exhibited firing that was related to bar touch, and 268 exhibited firing that was related to bar release. Among 60 single units, we found one neuron with cue light-related firing, 21 with bar touch-related firing, and 36 with release-related firing. This firing disappeared at individual sites when the monkeys performed a visual detection task. Our findings corroborate and extend recent findings on cross-modal activation in the auditory cortex and suggests that the auditory cortex can be activated by visual and somatosensory stimulation and by movements. We speculate that the multimodal corepresentation in the auditory cortex has arisen from the intensive practice of the subjects with the behavioral procedure and that it facilitates the performance of audiomotor tasks in proficient subjects.

Acoustic Stimulation↗

PubMed2005

Learning-induced plasticity in animal and human auditory cortex.

Recent data on learning-related changes in animal and human auditory cortex indicate functions beyond mere stimulus representation and simple recognition memory for stimuli. Rather, auditory cortex seems to process and represent stimuli in a task-dependent fashion. This implies plasticity in neural processing, which can be observed at the level of single neuron firing and the level of spatiotemporal activity patterns in cortical areas. Auditory cortex is a structure in which behaviorally relevant aspects of stimulus processing are highly developed because of the fugitive nature of auditory stimuli.

Acoustic Stimulation↗

PubMed2005

Volumetric magnetic resonance imaging of functionally relevant structural alterations in chronic epilepsy after pilocarpine-induced status epilepticus in rats.

PURPOSE: After pilocarpine-induced epilepsy in rats, volumetric magnetic resonance imaging (MRI) reveals significant morphologic changes in functionally relevant structures of the brain. To relate structural changes to functional alteration, we studied the correlation of regional brain atrophy (e.g., of the hippocampus) with lesion-induced learning deficits in the Morris water maze. METHODS: MRI experiments were performed on an MR scanner at 4.7 Tesla. For volumetric analysis, various cerebral structures were segmented in horizontal and coronal T(2)-weighted MR images. Before the MRI investigations, animals were trained for 10 days in a Morris water maze. RESULTS: Volumetric MRI revealed a significant loss in hippocampal size in both the dorsal and ventral parts, correlated with an increase in ventricular size. Furthermore, significant losses were found in the relative size of thalamus, putamen, cortex, and the combined areas of perirhinal, entorhinal, and piriform cortices adjacent to the hippocampus. A significant correlation of learning performance in the Morris water maze with the relative hippocampal area and not with other areas tested was observed in pilocarpine-treated animals. CONCLUSIONS: The data provide a quantitative analysis of functionally relevant structural alterations in rats with chronic epilepsy. Water maze performance of pilocarpine-treated animals correlates with the degree of hippocampal but not with the degree of cortical damage, demonstrating the potential of this method for the investigation of cognitive impairments in relation to cerebral changes. In addition, the data point to an important role of even the residual hippocampus in memory formation.

Animals↗

PubMed2005

Left auditory cortex and amygdala, but right insula dominance for human laughing and crying.

Evidence suggests that in animals their own species-specific communication sounds are processed predominantly in the left hemisphere. In contrast, processing linguistic aspects of human speech involves the left hemisphere, whereas processing some prosodic aspects of speech as well as other not yet well-defined attributes of human voices predominantly involves the right hemisphere. This leaves open the question of hemispheric processing of universal (species-specific) human vocalizations that are more directly comparable to animal vocalizations. The present functional magnetic resonance imaging study addresses this question. Twenty subjects listened to human laughing and crying presented either in an original or time-reversed version while performing a pitch-shift detection task to control attention. Time-reversed presentation of these sounds is a suitable auditory control because it does not change the overall spectral content. The auditory cortex, amygdala, and insula in the left hemisphere were more strongly activated by original than by time-reversed laughing and crying. Thus, similar to speech, these nonspeech vocalizations involve predominantly left-hemisphere auditory processing. Functional data suggest that this lateralization effect is more likely based on acoustical similarities between speech and laughing or crying than on similarities with respect to communicative functions. Both the original and time-reversed laughing and crying activated more strongly the right insula, which may be compatible with its assumed function in emotional self-awareness.

Acoustic Stimulation↗

PubMed2005

Left auditory cortex specialization for vertical harmonic structure of chords.

The representation of consonant and dissonant chords in the auditory cortex was investigated using low-noise functional magnetic resonance imaging and different experimental paradigms to separate the effects of vertical harmony from those of other musical features. The results revealed higher activation by consonant compared with dissonant chords in the left posterior auditory cortex, suggesting contributions of mechanisms of encoding the acoustical chord structure rather than mechanisms based on sequential integration of chords.

Acoustic Stimulation↗

PubMed2004

Age-dependent changes in MRI of motor brain stem nuclei in a mouse model of ALS.

Mice over-expressing the mutant human G93A-SOD1 are widely used as an animal model of amyotrophic lateral sclerosis (ALS). ALS is characterized by progressive degeneration of motor neurons in the motor cortex, brain stem and spinal cord. The underlying mechanisms for the selective death of motor neurons are still uncertain. To study factors that cause selective neuron degeneration or therapeutic approaches to delay the progression of the disease, a method is required to monitor the state of motor neurons under in-vivo conditions. Here, we demonstrate that in G93A-SOD1 mice the MRI signal intensities of nucleus V, VII, XII, and nucleus ambiguus show a time-dependent increase starting around day 90, parallel to first behavioral signs of a motoneuron disorder.

Aging↗